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STEP 2:
PREPARE THE VENTING SYSYTEM
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, wall or roof caps must not
exceed the equivalent of 140 feet.
For best performance, do not use more than three 90 degree elbows.
Below are the standard fittings and their equivalent length in feet.
1
To calculate the equivalent length of each ductpiece used, see the examples below.
For 3 1/4"x10" SYSTEMS
3 1/4"x10"
90˚ elbow
2ft.
1-3 1/4" x 10" 90˚ elbow
1-Wall Cap
8 feet straight duct
TOTAL LENGTH
2
3 1/4"x10"
3 1/4"x10" roof
to 6"=5ft.
4
5
3 1/4"x10"
wall cap
90˚ elbow
=40ft.
=10ft.
6ft.
wall cap
=
25 ft.
=
40 ft.
=
8 ft.
=
73 ft.
3
3 1/4"x10" 90˚
cap=24ft.
elbow=25ft.
6
7
45˚ elbow
=5ft.
Figure 9
Examples
For 6" ROUND SYSTEMS
90˚ elbows
transition
1-transition
2-90˚ elbows
1-Wall Cap
8 feet straight
TOTAL LENGTH
— 9 —
3 1/4"x10"
flat elbow
=10ft.
6ft.
2ft.
wall cap
=
5 ft.
=
20 ft.
=
40 ft.
=
8 ft.
=
73 ft.
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