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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 duct piece used, see the examples below.
For 3 1/4"x10" SYSTEMS
1-3 1/4" x 10" 90° elbow
1-Wall Cap
8 feet straight duct
TOTAL LENGTH
1
2
3 1/4" x 10"
to 6"=5ft.
4
5
3 1/4" x 10"
wall cap
90˚elbow
=40ft.
=10ft.
6ft.
wall cap
2ft.
=
25 ft.
=
40 ft.
=
8 ft.
=
73 ft.
3
3 1/4" x 10" roof
3 1/4" x 10" 90˚
cap=24ft.
elbow=25ft.
6
7
3 1/4" x 10"
flat elbow
45˚elbow
=5ft.
Figure 9
Examples
For 6"ROUND SYSTEMS
transition
1-transition
2-90° elbows
1-Wall Cap
8 feet straight
TOTAL LENGTH
10
=10ft.
wall cap
6ft.
2ft.
=
5 ft.
=
20 ft.
=
40 ft.
=
8 ft.
=
73 ft.
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