18 − The common vent diameter must always be at least as large as the largest vent connector diameter.
19 − In no case, shall the vent connector be sized more than two consecutive table size diameters over the size of the draft hood outlet or flue collar outlet.
20 − Do not install a manual damper, barometric draft regu- lator or flue restrictor between the furnace and the chimney.
21 − When connecting this appliance to an existing dedi- cated or common venting system, you must inspect the venting system’s general condition and look for signs of corrosion. The existing vent pipe size must conform to these instructions and the provided venting tables. If the existing venting system does not meet these re- quirements, it must be resized.
TABLE 5
Capacity of Type B Double−Wall Vents with Type B Double−Wall Connectors
Serving a Single Category I Appliance
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| Vent and Connector Diameter − D (inches) |
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Height | Lateral |
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| 3 Inch |
| 4 Inch |
| 5 Inch |
| 6 Inch | ||||||
H | L |
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| Appliance Input Rating in Thousands of Btu Per Hour |
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(feet) | (feet) |
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| MIN |
| MAX | MIN |
| MAX | MIN |
| MAX | MIN |
| MAX |
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| 0 | 0 |
| 78 | 0 |
| 152 | 0 |
| 251 | 0 |
| 375 |
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| 2 | 13 |
| 51 | 18 |
| 97 | 27 |
| 157 | 32 |
| 232 |
6 |
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4 | 21 |
| 49 | 30 |
| 94 | 39 |
| 153 | 50 |
| 227 | |
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| 6 | 25 |
| 46 | 36 |
| 91 | 47 |
| 149 | 59 |
| 223 |
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| 0 | 0 |
| 84 | 0 |
| 165 | 0 |
| 276 | 0 |
| 415 |
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| 2 | 12 |
| 57 | 16 |
| 109 | 25 |
| 178 | 28 |
| 263 |
8 |
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5 | 23 |
| 53 | 32 |
| 103 | 42 |
| 171 | 53 |
| 255 | |
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| 8 | 28 |
| 49 | 39 |
| 98 | 51 |
| 164 | 64 |
| 247 |
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| 0 | 0 |
| 88 | 0 |
| 175 | 0 |
| 295 | 0 |
| 447 |
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| 2 | 12 |
| 61 | 17 |
| 118 | 23 |
| 194 | 26 |
| 289 |
10 |
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5 | 23 |
| 57 | 32 |
| 113 | 41 |
| 187 | 52 |
| 280 | |
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| 10 | 30 |
| 51 | 41 |
| 104 | 54 |
| 176 | 67 |
| 267 |
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| 0 | 0 |
| 94 | 0 |
| 191 | 0 |
| 327 | 0 |
| 502 |
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| 2 | 11 |
| 69 | 15 |
| 136 | 20 |
| 226 | 22 |
| 339 |
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15 | 5 | 22 |
| 65 | 30 |
| 130 | 39 |
| 219 | 49 |
| 330 |
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| 10 | 29 |
| 59 | 40 |
| 121 | 51 |
| 206 | 64 |
| 315 |
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| 15 | 35 |
| 53 | 48 |
| 112 | 61 |
| 195 | 76 |
| 301 |
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| 0 | 0 |
| 97 | 0 |
| 202 | 0 |
| 349 | 0 |
| 540 |
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| 2 | 10 |
| 75 | 14 |
| 149 | 18 |
| 250 | 20 |
| 377 |
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| 5 | 21 |
| 71 | 29 |
| 143 | 38 |
| 242 | 47 |
| 367 |
20 |
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10 | 28 |
| 64 | 38 |
| 133 | 50 |
| 229 | 62 |
| 351 | |
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| 15 | 34 |
| 58 | 46 |
| 124 | 59 |
| 217 | 73 |
| 337 |
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| 20 | 48 |
| 52 | 55 |
| 116 | 69 |
| 206 | 84 |
| 322 |
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| 0 | 0 |
| 100 | 0 |
| 213 | 0 |
| 374 | 0 |
| 587 |
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| 2 | 9 |
| 81 | 13 |
| 166 | 14 |
| 283 | 18 |
| 432 |
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| 5 | 21 |
| 77 | 28 |
| 160 | 36 |
| 275 | 45 |
| 421 |
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30 | 10 | 27 |
| 70 | 37 |
| 150 | 48 |
| 262 | 59 |
| 405 |
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| 15 | 33 |
| 64 | 44 |
| 141 | 57 |
| 249 | 70 |
| 389 |
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| 20 | 56 |
| 58 | 53 |
| 132 | 66 |
| 237 | 80 |
| 374 |
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| 30 | NR |
| NR | 73 |
| 113 | 88 |
| 214 | 104 |
| 346 |
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NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45° elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi- mum listed capacity).
Page 15