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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″ 8.5 Ft. x ( ) = Ft.
Rect. 90°
elbow
3
1
⁄4″x 10″ 7 Ft. x ( ) = Ft.
Rect. 45°
elbow
3
1
⁄4″x 10″ 24 Ft. x ( ) = Ft.
Rect. 90°
flat elbow
3
1
⁄4″x 10″ 45 Ft. x ( ) = Ft.
Rect.
(7 ft. w/o
wall cap
damper)
x ( ) = Ft.
with
damper
3
1
⁄4″x 10″ 4.5 Ft. x ( ) = Ft.
Rect. to
6″ round
transition
3
1
⁄4″x 10″ 11.5 Ft. x ( ) = Ft.
Rect. to
6″ round
transition
90° elbow
6″ Round, 8 Ft. x ( ) = Ft.
90° elbow
6″ Round, 6.5 Ft. x ( ) = Ft.
45° elbow
Subtotal column 1 = Ft.
8
WORKSHEET – CALCULATE TOTAL EQUIVALENT DUCTWORK LENGTH
DUCT EQUIVALENT NUMBER
PIECES LENGTH x USED = TOTAL
6″Round 34 Ft. x ( ) = Ft.
wall cap
(6 ft. w/o
with
damper)
x ( ) = Ft.
damper
6″ Round 30 Ft. x ( ) = Ft.
roof cap
6″ Round 5.5 Ft. x ( ) = Ft.
to
3
1
⁄4″x 10″
rect.
transition
6″ Round 14.5 Ft. x ( ) = Ft.
to
3
1
⁄4″x 10″
rect.
transition
90° elbow
7″ Round, 8 Ft. x ( ) = Ft.
90° elbow
7″ Round, 6.5 Ft. x ( ) = Ft.
45° elbow
7″ Round 34 Ft. x ( ) = Ft.
wall cap (
6 ft. w/o
with
damper)
x ( ) = Ft.
damper
7″ Round 30 Ft. x ( ) = Ft.
roof cap
7″ Round 5.5 Ft. x ( ) = Ft.
to
3
1
⁄4″x 10″
rect.
transition
7″ Round 14.5 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.