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EFFECTIVE LENGTH POST FAN IS CALCULATED BY THE
FOLLOWING EQUATION:
Equation 2
NOTE: Blower Height is from closest horizontal surface below
fan.
Effective Duct Length = Vertical Run Up + (2 x Vertical Run
Down) + L1 + L2 + L3 + (3 x # of 90° bends) + (1.5 x # of 45°
bends)
EXAMPLE 2
Blower
Height
L₁
L₂
L₃
45°
Bends
90°
Bends
Total
Effective
Length
H 1
0
12ft
0
0
0
0
12ft
H 2
0
4ft 6ft 1.5ft
1
2
20ft
H 3
0
4.5ft 6ft
6ft
1
2
24ft
Vertical Run Up = (Blower V1) = 0
Vertical Run Down = 0ft.
Horizontal Length 1 = (12ft. + 0ft. + 0ft.) + (3 x 2) + (1.5 x 1) =
(12ft. +0ft. + 0ft.) = 12ft.
Horizontal Length 2 = (4ft. + 6ft. + 1.5ft.) + (3 x 2) + (1.5 x 1) =
(11.5ft. +6ft. + 1.5ft.) = 20ft.
Horizontal Length 3 = (4.5ft. + 6ft. + 6ft.) + (3 x 2) + (1.5 x 1) =
(16.5ft. +6ft. + 1.5ft.) = 24ft.
DUCT VENT INSTALLATION
Effective Combined length = Combined Horizontal Run +
length of 10” ducting
Effective Combined length = (H1 + H2 +H3) + L4
Effective Combined length = (12ft. + 20ft. + 24ft.) + 4ft.
Total Effective Combined Length = 60ft
L1
R1
R2
Ceiling/Wall
Register
Outlet
6” Wire Reinforced Ducting
(insulated recommended)
10” Wire Reinforced Ducting
(insulated recommended)
L1
L3
L2
R1
R1
R1
R2
L4
L3
L2
L1
H2
H1
H3