Hydronics and Propane
Exceptional Comfort – Exceptional Energy
Table of Contents
Executive Summary
Section 1: Propane, Exceptional Energy
Section 2:
What is Hydronic Heating?
Section 3: The Advantages of Hydronic Heating
Section 4:
The Basic Components of a Hydronic System
Section 5:
Propane-Fueled Heat Sources
Section 6:
Heat Emitter Options
Section 7:
Other Loads Supplied by Hydronics
Section 8:
Case Studies
Section 9:
Cooling Options for Use with Hydronic Heating
Section 10:
Additional Sources of Information
Executive Summary
N
orth Americans have many options when it comes to
heating and cooling their homes. Most can choose from
several locally available fuels, and then select from a
variety of equipment to convert the fuel into heat. Although not all
homeowners thoroughly research their heating options, they all
want a system that delivers comfort, reliability, and fuel efficiency.
When it comes to meeting these objectives, nothing matches a
propane-fueled heat source combined with a hydronic distribution
system.
This publication discusses the synergistic combination of
propane and hydronics technology in detail. It begins with an
overview of propane as a universal fuel for supplying virtually any
heating need in or around a home. These needs include space
heating, domestic water heating, cooking, clothes drying, patio
heating, and grilling. Beyond these tasks, propane can power
emergency generators, repel mosquitoes, operate outdoor lighting,
provide a cozy fireplace, and even power equipment that cools
buildings in warm weather. Given all these possible uses propane
truly is exception energy.
But a fuel source is only part of an overall heating system.
Delivering exceptional comfort precisely when and where it’s
needed requires a superior heat distribution method, and that’s
where modern hydronics technology comes in.
Hydronic heating systems use water as a “conveyor belt
for heat.” Heat is loaded onto a stream of flowing water within a
propane-fueled heat source such as a boiler or water heater. This
heat is carried throughout the building as the water flows along
a distribution system containing tubing, circulators, and other
components. Finally, the heat is unloaded from the water and
released into individual rooms using one of several types of
heat emitters.
The somewhat cooler water then returns to the heat source to
repeat the cycle.
Properly installed hydronic systems provide superior
comfort in every room of a house or commercial building. In
some systems this comfort is delivered by gently warmed room
surfaces such as floors, walls, or ceilings. Such systems have
no visible heating hardware within the rooms and thus do not
compromise the aesthetics or furniture placement within those
rooms. This approach is called hydronic radiant panel heating, and
it’s extensively described in this publication. Other heat emitters
to be discussed included fin-tube baseboard, panel radiators, and
air handlers. Some systems may even combine two or more types
of heat emitters to perfectly match the aesthetic, occupancy, and
budget constraints of the owners.
Propane-fueled hydronic systems can also provide an endless
supply of domestic hot water using the same heat source that
warms the building. Such systems can even be extended to melt
snow from steps and walkways, or heat a swimming pool. The
essence of a modern hydronic heating is a single heat source
supplying heat to several loads in and around the building. This
approach lowers installation cost, reduces service requirements,
and increases fuel efficiency compared to installing separate
heat sources for each heating requirement. It’s also a perfect
complement to other domestic uses of propane.
After reading this publication we hope you agree that the
combination of propane and modern hydronics technology offers
unmatched versatility and comfort. Section 10 provides a listing of
references and websites that can be used to further study of the
topics we’re about to discuss.
Enjoy.
1
Section 1:
Propane, Exceptional Energy
T
his publication discusses how propane, in combination
with water-based “hydronic” heating hardware, can
deliver superior comfort, low fuel bills, and reliable
operation over many years. However, this specialized topic is only
part of the story propane has to tell. Before discussing it in detail
lets look at the big picture.
Simply stated…
No other fuel offers the versatility, economy, environmental
benefits, and convenience of propane!
Here’s a quick look at each of these benefits.
Propane is Versatile
Almost any heating requirement in a modern house or commercial
building can be supplied by propane. These requirements include:
pace heating
S
Heat derived from propane can be delivered to buildings in many
ways. These include central forced-air furnaces and water-based
hydronic heating systems (the principle subject of this publication).
Other propane-fueled devices that provide heat include overhead
infrared heaters, unit heaters, through-the-wall console heaters and
propane fireplaces. Two or more of these methods can easily be
combined where they make the most sense in a given project. All
can be supplied by a modern, safe, and easily installed propane
distribution system.
omestic water heating
D
Virtually unlimited amounts of domestic hot water can be supplied
through properly-sized propane water heaters. These include
standard tank-type water heaters, as well as increasingly popular
“tankless” water heaters. It also includes “indirectly-fired” water
heaters that are used in combination with hydronic space heating.
anges and Ovens
R
Ask a professional chef if they prefer gas- or electric ovens and
cooktops. It’s a virtual certainty they’ll tell you a gas cooking
appliance is their first choice. Propane cooking appliances
respond faster than electric appliances and can deliver greater
heat output when needed. With more and more homeowners
opting for high performance (commercial grade) cooktops and
ovens, propane is ready to ensure their culinary pursuits will be
sizzling successes.
utdoor grills
O
Americans love their outdoor grills, and more than 63 percent of
those grills are fueled by propane. In homes with a central propane
supply system outdoor grills are ready to operate year round. There’s
no need to periodically change the propane tank.
earths
H
Who doesn’t enjoy relaxing in front of a warm hearth on a cold
winter evening? When fueled by propane, that fireplace is ready
to fire any time of the day
Figure 1-1
or night. Enjoy the warm,
efficient, radiant heat without
the mess, smoke, or residue
created by wood fires. Extend
this enjoyment from inside
to outside with a propane
fireplace or fire pit on the
deck or patio. It’s safe, clean, Propane fireplaces are ready
whenever you are.
smokeless, and ready to go
Source: PERC
whenever you want it.
lothes Dryers
C
Electrically operated clothes dryers can be one of the most
inefficient appliances to operate. At the same time they may
not always completely dry clothes, especially when people are
rushed. As is the case with cooktops, propane dryers have higher
rates of heat input and thus dry clothes faster. They can also cost
significantly less to operate than do electric clothes dryers.
atio Heaters
P
Want to enjoy your outdoor patio on a cool spring evening?
Consider a propane infrared radiant heater. Such devices provide
radiant comfort up to twenty feet away while operating in virtual
silence and without smelly emissions.
ool Heating
P
How many pool owners, especially those living in northern
climates, look at the inviting water knowing it’s often too cold
for an enjoyable swim? How many times does cool water stop
them from enjoying the pool they’ve spent thousands of dollars to
install?
It doesn’t have to be that way. A propane pool heater can raise
the temperature of a pool to a very comfortable level and ensure
it stays there. Swimming seasons can easily be extended one or
two months in Northern climates, and even maintained year round
in warmer locations. It’s even possible to heat the pool using the
same propane boiler that heats the house in winter. Section 7 of
the publication shows you how to do this.
Sec1:1
Other Uses for Propane
Figure 1-3
Most people associate propane with heating. The previous
discussion certainly confirms its many uses in this category.
However, there are several other (non-heating) domestic uses for
propane that you may not know about. They include:
Emergency generators
Few of us enjoy spending several hours, or worse, several days,
in a home without electricity. Did you know that propane-fueled
electrical generators are available as an option to conventional
gasoline-fueled generators? These modern devices can turn on
automatically within a few seconds of a power outage, and provide
stable and safe electric power to a home until utility-supplied
electricity is restored. Located outside, these devices are quieter
than gasoline- or diesel-powered generators, and operate without
the smoke and emissions that some other generators produce.
Figure 1-2
Propane-fuel CHP unit produces both heat and electricity
Source: Marathon Engine Systems
Propane-fueled emergency generator
Source: Generac Power Systems,Inc.
Outdoor lighting
Before electricity, many streetlights were operated by gas.
Propane-fueled outdoor lighting is still available in both wallmounted and post mounted fixtures. The light emitted combines
old style charm with energy efficiency. Even better, this lighting
requires no electricity and thus can operate in a power outage.
Some gas lights can even be adapted to an on/off switch just like
electric lights.
Mosquito Eliminators
Part of enjoying an outdoor patio with a grill, lighting, and heating
is not sharing that space with mosquitoes. Propane mosquito
eliminators generate non-toxic compounds that act like a magnet
for mosquitoes, drawing them away from patio areas and trapping
them in the device.
MicroCHP Systems
Imagine a propane-fueled device that produces both heat and
electricity. Such “cogeneration” devices have existed for several
decades, but only for large industrial applications. However, new
technology allows the concept to be scaled down for residential
and light commercial buildings. MicroCHP (Combined Heat
and Power) units consist of a small internal combustion engine
fueled by propane that turns the shaft of an electric generator.
Heat produced by the engine is collected through a liquid cooling
system and can be used to heat a building or domestic water.
Modern engineering allows such devices to operate with very low
noise levels. Low enough that they can be installed in a residence
just like a furnace or boiler.
Chilled Water Cooling
Although it may seem counterintuitive, it’s possible to economically
produce chilled water for building cooling by burning propane.
The process is called absorption cooling, and it has been used for
several decades in larger commercial buildings. Small absorption
cooling units are now available for cooling residential and light
commercial buildings. They’re discussed in more detail in section 9.
Propane is Economical
High performance condensing boilers and furnaces convert
propane to heat at efficiencies significantly higher than those of
current-generation oil-fired equipment. Higher efficiency means
lower fuel cost.
Sec1:2
But fuel cost is only part of the total operating cost of any heating
system. For example, propane-fueled boilers and furnaces typically
require less maintenance than do boilers and furnaces fired by fuel
oil. They do not require the annual replacement of fuel filters and
burner nozzles.
Most modern propane-fueled boilers and furnaces can also be
vented through exterior building walls thus eliminating the cost
of installing and maintaining a chimney. The installed cost of a
conventional chimney, even in a new home, can easily exceed
$2,500.
The use of propane rather than utility-supplied natural gas
eliminates the monthly service charge associated with having a
gas meter on the premises. Such charges are added to every
month’s utility invoice, and often exceed $200 per year. This adds
up to thousands of dollars over the life of the system.
Propane is Environmentally Friendly
Propane is one of the lightest, simplest hydrocarbons in existence.
This makes it one of the cleanest burning of all fossil fuels. The
on-site emissions associated with burning propane have lower
carbon content than gasoline, diesel, fuel oil, and ethanol.
A significant percentage of the electricity supplied in the United
States is generated by coal-burning power plants. Burning a
pound of coal releases more than twice the amount of carbon
dioxide as does burning a pound of propane. By using propane
rather than electricity, consumers can reduce emissions and help
preserve the environment.
Figure 1-5
According to the federal
Environmental Protection
Agency, much of the sulfur
dioxide in the atmosphere,
which produces acid rain,
comes from coal-fired power
plants. In contrast, the
production and combustion of
propane produces very little of
the compounds responsible for
acid rain.
Propane gas is nontoxic as well
as insoluble in water. If a leak
A modern propane storage tank
in a propane tank or supply
being installed underground
system should ever occur,
Source: PERC
the propane vaporizes and
dissipates into the air. It will not create dangerous floor puddles as
will other liquid fuels.
Approximately 90 percent of the propane used in the United
States is produced in the United States. This reduces dependence
on foreign energy suppliers as well as the transportation energy
required to import foreign fuel.
Propane is Convenient
Given all the uses for propane, you may be wondering how it’s
supplied to all the potential appliances. The answer is a modern
underground storage tank connected to a distribution piping
system within the building.
Figure 1-4
Underground storage tanks are quickly and easily installed by
propane professionals.
On-Site Emissions for Various Fuels
186.8
Excavation depths of 5
feet are usually sufficient
100
to bury a propane tank.
92.7
90
Only the small service
78.6
80
72.5
dome at the top of the
70.7
70.5
70
66.6
tank is visible above
62.7
60
ground, and can easily
52.8
50
be integrated with
40
landscaping so that
30
it’s virtually unnoticed.
