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10
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
T
sets (H
) in feet
O
H
- combined horizontal vent lengths in feet
R
H
- offset factor: .03(total degrees of offset - 135°* * * * * ) in
O
feet
V
- combined vertical vent lengths in feet
T
when (H
) < (V
)
T
T
Simple venting configuration (only one 45º and 90° elbow)
90°
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
W415-0484 / A / 07.26.06
R
HORIZONTAL TERMINATION
45º
)
T
.
ELBOW VENT LENGTH VALUES
1°
15°
30°
45°* * * * *
90°* * * * *
) and off-
* * * * * 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
45º
V
= 8 ft
1
V
= V
T
1
H
= 2.5 ft
1
H
= 2 ft
2
H
= H
R
1
H
= .03(one 45º elbow + two 90º elbows - 135º)
O
=0.3(225-135º) = 2.7ft
H
= H
T
R
H
+ V
= 7.2 +8 =15.2ft
T
T
Formula 1:
Formula 2:
Since both formulas are met, this vent configuration is ac-
ceptable.
feet
0.03
0.45
0.9
1.35
2.7
< V
T
T
+ V
< 40 feet
T
T
90°
V
1
H
1
90°
= 8 ft
+ H
= 2.5 + 2 = 4.5 ft
2
+ H
= 4.5 + 2.7 = 7.2 ft
O
H
< V
T
T
7.2 < 8
H
+ V
< 40 feet
T
T
15.2 < 40
inches
0.5
6.0
11.0
16.0
32.0
H
2
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