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DUCT EQUIVALENT NUMBER
PIECES LENGTH x USED = TOTAL
3
1
⁄4″x 10″ 1 Ft. x ( ) = Ft.
Rect.,
straight
7″ Round, 1 Ft. x ( ) = Ft.
straight
6″ Round, 1 Ft. x ( ) = Ft.
straight
3
1
⁄4″x 10″ 14 Ft. x ( ) = Ft.
Rect. 90°
elbow
3
1
⁄4″x 10″ 8 Ft. x ( ) = Ft.
Rect. 45°
elbow
3
1
⁄4″x 10″ 33 Ft. x ( ) = Ft.
Rect. 90°
flat elbow
3
1
⁄4″x 10″ 24 Ft. x ( ) = Ft.
Rect.
(18 ft. w/o
wall cap
damper)
x ( ) = Ft.
with
damper
3
1
⁄4″x 10″ 2 Ft. x ( ) = Ft.
Rect. to
6″ round
transition
3
1
⁄4″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
3
1
⁄4″x 10″
rect.
transition
6″ Round 4 Ft. x ( ) = Ft.
to
3
1
⁄4″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
3
1
⁄4″x 10″
rect.
transition
7″ Round 5 Ft. x ( ) = Ft.
to
3
1
⁄4″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 3
1
⁄4″ x 10″
rectangular, 6″ or 7″ diameter round duct should
not exceed 65 equivalent feet.