20
Underground storage
10
tanks for propane range
0
in size from 100 to 2000
Natural
LPG
Ethanol
Motor
Kerosene Distillate
Residual Bituminous Electricity
gallons. A 500-gallon
Gas
(E85)
Gasoline
Fuel
Fuel (Heavy
Coal
(Diesel)
Fuel Oil)
tank is usually sufficient
kg CO2 per MMBtu
Sources: DOE 1994, EPA 2007
to supply the needs of
a four-bedroom home.
Emissions of propane relative to other fuels
These
tanks
are
not
subject
to
the
stringent
inspections imposed
Source: PERC
on underground tanks storing fuel oil, gasoline, or other fuels. To
Sec1:3
find out more about propane and underground propane tanks go
to www.ces.pratt.edu and take a free on line course.
Figure 1-6
A single buried pipe routes propane to the building. From there it
can be divided into individually controlled branches serving each
propane appliance. Modern flexible stainless steel tubing can be
installed faster than traditional threaded iron pipe, and with far
fewer joints. A central propane distribution manifold can supply
several branch supply tubes, each one sized for the appliance it
serves.
Summary
As you can see, propane truly is exceptional energy. The sections
that follow show you one of the most unique ways to apply this
energy in systems that supply a wide range of heating and cooling
requirements for buildings. The combination of propane and
hydronics technology is both complementary and synergistic.
Together they’re a combination that’s hard to beat.
Propane can be easily distributed
to several appliances within a
home using modern flexible CSST
piping.
Source: Gastite
Sec1:4
Section 2:
What is Hydronic Heating?
T
he best way to describe a hydronic heating system is
as “a conveyor belt for heat.” This heat is loaded on at
the heat source, carried to where it’s needed by water
moving through the piping, and then unloaded at one or more
heat emitters as shown in figure 2-1. Within this concept are
thousands of options that allow hydronic heating systems to be
specifically tailored to the needs of the building and its owner.
Figure 2-1
circulator
water flow
The vast majority of residential and light commercial hydronic
heating systems are classified as closed-loop systems. The water
they contain is sealed in and under slight pressure. Ideally, the
same water recirculates through the system over and over, year
after year. Very small quantities of fresh water are added only when
necessary. This minimizes the potential for corrosion and allows
the system to last for decades.
Some hydronic heating systems are as simple as a water heater
connected to a loop of flexible plastic tubing that warms a
bathroom floor. Others may use multiple boilers and a wide
assortment of heat emitters specifically selected to match the
thermal, aesthetic, and budget constraints
heat released
of a particular building. Those same boiler(s)
may also provide the building’s domestic hot
water, heat the swimming pool, and even
melt snow as it falls on the driveway. The
versatility of hydronic systems makes such
options available in both new construction
and building retrofitting.
heat emitter
heat emitter
When properly planned and installed,
modern hydronic heating can provide years
of unsurpassed comfort in nearly all types
of homes as well as commercial buildings
— comfort so good you’ll literally forget its
winter as you walk in the door.
propane
boiler
“A hydronic heating system is a conveyor belt for heat.”
When water absorbs heat inside the heat source, its temperature
increases. It doesn’t change from a liquid to a vapor as in a steam
heating system. In fact, good hydronic system design prevents
liquid water from changing to a vapor at any point in the system.
As water travels through the distribution system, a small portion of
the heat it carries is released from the piping and other components.
When the water passes through a heat emitter more of the heat is
released. The rate at which heat moves from the heat emitter into the
room depends on several things, including the temperature of the
water as well as that of the room, the size of the heat emitter, and
the water flow rate.
Sec2:5
Section 3:
The Advantages of
Hydronic Heating
T
here are many unique benefits associated with using
a propane-fueled heat source in combination with a
hydronic distribution system. Any one of them might
be the “key” reason for a prospective customer to choose this
unique combination of fuel and heat delivery method. This section
describes and illustrates a synergistic collection of benefits that is
unrivaled by other heating options.
Consider the ducting installation shown in figure 3-2. Beyond their
unsightly appearance, such ducts reduce headroom and likely
prevent the ceiling from being finished. They also are subject to
sagging or damage over time.
Figure 3-2
uperior comfort
S
Hydronic heating has long enjoyed a well-deserved reputation
for providing excellent thermal comfort. Some hydronic systems
provide this comfort by warming the surfaces within a room as well
as the room’s air. Such systems address the fact that providing
true thermal comfort involves more than simply maintaining a
room at a given air temperature. They release heat into spaces in
harmony and balance with human physiological needs. Although
it may not be apparent where the heat is coming from it will be
obvious that the comfort is far superior to that provided by other
systems.
Ducting often compromises headroom in basements.
Figure 3-1
Figure 3-3
In contrast, the small flexible tubing shown in figure 3-3 is easily
routed through floor framing. This type of tubing is ideal for new
construction as well as retrofit applications where access to
building framing cavities is more difficult.
Barefoot-friendly floors on the coldest day of winter
nobtrusive installation: Another significant advantage of hydronic
U
heating is the ability to install it without having to drill, saw, or
otherwise hack out major pieces of the building’s structure.
This benefit is a direct result of the physical properties of water.
A given amount of water can absorb almost 3,500 times more heat
than the same amount of air. This implies that a hydronic system
only has to move about 1/3500 as much volume as does a forcedair system of equal heating capacity. This drastically reduced
volume requirement allows small flexible tubing to replace large
cumbersome ducting.
Small, flexible, hydronic tubing routed through floor framing
Here’s another way to put the difference between hydronic tubing
and forced-air ducting in perspective. A 3/4-inch diameter tube
can deliver the same amount of heat as an 8-inch high by 14-inch
wide duct when both systems are operated under typical
conditions. This contrast is shown in figure 3-4.
Sec3:6
Figure 3-4
2 x 12 joist
this cut would destroy the load-carrying
ability of the floor joists
14" x 8" duct
3/4" tube
A 3/4-inch diameter tube carrying water can deliver the same
amount of heat as 8-inch by 14-inch duct carrying air.
Figure 3-5
When necessary, a 3/4” tube is easily routed through the home’s
floor framing without having to drill large holes that could weaken
the structure. In many situations the entire hydronic distribution
system can be easily concealed within the home’s structure.
Accommodating an 8-inch x 14-inch duct in a similar situation is
a very different matter. With the possible exception of wooden
“I-joist” framing, or specially designed floor trusses, a duct this size
simply can’t be run laterally through the floor framing. The
necessary compromise is often to suspend the ducting from
the bottom of floor framing as shown in figure 3-2, or conceal
the ducting by building valences or soffits around it within living
spaces.
Why should the aesthetics of an otherwise meticulously planned
building be compromised to “shoe-horn” in the heating system?
Aesthetic issues aside, there are countless buildings in North
America where poor comfort is the result of a compromised
ducting system.
esign Flexibility
D
Hydronic heating offers virtually unlimited ways to accommodate
the comfort needs, usage, aesthetic tastes, and budget constraints
of any building. In many cases, a single propane-fueled boiler can
provide space heating, domestic hot water, as well as specialty
requirements such as pool or hot tub heating and melting snow off
steps, sidewalks, and driveways as shown in figure 3-5. No other
type of heating system offers this much versatility from a single
heat source.
Hydronic snowmelting keeps this walkway free of ice and snow.
Courtesy of Gary Todd
lean Operation
C
One of the leading complaints from owners of forced-air heating
systems is the amount of dust and other airborne pollutants their
systems distribute through the house. Although sometimes the
result of poorly maintained filters, this complaint demonstrates one
of the potential pitfalls of forced-air distribution systems.
Figure 3-6 shows the inside of ducting recently removed from a
house. The inside of the ducting is coated with dust, pet hair, and
mold spores from years of operation even when a filter was
present in the system. The occupants of this house had been
breathing air that, in some cases, passed through this ducting
several times each hour.
Sec3:7
Figure 3-6
Figure 3-8
Properly designed hydronic heating systems operate with virtually
no detectable noise
Inside of ducting recently removed from a forced-air heating
system
In contrast, most hydronic heat emitters induce very gentle, almost
imperceptible air circulation. The heat emitters that use small fans
or blowers create room air circulation rather than whole-house air
circulation. People with allergies or other respiratory conditions are
especially appreciative of the reduced air movement afforded by
hydronic heating.
onability
Z
A heating system that maintains an entire building at the same
temperature doesn’t give occupants with individual comfort
preferences much choice. The heating system in most homes
should divide the building into two or more independently
controlled comfort zones. Such systems can reduce energy
consumption by maintaining lower air temperatures in unoccupied
areas. They also allow the comfort level of rooms to be adjusted to
suit individual tastes and activity levels.
Figure 3-7
Imagine a heating system that automatically adjusts itself as
sunlight shines in the windows of some rooms but not others. One
that automatically reduces heat output when several people gather
in the living room, but still maintains a toasty warm bathroom for
another person to shower in. This type of “room-by-room” zoning is
easy to accomplish using hydronics without resorting to the
complex and costly hardware necessary for zoning forced air
systems. Some hydronic systems provide room-by-room comfort
control at each heat emitter without need of thermostats and
associated wiring. An example of such a product is shown in
figure 3-9.
Hydronic heating is especially well suited for those will allergies
or other respiratory conditions
Figure 3-9
uiet Operation
Q
Today’s homes are often thought of as a sanctuary from the noises
associated with work and public life. Why should this solace be
compromised by a noisy heating system?
A properly installed hydronic system will operate with virtually
no detectable sound in the occupied areas of a home. This is
especially true for modern propane-fueled boilers, which operate at
extremely low noise levels—so low that many people have to place
their ear against the boiler to hear any sound at all. Some modern
hydronic systems operate with continuous water circulation and
variable water temperature to eliminate piping expansion noises.
Non-electric thermostatic radiator valve allows for room-by-room
comfort control
Sec3:8
bundant Domestic Hot Water
A
Although most people think of hydronic heating as a method for
warming buildings, it also provides a unique and efficient way to
provide domestic hot water.
loss is very undesirable in situations where piping or ducting is
routed through cool basements, crawl spaces, or attics. Heat loss
to such spaces is truly heat lost—heat you paid for, and heat that’s
needed elsewhere in the building to maintain comfort.
Modern luxury homes, some with six or more bathrooms, can place
heavy demands on ordinary tank-type water heaters. In some
cases those heaters simply can’t keep pace with the demand,
especially when several fixtures are in use simultaneously. The
inevitable result is “scheduling” showers or baths in spaced out
sequence to avoid running out of hot water. The owners are forced
to conform to the ability of the water heater rather than to their
own convenience.
Even if the tubing and ducting were insulated with the same
material, heat loss from the ducting would remain much higher
than that of the hydronic tubing. It would also cost more to insulate
the ducting because of its greater surface area.
Why should owners of such homes, many of whom have spent
considerable funds for luxury bathrooms, have to compromise the
usage of those fixtures based on limitations in the water heating
equipment?
Fortunately, a properly configured propane-fueled boiler system
combined with a high capacity indirect water heater can supply
such hot water demands indefinitely. Such systems provide the
ideal combination of storage and heating capacity to efficiently
supply small hot water demands as well as the large demands
created when several bathrooms are in simultaneous use. Heat
for domestic hot water comes from the same propane-fueled
boilers that heat the house, warm the pool, and perhaps even
melt snow off the driveway. Special controls allow the system to
treat the domestic water heating load as a priority. The result is a
system that can always keep pace with the hot water demands of
a modern luxury home.
educed Operating
R
Cost
Hydronic systems reduce
the cost of heating a
building in several ways.
