Mechanical Ventilation with Heat Recovery
10 Most Common Site Problems
Mechanical Ventilation with Heat Recovery (MVHR) is an energy efficient method of meeting the
need to ventilate our homes and to maintain a healthy indoor environment. However, the issue of
installed performance has been highlighted by recent changes to Building Regulations and NHBC
guidance as poor installation can result in non-compliance, threaten the health of the occupants,
cause customer complaints and lead to potentially costly remedial repairs.
Here we set out the ten most common installation issues attributed to the most commonly
reported symptoms – poor ventilation, excessive noise and excessive energy consumption.
Identifying potential problems before and during the build process will significantly reduce the risk
of system failure and dissatisfaction.
1. Not using or following a professional system design
MVHR systems should be designed by a professional who will normally provide detailed
drawings of the layout, set out the product choices and state the design performance. These
factors are arrived at using Building Regulations guidance and are based on the individual
building’s characteristics. They determine the positioning of product, duct sizes and MVHR
unit performance. Any variation from the design provided should be approved by the
designer to ensure system performance is not adversely affected.
Titon offer comprehensive service support using experienced qualified personnel. We offer
certified BPEC installer training and on-site training to all our customers to minimise risks. For
details please call us on +44 (0) 1206 814879 or email [email protected].
Ventilation system design drawing
2. Excessive use of flexible ducting
Flexible ducting has a much greater resistance to airflow than smooth bore rigid ducting even
when it is installed properly. It is often used to connect ceiling air valves or the MVHR unit to
the solid ducting to allow for slight differences in alignment. Flexible ducting should only be
used in short lengths and pulled taut as it is easily crushed, twisted and damaged resulting in
leaks or blockages.
Reduce the risk of complaints and expensive remedial repairs by following this advice
Excessive use of flexible ducting damaged, crushed, twisted and not pulled taut causing a blockage or excessive resistance
to airflow
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3. Not adequately sealing or supporting ducts
5. Not installing ducting properly
Any leaks or obstructions in the ducting will affect performance so all joints should be airtight
with a long term seal and duct supported where necessary. Appropriate use of a performance
tested proprietary leak free duct coupler with a built in seal, or the application of a nonhardening sealant for conventional rigid ducting joints are advisable, as standard as duct tape
alone is insufficient to provide a long term airtight seal. It is advisable to double check all joints
and fixings prior to covering over with boarding. Increasing the MVHR unit speed to compensate
for ducting problems will be detrimental to the core system objectives.
To prevent the formation of condensation on the inside or the outside of the duct, all ducting
connected to the air outside should be fully insulated along the whole length of the duct run
back to the MVHR unit. Any other ducting should also be insulated if it is outside the heated
space. Insulation should include a vapour barrier, simply installing ducting under the loft
insulation is no longer acceptable. Excessive moisture on the outside of the duct may damage
surrounding structures and on the inside it can impair performance and reduce the working life
of the system.
Silicone sealed and bracketed
Titon Self Seal Connector
Ductwork soaked and dripping
Ductwork with no insulation
4. Using the wrong type of wall, roof or ceiling terminals
6. Wiring an MVHR unit incorrectly
MVHR systems run continuously and they require purpose made terminals that have been
performance tested. There are many products on the market sold as ventilation terminals but
most are designed for passive, intermittent or single room fans and will severely restrict airflow
causing underperformance and noise.
Failing to follow the wiring diagrams provided in the manual will often damage the most costly
components in an MVHR unit, so ensure that the hard wiring installed is suitable before making
connections. For example, boost control wiring may use zero volt circuits so connection to a
230v supply or switch circuit would be dangerous.
Innapropriate wall terminals can increase resistance, causing excessive noise from the MVHR unit
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Blown PCB controller
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7. Not installing appropriate controls
9. Not checking the MVHR unit filters
Most ventilation systems require appropriate controls to be installed. For example, boost
controls are normally required in all bathrooms and kitchens. They should be wired in to be
easily accessible and be clearly labelled. Some MVHR systems may need additional controls
for other functions such as auralite® or SUMMERboost® so always check the product manual
and follow the guidance provided.
MVHR units require regular servicing and filter changes. Filters are fitted to the intake and
exhaust air paths for protecting the internal components. We recommend these are checked
prior to handover as they can get clogged up with dust and debris arising from the building
process and impair system performance.
Titon G3 HRV filter
®
Titon auralite status indicator
Titon G4 HRV filter
Titon SUMMERboost switch
®
8. Not commissioning the MVHR system correctly
10. Boxing in the MVHR units
MVHR systems require commissioning on site to comply with Building Regulations.
Commissioning includes setting the unit speed and using a cone anemometer to set the
individual room airflow rates by adjusting the room air valves before locking them.
The installed performance must be recorded and we advise using the forms provided in the
Domestic Ventilation Compliance Guide that accompanies the Building Regulations.
MVHR units must remain safely accessible for regular maintenance, filter changes and
commissioning adjustments, they must not be permanently boxed in. This includes leaving
sufficient space around the unit to allow for future repair or end of life replacement. The product
manual provides detailed guidance on access requirements. There are also additional statutory
access requirements where units are installed out of normal reach.
Balancing MVHR settings
Using a cone anemometer
A boxed in MVHR unit
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An accessible MVHR unit
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Installation Checklist
1
Professional design provided and followed on site
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2
Limited use of flexible ducting, which is pulled taut
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3
All ducting is supported and properly sealed
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4
The external terminals are fit for purpose
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5
The ducting is properly insulated where required
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6
The MVHR unit is wired in according to the manual guidance
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The appropriate controls have been installed
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8
The system has been commissioned and the details recorded
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9
The filters were checked prior to handover
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10
The MVHR unit is safely accessible for future maintenance
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Finally, to fully comply with Building Regulations the dwelling owner must be given
sufficient information to be able to use and maintain the ventilation system properly.
This might include provision of the product manual and/or user guide and the
commissioning data.
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The owner information is available to handover
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BM98 Iss 01
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