Table 510.1.2(1) through Table 510.1.2(6) shall not be used where obstructions arc installed in the venting
system. The installation of vents serving listed appliances
with vent dampers shall be in accordance with the appliance manufacturer's installation instructions or in accordance with
the following:
 The maximum capacity of the vent system shall be determined using the NAT Max column.
 The minimum capacity shall be determined as though the appliance were a fanassisted appliance, using the FAN Min column to determine the minimum capacity of the vent system. Where the corresponding "FAN Min" is "NA", the vent configuration shall not be permitted and an alternative venting configuration shall be utilized. [NFPA 54:13.1.1]
Where the vent size determined from the tables is smaller than the appliance draft hood outlet or flue collar, the use of the smaller size shall be permitted provided that the installation is in accordance with the following requirements:
 The total vent height (H) is not less than 10 feet (3048 mm).
 Vents for appliance draft hood outlets or flue collars 12 inches (305 mm) in diameter or smaller are not reduced more than one table size.
 Vents for appliance draft hood outlets or flue collars exceeding 12 inches (305 mm) in diameter are not reduced more than two table sizes.
 The maximum capacity listed in the tables for a fanassisted appliance is reduced by 10 percent (0.90 x maximum table capacity).
 The draft hood outlet exceeds 4 inches ( 102 mm) in diameter. A 3 inch (76 mm) diameter vent shall not be connected to a 4 inch (102 mm) diameter draft hood outlet. This provision shall not apply to fanassisted appliances. [NFPA 54:13.1.2]
Singleappliance venting configurations
with zero lateral lengths in Table 510.1.2(1), Table
510.1.2(2), and Table 510.1.2(5) shall not have elbows in
the venting system. Singleappliance venting with lateral
lengths, include two 90 degree (1.57 rad) elbows. For
each additional elbow up to and including 45 degrees
(0.79 rad), the maximum capacity listed in the venting
tables shall be reduced by 5 percent. For each additional
elbow greater than 45 degrees (0.79 rad) up to and including
90 degrees (1.57 rad), the maximum capacity listed in
the venting tables shall be reduced by 10 percent. Where
multiple offsets occur in a vent, the total lateral length of
offsets combined shall not exceed that specified in Table
510.1.2(1) through Table 510.1.2(5). [NFPA 54:13.1.3]
TABLE 510.1.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(c)]^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.1.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(c)] (continued)^{*}^{}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.1.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(d)]^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thelmal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.1.2(6)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.1(f)]^{1, 2}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}, °C = (°F32)/1.8
Notes:
99% Winter Design Temperatures for the Contiguous United States
This map is a necessarily generalized guide to temperatures in the contiguous United States, Temperatures shown for areas such as mountainous regions and large urban centers may not be accurate. The data used to develop this map are from the 1993 ASHRAE Handbook  Fundamentals (Chapter 24, Table 1: Climate Conditions for the United States).
For 99% winter design temperatures in Alaska, consult the ASHRAE Handbook  Fundamentals.
99% winter design temperatures for Hawaii are greater than 37°F.
For SI units: °C = (°F32)/1.8
TABLE 510.1.2(1)
TYPE B DOUBLEWALL GAS VENT [NFPA 54: TABLE 13.1(a)]^{*}
TYPE B DOUBLEWALL GAS VENT [NFPA 54: TABLE 13.1(a)]^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
* NA: Not applicable.
TABLE 510.1.2(1)
TYPE B DOUBLEWALL GAS VENT [NFPA 54:TABLE 13.1(a)] (continued)
TYPE B DOUBLEWALL GAS VENT [NFPA 54:TABLE 13.1(a)] (continued)
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
TABLE 510.1.2(1)
TYPE B DOUBLEWALL GAS VENT [NFPA 54:TABLE 13.1(a)] (continued)
TYPE B DOUBLEWALL GAS VENT [NFPA 54:TABLE 13.1(a)] (continued)
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
TABLE 510.1.2(2)
TYPE B DOUBLEWALL GAS VENT [NFPA 54: TABLE 13.1(b)]^{*}
TYPE B DOUBLEWALL GAS VENT [NFPA 54: TABLE 13.1(b)]^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
* NA: Not applicable.