For starters, the small
tubing used in modern
hydronic systems loses far
less heat to its
surroundings than does a
duct of equivalent heating
capacity. For example, an
8-inch by 14-inch duct
loses about 16 times more
heat to its surroundings
than does a 3/4-inch
copper tube, assuming
both operate at the same
temperature. This heat
Another way hydronic systems reduce energy use is in the electrical
power demand of a circulator relative to that of a blower in a forcedair system such as used with furnaces or heat pumps. With good
design it’s possible to supply heat to a 2,500 square foot house
with a circulator that consumes 80 watts or less of electrical power
at full speed. By comparison, the blower in a geothermal heat pump
of equivalent heating capacity could demand over 1600 watts—20
times more electrical power! Assuming each distribution system
operated for 3,000 hours a year in an area where the current cost
of electricity is $0.10 per kilowatt-hour, the blower would require an
additional $456 dollars per year for electricity relative to that required
by the small circulator. Over the life of the system this would add up
to thousands of dollars in higher operating cost.
Figure 3-11
Figure 3-10
hydronic systems operate with less electrical power demand than
forced-air systems
Some hydronic systems, especially those that heat floors in rooms
with high ceilings, lower energy consumption by reducing the
tendency of warm air to rise to the ceiling while cool air pools at
floor level. This effect is called air temperature stratification. In
addition to creating higher heat loss through the ceiling, it’s just
the opposite of what’s needed for true thermal comfort.
Hydronic systems can also supply
high-capacity domestic water heating
Because hydronic floor heating doesn’t overheat room air it
discourages air temperature stratification. Air temperatures near
the ceiling of tall rooms heated by warm floors are typically lower
than air temperature at floor level. This enhances comfort and
reduces fuel usage.
Sec3:9
The ability to easily zone a hydronic system provides the ability
to maintain unoccupied rooms at reduced temperatures while
maintaining comfort in occupied rooms. Reduced air temperatures
decrease building heat loss and thus reduce fuel consumption.
Some propane-fueled boilers can operate with efficiencies of 95
percent plus when combined with low temperature hydronic
distribution systems. Such boilers extract almost all the available
energy in each gallon of propane and pass it to the hydronic
distribution system, which delivers it to the building in a way that’s
ideally matched to human comfort requirements.
Hydronic heating supplied by a propane-fueled boiler is a
combination that’s hard to beat. The sections that follow elaborate
on many of the options available with this combination of fuel and
delivery system. They will show you what modern hydronic heating
hardware looks like and how it’s assembled into a compact, quiet,
efficient, and affordable comfort system.
Sec3:10
SECTION 4:
The Basic Components of a
Hydronic System
Each of these options has strengths and limitations. Some
constrain the system design in terms of operating temperature, or
flow rates. Some can only be used with specific types of heat
emitters. The cost and local availability of certain fuels obviously
has a big impact on heat source selection.
T
hose wanting to design or install quality hydronic heating
systems must be committed to ongoing learning. New
products and design methods will vie for their attention
as the hydronic heating market grows and more people demand
the benefits it offers.
Figure 4-2
Learning must start with the fundamentals. What are the basics
components found in almost every type of hydronic heating
system, and what are their functions?
This section gives you a basic understanding of the “building
blocks” used in almost every residential and light commercial
hydronic system. Later sections will demonstrate the repeated
usage of these components in a wide variety of systems.
Figure 4-1 shows the fundamental components of a single circuit
hydronic system.
Figure 4-1
air
separator
heat released to building
circulator
flow
check
heat emitter
room
thermostat
pressure
relief
valve
boiler
high
limit
controller
make-up water
assembly
backflow preventer
pressure reducing valve
expansion
tank
purging
valve
propane
input
propane-fired boiler
The basic components in a hydronic system
Heat Source
The starting point in a hydronic system is getting heat into the
water. While it might be said that almost any device that heats
water is a potential hydronic heat source, some options are clearly
more practical than others.
One of the most common and most versatile hydronic heat
sources is a propane-fueled boiler. Such boilers are discussed in
detail in section 5. Other possible options include geothermal heat
pumps, solid fuel boilers, and solar energy systems.
An example of a modern wall-hung
propane-fueled boiler
Source: Triangle Tube
Circulator
Often referred to as a pump, the circulator is the
device that “motivates” fluid to flow through the
system in the intended direction, and at a suitable rate. The key
component within a circulator is its impeller, which is rotated by
an electric motor. As water flows through the spinning impeller
mechanical energy called “head” is transferred to the fluid. The
evidence of this added mechanical energy is higher pressure at
the circulator’s discharge port compared to its inlet port.
Water always flows from an area of higher pressure to an area
of lower pressure. The higher pressure water leaving a circulator
wants to get back to that circulator’s inlet. It will do so through
any available pathway. The fundamental concept in any hydronic
system is to create piping pathways that let water carry heat
throughout the building as it flows from the circulator’s outlet back
to its inlet.
Sec4:11
Figure 4-3 shows a typical residential scale hydronic circulator.
Such a product is specifically known as a “wet-rotor circulator.” It is
entirely cooled and lubricated by the fluid passing through it, and
does not require oiling as some earlier generation circulators do.
Wet-rotor circulators have been in use for over three decades and
have earned a reputation for reliability and quiet operation.
Figure 4-4
Many modern circulators can operate at different speeds
depending on the circuit they are installed in. A switch on the
junction box selects the operating speed.
Figure 4-3
A modern air separator
A modern multi-speed wet-rotor circulator
Air separator
Any closed-loop hydronic system operates best when free of
internal air. Some hydronic systems can’t even produce flow until
most of the air in the piping has been expelled.
An air separator is a component specifically designed to extract
air bubbles from the flowing water and channel them to a venting
device where they are automatically ejected from the system. Many
different types of air separators are currently available. All function
by reducing the fluid’s flow velocity, as well as providing surfaces
that air bubbles can cling to as they rise toward a venting device.
Air separators function best when located near the outlet of the
heat source, where the hottest fluid in the system passes through
them. This is where molecules of oxygen, nitrogen and other gases
are most likely to coalesce into bubbles that can be captured
and ejected.
Flow-check Valve
An important but often overlooked fact of hydronic heating is that
hot water wants to move up and cool water wants to move down.
This happens because hot water is less dense and therefore
lighter than cool water.
Figure 4-5
If an unblocked flow
path exists between
an area of heated
water and an area
of cool water, nature
makes sure a slow
but persistent flow
is established in an
attempt to equalize
these temperatures.
Such a flow can
occur even when
all circulators in the
system are off.
Example a flow-check valve
This natural
convection current has been called many things, including “ghost
flow”, “thermosyphoning” and “heat migration.” It can result in many
aggravating problems by moving heat into area of the building
where it’s not needed—a sort of “thermal leak” in the system.
Sec4:12
A flow-check valve is one way to prevent such a situation. It
contains a weighted metal plug that seats over the opening in the
valve. This plug is heavy enough to block flow until the circulator
turns on, at which time the plug pops up allowing flow through the
valve. As soon as the circulator stops, the plug drops back down
to block flow through the valve (in either direction).
Some hydronic circulators are now available with internal springload flow check valves. These eliminate the need to install a flow
check valve in the circuit, and generally reduce installation cost.
Expansion Tank
All fluids expand when heated. If a closed-loop hydronic system
where completely filled with water the pressure in that system
would rise rapidly as soon as the water temperature increased.
Dangerously high pressures that could rupture piping components
would quickly develop.
Figure 4-6
To prevent this, all
closed loop hydronic
systems must have
an expansion tank.
This tank contains a
sealed internal
chamber filled with
pressurized air. The
air is separated from
the water in the
system by a flexible
rubber diaphragm.
As the water is
heated the sealed air
volume behind the
diaphragm is partially
compressed by the
expanding water,
Example of a diaphragm-type
expansion tank
system pressure
increasing only slightly. When the system turns off and the water
cools, the pressurized air volume expands as the water shrinks
back to its original volume.
Pressure Relief Valve
The forces that expanding water can generate are very
powerful. To prevent dangerously high pressures from occurring
every closed-loop hydronic heating system must be equipped
with a pressure relief valve. Most systems used in residential or
light commercial buildings have pressure relief valves rated at 30
pounds per square inch (psi). Anything that allows internal
pressure to climb to this setting will open the valve and
immediately release fluid from the system, lowering its pressure.
Figure 4-7
Pressure relief
valves should
always be installed
with their stem in
a vertical upright
position as shown
in figure 4-7.
Most are installed
directly into the
boiler or close to
it. They should
be equipped
with a discharge
pipe that ends
near a floor drain.
This pipe cannot
contain any type of
valve or flow
A pressure relief valve
restrictor. The lever
at the top of the valve can be lifted to verify proper operation. This
should be done during annual maintenance checks.
Control System
An ideal hydronic heating system would always generate and deliver
heat to the building at exactly the same rate the building loses heat
to the outdoors. Such a “fully modulating” system could vary heat
output from zero to full capacity as necessary.
Figure 4-8
Unfortunately, such full
modulation is not currently
possible for combustion
type heat sources. In lieu of
this, many hydronic control
systems regulate heat output
by turning the heat source and
circulator(s) on and off. Heat
is delivered to the
building in intervals, the length
of which depends on how
large the load is. For example,
on a very cold day, a properly
sized boiler would remain on
most of the time. However,
during a milder day the heat
source may only be on 10-25
percent of the elapsed time.
A manually-reset temperature
limit control
The length of the on-cycle
and off cycle determines the total heat delivered to the load over a
given time. A room thermostat similar to that used in other heating
systems controls this on/off cycling.
Sec4:13
Figure 4-9
A controller that adjusts boiler temperature
based on outdoor temperature.
Figure 4-10
Hydronic heating
systems also have
controls that regulate
the water
temperature
delivered to different
parts of the system.
It is not uncommon
for a boiler to deliver
170 ºF water to fintube baseboard heat
emitters while at the
same time delivering
110 ºF water to a
radiant floor slab in a
different part of the
same building.
Still other controls provide safety against excessive high
temperatures or water loss in the system. In most situations, these
controls are required by code on all hydronic systems. A specific
type of safety control called a manual reset high limit—shown in
figure 4-8—turns off the boiler and prevents it from automatically
restarting if water leaving the boiler reaches a set temperature.
Think of this device as a “circuit breaker” for water temperature.
Figure 4-9 shows a modern microprocessor controller for
regulating water temperature in the distribution system based on
outdoor air temperature.
Make-Up Water Assembly
All hydronic systems experience minor pressure drops over time.
Sometimes it’s caused by air being expelled from vents. Other
times it’s the result of evaporation from valve packings or circulator
gaskets. Still other times it’s caused by water loss when a
component is serviced.
An automatic make-up water assembly feeds new water into the
system whenever the system’s pressure drops below a preset
value, typically in the range of 10 to 20 psi. Hence it “makes up”
for minor water losses.
An automatic make-up water assembly that maintains system
pressure. Courtesy of Caleffi North America
The pressure reducing valve detects when the system’s pressure
drops below a set lower limit and responds by allowing water in to
restore system pressure.
It’s important to understand that following their initial filling and air
purging, properly functioning closed-loop hydronic systems require
only minor amounts of makeup water. Large amounts of fresh
water are NOT good for closed loop systems containing iron or
steel components. The dissolved oxygen in fresh water
encourages corrosion and sludge formation. Frequent feeding
of fresh water through the pressure reducing valve is a sign the
system needs servicing.
Purging Valves
When a hydronic system is put in service it’s important to rid the
system of air as it is filled with water. Purging valves are used in
combination with the makeup water assembly to establish a rapid
water flow through the system as it is filled. This is called purging.
The rapid flow displaces air bubbles and pulls them along with the
water. The mixture of water and air exits through the side port of
the purging valve. When this exiting stream is free of air bubbles
Figure 4-11
A typical make-up water assembly consists of a backflow preventer,
pressure reducing valve, and shut off valve.
The backflow preventer does just what its name implies. It prevents
any fluid in the hydronic system from migrating backward into the
building’s potable water piping. Most plumbing and mechanical
codes mandate a backflow preventer on any hydronic system
connected to a building’s potable water system.
Example of a purging valve for removing air from the system.
Courtesy of Webstone Valve
Sec4:14
the purging process is complete, and the side port of the purging
valve is closed. The use and correct placement of purging valves is
essential to properly filling the system and preparing it for
operation. An example of a purging valve is shown in figure 4-11.
