Filter
Top Products
DUCT FITTINGS
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 6” round duct
75 foot for 3-1/4” x 12” duct
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 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.
This Hood Must Use a
6” Round Duct.
It Can Transition To
3-1/4” x 12” Duct
5
Installation Preparation
Total
Equivalent Quantity Equivalent
Duct Piece Dimensions Length* Used Length
Round, 1 ft.
straight (per foot
length)
3-1/4” x 12” 1 ft.
3-1/4” x 24” (per foot
straight length)
6” Round
90° elbow 15 ft.
6” Round
45° elbow 8 ft.
3-1⁄4” x 12”
90° elbow 11 ft.
3-1/4” x 12” or
45° elbow 6 ft.
3-1/4” x 12”
90° flat elbow 24 ft.
6” round to
3-1/4” x 12”
or 3-1/4” x 24” transition 1 ft.
3-1/4” x 12” to 6”
round transition 8 ft.
6” round
to 3-1/4” x 12” or
transition 90° elbow 16 ft.
3-1/4” x 12” to 6” round
round transition 90° elbow 17 ft.
6” round
wall cap
with damper 30 ft.
3-1/4” x 12” wall cap
with damper 30 ft.
6” Round
roof cap 26 ft.
6” Round
roof vent 26 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 ventilation hood.
Total Duct Run