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| Page 5 | |
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| Table 3 specifies the allowable length of piping for | |
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| 4' |
| various situations. | |
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| The following examples illustrate use of table 3: | |
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Total Length: 42' | 8' |
| 1. A Model 350 heater is to be installed in a one- | ||||
Total Elbows: 5 |
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| pipe system (see Figure 5). The vent pipe is 42 | |||
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| 18' |
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| feet long and has five elbows. Per Table 3, 5" | |
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| 10' |
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| piping must be used. (Only 16 feet of 4" vent pipe |
EHE350 |
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| would be allowable.) | |||
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| 2' |
| 2. | A Model 220 heater is to be installed in a two- |
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| pipe system (see Figure 6). The combustion air | |
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| pipe is to be 13 feet long with three elbows and |
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| the vent pipe is to be 9 feet long with one elbow. |
Figure 5. |
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| Since the total is 22 feet and four elbows, 4" pipe | ||||
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| must be used. (Table 3 indicates that the |
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| 4' |
| Vent |
| maximum length of 3" pipe is 11 feet for a system |
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| with four elbows.) | ||
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| Pipe |
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| 4' |
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Combustion |
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| Installation | ||
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| 5' |
| The | |||
| Air Pipe | 7' |
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| not be vented in common with any other appliance, | ||
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| even if that appliance is of the condensing type. | |
Comb. |
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| Common venting can result in severe corrosion of the | |||
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| Air | Vent | Total |
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Length | 13' | 9' | 22' |
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| escape of combustion product gases through such | |
Elbows | 3 | 1 | 4 |
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| appliances or vents. Do not vent the | |
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| EHE220 | fireplace chimney or building chase. | |
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| Combustion air ducting, when provided, must not | |
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| be shared with any other appliance or with another Hi- | |
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| 2' |
| E2. Doing so may result in flow of air through the | |
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| other appliances instead of directly from the outdoors. | ||
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Figure 6. |
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| The combustion air intake and vent outlet must | ||||
| be located exterior to the building and in the same | ||||||
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Combustion air piping may be | pressure zone - i.e. both through the roof or both | ||||||
through a side wall. The vent terminal must be located | |||||||
galvanized steel pipe or any of the above materials. | in accordance with local codes, as applicable, and in | ||||||
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| accordance with the following: | |
2G-3c. Size and Length of Combustion Air and Vent Piping
Piping for combustion air and venting must be large enough to avoid restriction of the heater combustion system. Pipe diameter, number of elbows and length of pipe determine how much it restricts flow to or from the heater. Also, a large heater requires larger pipe than a small heater because it operates with higher flow of combustion air and exhaust products.
1.Locate the vent terminal so that it will not be damaged by pedestrians and other traffic, and so that the discharge is not offensive. The National Fuel Gas Code requires a
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| Number of Elbows |
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| Pipe Size |
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Model | 1 |
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| 4 |
| 5 | 6 | 7 | 8 | 9 | 10 | ||
Inches (cm) |
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| Total Length of Pipe - Feet (m) |
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220 | 3" | 35 (10.6) | 27 | (8.2) | 19 (5.8) | 11 | (3.4) | NA | NA | NA | NA | NA | NA | ||
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4" | 173 (52.7) | 163 | (49.6) | 153 (46.6) | 143 | (43.5) | 132 | (40.2) | 122 (37.1) | 112 (34.1) | 102 (31) | 92 (28) | 81 (24.6) | ||
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350 | 4" | 61 (18.6) | 50 (15.2) | 39 (11.9) | 27 | (8.2) | 16 | (4.8) | NA | NA | NA | NA | NA | ||
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5" | 225 (68.6) | 211 | (64.3) | 197 (60) | 184 (56) | 170 | (51.8) | 157 (47.8) | 143 (43.5) | 130 (39.6) | 116 (35.4) | 103 (31.4) | |||
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Table 3. Maximum Combined Length of Combustion Air and Vent Piping in Feet.