Figure 4-13
Heat Emitters
All hydronic heat emitters extract heat from water flowing through
them, and deliver that heat to the building space in which they
are located. However, various types of heat emitters use different
forms of heat transfer to accomplish this task.
Some devices, like the fin-tube baseboard (see figure 4-12), and
fan-coils rely on convective heat transfer. They directly heat room
air as it passes through them. The heated air flows into the room
carrying the added heat with it.
Figure 4-12
An example of a fin-tube baseboard convector.
Courtesy of Weil-McLain
Other types of hydronic heat emitters rely on thermal radiation to
carry the majority of their heat output into the room. An example
of such a heat emitter is a concrete slab with embedded tubing.
Figure 4-13 shows tubing installed over polystyrene insulation
awaiting the concrete slab.
Although the term “thermal radiation” may sound ominous, it is
simply low intensity infrared light. Such radiation is completely
natural and not harmful in any way. It behaves similar to visible light,
but our eyes can’t see it. It travels out from the heat emitter and is
quickly absorbed by the objects and surfaces within the room. The
instant thermal radiation strikes these surfaces it ceases to exist as
radiation and becomes heat, warming the object that absorbed it.
The warming of objects and room surfaces significantly improves
comfort.
Flexible hydronic tubing that will be embedded in a concrete
floor. Courtesy of HYtech Heating
Where Does This Equipment Go In A Building?
Traditionally, the boiler of a residential hydronic heating system is
installed in the basement or crawl space. An example of such an
installation is shown in figure 4-14. In commercial buildings the
boiler is typically be installed in a separate mechanical room.
Figure 4-14
Although such
installations are
common, they are not
the only option. Many
modern propanefueled boilers are
compact enough to
be installed in spaces
such as laundry rooms,
utility closets, pantries,
or garages. Such
boilers are often wallmounted as shown
in figure 4-15 (next
page).
Example of a boiler installed in a basement. Courtesy of ECR International
Don’t be fooled by the
small size of wall hung
boilers. In most cases they’re able to supply all the space heating
and domestic hot water requirements of a typical home.
Most of the piping used in a hydronic distribution system is usually
concealed within the wall and floor structure of the building. This is
possible because the piping is usually less than 1-inch in diameter,
and easily slides through holes in floor joists or studs. Some of
the distribution systems discussed in section 7 of this publication
make use of 1/2-inch and even 3/8-inch diameter flexible tubing as
shown in figure 4-16. This small flexible tubing is easily and quickly
Sec4:15
pulled through building structures much like electrical cable. The
remaining piping and components are typically mounted close to
the boiler as shown in figure 4-17.
Figure 4-15
The location of heat emitters
depends upon their design.
One of the traditional
hydronic heat emitters used
in North America is called fintube baseboard. It consists
of a metal enclosure a few
inches tall that houses a
copper tube with closely
spaced aluminum fins. Fintube baseboard is installed
along the base of walls in
place of traditional wooden
baseboard as shown in figure
4-18.
Figure 4-17
Typical boiler room piping. Courtesy of HYtech Heating
Figure 4-18
A wall-mounted boiler installed
in a laundry room. Courtesy of
Monitor Products
Another type of hydronic
heat emitter is called a panel
radiator. Such radiators are
installed on walls and come in a wide variety of shapes, sizes, and
colors.
Figure 4-16
A short length of fin-tube baseboard
Figure 4-19
Example of 1/2-inch size flexible PEX-AL-PEX tubing.
A special type of panel radiator intended for use in bathrooms,
kitchens, and vestibules is called a “towel warmer.” It not only
warms the room, but also provides a rack that can quick dry damp
towels, gloves, and garments. An example is shown in figure 4-19.
The ultimate “out-of-sight”
hydronic heat emitter is a
heated floor, wall, or ceiling.
Flexible tubing is
embedded within one or
more of these room
surfaces during
construction, and is
completely out of site when
those surfaces are finished.
The only difference that will
be noticed is gentle radiant
warmth from what might
otherwise be cold
uninviting surface.
We’ll discuss options for
propane-fueled boilers,
Wall hung towel-warmer radiator.
Courtesy of Myson
distribution systems, and
heat emitters in more detail in sections 5, 6 and 7.0
Sec4:16
Section 5:
Propane-Fueled Heat Sources
Figure 5-2
The lower thermal mass of
a copper tube boiler allows
it to reach normal operating
temperatures quickly after
start-up.
A
lthough there are many options for hydronic heat
sources, one of the most versatile is a modern
propane-fueled boiler. Almost every boiler designed
to operate with natural gas can be easily configured to operate
with propane. This includes traditional cast-iron, steel, and copper
tube boilers, as well as the ultra-high efficiency modulating /
condensing (mod/con) boilers. When fueled by propane, all such
boilers provide clean combustion, high efficiency, and very low
sound levels.
Figure 5-1
Cast-Iron Boilers
Figure 5-1 shows an example
of a propane-fueled boiler that
has a cast-iron heat exchanger.
Cast-iron boilers have been used
for over a century. They are often
found in traditional higher
temperature hydronic systems
such as those supplying fin-tube
baseboards. They can also be
used in modern low temperature
radiant panel heating systems,
as well as “multi-load / multitemperature” systems that supply
heat to pools and snowmelting
subsystems.
One very well established
advantage of cast-iron boilers is
long life. It’s not uncommon to find
such boilers operating 30 years
after they were installed. Very few other home appliances can claim
such a long service life. As with any boiler, this long life is the result
of proper application and annual maintenance.
Example of a cast-iron boiler.
Courtesy of Weil-McLain
Cast-iron boilers also provide significant thermal mass to the
system. This provides stability to systems that supply several
independently-controlled zones, and prevents short-cycling.
Copper Tube Boilers
Another type of boiler that can operate with propane has a heat
exchanger constructed of specially formed copper tubing. Because
copper transfers heat better than cast iron, less metal is required
for the boiler’s internal heat exchanger. This results in a lighter, and
more compact boiler. Such characteristics are desirable in
situations where space is limited, or where low weight is needed
due to access or structural limitations of the building.
Example of a copper tube boiler.
Courtesy of Lochinvar
Both cast-iron and copper
tube boilers are categorized
as conventional boilers.
They are intended to
operate at temperatures
high enough to prevent
water vapor in the exhaust
stream from condensing
(e.g. changing from vapor to
liquid) within the boiler or its
vent pipe.
Well-maintained cast-iron and copper tube boilers typically operate
with combustion efficiencies in the range of 85 to 87 percent. They
are usually vented through a chimney, although some cast-iron and
copper tube boilers can be vented directly through the exterior
wall of building and thus eliminate the need for a chimney.
Modulating / Condensing Boilers
During the last decade a new class of propane-fueled boilers has
steadily gained market share—mod/con (modulating burner,
condensing) boilers. These boilers are equipped with heat
exchangers made of stainless steel or aluminum, and designed
so that vapors produced during combustion can condense within
the boiler – just the opposite intent of the previously discussed
conventional boilers. Why the difference? In a word: Efficiency.
Boilers capable of condensing all the water vapor in the exhaust
stream will experience a nominal 10 percent increase in thermal
efficiency relative to boilers that do not operate with such
condensation. In the right application, a propane-fueled mod/con
boiler can attain thermal efficiencies of 95 percent or more.
The stainless steel or aluminum heat exchangers used in mod/con
boilers are specifically designed to operate under these conditions
without the corrosion that would beset cast-iron, steel or copper
boilers under the same conditions.
The key to operating a mod/con boiler at sustained high efficiency
is to match it with a low temperature distribution system. Slab-type
radiant floor heating is a good example of such a low temperature
system. Without such low temperature operation, flue gases will
not condense to the extent necessary to achieve sustained high
efficiency.
Sec5:17
Figure 5-3
Multiple Boiler Systems
Most people think that all houses with hydronic heating have a
single boiler. They assume that a small boiler is used in a small
house, while a large boiler is required in a big house. Although
this is common for many single family houses, it’s not the only
possibility.
Many large homes with multiple hydronic heating loads such as
space heating, domestic water heating, pool heating, and snowmelting are excellent candidates for a multiple boiler system.
The concept of a multiple boiler system is simple: Instead of using
a single boiler with sufficient heat output to handle all loads, two
or three smaller boilers with the same total heating capacity are
installed. There are several reasons that favor this approach.
First, having multiple boilers allows for partial heat delivery if one
boiler is not operating due to a malfunction. Simply put, it’s better
to have some heat rather than no heat. This is especially important
in locations where extreme temperatures might freeze up
non-operational systems.
A wall-hung propane-fueled mod/con boiler.
Courtesy of HYTech Heating
Many mod/con boilers are small enough and light enough for wall
mounting as shown in figure 5-3. This conserves floor space within
buildings and allows mechanical rooms to be smaller than with
traditional floor-mounted boilers. The extremely low sound levels at
which these boilers operate do not create annoying noises inside
the building.
Second, multiple boiler systems deliver higher seasonal
efficiencies compared to a single large boiler of equivalent heating
capacity. This comes from the ability of a multiple boiler system
to “track” the total heating load of the system and only operate
the boiler(s) necessary to meet that load at any given time. This is
called “staging” the boilers. Thus, when a small zone needs space
heating only one of three boilers in a multiple boiler system may
operate. However, when two or three showers go into
Figure 5-4
Mod/con boilers are designed as “sealed combustion” appliances.
All air needed for the combustion process is drawn from outside
the building, typically through PVC pipe as small as 2-inch in
diameter. The cooled combustion gases leaving the boiler are also
directed outside through a separate PVC, CPVC, or stainless steel
pipe. A boiler using sealed combustion does not draw any air from
within the building. This prevents interference between the
combustion stream of the boiler and others fans that may be
operating within the building. Sealed combustion also prevents
contaminants such as vapors from cleaning fluids or chlorine
bleach that might be present within the building, from being drawn
into the boiler where they can cause corrosion. Finally, sealed
combustion boilers are very safe in that they constantly monitor the
proper flow of exhaust gases. If the internal combustion fan cannot
establish and maintain proper flow the boiler automatically turns off
until it can be serviced.
A residential multiple boiler system supplying several loads.
Courtesy of Paul Rohrs
Sec5:18
simultaneous operation, or it’s time to melt snow off the driveway,
all three boilers will automatically turn on. The intelligence to
operate a multiple boiler system is provided by a small
microprocessor-based controller. In some cases this intelligence
is even built into the boiler’s electronics and only needs to be
activated when the system is installed.
Figure 5-6
Finally, multiple boiler systems use smaller lighter boilers that are
easier to move into or out of a building compared to a single large
boiler. This is especially important in retrofit applications.
Figure 5-4 (previous page) is an example of a multiple mod/con
boiler system in a residential application. Notice that these boilers
supply several independently controlled circulators seen at on left
side of the figure. The PVC tubing used for combustion air supply
and venting is visible behind the boilers, as is the PVC condensate
drainage piping required on all mod/con boilers.
Both conventional and mod/con boilers can be set up in multiple
boiler groups. An example of a residential system with dual castiron boilers is shown in figure 5-5. A system with dual wall-mounted
mod/con boilers is shown in figure 5-6. Section 7 of this
publication shows how the piping is configured in such systems.
Two wall-mounted mod/con boilers operated as a
multiple boiler system. Courtesy of Foley Mechanical
When the distribution system can operate at water temperatures
lower than 140 ºF for many hours each year a mod/con boiler will
provide higher fuel efficiency, albeit at a higher installed cost.
Figure 5-5
It’s also important that the boiler selected can be locally serviced.
Few would debate that mod/con boilers are more sophisticated
devices than traditional cast-iron and copper tube boilers. It’s
imperative that those installing such products are fully familiar with
their operation and can service them when necessary.
