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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 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.
3-1/4"x10" to 6" = 5ft.
3-1/4"x10" roof cap = 24ft.
3-1/4"x10" 90° elbow = 25ft.
90° elbow = 1Oft.
3-1/4"x10" wall cap
= 40ft.
45 ° elbow = 5ft. 3-1/4"x10" fiat elbow
= 1Oft.
Figure 9
To calculate the equivalent length of each duct piece used, see the examples below.
For 3-1/4"x10" SYSTEMS
3-1/4"x10" _ 6ft. _ wall cap
90 ° elbow *_fr_ I 0_"
1 3-1/4" x 10" 90° elbow = 25ft.
1 wall cap = 40 ft.
8 feet straight duct = 8 ft.
TOTAL LENGTH = 73 ft.
Exam )les
For 6" ROUND SYSTEMS
90°elbows _--- 6ft. -_/wall cap
transi_
1 transition = 5 ft.
2 90 ° elbows = 20 ft.
1 wall cap = 40 ft.
8 feet straight = 8 ft.
TOTAL LENGTH = 73 ft.