9
W415-0221 / E / 04.09.02
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
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
ELBOW VENT LENGTH VALUES
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°
when
(H
T
) < (V
T
)
Simple venting configuration (only one 90° elbow)
VERTICAL
RISE IN
FEET
V
T
TOP EXIT / HORIZONTAL TERMINATION
FIGURE 5
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 6
90°
H
1
V
2
H
2
V
1
HORIZONTAL VENT RUN PLUS OFFSET IN FEET
H
H
H
H
H
T
T
T
T
T
The shaded area within the lines represents acceptable
values for H
T
and V
T
.