Another factor that might tip the scales is the type of venting
desired. As previously mentioned, many conventional boilers are
designed to be vented by a chimney. Some are available for sidewall venting. In situations where a chimney is not possible, boiler
selection will be limited to those units that can be sidewall vented.
Two cast-iron boilers operated as a multiple boiler system
Which Propane-Fueled Boiler is Right for You?
Asking which propane-fueled boiler is right for you is like asking
which automobile, or which house, is right for you. There are literally
hundreds of propane-fueled boilers on the North American market
in various models and sizes supplied by dozens of manufacturers.
Boiler selection should only be done by a knowledgeable and
competent heating professional. The boiler’s heating capacity
should be determined based on a proper heating load estimate
of the building. Without such an estimate, the boiler can only by
sized by guessing. This usually results in oversizing, and in some
cases gross oversizing. The result is a needlessly expensive boiler
that operates at reduced fuel efficiency. The owner pays more for
the boiler and related hardware installation, as well as more for
increased fuel usage due to reduced efficiency.
From a technical standpoint, the use of cast-iron or copper tube
boilers makes sense when the distribution system the boiler serves
consistently operates at water temperatures of 140 ºF or higher.
This is common for traditionally designed systems using fin-tube
baseboard, or hydronic fan-coils as heat emitters.
Sec5:19
Propane-Fueled Water Heaters as Hydronic Heat Sources
There are situations where a small hydronic system may be
incorporated into a home with forced-air or other type of heating.
An example would be use of hydronic floor heating in the
bathrooms and kitchen, with forced air heating elsewhere. In such
situations it’s possible to draw sufficient heat for the hydronic
system from a specialized water heating device. An example of
such a device is shown in figure 5-7.
Figure 5-7
This propane-fueled water
heater contains an
internal heat exchanger coil
in the upper portion of the
tank. This coil can extract
heat from the tank to serve
as the heat source for the
small hydronic distribution
system. The domestic water
in the tank never contacts
or mixes with the water in
the hydronic system. This
allows a single compact tank
to supply both domestic hot
water and a small hydronic
heating load.
Whenever a water heater is used as a hydronic heat source a
thermostatic mixing valve must be installed in the piping supplying
hot water to the fixtures in the building.
Summary
There are many types of propane-fueled boilers and water heaters
currently on the North American market. They are available in a
wide range of heating capacities, sizes, venting options, and
materials. Given such options it’s possible to closely match a boiler
or water heater to a specific hydronic heating requirement. Doing
so assures that appliance will operate reliably for many years as it
provides superior comfort and high efficiency.
Another appliance that has
gained significant market
share in recent years is the
propane-fueled tankless
water heater. These devices
turn on their burner as soon
as domestic water begins flowing through them on its way to hot
water faucets. They do not store water as does a conventional
tank-type water heater.
Propane-fueled tank-type water
heater with internal heat
exchanger coil that serves as a
hydronic heat source.
Courtesy of Bradford White
Figure 5-8
Propane-fueled
tankless water
heater that could
serve as a hydronic
heat source.
Courtesy of Rinnai
Given their size and heating capacity,
such units can serve as hydronic heat
sources in certain types of applications.
An example of a tankless water heater
that could be used for hydronic heating is
shown in figure 5-8
It is important that hydronic system
designers understand the differences
between tankless water heaters and
conventional boilers. Tankless water
heaters may require changes in circulator
sizing or piping design relative to those
used for conventional boilers.
Sec5:20
H
ydronic heat emitters remove heat from water flowing
through them and deliver it to occupied spaces. They
vary in size from small “kickspace” heaters installed
under cabinets to the entire floor of a large commercial building.
They also vary in the physical processes used to deliver their heat
to the space.
This section gives an overview of the some modern hydronic heat
emitters as well as a brief description of their performance
characteristics. It also shows options for the distribution systems
these heat emitters can be used in.
Finned-Tube Baseboard
Most residential hydronic heating systems installed in North
America up through the 1980s used finned-tube baseboard
convectors for heat emitters. This type of heat emitter continues
to be a staple in North American hydronics. Their heat output
per dollar of installed cost is hard to beat. A close up of a typical
finned-tube baseboard is shown in figure 6-1.
Figure 6-1
Finned-tube baseboard is typically sold in straight lengths between
2 to 10 feet long. The finned-tube element and enclosure are sold
together. Manufacturers also offer accessories for the enclosure
including end caps, couplings, and corner trim.
Heat output from finned tube baseboard depends on the water
temperature supplied to the element. The heat output of a typical
residential-class finned-tube baseboard versus the average water
temperature in its element is shown in figure 6-2. Traditionally,
finned-tube baseboards are sized assuming water temperatures
in the range of 150 to 200 ºF. Such temperatures are within the
normal operating range of conventional boilers, and high enough
to prevent sustained flue gas condensation in the boiler.
Figure 6-2
Baseboard heat output
per foot of element (Btu/hr/ft)
Section 6:
Heat Emitter Options
700
Air temperature near
floor of room assumed
to be 65 ºF
600
500
400
300
200
100
0
65
85 105 125 145 165 185 205
Average water temperature in baseboard (ºF)
Image courtesy of HYTech Heating
Finned-tube baseboard consists of two basic components: The
element, and the enclosure. The element is copper tubing in sizes
ranging from 1/2-inch to 1-inch, with mechanically attached
aluminum fins. These fins conduct heat away from the tube and
transfer it to surrounding air by convection. The warmed air rises
out of the upper slot of the steel enclosure. Cool air near the floor
flows into the bottom slot to sustain the process.
The function of the enclosure is to channel air through the element,
as well as protect it. The enclosure must be installed so air can
freely flow into the bottom opening. Most baseboard enclosures
have a pivoting damper along the air outlet slot, which can be
adjusted to partially regulate this air flow and thus the rate of heat
output.
If finned-tube baseboard will be used with a mod/con boiler it
should be sized for lower supply temperatures in the range of 120
to 140 ºF. These lower temperatures will necessitate substantially
longer baseboards to achieve equivalent heat output relative to
those required for higher temperature systems. The designer
should be certain there is ample wall space to accommodate
these longer lengths prior to committing to this approach.
Assuming sufficient wall space does exist, operating baseboard at
lower water temperatures allows a mod/con boiler to achieve
thermal efficiencies in the 90 to 95 percent range, albeit at the
added cost of longer baseboards.
Designers should keep in mind that residential-class finned-tube
baseboards are not designed for heavy traffic areas or other
situations where it might be subject to physical impact. They
should also not be used in high moisture environments, which
encourage corrosion of the steel enclosure.
Traditionally, finned-tube baseboards have been installed in series
piping circuits as shown in figure 6-3 (next page).
Sec6:21
Figure 6-3
baseboard #1
baseboard #2
baseboard #4
Finally, soldering hundreds of
pieces of rigid copper tubing together to construct series circuits
is labor intensive compared to other installation methods now
available.
propane
input
propane-fired boiler
Although such distribution systems are still viable, they do have
limitations. First, the water temperature decreases as it passes
through each heat emitter (finned-tube baseboard or other type).
This implies that baseboards farther “downstream” receive water
temperatures significantly lower than those near the beginning of
the circuit. This effect must be taken into account through careful
design. The result will be longer baseboards to achieve a given
rate of heat output depending on how far downstream that
baseboard is located.
Secondly, very little can be done to adjust the heat output of a
given heat emitter in a series circuit without affecting the heat
Figure 6-4
baseboard #3
baseboard #2
thermostatic
radiator valves
(TRV)
baseboard #1
to / from
other
heat
emitters
manifold station
propane
input
propane-fired boiler
baseboard #3
SERIES CIRCUIT
output of all heat emitters
on that circuit. For example,
assume one baseboard in the
series circuit was inadvertently
oversized for the heating load
of the room it serves. If the
flow rate in the circuit were
lowered to reduce heat output
of this baseboard it would
also reduce heat output from
all other baseboards on the
circuit.
A modern alternative to series distribution systems, a “homerun
system,” is shown in figure 6-4. Each baseboard (or other heat
emitter) has its own supply and return tubing from a manifold
location. The tubing used is flexible PEX (crosslinked polyethylene)
or PEX-AL-PEX (composite of PEX and Aluminum). Such tubing
is easily routed through buildings in continuous pieces from the
manifold location to each heat emitter.
Homerun distribution systems supply the same water temperature to
each baseboard and thus eliminate the temperature drop
associated with series circuits. They also allow flow adjustment to
each baseboard when needed to regulate heat output. Flow to any
baseboard can be completely turned off, while flow to other
baseboards continues. This allows room-by-room comfort control.
Given these advantages the homerun distribution system is the
preferred method of
Figure 6-5
connecting finned-tube
baseboard in modern
hydronic system installations.
Panel Radiators
Long a staple in European
hydronic systems, panel
radiators are quickly gaining
popularity in North America.
Available in hundreds of
shapes, sizes, colors, and
tubing designs, steel panel
radiators are very different
from their cast iron
predecessors. An example
of an installed panel radiator
is shown in figure 6-5.
Image courtesy of DiaNorm
Sec6:22
This style of panel is fabricated from preformed steel sheets
welded together at edges and across the face of the panel. As
warm water circulates through the channels in the front surface it
emits gentle radiant heat to the room and its occupants. Steel fins
welded to the rear of the panel enhance convective heat output.
A cut-away of a typical panel radiator is shown in figure 6-6. The
left side shows the finished surface and water channels. The right
side shows the folded steel fins attached to the rear of panel. Also
visible are the supply and return connections at the bottom right,
and thermostatic radiator valve at upper right. This valve regulates
water flow through the panel and hence its heat output.
Panel radiators are also ideally suited for homerun distribution
systems as depicted in figure 6-10. Heat output from each panel
can be individually regulated for precise room-by-room comfort
control. This is all accomplished without need of electric room
thermostats and their associated wiring, which speeds installation
and reduces cost.
Figure 6-8
Figure 6-9
Figure 6-6
Image courtesy of DiaNorm
This type of panel is available in a wide range of widths, heights,
and depths as shown in figure 6-7.
There are also designer panel radiators as shown in figure 6-8 and
6-9. These contemporary designs are true interior design elements
that also deliver silent comfort to the spaces they serve.
Image courtesy of Myson
Image courtesy of Vasco
Figure 6-10
Figure 6-7
Image courtesy of DiaNorm
Image courtesy of DiaNorm
Sec6:23
are also occasionally used as a “supplemental heat emitters” in
spaces with especially high heat losses.
Hydronic Air Handlers
There are times when a “hybrid” approach to space heating, one
that combines elements of both hydronic and forced air, is ideally
suited to a project. An example would be when wall space is not
available for other types of heat emitters, or when a forced-air
system will also be used for summer cooling.
Radiant Panel Heating
Nothing demonstrates the versatility of hydronic heating better
than site-built radiant panels. In short, this is the concept of
integrating small flexible polymer tubing into the floors, walls, and
ceilings of rooms. As warm water passes through this tubing heat
is conducted to the surface and released into the room,
mostly as low intensity radiant energy, resulting in
unsurpassed comfort.
Figure 6-11
air handler
air handler
air handler
coil
air filter
to/from
other zoned
air handlers
blower
Hydronic radiant panel heating has been used for decades.
Early systems used copper or steel tubing and boilers with
minimal controls. Although unrefined by today’s standards,
these systems produced outstanding comfort relative to
alternative methods of the time.
zone
valves
circulator
Hydronic air handlers
make this hybrid approach
possible. They receive
heat from a hydronic
distribution, but deliver
that heat to the building
using forced-air. The air
flow is created by a small
blower or fan within the
boiler
unit. Room air moves
across a “coil” consisting
of copper tubing and closely spaced aluminum fins. Heat is
transferred from the copper tubing to the aluminum fins, and then
to the air stream. The heated air may be blown directly into the
space, or travel through ducting to enter the space from several
locations at the same time.
purge
valves
The development of crosslinked polyethylene
(PEX), and composite (PEX-AL-PEX) tubing
revolutionized the hydronic radiant panel heating
market in North American starting in the 1980’s.
