12
Recommended Vent Length
A 3¹⁄
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.
3¹⁄
4
" x 10" (8.3 x 25.4 cm) vent system = 73 ft (22.2 m) total
.
6" (15.2 cm) vent system = 73 ft (22.2 m) total
.
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.
A
B
C
E
F
D
3" (7.6 cm)
A. Roof cap
B. 6" (15.2 cm) min. diameter round vent
C. Elbow (for wall venting only)
D. Wall cap
E. 3¹⁄
4
" x 10" to 6" (8.3 x 25.4 cm to 15.2 cm)
rectangular to round transition piece
F. Vent extension piece, at least 3" (7.6 cm) high
A B
C
6 ft (1.8 m)
2 ft
(0.6 m)
A. One 3¹⁄
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)
A B
C D
6 ft (1.8 m)
2 ft
(0.6 m)
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)
