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.
To calculate the equivalent length of each ductpiece used, see the examples below.
— 9 —
Figure 9
1
4
5
6
7
2
3
3 1/4"x10"
to 6"=5ft.
90û elbow
=10ft.
45û 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" 90û
elbow=25ft.
Examples
For 3 1/4"x10" SYSTEMS
1-3 1/4" x 10" 90û elbow
1-Wall Cap
8 feet straight duct
TOTAL LENGTH
1-transition
2-90û elbows
1-Wall Cap
8 feet straight
TOTAL LENGTH
For 6" ROUND SYSTEMS
6ft.
2ft.
2ft.
3 1/4"x10"
90û elbow
wall cap
6ft.
90û elbows
transition
wall cap
=
25 ft.
=
40 ft.
=
8 ft.
=
73 ft.
=
5 ft.
= 20 ft.
= 40 ft.
=
8 ft.
= 73 ft.
