GE Profile JGP656 Series Technical Service Manual page 17

Duct Fittings
Note: Any home ventilation system, such as
a cooktop with a downdraft exhaust
mechanism, may interrupt the proper flow of
combustion air and exhaust required by
fireplaces, gas furnaces, gas water heaters,
and other naturally vented systems. To
minimize the chance of interruption of such
naturally vented systems, follow the heating
equipment manufacturer's guidelines and
safety standards such as those published by
NFPA and ASHRAE.
Use the chart at the right to compute the
maximum permissible lengths for duct runs
to outdoors.
Note: Do not exceed maximum permissible
equivalent lengths.
Flexible ducting
WARNING: Do not use flexible plastic
ducting.
If flexible metal ducting is used, all the
equivalent length values entered on the
worksheet for flexible ducting should be
doubled. The flexible metal duct should be
straight and smooth, and extended as much
as possible.
Vent installation should not exceed 150 feet
equivalent length.
Table of Equivalent Lengths
Duct Pieces
6 " round,
straight
3 1 4 " x 10"
straight
6", 90
elbow
6 ", 45
elbow
3 1 4 " x 10"
90 elbow
3 1 4 " x 10"
45 elbow
3 1 4 " x 10"
90 flat elbow
6 " round
to 3 " x 10"
1 4
transition
3 1 4 " x 10"
to 6" round
transition
6" round
to 3 1 4 " x 10"
transition
90 elbow
3 1 4 " x 10"
to 6" round
transition
90 elbow
6 " round wall
cap with damper
3 1 4 " x 10" wall
cap with damper
6" round
roof cap
6" round
roof vent
Total duct run should not exceed 150 ft.
– 15 –
Total
Equivalent Number Equivalent
Length* Used Length
1 ft.
(per foot
length) feet
1 ft.
(per foot
length) feet
15 ft.
9 ft.
16 ft.
5 ft.
18 ft.
7 ft.
5 ft.
20 ft.
12 ft.
21 ft.
27 ft.
20 ft.
24 ft.
GEA00240