Today there are several methods of integrating
this durable tubing into floors, walls, and ceilings.
We will discuss the most common approaches.
Radiant Floor Heating
The best-known type of hydronic radiant panel is a heated
concrete floor. Because the concrete slab is already a part of the
building, this approach has a low cost per square foot compared
to other methods of radiant panel construction. Although the
resulting floor is visually indistinguishable from a standard concrete
floor, the difference is room comfort relative to other methods of
heating is very noticeable.
The typical construction of a hydronically heated slab is shown in
figure 6-12.
Figure 6-12
Hydornic air handlers include wall-mounted “console” units, as well
as larger horizontal and vertical “cabinet” air handlers. Console
units are used to heat individual rooms. Cabinet air handlers are
typically used to heat a zone consisting of two or more rooms. A
representation of zoned air handler system is show in figure 6-11
It’s also possible to add a chilled water coil or refrigeration coil
to some types of hydronic air handlers. This enables the unit to
supply cooling in summer as well as heat in winter. Air handlers
Example of slab-on-grade floor heating.
Courtesy of IPEX Inc.
Sec6:24
The installation starts with placement of a polyethylene vapor
barrier and extruded polystyrene foam insulation over a level and
firm sub grade. The insulation limits heat loss from the underside
of the slab to the soil. Steel mesh placed over the foam provides
structural reinforcement for the slab. PEX or PEX-AL-PEX tubing is
attached to this mesh using wire or plastic ties. All tubing circuits
are pressure tested to ensure there are no leaks. This is followed by
the concrete placement and finishing.
above or below a wood subfloor. Above floor installation is typical
when a nailed-down hardwood finish floor will be installed. Below
floor plates are common for use with tile or carpet finish floor. An
example of an above floor tube and plate installation is shown in
figure 6-14.
Figure 6-14
Heated slabs can be covered with various finish floorings including
ceramic tile, stone, vinyl, engineered wood and carpet. However,
heat output from the floor is strongly dependent on the R-value
(thermal resistance) of the finish floor. For the best performance
the finish floor R-value should be as low as possible.
Thin Slab Floor Heating
Another method radiant floor construction uses a thin (1.5-inch to
2-inch thick) layer of concrete or poured gypsum
underlayment over tubing that has been previously fastened to a
plywood subfloor. This is called a thin-slab system, an example is
shown in figure 6-13.
Figure 6-13
Example of above floor tube-and-plate floor heating.
Courtesy of IPEX Inc.
Tube-and-plate radiant panels are much lighter than thin-slab
radiant panels. They also respond faster to temperature changes
because of their lower thermal mass. Again, a minimum of R-19
underside insulation is critical to ensure that most heat output
goes upward into the room.
Radiant Wall Heating
The same type of tube and plates used in floor heating can also be
adapted to wall heating. Such systems are excellent in situations
where high thermal resistance floor coverings are desired, and
thus floor heating is not an option. Their low thermal mass allows
rapid response. The appearance of the finished wall gives no clue
that it’s a heat emitter capable of warming the entire room.
Example of thin-slab floor heating. Courtesy of IPEX Inc.
Figure 6-15
Thin-slabs provide good heat output at low water temperatures
similar to slab-on- grade systems. They require a floor structure
designed to handle the added weight of the slab, (typically 14 to
18 pounds per square foot). Like a heated slab-on-grade floor they
can be covered with a variety of finish floorings. The underside of
the floor framing should always be insulated to a minimum of R-19
to force most of the heat output in the upward direction.
Tube-and-Plate Floor Heating
Still another method of radiant floor heating uses preformed
aluminum plates to extract heat from the tubing and disperse
it across the floor. These thin aluminum plates can be installed
A radiant wall panel under construction
Sec6:25
A partially installed radiant wall is shown in figure 6-15 (previous
page). The aluminum heat transfer plates are fastened to foil-faced
insulation strips using contact cement. The tubing is then snapped
into the plates and drywall is screwed in place to complete the
assembly.
It’s important that furniture or other large objects are not placed
directly in front of or against heated walls. Doing so reduces
radiant heat delivery into the space.
floor system in the main living areas, and radiant ceiling heating in
bedrooms. It’s also possible to combine radiant panels with other
hydronic heat emitters like finned-tube baseboard and panel
radiators. Examples of such multi-load / multi-temperature systems
are shown in section 7.
Figure 6-16
Radiant Ceiling Heating
Many people do not believe it’s possible to heat a room from the
ceiling down. They rationalize this by stating that “heat rises.” This
is not true. Warm air rises due to its lower density, but heat travels
from warm areas to cold areas regardless of direction. This is
especially true of radiant heating. The low intensity infrared light
emitted by a warm ceiling travels down into the room just like
visible light from a ceiling lamp. The difference is that our eyes
cannot see the infrared light. The floor and other objects in the
room absorb this radiant energy. The resulting comfort is excellent.
Like radiant walls, radiant ceilings are an excellent option when floor
heating is ruled out due to high thermal resistance floor coverings.
It can be installed using the same materials and methods shown in
figure 6-15. The only difference it that it’s fastened to ceiling
framing rather than wall framing.
This tub platform does not provide sufficient area for floor heating
Figure 6-17
Radiant ceilings also respond quickly to thermostat adjustments.
They can turn on quickly when it’s time to raise the comfort level
of a room from a previous setback condition. They can also turn
off quickly in response to internal heat gains from sun, people or
equipment. Radiant ceilings can also operate at higher heat output
rates because people are not in direct contact with the surface as
they are with heated floors. This implies that a radiant ceiling panel
can be smaller than a radiant floor panel and yet produce the same
heat output.
Radiant ceilings are very unlikely to be covered by other
materials over the life of the building, and thus can perform for
decades regardless of changes in floor coverings, furniture
arrangement, etc.
The ceiling above the tub is heated to gently warm the tub and
surround platform surfaces
Finally, radiant ceilings are excellent above large tub platforms,
especially when those platforms are surrounded by lots of
windows as shown in figures 6-16 and 6-17. They are also a good
choice for bedrooms where furniture placement would partially
block heat output from floors.
Designers should remember that radiant floors, walls, and ceilings
can be combined within the same system. An example would be a
heated slab floor in the basement combined with a tube and plate
Sec6:26
Section 7:
Other Loads Supplied by
Hydronics
A
lthough most people think of a propane-fueled boiler
as a device for space heating, it can also provide heat
to several other loads in and around the building. This
ability is unique to hydronics. When properly designed, such
multi-load hydronic systems increase combustion efficiency
relative to using separate heating appliances for each load. Such
systems also reduce installation cost by eliminating redundant
hardware. It’s a win/win scenario, and represents the essence of
modern hydronics technology.
This section describes several loads, other than space heating,
that are commonly served by a multi-load hydronic system. It goes
on to show examples of how all these loads can be handled by a
single propane-fueled heat plant.
Abundant Domestic Hot Water
Domestic hot water is one thing that no modern home, small or
large, can do without. It must be available 24/7 in quantities that
allow occupants to use it as they choose. Few nuances around the
home are as aggravating as not having enough hot water to finish
a long shower, or not being able to use the clothes washer when
someone is filling a bathtub.
A distinct trend in residential construction has been increased
interest in luxury bathrooms. The North American plumbing
industry has done a superb job of promoting such bathrooms as
luxurious escapes from the cares of life. Central to that concept is
surrounding oneself
Figure 7-1
with lavish amounts
of warm water, be it
in a deep whirlpool
tub or a simulated
tropical downpour
showering
experience. An
example of a luxury
residential shower
is shown in figure
7-1.
Example of a luxury shower / tub
combination
Homes with
several bathrooms
can place very
heavy demands on
ordinary tank-type
water heaters.
In some cases standard water heaters can’t keep pace with
the demand, especially when several fixtures are in use at the
same time. This forces the occupants to “schedule” showers
or baths to avoid running out of hot water. The occupants are
forced to conform to the ability of the water heater rather than
their own convenience.
Why should owners of such homes, many of whom have spent lots
of money for luxury bathrooms, have to compromise the usage of
those fixtures based on limitations of the water heating equipment?
Fortunately, a properly configured propane-fueled boiler system
combined with a high capacity hydronic water heater can
supply such demands indefinitely. Such systems provide a modest
amount of storage capacity for handling small hot water demands
without need of operating the boiler every time a faucet is opened.
They are also capable “ramping up” domestic hot water
production to supply several bathrooms in simultaneous use.
The type of water heating device used in such systems is called
an “indirect water heater.” It consists of a well-insulated hot water
storage tank equipped with an internal heat exchanger. As the
tank’s temperature begins to drop, the boiler is fired, and hot water
from the boiler is circulated through this coil. The boiler water
never mixes with the potable water in the storage tank. However,
heat is quickly and efficiently transferred from the hot boiler water
through the metal walls of the internal heat exchanger and into
the cooler domestic water. The concept is shown in figure 7-2.
Figure 7-2
space heating
circulator
to/from
space heating
domestic
hot
water
domestic
cold
water
DHW
tank
circulator
propane-fired boiler
internal
heat exchanger
indirect water heater
Piping schematic for an indirect water heater
Sec7:27
An example of
an indirect water
heater is shown in
figure 7-3.
Indirect water
heaters have
several
advantages
compared to
“direct-fired” water
heaters.
First, this method
of water heating
requires only one
heat source to
supply both space
heating and
domestic hot
Example of an indirect water heater
water. This reduces
installation and maintenance costs relative to having separate
burners for each load.
temperature the other loads are allowed to come back online. This
strategy has been successfully used for many years in all types of
hydronic heating systems.
Figure 7-4
propane-fired
mod/con
boiler system
boiler
circulators
Figure 7-3
hydraulic
separator
space heating
circulator
space heating
distribution
system
domestic
hot
water
domestic
hot
water
DHW
tank
circulator
Second, this approach can usually heat water significantly faster
than a typical direct-fired water heater. This is especially important
in situations where several appliances are using hot water at the
same time.
Third, because the heat exchanger surfaces within an indirect
water heater do not get as hot as the elements in an electrical
water heater, or the surfaces in a direct-fired water heater, they are
less likely to build lime scale, which can reduce efficiency
over time.
Finally, the combustion efficiency of a modern propane-fueled
mod/con boiler is higher than that of a direct-fired water heater.
Higher efficiency means less fuel is needed to produce a given
amount of domestic hot water relative to other heating options.
A piping schematic for a hydronic system that provides both space
heating and high capacity domestic water is shown in figure 7-4.
All heat for the building as well as domestic water heating is
generated by the propane-fueled multiple boiler system.
Special controls allow the system to treat domestic water heating
as a “priority load.” When the hot water storage tank needs heat,
all other loads in the system are temporarily turned off so the full
output of the boilers can be dedicated to domestic water heating.
Once the domestic hot water tank returns to the proper
high capacity
indirect water heater
Use of a high capacity indirect water heater in combination with a
multiple boiler system
When properly sized, propane-fueled mod/con boilers can
provide the heat generation needed to keep up with any demand
for domestic hot water. This ensures that all bath and shower
fixtures in the building can be operated without the concern for
running out of hot water.
Hydronic Snow and Ice Melting
Many hydronically-heated buildings are located in areas that
receive significant snowfall. This snow must be repeatedly cleared
from steps, sidewalks, and driveways. Mechanical methods of
snow removal include shoveling, snow blowers, and plowing. All
have their pros and cons.
The alternative to mechanical methods of snow and ice removal
is to do what nature does every spring – melt the snow and ice
from pavements. This is an ideal task for modern hydronic heating
technology. PEX or PEX-AL-PEX tubing can be embedded within
Sec7:28
pavements similar to how they are built into interior floor slabs.
These tubing circuits are filled with antifreeze solutions that can be
heated and circulated when snow melting is required. As in a car,
the antifreeze solution prevents any damage to the snowmelting
components when the system is idle during subfreezing
temperatures.
Hydronic snow and ice melting systems offers several benefits
over traditional methods of snow removal.
