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10
DEFINITIONS
for the following symbols used in the venting calculations
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
(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 confi guration (only one 45º and 90° elbow)
FIGURE6
REQUIRED
VERTICAL
R I S E
I N
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
W415-0381 / H / 12.07.07
) and offsets
R
HORIZONTAL TERMINATION
90°
45º
)
T
.
ELBOW VENT LENGTH VALUES
1°
15°
30°
45°*
90°*
* the fi rst 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 confi gurations requiring more than one 45º and 90°
elbow, the following formulas apply:
Formula 1: H
< V
T
Formula 2: H
+ V
T
T
Example 1:
FIGURE 7
45º
H
1
V
= 8 ft
1
V
= V
= 8 ft
T
1
H
= 2.5 ft
1
H
= 2 ft
2
H
= H
+ H
= 2.5 + 2 = 4.5 ft
R
1
2
H
= .03(one 45º elbow + two 90º elbows - 135º)
O
=0.3(225-135º) = 2.7ft
H
= H
+ H
= 4.5 + 2.7 = 7.2 ft
T
R
O
H
+ V
= 7.2 +8 =15.2ft
T
T
Formula 1:
H
< V
T
T
7.2 < 8
Formula 2:
H
+ V
< 40 feet
T
T
15.2 < 40
Since both formulas are met, this vent confi guration is
acceptable.
feet
inches
0.03
0.5
0.45
6.0
0.9
11.0
1.35
16.0
2.7
32.0
T
< 40 feet
90°
H
2
V
1
90°
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