6
W415-0583 / B / 05.23.07
VERTICAL
RISE IN
FEET
VT
FIGURE 4
when (HT) < (VT)
Simple venting confi guration (only one 90° elbow)
See graph to determine the required vertical rise VT for the
required horizontal run HT.
For vent confi gurations requiring more than one 90° elbow,
the following formulas apply:
Formula 1: HT < VT
Formula 2: HT + VT < 40 feet
90°
90°
Example 1:
V1 = 3 ft
V2 = 8 ft
VT =
V1
+
V2 =
3 + 8 = 11 ft
H1 = 2.5 ft
H2 = 2 ft
HR = H1 + H2 = 2.5 + 2 = 4.5 ft
HO = .
03 (three 90° elbows - 90°) = .03(270° - 90°) = 5.4 ft
HT = HR + HO = 4.5 + 5.4 = 9.9 ft
HT + VT = 9.9 + 11 = 20.9 ft
Formula 1: H
T < VT
9.9 < 11
Formula 2: H
T + VT < 40 feet
20.9 < 40
Since both formulas are met, this vent confi guration is
acceptable.
FIGURE 5
90°
H1
V2
H2
V1
HORIZONTAL VENT RUN PLUS OFFSET IN FEET HT
The shaded area within the lines represents acceptable
values for HT and VT .
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
HT - total of both horizontal vent lengths (HR) and offsets
(HO) in feet
HR - combined horizontal vent lengths in feet
HO - offset factor: .03(total degrees of offset - 90°*) in
feet
VT - 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 fi rst 90° offset has a zero value and is shown in the
formula as -90°