TABLE 510.1.2(2)
TYPE B DOUBLEWALL GAS VENT [NFPA 54: TABLE 13.1(b)] (continued)^{*}
TYPE B DOUBLEWALL GAS VENT [NFPA 54: TABLE 13.1(b)] (continued)^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
* NA: Not applicable.
TABLE 510.1.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(c)]^{*}
NUMBER OF APPLIANCES:  SINGLE  
APPLIANCE TYPE:  CATEGORY I  
APPLIANCE VENT CONNECTION:  TYPE B DOUBLEWALL CONNECTOR  
TYPE B DOUBLEWALL CONNECTOR DIAMETER  D (inch) TO BE USED WITH CHIMNEY AREAS WITHIN THE SIZE LIMITS AT BOTTOM 

3  4  5  6  7  
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR  
HEIGHT H (feet) 
LATERAL L (feet) 
FAN  NAT  FAN  NAT  FAN  NAT  FAN  NAT  FAN  NAT  
Min  Max  Max  Min  Max  Max  Min  Max  Max  Min  Max  Max  Min  Max  Max  
6  2 5 
NA NA 
NA NA 
28 25 
NA NA 
NA NA 
52 49 
NA NA 
NA NA 
86 82 
NA NA 
NA NA 
130 117 
NA NA 
NA NA 
180 165 
8  2 5 8 
NA NA NA 
NA NA NA 
29 26 24 
NA NA NA 
NA NA NA 
55 52 48 
NA NA NA 
NA NA NA 
93 88 83 
NA NA NA 
NA NA NA 
145 134 127 
NA NA NA 
NA NA NA 
198 183 175 
10  2 5 10 
NA NA NA 
NA NA NA 
31 28 25 
NA NA NA 
NA NA NA 
61 57 50 
NA NA NA 
NA NA NA 
103 96 87 
NA NA NA 
NA NA NA 
162 148 139 
NA NA NA 
NA NA NA 
221 204 191 
15  2 5 10 15 
NA NA NA NA 
NA NA NA NA 
35 35 28 NA 
NA NA NA NA 
NA NA NA NA 
67 62 55 48 
NA NA NA NA 
NA NA NA NA 
114 107 97 89 
NA NA NA NA 
NA NA NA NA 
179 164 153 141 
53 NA NA NA 
475 NA NA NA 
250 231 216 201 
20  2 5 10 15 20 
NA NA NA NA NA 
NA NA NA NA NA 
38 36 NA NA NA 
NA NA NA NA NA 
NA NA NA NA NA 
74 68 60 NA NA 
NA NA NA NA NA 
NA NA NA NA NA 
124 116 107 97 83 
NA NA NA NA NA 
NA NA NA NA NA 
201 184 172 159 148 
51 80 NA NA NA 
522 503 NA NA NA 
274 254 237 220 206 
30  2 5 10 15 20 30 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
41 NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
82 76 67 NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
137 128 115 107 91 NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
216 198 184 171 159 NA 
47 75 NA NA NA NA 
581 561 NA NA NA NA 
303 281 263 243 227 188 
50  2 5 10 15 20 30 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
92 NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
161 151 138 127 NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
251 230 215 199 185 NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
351 323 304 282 264 NA 
Minimum internal area of chimney (square inches) 
12  19  28  38  50  
Maximum internal area of chimney (square inches) 
Seven times the listed appliance categorized vent area, flue collar area, or draft hood outlet areas. 
* NA: Not applicable.
