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DEFINITIONS
for the following symbols used in the venting calcula-
tions and examples are:
> - greater than
> - equal to or greater than
< - less than
< - equal to or less than
H - total of both horizontal vent lengths (H ) and off-
sets (H ) in feet
H - combined horizontal vent lengths in feet
H - offset factor: .03(total degrees of offset - 135°*) in
feet
V - combined vertical vent lengths in feet
HORIZONTAL TERMINATION
when (H ) < (V )
Simple venting configuration (only one 45º and 90° elbow)
FIGURE 5
REQUIRED
VERTICAL
RISE IN FEET
(V
)
T
CALCULATED HORIZONTAL VENT RUN
PLUS OFFSETS IN FEET (H
The shaded area within the lines represents acceptable
values for H
and V
.
T
T
* the first 45º and 90° offset has a zero value and is
shown in the formula as -45° and -90º respectively
or -135º when combined.
For vent configurations requiring more than one 45º and
90° elbow, the following formulas apply:
Formula 1: H
Formula 2: H
Example 1:
FIGURE 6
V
1
V
T
H
1
H
2
H
R
H
O
=0.3(225-135º) = 2.7ft
H
T
)
T
H
+ V
T
Formula 1:
Formula 2:
Since both formulas are met, this vent configuration is ac-
ceptable.
ELBOW VENT LENGTH VALUES
feet
1°
0.03
15°
0.45
30°
0.9
45°*
1.35
90°*
2.7
< V
T
T
+ V
< 40 feet
T
T
45º
H
= 8 ft
= V
= 8 ft
1
= 2.5 ft
= 2 ft
= H
+ H
= 2.5 + 2 = 4.5 ft
1
2
= .03(one 45º elbow + two 90º elbows - 135º)
= H
+ H
= 4.5 + 2.7 = 7.2 ft
R
O
= 7.2 +8 =15.2ft
T
H
< V
T
T
7.2 < 8
H
+ V
< 40 feet
T
T
15.2 < 40
9
inches
0.5
6.0
11.0
16.0
32.0
H
90°
W415-0381 / C / 05.13.04
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