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W415-0385 / A / 10.02.03
ELBOW VENT LENGTH VALUES
DEFINITIONS
HORIZONTAL TERMINATION
REQUIRED
VERTICAL
RISE IN
FEET
(V
T
)
CALCULATED HORIZONTAL VENT RUN
PLUS OFFSETS IN FEET (H
T
)
FIGURE 5
45º
FIGURE 6
90°
H
1
H
2
when (H
T
) < (V
T
)
Simple venting configuration (only one 45º and 90° elbow)
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
T
- total of both horizontal vent lengths (H
R
) and off-
sets (H
O
) in feet
H
R
- combined horizontal vent lengths in feet
H
O
- offset factor: .03(total degrees of offset - 135°*) in
feet
V
T
- combined vertical vent lengths in feet
feet inches
1° 0.03 0.5
15° 0.45 6.0
30° 0.9 11.0
45°* 1.35 16.0
90°* 2.7 32.0
* 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
T
< V
T
Formula 2: H
T
+ V
T
< 40 feet
Example 1:
V
1
=8 ft
V
T
=
V
1
= 8 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(one 45º elbow + two 90º elbows - 135º)
=0.3(225-135º) = 2.7ft
H
T
= H
R
+ H
O
= 4.5 + 2.7 = 7.2 ft
H
T
+ V
T
= 7.2 +8 =15.2ft
Formula 1: H
T
< V
T
7.2 < 8
Formula 2: H
T
+ V
T
< 40 feet
15.2 < 40
45º
90°
Since both formulas are met, this vent configuration is ac-
ceptable.
V
1
90°
The shaded area within the lines represents acceptable
values for H
T
and V
T
.