TABLE 510.1.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(c)] (continued)^{*}^{}
NUMBER OF APPLIANCES:  SINGLE  
APPLIANCE TYPE:  CATEGORY I  
APPLIANCE VENT CONNECTION:  TYPE B DOUBLEWALL CONNECTOR  
TYPE B DOUBLEWALL CONNECTOR DIAMETER  D (inch) TO BE USED WITH CHIMNEY AREAS WITHIN THE SIZE LIMITS AT BOTTOM 

8  9  10  12  
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR  
HEIGHT H (feet) 
LATERAL L (feet) 
FAN  NAT  FAN  NAT  FAN  NAT  FAN  NAT  
Min  Max  Max  Min  Max  Max  Min  Max  Max  Min  Max  Max  
6  2 5 
NA NA 
NA NA 
247 231 
NA NA 
NA NA 
320 298 
NA NA 
NA NA 
401 376 
NA NA 
NA NA 
581 561 
8  2 5 8 
NA NA NA 
NA NA NA 
266 247 239 
84 NA NA 
590 NA NA 
350 328 318 
100 149 173 
728 711 695 
446 423 410 
139 201 231 
1024 1007 990 
651 640 623 
10  2 5 10 
68 NA NA 
519 NA NA 
298 277 263 
82 124 155 
655 638 610 
388 365 347 
98 146 182 
810 791 762 
491 466 444 
136 196 240 
1144 1124 1093 
724 712 668 
15  2 5 10 15 
64 99 NA NA 
613 594 565 NA 
336 313 296 281 
77 118 148 171 
779 759 727 698 
441 416 394 375 
92 139 173 198 
968 946 912 880 
562 533 567 485 
127 186 229 259 
1376 1352 1315 1280 
841 828 777 742 
20  2 5 10 15 20 
61 95 122 NA NA 
687 658 627 NA NA 
375 350 332 314 296 
73 113 143 165 186 
867 845 811 780 750 
491 463 440 418 397 
87 133 167 191 214 
1083 1059 1022 987 955 
627 597 566 541 513 
121 179 221 251 277 
1548 1523 1482 1443 1406 
953 933 879 840 807 
30  2 5 10 15 20 30 
57 90 115 NA NA NA 
762 741 709 NA NA NA 
421 393 373 353 332 288 
68 106 135 156 176 NA 
985 962 927 893 860 NA 
558 526 500 476 450 416 
81 125 158 181 203 249 
1240 1216 1176 1139 1103 1035 
717 683 648 621 592 555 
111 169 210 239 264 318 
1793 1766 1721 1679 1638 1560 
1112 1094 1025 981 940 877 
50  2 5 10 15 20 30 
51 83 NA NA NA NA 
840 819 NA NA NA NA 
477 445 424 400 376 327 
61 98 126 146 165 NA 
1106 1083 1047 1010 977 NA 
633 596 567 539 511 468 
72 116 147 170 190 233 
1413 1387 1347 1307 1269 1196 
812 774 733 702 669 623 
99 155 195 222 246 295 
2080 2052 2006 1961 1916 1832 
1243 1225 1147 1099 1050 984 
Minimum internal area of chimney (square inches) 
63  78  95  132  
Maximum internal area of chimney (square inches) 
Seven times the listed appliance categorized vent area, flue collar area, or draft hood outlet areas. 
* NA: Not applicable.
TABLE 510.1.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(d)]^{*}
NUMBER OF APPLIANCES:  SINGLE  
APPLIANCE TYPE:  CATEGORY I  
APPLIANCE VENT CONNECTION:  TYPE B DOUBLEWALL CONNECTOR  
TYPE B DOUBLEWALL CONNECTOR DIAMETER  D (inch) TO BE USED WITH CHIMNEY AREAS WITHIN THE SIZE LIMITS AT BOTTOM 

3  4  5  6  7  
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR  
HEIGHT H (feet) 
LATERAL L (feet) 
FAN  NAT  FAN  NAT  FAN  NAT  FAN  NAT  FAN  NAT  
Min  Max  Max  Min  Max  Max  Min  Max  Max  Min  Max  Max  Min  Max  Max  
6  2 5 
NA NA 
NA NA 
28 25 
NA NA 
NA NA 
52 48 
NA NA 
NA NA 
86 81 
NA NA 
NA NA 
130 116 
NA NA 
NA NA 
180 164 
8  2 5 8 
NA NA NA 
NA NA NA 
29 26 23 
NA NA NA 
NA NA NA 
55 51 47 
NA NA NA 
NA NA NA 
93 87 82 
NA NA NA 
NA NA NA 
145 133 126 
NA NA NA 
NA NA NA 
197 182 174 
10  2 5 10 
NA NA NA 
NA NA NA 
31 28 24 
NA NA NA 
NA NA NA 
61 56 49 
NA NA NA 
NA NA NA 
102 95 86 
NA NA NA 
NA NA NA 
161 147 137 
NA NA NA 
NA NA NA 
220 203 189 
15  2 5 10 15 
NA NA NA NA 
NA NA NA NA 
35 32 27 NA 
NA NA NA NA 
NA NA NA NA 
67 61 54 46 
NA NA NA NA 
NA NA NA NA 
113 106 96 87 
NA NA NA NA 
NA NA NA NA 
178 163 151 138 
166 NA NA NA 
473 NA NA NA 
249 230 214 198 
20  2 5 10 15 20 
NA NA NA NA NA 
NA NA NA NA NA 
38 35 NA NA NA 
NA NA NA NA NA 
NA NA NA NA NA 
73 67 59 NA NA 
NA NA NA NA NA 
NA NA NA NA NA 
123 115 105 95 80 
NA NA NA NA NA 
NA NA NA NA NA 
200 183 170 156 144 
163 NA NA NA NA 
520 NA NA NA NA 
273 252 235 217 202 
30  2 5 10 15 20 30 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
41 NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
81 75 66 NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
136 127 113 105 88 NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
215 196 182 168 155 NA 
158 NA NA NA NA NA 
578 NA NA NA NA NA 
302 279 260 240 223 182 
50  2 5 10 15 20 30 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
91 NA NA NA NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
160 149 136 124 NA NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
250 228 212 195 180 NA 
NA NA NA NA NA NA 
NA NA NA NA NA NA 
350 321 301 278 258 NA 
Minimum internal area of chimney (square inches) 
12  19  28  38  50  
Maximum internal area of chimney (square inches) 
Seven times the listed appliance categorized vent area, flue collar area, or draft hood outlet areas. 
