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Effects of Installation on Performance
Any installation with inlet or discharge configurations that deviate from these recommendations may result in
reduced fan performance. Restricted or unstable flow at the fan inlet can cause pre-rotation of incoming air or
uneven loading of the fan propeller yielding large system losses and increased sound levels. Free discharge or
turbulent flow in the discharge ductwork will also result in system effect losses.
The most common inlet and discharge conditions which affect fan performance are:
Inlet Duct Turns
INLET DUCT TURNS
1 Fan
Dia.
Turning
Vanes
Good
Installation of a duct turn or elbow too close to the fan inlet reduces fan performance because air is loaded unevenly
into the fan prop. To achieve full fan performance there should be at least one to two fan diameters between the turn
or elbow and the fan inlet.
DISCHARGE DUCT TURNS
Discharge Duct Turns
Poor
Good
Fan performance is reduced when duct turns are made immediately off the fan discharge. To achieve cataloged fan
1 Fan
Dia.
performance, there should be at least three equivalent fan diameters of straight ductwork between the fan discharge
and any duct turns.
For curb mounted exhaust or supply systems using "Bottom Inlet" duct connections, installation of drain locations
within the ductwork is recommended to allow for safe removal of any water that enters the duct system. This
Air Flow
requires the installing contractor to determine whether insulation, watertight construction, or sloped and drained
ductwork are required. For curb mounted exhaust or supply systems with "Free Inlet Bottom Intake" connections
(free air inlet conditions), it is recommended to install a moisture collecting drip pan at least one housing diameter
below the inlet of the fan.
Poor
4
Tubular Inline Fans
Air Flow
Poor
3 Diameters of
Straight Duct
NOTE
®
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