Specifications

DUCT FITTINGS
Use this chart to compute
maximum permissible lengths for
duct runs to outdoors.
NOTE: Do not exceed maximum
permissible equivalent lengths!
Maximum duct length:
100 foot for 8″ round 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 an
8″ Round Duct.
9
Advance Planning
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)
8″ round
90° elbow 17 ft.
8″ round
45° elbow 10 ft.
3-1⁄4″ x 10″ 14 ft.
3-1⁄4″ x 12″ 15 ft.
90° elbow
3-1/4″ x 10″ 8 ft.
3-1/4″ x 12″ 9 ft.
45° elbow
3-1/4″ x 10″ 33 ft.
3-1/4″ x 12″ 36 ft.
90° flat elbow
8″ to 3-1/4″ x 10″ 2 ft.
8″ to 3-1/4″ x 12″ 2 ft.
or 3-1/4″ x 10″ transition 2 ft.
3-1/4″ x 10″ to 8″ 2 ft.
3-1/4″ x 12″ to 8″ 2 ft.
round transition
8″ to 3-1/4″ x 10″ 7 ft.
8″ to 3-1/4″ x 12″ 6 ft.
transition 90° elbow
3-1/4″ x 10″ to 8″ 5 ft.
3-1/4″ x 12″ to 8″ 5 ft.
round transition 90° elbow
8″ round
wall cap
with damper 32 ft. with damper
3-1/4″ x 12″ wall cap
with damper 26 ft. with damper
8″ round
roof cap 44 ft.
3-1/4″ x 10″ wall cap
w/ damper 24 ft.
round roof vent
*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
NETSPACE
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