* NA: Not applicable.
TABLE 510.1.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(d)] (continued)^{*}
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(d)] (continued)^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
* NA: Not applicable.
TABLE 510.1.2(5)
SINGLEWALL METAL PIPE OR TYPE B ASBESTOSCEMENT VENT [NFPA 54: TABLE 13.1(e)]^{*}
SINGLEWALL METAL PIPE OR TYPE B ASBESTOSCEMENT VENT [NFPA 54: TABLE 13.1(e)]^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
* NA: Not applicable.
TABLE 510.1.2(6)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.1(f)]^{1, 2}
NUMBER OF APPLIANCES:  SINGLE  
APPLIANCE TYPE:  CATEGORY I  
APPLIANCE VENT CONNECTION:  TYPE B DOUBLEWALL CONNECTOR  
MINIMUM ALLOWABLE INPUT RATING OF SPACEHEATING APPLIANCE IN THOUSANDS OF BTU PER HOUR  
VENT HEIGHT H (feet) 
INTERNAL AREA OF CHIMNEY (square inches)  
12  19  28  38  50  63  78  113  
6 8 10 15 20 30 50 
Local 99% winter design temperature: 37°F or greater  
0 0 0 NA NA NA NA 
0 0 0 0 NA NA NA 
0 0 0 0 123 NA NA 
0 0 0 0 190 NA NA 
0 0 0 0 249 NA NA 
0 0 0 0 184 393 NA 
0 0 0 0 0 334 NA 
0 0 0 0 0 0 579 

6 8 10 15 20 30 50 
Local 99% winter design temperature: 27°F to 36°F  
0 0 0 NA NA NA NA 
0 0 51 NA NA NA NA 
68 82 97 NA NA NA NA 
116 127 141 NA NA NA NA 
156 167 183 233 NA NA NA 
180 187 201 253 307 419 NA 
212 214 225 274 330 445 NA 
266 263 265 305 362 485 763 

6 8 10 15 20 30 50 
Local 99% winter design temperature:17°F to 26°F  
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA 197 214 NA NA NA NA 
215 226 245 296 352 NA NA 
259 264 278 331 287 507 NA 
349 352 358 398 457 581 NA 

6 8 10 15 20 30 50 
Local 99% winter design temperature: 5°F to 16°F  
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA 289 NA NA NA NA 
NA 312 331 393 450 NA NA 
416 423 430 485 547 682 972 

6 8 10 15 20 30 50 
Local 99% winter design temperature: 10°F to 4°F  
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
484 494 513 586 650 805 1003 

Local 99% winter design temperature: 11°F or lower Not recommended for any vent configurations 
Notes:
^{1} See Figure 510.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
^{2} NA: Not applicable.
99% Winter Design Temperatures for the Contiguous United States
This map is a necessarily generalized guide to temperatures in the contiguous United States, Temperatures shown for areas such as mountainous regions and large urban centers may not be accurate. The data used to develop this map are from the 1993 ASHRAE Handbook  Fundamentals (Chapter 24, Table 1: Climate Conditions for the United States).
For 99% winter design temperatures in Alaska, consult the ASHRAE Handbook  Fundamentals.
