DEFINITIONS
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
7
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
TOP EXIT / HORIZONTAL TERMINATION
FIGURE 4
See graph to determine the required vertical rise VT for the required horizontal run HT.
VERTICAL
RISE IN
FEET
VT
HORIZONTAL VENT RUN PLUS OFFSET IN FEET HT
The shaded area within the lines represents acceptable values for HT and VT .
For vent configurations requiring more than one 90° elbow, the following formulas apply:
Formula 1: HT < VT
Formula 2: HT + VT < 40 feet
Example 1: | 90° | H2 |
|
|
FIGURE 5 | V2 |
90°
H1
90°
V1
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: HT < VT 9.9 < 11
Formula 2: HT + VT < 40 feet 20.9 < 40
Since both formulas are met, this vent configuration is acceptable.
