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Calculate Total Equivalent Ductwork Length
Equivalent Number Equivalent
Duct Pieces Length* x Used = Length
5″ round
straight 2.7 ft. x ( ft.)
†
= ft.
6″ round
straight 1 ft. x ( ft.)
†
= ft.
3
1
⁄4″ x 10″
straight 1 ft. x ( ft.)
†
= ft.
5″, 90°
elbow 37 ft. x ( ) = ft.
6″, 90°
elbow 12 ft. x ( ) = ft.
5″, 45°
elbow 18 ft. x ( ) = ft.
6″, 45°
elbow 7 ft. x ( ) = ft.
Flexible
metal offset See Calculations in
adapter Step 5A. ft.
3
1
⁄4″ x 10″
90° elbow 14 ft. x ( ) = ft.
3
1
⁄4″ x 10″
45° elbow 8 ft. x ( ) = ft.
3
1
⁄4″ x 10″
90° flat elbow
33 ft. x ( ) = ft.
5″ round
to 3
1
⁄4″ x 10″
transition 3 ft. x ( ) = ft.
6″ round
to 3
1
⁄4″ x 10″
transition 2 ft. x ( ) = ft.
Subtotal Column 1 = ft.
*Equivalent lengths of duct pieces are based on
actual tests and reflect requirements for good
venting performance with any downdraft cooktop.
†Measure and list feet of straight duct used. Count
and list the quantity of all other duct pieces for
the “Number Used” of each type.
IMPORTANT:
For maximum efficiency, use the shortest and
straightest duct run possible, with as few fittings
as possible. For satisfactory performance, the duct
run should not exceed 100 feet equivalent length.
Venting performance is improved by using larger
diameter duct.
Equivalent Number Equivalent
Duct Pieces Length* x Used = Length
5″ round
to 3
1
⁄4″ x 10″
transition
90° elbow 37 ft. x ( ) = ft.
6″ round
to 3
1
⁄4″ x 10″
transition
90° elbow 4 ft. x ( ) = ft.
3
1
⁄4″ x 10″
to 6″ round
transition 2 ft. x ( ) = ft.
3
1
⁄4″ x 10″
to 6″ round
transition
90° elbow 4 ft. x ( ) = ft.
Tapered 5″
round to
6″ round
transition 6 ft. x ( ) = ft.
5″ round collar
to 6″ round
transition 13 ft. x ( ) = ft.
5″ round
wall cap
with damper 84 ft. x ( ) = ft.
6″ round
wall cap
with damper 24 ft. x ( ) = ft.
3
1
⁄4″ x 10″
wall cap
with damper 24 ft. x ( ) = ft.
6″ round
roof cap 33 ft. x ( ) = ft.
Subtotal Column 2 = ft.
Subtotal Column 1 = ft.
TOTAL DUCTWORK = ft.
Should not exceed 100 feet.
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.
Vent installation should not exceed 100 feet
equivalent length.
Blower is rated at 400 CFM at 0.1 inch of
water back pressure.
18
DUCTWORK CALCULATIONS
Installation Instructions
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