Ducting Calculation Sheet
Duct pieces
Total
Equivalent number
length x used =
3- 1/ 4” x 10”
Rect.,
straight
1 Ft. x ( ) =
Ft.
3- 1/ 4” x 10”
Rect. to
6” round
transition
5 Ft. x ( ) =
Ft.
3- 1/ 4” x 10”
Rect. to
6” round
transition
90
0
elbow
20 Ft. x ( ) =
Ft.
6”, 7”, 8”, 10”
Round,
90
0
15 Ft.
x ( ) =
Ft.
6”, 7”, 8”, 10”
Round,
45
0
9 Ft. x ( ) =
Ft.
Ft.
6”, 7”, 8”, 10”
Round,
straight
1 Ft. x ( ) =
Ft.
Subtotal column 1 =
Duct pieces
Total
Equivalent number
length x used =
6”, 7”, 8”, 10”
Round, wall
cap with
damper
30 Ft. x ( ) =
Ft.
Ft.
Ft.
Ft.
6”, 7”, 8”, 10”
Round
roof cap
30 Ft. x ( ) =
Ft.
Subtotal column 2 =
Subtotal column 1 =
Total ductwork =
Maximum Duct Length:
For satisfactory air movement,
the total duct length
should not exceed 150 equivalent feet.
6” round to
3- 1/ 4” x 10”
rect.
transition
1 Ft. x ( ) =
Ft.
6” round to
3- 1/ 4” x 10”
rect.
transition
90
0
elbow
16 Ft. x ( ) =
Ft.
7” round to
3 1/ 4” x 10”
rect.
transition
8 Ft. x ( ) =
Ft.
7” round to
3- 1/ 4” x 10”
rect.
transition
90
0
elbow
23 Ft. x ( ) =
Ft.
elbow
elbow
7” to 6” or
8” to 7” Round
tapered
reducer
25 Ft.
x ( ) =
Ft.
3- 1/ 4” x 10”
Rect. 90
0
elbow
15 Ft. x ( ) =
Ft.
3- 1/ 4” x 10”
Rect. 45
0
elbow
9 Ft. x ( ) =
Ft.
3- 1/ 4” x 10”
Rect. 90
0
flat elbow
24 Ft. x ( ) =
Ft.
3- 1/ 4” x 10”
Rect.
wall cap
with damper
30 Ft. x ( ) =
Ft.
Ft. x ( ) =
Ft.
15
6”, 7“, 8”
Round
in-line
damper
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