Table of Contents
Advertisement
Use this chart to
Duct
compute maximum
fittings
permissable lengths
for duct runs to
outdoors.
Note:
permissable equivalent lengths!
Maximum duct length:
100 foot for range 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
plastic ducting.
Note:
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.
Note:
is 4-1/2" x 18-1/2".
Duct Piece Dimensions
Do not exceed maximum
Any home ventilation
48" Hoods Must Use
10" Round Duct
or 3-1/4" x 24"
Outlet on top of 48" hood
30" and 36" Hoods
May Use 7" to 10"
Round, or 3-1/4" x 12"
* Actual length of straight duct plus duct fitting
equivalent. Equivalent length of duct pieces are based
to 3-1/4" x 24"
on actual tests conducted by GE Evaluation Engineer-
ing and reflect requirements for good venting
performance with any ventilation hood.
Installation Preparation
Professional Vent Hoods
Equivalent Quantity Equivalent
Length*
Round,
1 ft.
straight
(per foot
length)
3-1⁄4" x 12" or
1 ft.
3-1/4" x 24"
(per foot
straight
length)
90 elbow
15 ft.
45 elbow
9 ft.
3-1⁄4" x 12" or
3-1/4" x 24"
90 elbow
15 ft.
3-1⁄4" x 12" or
3-1/4" x 24"
45 elbow
9 ft.
3-1⁄4" x 12" or
3-1/4" x 24"
90 flat elbow
20 ft.
7" round to
3-1⁄4" x 12" or 10" round
to 3-1/4" x 24" transition
1 ft.
3-1⁄4" x 12" to 7" round
or 3-1/4" x 24" to 10"
round transition
5 ft.
7" round to
3-1/4" x 12" or 10" round
to 3-1/4" x 24"
transition 90 elbow
5 ft.
3-1⁄4" x 12" to 7" round
or 3-1/4" x 24" to 10"
round transition 90 elbow 15 ft.
Round
wall cap
with damper
30 ft.
3-1⁄4" x 12" or
3-1/4" x 24" wall cap
with damper
30 ft.
Round
roof cap
26 ft.
Round
roof vent
24 ft.
Total
Used
Length
Total Duct Run
6
Advertisement
Table of Contents