99% winter design temperatures for Hawaii are greater than 37°F.
For SI units: °C = (°F32)/1.8
Zero lateral (L) shall apply to a
straight vertical vent attached to a top outlet draft hood or
flue collar. [NFPA 54:13.1.4]
Sea level input ratings shall be used where determining maximum capacity for highaltitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for highaltitude installation. [NFPA 54:13.1.5]
For appliances with more
than one input rate, the minimum vent capacity (FAN Min)
determined from the tables shall be less than the lowest
appliance input rating, and the maximum vent capacity
(FAN Max/NAT Max) determined from the tables shall
exceed the highest appliance rating input. [NFPA 54:13.1.6]
Listed corrugated metallic chimney liner systems in masonry chimneys shall be sized by using Table 510.1.2(1) or Table 510.1.2(2) for Type B vents with the maximum capacity reduced by 20 percent (0.80 x maximum capacity) and the minimum capacity as shown in Table
510.1.2(1) or Table 510.1.2(2).
Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 510.1.2. The 20 percent reduction for corrugated metallic chimney liner systems includes an allowance for one long radius 90 degree (1.57 rad) turn at the bottom of the liner. [NFPA 54:13.1.7]
Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 510.1.2. The 20 percent reduction for corrugated metallic chimney liner systems includes an allowance for one long radius 90 degree (1.57 rad) turn at the bottom of the liner. [NFPA 54:13.1.7]
Connections
between chimney liners and listed doublewall connectors
shall be made with listed adapters designed for such
purposes. [NFPA 54:13.1.8]
Where the vertical vent has a larger diameter than the vent connector the vertical vent diameter shall be used to determine the minimum vent capacity, and the connector diameter shall be used to determine the maximum vent capacity. The flow area of the vertical vent shall not exceed seven times the flow area of the listed appliance categorized vent area, flue collar area, or draft hood outlet area unless designed in accordance with approved
engineering methods. [NFPA 54:13.1.9]
Draft hood conversion accessories for use with masonry
chimneys venting listed Category I fanassisted appliances
shall be listed and installed in accordance with the listed accessory manufacturer's installation instructions. [NFPA 54:13.1.10]
Table
510.1.2(1) through Table 510.1.2(5) shall be used for
chimneys and vents not exposed to the outdoors below
the roof line. A Type B vent or listed chimney lining system
passing through an unused masonry chimney flue
shall not be considered to be exposed to the outdoors.
Where vents extend outdoors above the roof more than 5
feet (1524 mm) higher than required by Table 509.6.2,
and where vents terminate in accordance with Section
509.6.2(1), the outdoor portion of the vent shall be
enclosed as required by this section for vents not considered
to be exposed to the outdoors or such venting system
shall be engineered. A Type B vent passing through an
unventilated enclosure or chase insulated to a value of not
less than R8 shall not be considered to be exposed to the
outdoors. Table 510.1.2(3) in combination with Table
510.1.2(6) shall be used for claytilelined exterior masonry
chimneys, provided the following requirements are met:
 The vent connector is Type B double wall.
 The vent connector length is limited to 18 inches per inch (18 mm/mm) of vent connector diameter.
 The appliance is draft hoodequipped.
 The input rating is less than the maximum capacity given in Table 510.1.2(3).
 For a water heater, the outdoor design temperature shall be not less than 5°F (15°C).
 For a spaceheating appliance, the input rating exceeds the minimum capacity given by Table 510.1.2(6). [NFPA 54:13.1.11]
Corrugated
vent connectors shall not be smaller than the listed appliance
categorized vent diameter, flue collar diameter, or
draft hood outlet diameter. [NFPA 54:13.1.12]
Vent connectors shall not be upsized
more than two sizes exceeding the listed appliance categorized
vent diameter, flue collar diameter, or draft hood
outlet diameter. [NFPA 54:13.1.13]
In a single run of vent or
vent connector, more than one diameter and type shall
be permitted to be used, provided that the sizes and types
are permitted by the tables. [NFPA 54:13.1.14]
Interpolation shall be permitted
in calculating capacities for vent dimensions that fall
between table entries. [NFPA 54:13.1.15]
Extrapolation beyond the table
entries shall not be permitted. [NFPA 54:13.1.16]
For vent heights lower
than 6 feet (1829 mm) and higher than vent heights
shown in the tables, engineering methods shall be used to
calculate vent capacities. [NFPA 54:13.1.17]
Where the actual height of a
vent falls between entries in the height column of the
applicable table in Table 510.1.2(1) through Table
510.1.2(6), one of the following shall be used:
 Interpolation.
