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Installation Instructions
9
Use this chart to compute maximum
permissable lengths for duct runs to
outdoors.
Note:
Do not exceed maximum permissable
equivalent lengths!
Maximum duct length:
100 foot for vent hoods.
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 ducting.
Note:
Any home ventilation system, such as a
ventilation hood, 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.
DUCT FITTINGS
Using a smaller diameter duct
size will reduce performance
*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 ventilation hood.
Duct Piece
Quantity
Used
Total
Equivalent
Length
1 Ft = 0.3 m
1” = 2.5 cm
Equivalent
Length*
1 ft.
(per foot
length
1 ft.
(per foot
length
8 ft.
6 ft.
15 ft.
9 ft.
20 ft.
1 ft.
5 ft.
5 ft.
15 ft.
30 ft.
30 ft.
30 ft.
24 ft.
Dimensions
Round,
straight
3¼” x 12”
straight
90° elbow
45° elbow
3¼” x 12” or
90° elbow
3¼” x 12” or
45° elbow
3¼” x 12” or
90° flat elbow
7” round to
3¼” x 12”
transition
3¼” x 12” to 7” round
transition
7” round to
3¼” x 12”
transition 90° elbow
3¼” x 12” to7” round
transition 90° elbow
Round
wall cap
with damper
3¼” x 12”
wall cap with
damper
7” round
roof cap
Round
roof vent
Total Duct Run