6
DUCT
EQUIVALENT NUMBER
PIECES
LENGTH
x USED
= TOTAL
3¼
”
x 10
”
1 Ft.
x ( )
=
Ft.
Rect.,
straight
7
”
Round,
1 Ft.
x ( )
=
Ft.
straight
6
”
Round,
1 Ft.
x ( )
=
Ft.
straight
3¼
”
x 10
”
14 Ft.
x ( )
=
Ft.
Rect. 90°
elbow
3¼
”
x 10
”
8 Ft.
x ( )
=
Ft.
Rect. 45°
elbow
3¼
”
x 10
”
33 Ft.
x ( )
=
Ft.
Rect. 90°
flat elbow
3¼
”
x 10
”
24 Ft.
x ( )
=
Ft.
Rect.
(18 ft. w/o
wall cap
damper)
x ( )
=
Ft.
with
damper
3¼
”
x 10
”
2 Ft.
x ( )
=
Ft.
Rect. to
6
”
round
transition
3¼
”
x 10
”
4 Ft.
x ( )
=
Ft.
Rect. to
6
”
round
transition
90° elbow
6
”
Round,
12 Ft.
x ( )
=
Ft.
90° elbow
6
”
Round,
7 Ft.
x ( )
=
Ft.
45° elbow
Subtotal column 1
=
Ft.
WORKSHEET—CALCULATE TOTAL EQUIVALENT DUCTWORK LENGTH*
DUCT
EQUIVALENT
NUMBER
PIECES
LENGTH
x USED
= TOTA
L
6
”
Round
24 Ft.
x ( )
=
Ft.
wall cap
(18 ft. w/o
with
damper)
x ( )
=
Ft.
damper
6
”
Round
33 Ft.
x ( )
=
Ft.
roof cap
6
”
Round
2 Ft.
x ( )
=
Ft.
to
3¼
”
x 10
”
rect.
transition
6
”
Round
4 Ft.
x ( )
=
Ft.
to
3¼
”
x 10
”
rect.
transition
90° elbow
7
”
Round,
14 Ft.
x ( )
=
Ft.
90° elbow
7
”
Round,
9 Ft.
x ( )
=
Ft.
45° elbow
7
”
Round
28 Ft.
x ( )
=
Ft.
wall cap
(21 ft. w/o
with
damper)
x ( )
=
Ft.
damper
7
”
Round
39 Ft.
x ( )
=
Ft.
roof cap
7
”
Round
1 Ft.
x ( )
=
Ft.
to
3¼
”
x 10
”
rect.
transition
7
”
Round
5 Ft.
x ( )
=
Ft.
to
3¼
”
x 10
”
rect.
transition,
90° elbow
Subtotal column 2
=
Ft.
Subtotal column 1
=
Ft.
Total ductwork
=
Ft.
Installation Instructions
MAXIMUM DUCT LENGTH:
For satisfactory air
movement, the total duct length of a 3¼” x 10”
rectangular, 6” or 7” diameter round duct
should
not exceed 65 equivalent feet.
* 1 Ft = 0.3 m
1” = 2.5 cm
