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
9
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
(HT) < (VT)
Simple venting configuration |
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(only one 90° elbow) | FIGURE 7 |
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See graph to determine the required vertical rise VT for the required horizontal run HT.
39 40
VERTICAL
RISE 30
IN FEET
VT20
10
0 | 2.5 | 5 | 7.5 | 10 | 12.5 | 15 | 17.5 | 20 |
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
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FIGURE 8 |
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90° |
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Example 1:
V1 | = | 3 ft |
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V2 | = | 8 ft | + V2 = 3 + 8 = 11 ft |
VT | = V1 | ||
H1 | = | 2.5 ft | |
H2 | = | 2 ft | + H2 = 2.5 + 2 = 4.5 ft |
HR | = H1 | ||
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.
