Friction Loss Diagram
Friction loss
(head loss) in
standard air
ducts are
indicated in the
diagram below:
3
The diagram is based on standard air 0.075 lb/ft in clean round galvanized metal ducts.
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1 inch water = 248.8 N/m2 (Pa)= 0.0361 lb/in2 (psi) = 25.4 kg/m2 =
0.0739 in mercury
1 ft3/min (cfm) = 1.7 m3/h = 0.47 l/s
1 ft/min = 5.08x10-3 m/s
1 inch = 25.4 mm = 2.54 cm = 0.0254 m = 0.08333 ft
Friction Loss Diagram
Example - Friction Loss in Air Duct
The friction loss in a 20 inches duct with air flow 4000 cfm can be estimated to approximately 0.23 inches
water per 100 feet duct as shown in the diagram below. The air velocity can be estimated to
approximately 1850 feet per minute.