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Ductwork
Gas Downdraft Cooktop
Duct
Fittings
Total
Equivalent Quantity Equivalent
Duct Piece Dimensions Length* Used Length
1 ft.
6" round, (per foot
straight length)
1 ft.
3-1⁄4" x 10" (per foot
straight length)
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"
round to 6"
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
Use this form 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.
Gas Downdraft
Cooktop
Model ZGU365
150' maximum
equivalent length
*Actual length of straight duct plus duct fitting
equivalent. Equivalent length of duct pieces are based
on actual tests conducted by GE Evaluation Engineer-
ing and reflect requirements for good venting
performance with any downdraft cooktop.
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 inter-
ruption of such
naturally vented
systems, follow the
heating equipment
manufacturer’s
guidelines and safety
standards such as those
published by NFPA
and ASHRAE.