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W415-0788 / A / 09.22.09
3.10 REAR EXIT HORIZONTAL TERMINATION
For vent configurations requiring more than two 90° elbows, the following formulas apply:
Formula 1: H
T
< V
T
Formula 2: H
T
+ V
T
< 40 feet
Example 4:
V
1
= 9 FT
V
2
= 6 FT
V
T
= V
1
+ V
2
= 9 + 6 = 15 FT
H
1
= 3 FT
H
2
= 2 FT
H
3
= 1.5 FT
H
R
= H
1
+ H
2
+ H
3
= 3 + 2 + 1.5 = 6.5 FT
H
O
= .03 (four 90° elbows - 90°) = .03 (360° - 90°) = 8.1 FT
H
T
= H
R
+ H
O
= 6.5 + 8.1 = 14.6 FT
H
T
+ V
T
= 14.6 + 15 = 29.6 FT
Formula 1: H
T
< V
T
14.6 < 15
Formula 2: H
T
+ V
T
< 40 FT
29.6 < 40
Since both formulas are met, this vent configuration is acceptable.
0
2.5 5 7.5 10 12.5 15
40
10
20
30
17.5 20
1.6
1.6
38.3
90°
V
1
V
2
H
1
H
2
90°
90°
90°
H
3
Simple venting configuration
(only two 90° elbows)
See graph to determine the required vertical rise V
T
for the required
horizontal run H
T
.
REQUIRED
VERTICAL
RISE IN
FEET V
T
HORIZONTAL VENT RUN PLUS OFFSET IN FEET H
T
The shaded area within the lines represents acceptable values for H
T
and H
T
(H
T
) < (V
T
)
16.3
FIGURE 3.10a
FIGURE 3.10b