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Simple venting configuration (only one 90° elbow)
For vent configurations requiring more than one 90° elbow, the following formulas apply:
Formula 1: H
< 4.2 V
T
T
Formula 2: H
+ V
< 24.75 feet
T
T
Example:
V
= V
= 6 FT
1
T
H
= 3 FT
1
H
= 5 FT
2
H
= H
+ H
= 3 + 5 = 8 FT
R
1
2
H
= .03 (two 90° elbows - 90°) = .03 (180° - 90°) = 2.7 FT
O
H
= H
+ H
= 8 + 2.7 = 10.7 FT
T
R
O
H
+ V
= 10.7 + 6 = 16.7 FT
T
T
Formula 1:
H
< 4.2 V
T
4.2 V
10.7 < 25.2
Formula 2:
H
+ V
< 24.75 FT
T
T
16.7 < 24.75
Since both formulas are met, this vent configuration is acceptable.
Example:
V
= 4 FT
1
V
= 1.5 FT
2
V
= V
+ V
= 4 + 1.5 = 5.5 FT
T
1
2
H
= 2 FT
1
H
= 1 FT
2
H
= 1 FT
3
H
= 1.5 FT
4
H
= H
+ H
+ H
+ H
= 2 + 1 + 1 + 1.5 = 5.5 FT
R
1
2
3
4
H
= .03 (four 90° elbows - 90°) = .03 (360° - 90°) = 8.1 FT
O
H
= H
+ H
= 5.5 + 8.1 = 13.6 FT
T
R
O
H
+ V
= 13.6 + 5.5 = 19.1 FT
T
T
Formula 1:
H
< 4.2 V
T
4.2 V
13.6 < 23.1
Formula 2:
H
+ V
< 24.75 FT
T
T
19.1 < 24.75
Since both formulas are met, this vent configuration is acceptable.
(H
T
= 4.2 x 6 = 25.2 FT
T
T
= 4.2 x 5.5 = 23.1 FT
T
) > (V
)
T
T
See graph to determine the required vertical rise V
required horizontal run H
150
147"
100
REQUIRED
VERTICAL
RISE IN
INCHES V
T
57"
50
19 1/2"
0
2'
HORIZONTAL VENT RUN PLUS OFFSET IN FEET H
The shaded area within the lines represents acceptable
values for H
90°
V
1
90°
V
1
.
T
5
10
15
20
19.5'
12.5'
and V
T
T
H
1
H
90°
90°
90°
H
1
V
2
H
H
2
3
90°
16.1_2
W415-0748 / C / 08.20.12
15
for the
T
T
2
H
4
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