• They can provide fully automatic and unattended snow and ice
removal whenever required.
• They remove snow without creating banks or piles that often
Snowmelting requires significantly more heat output per square
foot of slab surface than does space heating. Snowmelting
systems that serve entire driveways typically require heat
production rates of several hundred thousand Btus per hour. This
is usually handled by a multiple boiler system like that discussed
earlier for high capacity domestic water heating. In the event that
snowmelting and domestic water heating are required at the same
time, the domestic water heating load is given priority. As soon as
the hot water storage tank has recovered to its setpoint
temperature heat is directed back to snowmelting. The large
thermal mass of a heated pavement allows such an operation to
go virtually unnoticed.
Figure 7-6
mixing
valve
stainless steel
heat exchanger
embedded snowmelting circuits
boiler
circulators
lead to drifting and/or damage to landscaping.
• They eliminate the need for and cost associated with sanding
pavements. This also eliminates the associated mess and floor
covering damage when sand is tracked
propane-fired
into buildings.
mod/con
boiler system
• They eliminate the need for and cost
associated with salting, as well as the
potential damage to landscaping and
the surrounding environment.
• Pavement damage due to frost,
salt, and plowing is reduced. This
is especially important for surfaces
covered with pavers.
• Snow and ice-free pavements reduce
likelihood of slips, falls, or vehicular
hydraulic
separator
accidents.
• Snowmelting improves property
appearance in winter by eliminating
snow banks and sand/salt residue.
Hydronic snowmelting can also be incorporated into asphalt
pavements as well as those finished with pavers.
An example of how tubing for hydronic snowmelting is
installed in concrete paving is shown in figure 7-5.
Figure 7-5
This portion of the system filled with antifreeze solution
space heating
circulator
domestic
hot
water
domestic
hot
water
slope pavement away from building
(also slope away from unmelted pavement)
melt water
slope to drain
underslab insulation
trench drain
building foundation
route drainage to non-freezing location
Notice the insulation under the slab. This is necessary to prevent
excessive heat loss to the soil under the pavement. It is also very
important to slope the pavement and provide proper drainage for
the melt water. Not doing so can result in melt water freezing back
into ice.
Multiple propane-fueled boiler
system supplies domestic water
heating and snowmelting.
DHW
tank
circulator
embedded tubing
grating
space heating
distribution
system
high capacity
indirect water heater
Figure 7-6 shows how the
schematic of figure 7-5 can be
modified to allow the multiple
propane-fueled boilers to provide
both high capacity domestic water
heating and snowmelting.
Pool / Spa Heating
Most people who own swimming pools or spas consider heating
them to extend the swimming season or simply enjoy the comfort of
a spa year round. Traditionally, this is done with a direct-fired pool
heater, electric pool heater, or specialized heat pump. However,
the versatility of a propane-fueled boiler system in combination with
hydronic distribution system allows the same boiler(s) that heats
the house to heat the pool.
Sec7:29
well as the installed boiler capacity, it’s possible to bring the pool
temperature up 25 or 30 ºF within a 12 hour period. Very few
residential size pool heaters come close to this heating ability.
Some would require several days to bring an average residential
pool from ambient temperature up to a comfortable swimming
temperature.
Think about it. The time of year when most outdoor swimming
pools are in use does not correspond to peak space heating
demand. During late spring and early fall the boiler may be doing
little other than heating domestic water for the building. Why not
use the available heating capacity of the boiler to heat the pool
rather than install a separate pool heater? Doing so improves the
efficiency of the existing boiler(s) and reduces the cost associated
with installing an alternate means of pool heating.
Summary
A hydronic heating system with a propane-fueled boiler can supply
just about any heating requirement associated with a house or
commercial building. This ability is unmatched by forced-air, heat
pump, geothermal, or electric heating systems. It allows efficient
use of both propane and the hardware needed to convert it into
heat. It then delivers that heat precisely when and where it’s
needed. Multi-load systems are the essence of modern hydronics
technology, and the key to the efficient use of Propane,
Exceptional energy.
Figure 7-7 demonstrates how the previous piping schematic can
be expanded to include pool heating along with space heating,
domestic water heating and snowmelting.
A stainless steel heat exchanger separates the chlorinated pool or
spa water from the water in the hydronic system. Heat is readily
passed from the hot boiler water to the pool water without ever
mixing the two fluids. The pool’s filter pump provides flow through
heat exchanger. Hot water from the boiler(s) is circulated through
the other side of the heat exchanger whenever pool heating is
required. A similar arrangement with smaller hardware would be
used for spa heating.
Once again, the high heating capacity of a multiple propane-fueled
boiler system comes into play. In this case, it enables rapid pool
heating. Depending on the size and temperature of the pool, as
Figure 7-7
propane-fired
mod/con
boiler system
stainless steel
heat exchanger
mixing
valve
embedded snowmelting circuits
boiler
circulators
SNOW MELTING
space heating
circulator
space heating
distribution
system
hydraulic
separator
domestic
hot
water
domestic
hot
water
POOL HEATING
DHW
tank
circulator
pool
stainless steel
heat exchanger
pool filter
DOMESTIC
WATER
HEATING
pool pump
high capacity
indirect water heater
Multiple propane-fueled boiler system supplies domestic water heating, snowmelting, and pool heating.
Sec7:30
Section 8:
Case Studies
Figure 8-2
T
he combination of a propane-fueled heat source and a
hydronic distribution system is applicable to many types
of buildings from small homes to large commercial or
industrial facilities. This section discusses two examples of this
combined technology.
outdoor
temp.
sensor
first floor
heating circuits
propane-fired
mod/con boiler
second floor
heating circuits
Big Moose Residence
The first case study is a modest
residence recently constructed in
the Adirondack region of upstate
domestic
hot water
New York (figure 8-1). The winters
are harsh in this climate, and the
owner wanted both comfort and fuel
efficiency for his new home. Based on
previous positive experiences with propane in
combination with through-the-wall unit heaters,
the owner approached the designer with a
request for the same type of system. However,
the designer raised a concern over the
likelihood of cold concrete slab floors on the
main level (even though the unit heater could
maintain the proper air temperature within the
garage floor
heating circuits
indirect water heater
(prioritized load)
Figure 8-1
Piping schematic for hydronic heating system
with 2-inches of extruded polystyrene insulation. All windows have
argon-filled double glazing with a low-E coating. The result is a
2,100 square foot home with a low design heat loss of
approximately 22,000 Btu/hr. Garage heating adds approximately
16,300 Btu/hr making the total design heating load 38,300 Btu/hr.
Exterior of residence
space). After considering this, the owner elected to use hydronic
floor heating in both the slab-on-grade first floor areas, as well as
the wood-framed second floor. With a hydronic-based system now
in play, the designer encouraged extending its duties to include
garage heating as well as domestic water heating. This allows a
single compact propane-fueled boiler to handle all heating loads
within the building.
A piping schematic of the system is shown in figure 8-2.
This home is very well insulated. All exterior wall cavities were filled
with sprayed urethane foam insulation yielding a wall R-value of
approximately 38. The ceiling is insulated with the same material
to R-50. All slab areas were insulated on the underside and edges
A small wall-hung boiler with a output of 45,000 Btu/hr can easily
handle this load. The boiler uses sealed-combustion with supply air
and venting handled by 2-inch PVC (supply air), and 2-inch CPVC
(venting) piping. This small diameter piping was easily routed from
the second floor mechanical closet to just under the edge of the
roof overhang. This eliminated the need to route piping or a
conventional chimney through the metal roofing (which had no
other piping or chimney penetrations). The end of the vent was
located so it would not be damaged by frequent snow-slides from
the roof.
First floor heating is handled by six circuits of 1/2-inch PEX-ALPEX tubing embedded within the concrete slab as shown in figure
8-3 (next page). Although the entire first floor is operated as a
single zone, room-by-room circuit layout enables the heat output to
be adjusted through flow balancing.
Sec8:31
Figure 8-4
Figure 8-3
freezing the hydronic
floor circuits.
317+10=327 ft.
CLOSET
291+10=301 ft.
M. BEDROOM
123+10=133 ft.
M. BATH
GARAGE
1/2 BATH/
LAUNDRY
228+10=238 ft.
KITCHEN
272+10=282 ft.
341+10=351ft.
Tubing layout for heated floor slab
A tube-and-plate radiant panel heats the second floor. The same
1/2-inch PEX-AL-PEX tubing used in the first floor slab was
installed on the underside of the second floor deck and supported
by aluminum heat transfer plates, which were stapled in place as
seen in figure 8-4. These plates and tubes are backed by a 6-inch
layer of fiberglass insulation to force most of the heat output in the
upward direction.
v
op en
fir an ted
ep e-f
la ire
ce d
LIVING
pr
275+10=285 ft.
refrig.
coat closet
W
DINING
D
Domestic hot water is
heated by a 40 gallon
indirect water heater
that’s operated as a
priority load. When the
tank requires heating all
other loads are
temporarily disabled to
allow the full boiler
Photo courtesy of Harvey Youker/ output to quickly
HYtech Heating
restore the tank to its
setpoint temperature.
As soon as this occurs, the space heating circuits are
allowed to operate. The high thermal mass of the radiant
floor slab allows this process to go unnoticed. This strategy
eliminates the need to size the boiler to the combined load
of space heating and domestic water
heating. The result is maximum domestic water heating,
reduced cost, and improved seasonal efficiency. A photo of
the installed mechanical closet is shown in figure 8-5.
The low operating temperature of the heated floors allows
the mod/con boiler to operate at high efficiencies throughout
the heating season to minimize propane consumption. Total
projected propane usage to fully heat the house and garage
in this cold Northern climate is 660 gallons per year.
In summary, this system provides unsurpassed comfort,
compact installation, quiet operation, and high fuel efficiency.
Figure 8-5
The garage is also heated by tubing embedded within the
concrete floor slab, and operated as a separate zone. This enables
the owner to maintain the garage at a reduced temperature
without sacrificing comfort in occupied areas. It also allows the
garage to be heated to full comfort temperature when used as a
workshop during cold weather.
The entire hydronic system is filled with a non-toxic propylene
glycol antifreeze solution. This protects the system against
freezing in the event of an extended power outage. It also allows
the garage to remain unheated if desired without concern of
Mechanical closet showing wall-hung boiler and indirect water
heater
Sec8:32
North Lake Residence
Another recently-constructed luxury home using propane-fueled
hydronic heating is shown in figure 8-6.
Figure 8-6
the garage. Propane is also used for the fireplace, clothes dryer
and kitchen stove.
Although this home is located in a climate where winter temperatures
routinely drop to –20 ºF, total propane usage for all space heating,
garage heating, domestic hot
water and appliances is
approximately 800 gallons per
year.
The use of tube-and-plate floor
heating system, seen under
construction in figure 8-8, allows
a variety of floor coverings. The
PEX-AL-PEX tubing is cradled
by thin aluminum heat transfer
plates that spread heat across
the floor. This hardware is
then covered by a thin layer of
plywood to provide a smooth
substrate for finish flooring. See
finished results in Figure 8.9
(next page).
Exterior of home. Courtesy of HYTech Heating
This 5,000 square foot home includes 4 bedrooms and 3
bathrooms. It has a heated basement floor slab as well as tubeand-plate floor heating on the first and second floors. The latter are
finished with a mixture of hardwood and ceramic tile. The hydronic
system also provides domestic hot water for the home, and heats
Figure 8-8
Figure 8-7
Tube-and-plate floor heating being installed.
Courtesy of HYTech Heating
Prior to installation, the hydronics professional developed a tubing
layout diagram for the entire system. This ensures the lengths of
all circuits are acceptable, speeds the installation, and provides a
permanent record of where all tubing is located.
Ample hot water for this master bath comes from a propanefueled boiler with indirect water heater.
Courtesy of HYTech Heating
The mechanical equipment is shown in figure 8-10 (next page).
