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W415-0210 / E / 06.25.03
when (H
T
) < (V
T
)
Simple venting configuration (only one 90° elbow)
VERTICAL
RISE IN
FEET
V
T
FIGURE 6
See graph to determine the required vertical rise V
T
for the
required horizontal run H
T
.
For vent configurations requiring more than one 90° el-
bow, the following formulas apply:
Formula 1: H
T
< V
T
Formula 2: H
T
+ V
T
< 40 feet
Example 1:
90°
90°
V
1
=3 ft
V
2
=8 ft
V
T
=
V
1
+
V
2
=
3 + 8 = 11 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(three 90° elbows - 90°) = .03(270° - 90°) = 5.4 ft
H
T
= H
R
+ H
O
= 4.5 + 5.4 = 9.9 ft
H
T
+ V
T
= 9.9 + 11 = 20.9 ft
Formula 1: H
T
< V
T
9.9 < 11
Formula 2: H
T
+ V
T
< 40 feet
20.9 < 40
Since both formulas are met, this vent configuration is ac-
ceptable.
FIGURE 7
90°
H
1
V
2
H
2
V
1
HORIZONTAL VENT RUN PLUS OFFSET IN FEET H
T
The shaded area within the lines represents acceptable
values for H
T
and V
T
.
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 offsets
(H
O
) in feet
H
R
- combined horizontal vent lengths in feet
H
O
- offset factor: .03(total degrees of offset - 90°*) 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 90° offset has a zero value and is shown in
the formula as -90°
DEFINITIONS
ELBOW VENT LENGTH VALUES
TOP EXIT / HORIZONTAL TERMINATION