22
Recommended Vent Length
A 3
1
/
4
" x 10" (8.3 x 25.4 cm) rectangular or 6" (15.2 cm) round
vent should be used.
The total length of the vent system including straight vent,
elbow(s), transitions and wall or roof caps must not exceed the
equivalent of 140 ft (42.7 m) for either type of vent. See the
“Recommended Standard Fittings” section for equivalent lengths.
For best performance, use no more than three 90° elbows.
To calculate the length of the system you need, add the equivalent
lengths of each vent piece used in the system. See the following
examples:
3
1
/
4
" x 10" (8.3 x 25.4 cm) vent system = 73 ft (22.2 m) total
A. One 3
1
/
4
" x 10" (8.3 x 25.4 cm) 90° elbow= 25 ft (7.6 m)
B. 1 wall cap = 40 ft (12.2 m)
C. 2 ft (0.6 m) + 6 ft (1.8 m) straight = 8 ft (2.4 m)
D. 6 ft (1.8 m)
E. 2 ft (0.6 m)
6" (152 mm) vent system = 73 ft (22.2 m) total
A. Two 90° elbows = 20 ft (6.1 m)
B. 1 wall cap = 40 ft (12.2 m)
C. 1 rectangular-to-round transition piece = 5 ft (1.5 m)
D. 2 ft (0.6 m) + 6 ft (1.8 m) straight = 8 ft (2.4 m)
E. 6 ft (1.8 m)
F. 2 ft (0.6 m)
If the existing vent is round, a rectangular to round transition piece
must be used. In addition, a rectangular 3" (7.6 cm) extension
vent between the damper assembly and rectangular to round
transition piece must be installed to keep the damper from
sticking.
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