5
Rectangular to Round Transition
NOTE: The minimum 3" (7.6 cm) clearance must exist between
the top of the damper assembly and the rectangular to round
transition piece so that the damper can open freely and fully.
Recommended Standard Fittings
The following length equivalents are for use when figuring vent
length. See the examples in “Recommended Vent Length.”
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
“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
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. Roof cap
B. 6" (15.2 cm) min. diameter round vent
C. Elbow (for wall venting only)
D. Wall cap
E. 3
¹⁄₄
" 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. Rectangular to round transition piece: 3
¹⁄₄
" x 10" to 6" = 5 ft
(8.3 x 25.4 cm to 15.2 cm = 1.5 m)
B. Roof cap: 3
¹⁄₄
" x 10" = 24 ft (8.3 x 25.4 cm = 7.3 m)
C. 90° elbow: 3
¹₄
" x 10" = 25 ft (8.3 x 25.4 cm = 7.6 m)
D. 90° elbow: 6" = 10 ft (15.2 cm = 3 m)
E. Wall cap: 3
¹⁄₄
" x 10" = 40 ft (8.3 x 25.4 cm = 12.2 m)
F. 45° elbow: 6" = 5 ft (15.2 cm = 1.5 m)
G. 90° flat elbow: 3
¹⁄₄
" x 10" = 10 ft (8.3 x 25.4 cm = 3 m)
A
B
C
E
F
D
3" (7.6 cm)
A B C
D E F G
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)
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)
A B
C
6 ft (1.8 m)
2 ft
(0.6 m)
A B
C D
6 ft (1.8 m)
2 ft
(0.6 m)
