10
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
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) | For vent configurations requiring more than one 90° elbow, |
the following formulas apply: | |
FIGURE 7 | Formula 1: H < V |
| Formula 2: HTT+ VTT< 35 feet |
Simple venting configuration |
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| 90° | H2 | |||
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(only one 90° elbow) |
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| FIGURE 8 |
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| 90° |
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| 90° | H1 |
See graph to determine the required vertical rise VT for the |
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| V1 |
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required horizontal run HT. |
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33.3 |
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| Example 1: |
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35 |
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30 |
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| V1 | = | 3 ft |
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REQUIRED |
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VERTICAL |
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| V2 | = | 8 ft |
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RISE IN 17.5 |
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| VT | = V1 + V2 = 3 + 8 = 11 ft |
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20 |
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FEET VT |
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| H1 | = | 2.5 ft |
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| H2 | = | 2 ft |
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10 |
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| HR | = H1 | = 2.5 + 2 = 4.5 ft |
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0 .5 |
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| HO | = .03(three 90° elbows - 90°) = .03(270° - 90°) = 5.4 | ||||
2.5 | 5 | 7.5 | 10 | 12.5 | 15 | 17.5 | 20 | ft |
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HORIZONTAL VENT RUN PLUS OFFSET IN FEET HT |
| HT | = | HR + HO = 4.5 + 5.4 = 9.9 ft |
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| HT | + VT | = 9.9 + 11 = 20.9 ft |
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The shaded area within the lines represents acceptable |
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Formula 1: | HT | < VT |
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values for HT and VT . |
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| 9.9 < 11 |
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| Formula 2: | HT | + VT < 35 feet |
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| 20.9 < 35 |
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Since both formulas are met, this vent configuration is acceptable.