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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 = TOTAL
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