The propane-fueled mod/con boiler uses internal state-of-the-art
controls to adjust the water temperature and heat output in
response to outdoor temperature. The boiler also uses sealed
combustion in which all combustion air is routed directly to the
boiler through 3-inch PVC piping. All exhaust gases are vented
outside through another 3-inch PVC pipe. The air supply and
venting pipes can be seen at the top of the boiler.
Sec8:33
The small circulators at the left of the boiler
distribute heat to building zones precisely when
and where it’s needed. The indirect domestic
water heater tank at the far left is also heated by
the boiler. This professionally installed system is
compact and easily serviced. All space heating
and domestic water heating is provided by a
single highly efficient heat source, demonstrating
the synergy of function and form that’s possible
using propane in combination with hydronic
heating.
Figure 8-9
The heated floors are finished in both hardwood and ceramic tile.
Courtesy of HYTech Heating
Figure 8-10
Mechanical room with propane-fueled boiler, zone circulators, and indirect water heater.
Courtesy of HYTech Heating
Sec8:34
Section 9:
Cooling Options for Use with
Hydronic Heating
Figure 9-1
refrigeration piping
M
any discussions between comfort professionals and
potential customers eventually move from heating to
the inevitable question: “What do I do about cooling?”
The vast majority of new home buyers in all but the coldest regions
of the United States expect their homes to be comfortable
throughout the summer as well as in winter. Professionals who
integrate cooling and heating in ways that provide year round
comfort and efficiency are certainly well positioned for success. As
you’re about to see, hydronics technology combined with propane
can provide an elegant solution for cooling as well as heating.
There are several options for cooling buildings equipped with
hydronic heating. Perhaps the most obvious is to install a separate
central cooling system with traditional ducting. Although this has
been done in many buildings, it often involves the complications
associated with routing traditionally sized ducting throughout the
building. It should not be dismissed as a possibility, but neither
should it be accepted as unavoidable in light of alternatives to be
discussed.
For the sake of discussion, we’ll categorize cooling options into
non-hydronic and mixed “hydro-air” systems. The first category
includes “ductless” cooling systems, as well as what are commonly
known as direct expansion “miniduct” systems. The second
category includes chilled water distribution systems supplied by
either electrically powered compressor-based chillers, or propanefueled absorption chillers.
Non-Hydronic Cooling Options
As previous sections have shown, a strength of hydronic heating is
the ability to integrate the required hardware into almost any
building with minimal disruption of structure or finish surfaces. When
cooling is being planned these attributes are equally important, and
often preclude the use of conventional ducting due to the size and
routing requirements necessary for proper operation.
indoor
evaporator &
air handler
air-cooled condensors
Concept of a “ductless” cooling system
The only connection between the outdoor condenser unit and
the indoor evaporator unit is a refrigerant line set (flexible copper
tubing) and electrical cabling. These relatively small tubes and
cables can be routed through partitions and around other building
structure much easier than ducting. Each indoor evaporator unit
also requires a plastic pipe or hose to route condensate (water
vapor condensed to liquid) to a suitable drain.
Ductless cooling provides the advantage of zoning. Each individual
wall-hung unit can operate independently. From the standpoint of
aesthetics, not everyone appreciates wall-mounted hardware in
several rooms of the building. Some manufacturers offer flushmounted ceiling units for these situations.
Mixed “Hydro-Air” Cooling Systems
Over the last two decades, several North American companies
have put forth cooling systems that rely on small (2-inch internal
diameter) flexible ducting to distribute cool air to locations where
conventional ducting simply won’t fit. To deliver sufficient cooling
to a space, these small ducts must operate at higher flow
velocities. This is achieved through the use of special high static
pressure blowers in the air handling unit. A schematic of the
concept is shown in figure 9-2. An example of a small air handler
Figure 9-2
air handler
insulated trunk duct
It is possible to provide zoned cooling without need of any ducting.
The concept is shown in figure 9-1.
Ductless systems typically have wall-mounted indoor evaporator
units in each cooling zone of the building. A refrigeration line set
runs from each indoor evaporator unit to an outdoor condenser
unit. In some cases a separate pad-mounted condenser unit is
used for each indoor unit. In other cases two, three and even
four independent condenser units are housed within a common
outdoor unit.
2-inch
insulated
flex ducting
refrigerant
piping
air-cooled condensor
Concept of a “miniduct” cooling system
Sec9:35
installed in the attic space of a home, and supplying several small
flex ducts is shown in figure 9-3.
Figure 9-3
The cooling capacity for most miniduct systems is supplied from a
refrigerant-based evaporator coil within the air handler. However, in
some systems the cooling capacity is supplied using chilled water.
The latter is a form of hydronics technology using cool water rather
than heated water.
The concept of a hydronic homerun system for distributing chilled
water to several independently controlled air handlers is shown in
figure 9-4.
In this system, chilled water is “produced” by removing heat from
water in the insulated storage tank. This is done using a standard
direct expansion condenser unit connected to a flat plate heat
exchanger. Liquid refrigerant is evaporated in one side of the flat
plate heat exchanger. As the refrigerant within the heat exchanger
changes from a liquid to a gas, it extracts heat from the water
flowing through the other side of the heat exchanger. This chilled
water is then routed back to the storage tank as warmer water
moves into the heat exchanger for cooling. The process is
controlled by monitoring the water temperature within the storage
tank. A typical system maintains this water between 40ºF and 50ºF
when the cooling system is active.
Small air handler located in attic supplies several miniducts
Figure 9-4
air handlers
w/ chilled water coils
insulated trunk duct
This hydronic distribution system uses small diameter PEX
or PEX-AL-PEX tubing—the same tubing previous discussed
for hydronic heating applications—to carry chilled water to
each air handler. Another length of tubing returns warmed
water from the air handler to the storage tank. Each air
handler is controlled by a separate zone thermostat. Water
flow through the coil in each air handler is controlled by an
electrically-operated zone valve.
2-inch diameter
insulated flex ducting
ceiling
diffuser
5/8"
PEX-AL-PEX
tubing
(insulated w/
closed-cell foam)
1" copper (insulated with closed-cell foam)
zone
valves
One advantage of chilled water cooling is the elimination of larger
ducting between a central air handler and the points where cool air
is introduced to the building. Just as in heating, a flowing stream of
water carries almost 3,500 times as much heat (or cooling effect)
as an equivalent stream of air. This allows small tubing to convey
the same cooling capacity as much larger ducting.
temperature
controller
INSIDE
OUTSIDE
refrigerant
pipine
air-cooled condensor
insulated
chilled water
storage tank
Use of hydronic distribution system to deliver chilled water to
zoned air handlers
Another advantage of chilled water cooling is the relative ease of
creating zones within a building. The basic concept is to locate
a small chilled water air handler within each cooling zone of the
building. That air handler operates only when cooling is needed in
that zone. This reduces power consumption under part load
conditions when not all zones are active. It also greatly improves
comfort by delivering cooling precisely when and where it’s
needed. Finally, the controls needed to extensively zone a chilled
water cooling system are far less complicated and less costly than
those needed to properly regulate a zoned forced air system.
Sec9:36
When installing a chilled water cooling system, it’s crucial that all
piping and piping components carrying chilled water are insulated,
and subsequently vapor sealed. Not doing so allows water vapor
in the surrounding air to condense on the piping. This can quickly
lead to dripping that can stain ceilings and, over time, create mold
within the building.
Chilled Water Using a Propane-Fueled Absorption Chiller
Although lesser known, there is a well-establish technology for
using heat from a combustion process to produce chilled water.
That process is called absorption cooling, and it’s been used in
larger buildings for several decades. Recently, this technology
has been scaled down for use in residential and small commercial
buildings. Propane is an ideal energy source to power a small
absorption chiller.
Unlike conventional cooling equipment, absorption chillers do not
use a motor-driven compressor. Instead they rely on a cycle in
which ammonia, hydrogen gas, and water are used to
generate chilled water. This process requires heat from a gas
burner to sustain it. The heat extracted from the water flowing
through the absorption chiller as well as the heat generated by the
gas burner are eventually rejected to outside air.
They have very few moving parts and thus require little
maintenance. Although more expensive to install than standard
chillers, they typically last two to three times longer and thus
provide comparable, if not favorable, economics. They add very little
to peak summer electrical demands. Some companies even offer
variants on standard absorption chillers that supply both chilled and
heated water when needed at the same time. In combination with
propane and a hydronic delivery system, absorption chillers
represent a state-of-the-art cooling option for residential and
commercial applications.
Summary
There are several ways cooling can be integrated along with
propane-fueled hydronic heating to provide year round comfort.
The use of chilled water to convey the cooling throughout a
building holds many advantages over forced air distribution. The
chilled water can be produced using standard compressor driven
chillers or through modern propane-fueled absorption chillers.
An example of a residential size propane-fueled absorption chiller
is shown in figure 9-5.
Water cooled by an absorption chiller can be stored in the same
type of insulated storage tank previously described for a
compressor type chiller. This water can be distributed to remote air
handlers through the same type of hydronic distribution system.
Modern propane-fueled absorption chillers use up to 87 percent
less electrical energy than a standard compressor driven chiller.
Figure 9-5
A small propane-fueled absorption chiller for residential cooling
Sec9:37
Section 10:
Additional Sources of
Information
Hydronics Technology
1. Publications:
a. Plumbing & Mechanical magazine www.pmmag.com
b. PM Engineer magazine www.pmengineer.com
c. Contractor magazine www.contractormag.com
d. Radiant Living magazine www.radiantlivingmag.com
2. Associations:
a. Radiant Panel Association
www.radiantpanelassociation.com
b. Hydronics Industry Alliance
www.myhomeheating.com
c. Hydronic Heating Association
www.comfortableheat.net
d. Plumbing-Heating-Cooling Contractors Association
www.phccweb.org
3. Other hydronic heating Websites:
a. www.hydronicpros.com
b. www.heatinghelp.com
c. www.healthyheating.com
d. www.radiantandhydronics.com
4. Technical Reference Books:
a. Modern Hydronic Heating: For Residential & Light
Commercial Buildings, 2nd Edition,
ISBN 0-7668-1637-0
b. Radiant Basics: A Basic Course for Radiant Panel
Heating Systems
ISBN 1-932137-00-9. Published by the Radiant
Panel Association
c. Guide 2000 Residential Hydronic Heating –
Installation and Design
Training manual published by the Gas Appliance
Manufacturers Association
Contributors’ Directory
Listing of companies and individuals contributing graphics to the
publication
Bradford White
Caleffi North America
ECR International
Gastite Corporation
Generac Power Systems, Inc.
Heatlines, Inc
IPEX Corporation
Lochinvar Corporation
Marathon Engine Systems
Monitor Products, Inc.
Myson Incorporated
Rinnai America Corporation
Robur
Triangle Tube
Vasco
Webstone Company, Inc.
Weil-McLain
Heating Professionals
Dan Foley
Gary Todd
Harvey Youker
Larry Drake
Paul Rohrs
www.bradfordwhite.com
www.caleffi.com
www.ecrinternational.com
www.gastite.com
www.generac.com
www.heatlines.com
www.ipexinc.com
www.lochinvar.com
www.marathonengine.com
www.monitorproducts.com
www.mysoninc.com
www.rinnai.us
www.robur.com
www.triangletube.com
www.theheatingcompany.com
www.webstonevalves.com
www.weil-mclain.com
www.southjerseyoilheat.com/foley.html
Televisual Productions, Greensboro, NC
phone 336-643-1221
www.hytechheating.com
www.radiantpanelassociation.com
www.biggerstaffradiantsolutions.com
For more information
Contact:
Tracy Burleson
Director, Residential Trade Outreach and Partnerships
PERC
[email protected]
Propane
a. Propane Education and Research Council (PERC)
www.propanecouncil.org
b. Gas Appliance Manufacturers Association
www.gamanet.org
c. BuildwithPropane.com
d. F
ind a Propane Retailer www.usepropane.com/find/
Sec10:38