Calculate Total equivalent Ductwork length
Equivalent
Number
Equivalent
Duct Pieces
Length* x
Used =
Length
5" round
straight
2 .7 ft . x
( ft .)
†
=
ft .
6” round
straight
1 ft .
x
( ft .)
†
=
ft .
3
1
⁄
4
” x 10”
straight
1 ft .
x
( ft .)
†
=
ft .
5”, 90°
elbow
37 ft . x
( ) =
ft .
6”, 90°
elbow
12 ft . x
( ) =
ft .
5”, 45°
elbow
18 ft . x
( )
=
ft .
6”, 45°
elbow
7 ft .
x
( )
=
ft .
Flexible
metal offset
adapter
34 ft . x
( )
=
ft .
3
1
⁄
4
” x 10”
90° elbow
14 ft . x
( ) =
ft .
3
1
⁄
4
” x 10”
45° elbow
8 ft .
x
( ) =
ft .
3
1
⁄
4
” x 10”
90° flat elbow 33 ft . x
( )
=
ft .
5” round
to 3
1
⁄
4
” x 10”
transition
3 ft .
x
( ) =
ft .
6” round
to 3
1
⁄
4
” x 10”
transition
2 ft .
x
( ) =
ft .
Subtotal Column 1 =
ft .
* Equivalent lengths of duct pieces are based on actual
tests and reflect requirements for good venting
performance with any downdraft cooktop .
† Measure and list feet of straight duct used . Count and
list the quantity of all other duct pieces for the “Number
Used” of each type .
ImPoRTANT:
For maximum efficiency, use the shortest and straightest
duct run possible, with as few fittings as possible .
for
satisfactory performance, the duct run should not
exceed 100 feet equivalent length.
Venting performance is improved by using larger
diameter duct .
Equivalent
Number
Equivalent
Duct Pieces
Length* x
Used =
Length
5” round
to 3
1
⁄
4
” x 10”
transition
90° elbow
37 ft .
x
( ) =
ft .
6” round
to 3
1
⁄
4
” x 10”
transition
90° elbow
4 ft .
x
( ) =
ft .
3
1
⁄
4
” x 10”
to 6” round
transition
2 ft .
x
( ) =
ft .
3
1
⁄
4
” x 10”
to 6
≤
round
transition
90° elbow
4 ft .
x
( )
=
ft .
Tapered 5”
round to
6”
round
transition
6 ft .
x
( )
=
ft .
5” round collar
to 6” round
transition
13 ft . x
( )
=
ft .
5” round
wall cap
with damper
84 ft .
x
( ) =
ft .
6” round
wall cap
with damper
24 ft .
x
( ) =
ft .
3
1
⁄
4
” x 10”
wall cap
with damper
24 ft .
x
( ) =
ft .
6" round
roof cap
33 ft . x
( ) =
ft .
Subtotal Column 2 =
ft .
Subtotal Column 1 =
ft .
ToTAl DuCTWoRk =
ft .
Should not exceed 100 feet.
If flexible metal ducting is used, all the equivalent
feet values in the table should be doubled . The
flexible metal duct should be straight and smooth
and extended as much as possible .
Do NoT use flexible plastic ducting.
Vent installation should not exceed 100 feet
equivalent length .
18
DuCTWoRk CAlCulATIoNs
Installation Instructions
