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W415-0788 / A / 09.22.09
3.9 TOP EXIT HORIZONTAL TERMINATION
16.1
Simple venting confi guration (only one 90° elbow)
(H
T
) < (V
T
)
For vent confi gurations requiring more than one 90° elbow, the following formulas apply:
Formula 1: H
T
< V
T
Formula 2: H
T
+ V
T
< 40 feet
Example 1:
V
1
= 3 FT
V
2
= 8 FT
V
T
= V
1
+ V
2
= 3 FT + 8 FT = 11 FT
H
1
= 2.5 FT
H
2
= 2 FT
H
R
= H
1
+ H
2
= 2.5 + 2 = 4.5 FT
H
O
= .03 (three 90° elbows - 90°) = .03 (270° - 90°) = 5.4 FT
H
T
= H
R
+ H
O
= 4.5 + 5.4 = 9.9 FT
H
T
+ V
T
= 9.9 + 11 = 20.9 FT
Formula 1: H
T
< V
T
9.9 < 11
Formula 2: H
T
+ V
T
< 40 FT
20.9 < 40
Since both formulas are met, this vent confi guration is acceptable.
See graph to determine the required vertical
rise V
T
for the required horizontal run H
T
.
The shaded area within the lines represents
acceptable values for H
T
and V
T
0
2.5 5 7.5 10 12.5 15
40
10
20
30
17.5 20
39
REQUIRED
VERTICAL
RISE IN
FEET V
T
HORIZONTAL VENT RUN PLUS OFFSET IN
FEET H
T
90°
90°
90°
V
1
V
2
H
1
H
2
FIGURE 3.9a
FIGURE 3.9b