10
W415-0381 / H / 12.07.07

ELBOW VENT LENGTH VALUES

DEFINITIONS

HORIZONTAL TERMINATION
REQUIRED
VERTICAL
RISE IN
FEET (VT)
CALCULATED HORIZONTAL VENT RUN
PLUS OFFSETS IN FEET (HT)
FIGURE6

45º

FIGURE 7
90°
H1
H2
when (HT) < (VT)
Simple venting confi guration (only one 45º and 90° elbow)
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 - 135°*) 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 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: HT < VT
Formula 2: HT + VT < 40 feet
Example 1:
V1 = 8 ft
VT =
V1
= 8 ft
H1 = 2.5 ft
H2 = 2 ft
HR = H1 + H2 = 2.5 + 2 = 4.5 ft
HO = .
03(one 45º elbow + two 90º elbows - 135º)
=0.3(225-135º) = 2.7ft
HT = HR + HO = 4.5 + 2.7 = 7.2 ft
HT + VT = 7.2 +8 =15.2ft
Formula 1: H
T < VT
7.2 < 8
Formula 2: H
T + VT < 40 feet
15.2 < 40

45º

90°
Since both formulas are met, this vent confi guration is
acceptable.
V1
90°
The shaded area within the lines represents acceptable
values for HT and VT .