18
INSTALLATION INSTRUCTIONS
(continued)
DUCT FITTINGS
Use the chart at the right to compute maximum
permissible lengths for duct runs to outdoors.
NOTE: Do not exceed maximum permissible
equivalent lengths!
Flexible ducting:
If flexible metal ducting is used, all the
equivalent feet values in the table should be
doubled. The flexible metal duct should be
straight and smooth and extended as much
as possible.
Do NOT use flexible plastic ducting.
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.
Total
Equivalent Number Equivalent
Duct Pieces
Length*
Used
Length
1 ft.
6
″
round,
(per foot
straight
length)
feet
1 ft.
3
1
⁄
4
″
x 10
″
(per foot
straight
length)
feet
6
″
,
90
°
elbow
15 ft.
6
″
,
45
°
elbow
9 ft.
3
1
⁄
4
″
x 10
″
90° elbow
16 ft.
3
1
⁄
4
″
x 10
″
45° elbow
5 ft.
3
1
⁄
4
″
x 10
″
90° flat elbow
18 ft.
6
″
round
to 3
1
⁄
4
″
x 10
″
transition
7 ft.
3
1
⁄
4
″
x 10
″
to 6
″
round
transition
5 ft.
6
″
round
to 3
1
⁄
4
″
x 10
″
transition
90° elbow
20 ft.
3
1
⁄
4
″
x 10
″
to 6
″
round
transition
90° elbow
12 ft.
6
″
round wall
cap with damper
21 ft.
3
1
⁄
4
″
x 10
″
wall
cap with damper
27 ft.
6
″
round
roof cap
20 ft.
6
″
round
roof vent
24 ft.
Total duct run should not exceed 150 ft.
*Actual length of straight duct plus duct fitting
equivalent. Equivalent length of duct pieces are
based on actual tests conducted by GE Evaluation
Engineering and reflect requirements for good
venting performance with any downdraft cooktop.
