6
Advance Planning
DUCT FITTINGS
Total
Equivalent Quantity Equivalent
Duct Piece Dimensions
Length*
Used
Length
Round,
1 ft.
straight
(per foot
length)
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 24"
45
°
elbow
9 ft.
3-1/4" x 24"
90
°
flat elbow
20 ft.
10" round to
3-1/4" x 24" transition
1 ft.
3-1/4" x 24" to 10"
round transition
5 ft.
10" round
to 3-1/4" x 24"
transition 90
°
elbow
5 ft.
3-1/4" x 24" to 10"
round transition 90
°
elbow 15 ft.
Round
wall cap
with damper
30 ft.
3-1/4" x 24" wall cap
with damper
30 ft.
Round
roof cap
26 ft.
Round
roof vent
24 ft.
Use this chart to compute maximum
permissable lengths for duct runs to
outdoors.
Note:
Do not exceed maximum permissable
equivalent lengths!
Maximum recommended duct
length for these hoods: 150 feet
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.
Total Duct Run
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.
* 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.
Hoods Are Equipped
For 10" Round Duct
*Hoods are supplied with a 10"
round transition. A locally
supplied transition is required
for other sizes.
Note:
Outlet on top of hood is
8-1/8" x 8".