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W415-0661 / C / 02.20.08
For vent confi gurations requiring more than one 90° elbow the fol-
lowing formulas apply:
Formula 1: H
T
< 4.2 V
T
Formula 2: H
T
+ V
T
< 24.75 feet
Example 2:
See graph to determine the required vertical
rise V
T
for the required horizontal run H
T
.
V
1
=V
T
= 6 ft
H
1
=3 ft
H
2
=5 ft
H
R
=H
1
+ H
2
= 3 + 5 = 8 ft
H
O
=.03 (two 90° elbows - 90°) = .03(180° - 90°) = 2.7 ft
H
T
=H
R
+ H
O
= 8 + 2.7 = 10.7 ft
H
T
+ V
T
=
10.7 + 6 =16.7
Formula 1: H
T
< 4.2 V
T
4.2 V
T
= 4.2 x 6 = 25.2 ft
10.7 < 25.2
Formula 2: H
T
+ V
T
< 24.75 feet
16.7 < 24.75
Since both formulas are met, this vent confi guration is acceptable.
REQUIRED VERTICAL RISE
IN INCHES V
T
HORIZONTAL VENT
RUN PLUS OFFSET IN
FEET H
T
The shaded area within the lines represents acceptable values
for H
T
and V
T
.
when (H
T
) > (V
T
)
Simple venting confi guration (only one 90°
elbow)
BGD36CF(G) TOP EXIT / HORIZONTAL TERMINATION
H
2
H
1
V
1
90°
FIGURE 23
H
2
H
4
V
2
90°
H
3
H
1
V
1
90°
FIGURE 24
FIGURE 22
Example 3:
V
1
= 4 ft
V
2
= 1.5 ft
V
T
= V
1
+ V
2
= 4 + 1.5 = 5.5 ft
H
1
= 2 ft
H
2
= 1 ft
H
3
= 1 ft
H
4
= 1.5 ft
H
R
= H
1
+ H
2
+ H
3
+ H
4
= 2 + 1 + 1 + 1. 5 = 5.5 ft
H
O
= .03 (four 90° elbows - 90°) = .03(360° - 90°) = 8.1 ft
H
T
= H
R
+ H
O
= 5.5 + 8.1 = 13.6 ft
H
T
+ V
T
= 13.6 + 5.5 = 19.1 ft
Formula 1: H
T
< 4.2 V
T
4.2 V
T
= 4.2 x 5.5 = 23.1 ft
13.6 < 23.1
Formula 2: H
T
+ V
T
< 24.75 feet
19.1 < 24.75
Since both formulas are met, this vent confi guration is ac-
ceptable.