Installation guide
5
Duct pieces 
To t a l
Equivalent number
length  x used   =
3- 1/ 4” x 10”
Rect.,
straight
1 Ft.  x ( ) =
Ft. 
8” Round,
straight
1 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. 
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” Round,
90
0 
elbow
15 Ft.  x ( )  =
Ft. 
6” Round,
45
0 
elbow
9 Ft.  x ( ) =
Ft. 
Ft. 
7” Round,
straight
1 Ft.  x ( ) =
Ft. 
Subtotal column 1 =
Duct pieces 
To t a l
Equivalent number
length  x used   =
6”- 8” Round
wall cap
with damper
30 Ft.  x (  )  =
Ft. 
Round
wall cap
with damper
30 Ft.  x (  )  =
Ft. 
7” or 8” 
Round,
90
0 
elbow
15 Ft.  x ( )  =
Ft. 
7” or 8” 
7” or 8” 
Round,
45
0 
elbow
9 Ft.  x ( ) =
Ft. 
Ft. 
Ft. 
Ft. 
6”- 8” Round,
roof cap
30 Ft.  x (  )  =
Ft. 
7” or 8”
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 of a 3 1/ 4” x 10” rectangular  6” or 7”
diameter round duct should not exceed 100 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. 
Installation – Ducting Calculation Sheet










