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
adapter
34 ft.
x
(
) =
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
