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INSTALLATION
STEP 2: PREPARE THE VENTING SYSTEM
STANDARD FITTINGS
NOTE: If the existing duct is round, you must use a rectangular-to-round adapter, with a rectangular 3"
extension duct installed between the damper assembly and the adapter to prevent the exhaust
damper’s sticking.
DUCT LENGTH
The total length of the duct system, including straight duct, elbows, transitions, and wall or roof caps must not
exceed the equivalent of 140 feet.
For best performance, do not use more than three 90 degree elbows, and keep length as short as possible.
Below are the standard fittings and their equivalent length in feet.
To calculate the equivalent length of each ductpiece used, see the examples below.
Figure 9
1
4
5
6
7
2
3
3 1/4"x10"
to 6"=5ft.
90˚ elbow
=10ft.
45˚ elbow
=5ft.
3 1/4"x10"
wall cap
=40ft.
3 1/4"x10"
flat elbow
=10ft.
3 1/4"x10" roof
cap=24ft.
3 1/4"x10" 90˚
elbow=25ft.
Examples
For 3 1/4"x10" SYSTEMS
1-3 1/4" x 10" 90˚ elbow
1-Wall Cap
8 feet straight duct
TOTAL LENGTH
1-transition
2-90˚ elbows
1-Wall Cap
8 feet straight
TOTAL LENGTH
For 6" ROUND SYSTEMS
6ft.
2ft.
2ft.
3 1/4"x10"
90˚ elbow
wall cap
6ft.
90˚ elbows
transition
wall cap
= 25 ft.
= 40 ft.
= 8 ft.
= 73 ft.
= 5 ft.
= 20 ft.
= 40 ft.
= 8 ft.
= 73 ft.