 The lower appliance input rating shown in the table entries for FAN Max and NAT Max column values; and the higher appliance input rating for the FAN Min column values. [NFPA 54:13.1.18]
Table 510.2(1) through Table 510.2(9) shall
not be used where obstructions are installed in the venting
system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance
manufacturer's installation instructions or in accordance with
the following:
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)] (continued) For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)] (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)] (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(2)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(b)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(2)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(b)] (continued) For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
TABLE 510.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)] (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(d)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(d)) (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(6)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(f)]^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(8)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(h)]^{*}
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
 The maximum capacity of the vent connector shall be determined using the NAT Max column.
 The maximum capacity of the vertical vent or chimney shall be determined using the FAN + NAT column where the second appliance is a fanassisted appliance, or the NAT + NAT column where the second appliance is equipped with a draft hood.
 The minimum capacity shall be determined as if the appliance were a fanassisted appliance, as follows:
 The minimum capacity of the vent connector shall be determined using the FAN Min column.
 The FAN + FAN column shall be used where the second appliance is a fanassisted appliance, and the FAN + NAT column shall be used where the second appliance is equipped with a draft hood, to determine whether the vertical vent or chimney configuration is not permitted (NA). Where the vent configuration is NA, the vent configuration shall not be permitted and an alternative venting configuration shall be utilized. [NFPA 54:13.2.1]
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)] (continued) For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)] (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(1)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(a)] (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(2)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(b)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(2)
TYPE B DOUBLEWALL VENT [NFPA 54: TABLE 13.2(b)] (continued) For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
TABLE 510.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)] (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(d)]^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(d)) (continued)^{*} For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
TABLE 510.2(5)
SINGLEWALL METAL PIPE ORTYPE B ASBESTOSCEMENT VENT [NFPA 54: TABLE 13.2(e)]^{*}
SINGLEWALL METAL PIPE ORTYPE B ASBESTOSCEMENT VENT [NFPA 54: TABLE 13.2(e)]^{*}
NUMBER OF APPLIANCES:  TWO OR MORE  
APPLIANCE TYPE:  DRAFT HOODEQUIPMENT  
APPLIANCE VENT CONNECTION:  DIRECT TO PIPE OR VENT  
VENT CONNECTOR CAPACITY  
VENT CONNECTOR DIAMETER  D (inch)  
TOTAL VENT HEIGHT H (feet) 
CONNECTOR RISE R (feet) 
3  4  5  6  7  8 
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR  
68  1 2 3 
21 28 34 
40 53 61 
68 86 98 
102 124 147 
146 178 204 
205 235 275 
15  1 2 3 
23 30 35 
44 56 64 
77 92 102 
117 134 155 
179 194 216 
240 265 298 
30 and up 
1 2 3 
25 31 36 
49 58 68 
84 97 107 
129 145 164 
190 211 232 
270 295 321 
COMMON VENT CAPACITY  
COMMON VENT DIAMETER  D (inch)  
TOTAL VENT HEIGHT H (feet) 
4  5  6  7  8  10  12 
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR  
6 8 10 15 20 30 50 
48 55 59 71 80 NA NA 
78 89 95 115 129 147 NA 
111 128 136 168 186 215 NA 
155 175 190 228 260 300 360 
205 234 250 305 340 400 490 
320 365 395 480 550 650 810 
NA 505 560 590 790 940 1190 
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}
* NA: Not applicable.
* NA: Not applicable.
TABLE 510.2(6)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(f)]^{*}
NUMBER OF APPLIANCES:  TWO OR MORE  
APPLIANCE TYPE:  NAT + NAT  
APPLIANCE VENT CONNECTION  TYPE B DOUBLEWALL CONNECTOR  
COMBINED APPLIANCE MAXIMUM INPUT RATING IN THOUSANDS OF BTU PER HOUR  
VENT HEIGHT H (feet) 
INTERNAL AREA OF CHIMNEY (square inches)  
12  19  28  38  50  63  78  113  
6 8 10 15 20 30 50 100 
25 28 31 NA NA NA NA NA 
46 53 56 67 NA NA NA NA 
71 82 90 106 NA NA NA NA 
103 119 131 152 NA NA NA NA 
143 163 177 212 NA NA NA NA 
188 218 236 283 325 NA NA NA 
246 278 302 365 419 496 NA NA 
NA 408 454 546 648 749 922 NA 
* NA: Not applicable.
TABLE 510.2(7)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(g)]^{1,2}
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(g)]^{1,2}
NUMBER OF APPLIANCES:  TWO OR MORE  
APPLIANCE TYPE:  NAT + NAT  
APPLIANCE VENT CONNECTION:  TYPE B DOUBLEWALL CONNECTOR  
MINIMUM ALLOWABLE INPUT RATING OF SPACEHEATING APPLIANCE IN THOUSANDS OF BTU PER HOUR  
VENT HEIGHT H (feet) 
INTERNAL AREA OF CHIMNEY (square inches)  
12  19  28  38  50  63  78  113  
Local 99% winter design temperature: 37°F or greater  
6 8 10 15 20 30 50 100 
0 0 0 NA NA NA NA NA 
0 0 0 0 NA NA NA NA 
0 0 0 0 NA NA NA NA 
0 0 0 0 NA NA NA NA 
0 0 0 0 NA NA NA NA 
0 0 0 0 184 393 N A NA 
0 0 0 0 0 334 NA NA 
NA 0 0 0 0 0 579 NA 
Local 99% winter design temperature: 27°F to 36°F  
6 8 10 15 20 30 50 100 
0 0 0 NA NA NA NA NA 
0 0 51 NA NA NA NA NA 
68 82 NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
180 187 201 253 307 NA NA NA 
212 214 225 274 330 445 NA NA 
NA 263 265 305 362 485 763 NA 
Local 99% winter design temperature:17°F to 26°F  
6 8 10 15 20 30 50 100 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA 264 278 331 287 NA NA NA 
NA 352 358 398 457 581 862 NA 
Local 99% winter design temperature: 5°F to 16°F  
6 8 10 15 20 30 50 100 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
NA NA 430 485 547 682 NA NA 
Local 99% winter design temperature: 4°F or lower Not recommended for any vent configurations 
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}, °C = (°F32)/1.8
Notes:
Notes:
^{1} See Figure 510.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
^{2} NA: Not applicable.TABLE 510.2(8)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(h)]^{*}
NUMBER OF APPLIANCES:  TWO OR MORE  
APPLIANCE TYPE:  FAN + NAT  
APPLIANCE VENT CONNECTION  TYPE B DOUBLEWALL CONNECTOR  
COMBINED APPLIANCE MAXIMUM INPUT RATING IN THOUSANDS OF BTU PER HOUR  
VENT HEIGHT H (feet) 
INTERNAL AREA OF CHIMNEY (square inches)  
12  19  28  38  50  63  78  113  
6 8 10 15 20 30 50 100 
74 80 84 NA NA NA NA NA 
119 130 138 152 NA NA NA NA 
178 193 207 233 250 NA NA NA 
257 279 299 334 368 404 NA NA 
351 384 409 467 508 564 NA NA 
458 501 538 611 668 747 831 NA 
582 636 686 781 858 969 1089 NA 
853 937 1010 1156 1286 1473 1692 1921 
* NA: Not applicable.
TABLE 510.2(9)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(i)]^{1, 2}
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(i)]^{1, 2}
NUMBER OF APPLIANCES:  TWO OR MORE  
APPLIANCE TYPE:  FAN + NAT  
APPLIANCE VENT CONNECTION:  TYPE B DOUBLEWALL CONNECTOR  
MINIMUM ALLOWABLE INPUT RATING OF SPACEHEATING APPLIANCE IN THOUSANDS OF BTU PER HOUR  
VENT HEIGHT H (feet) 
INTERNAL AREA OF CHIMNEY (square inches)  
12  19  28  38  50  63  78  113  
Local 99% winter design temperature: 37°F or greater  
6 8 10 15 20 30 50 100 
0 0 0 NA NA NA NA NA 
0 0 0 0 NA NA NA NA 
0 0 0 0 123 NA NA NA 
0 0 0 0 190 334 NA NA 
0 0 0 0 249 398 NA NA 
0 0 0 0 184 393 714 NA 
0 0 0 0 0 334 707 NA 
0 0 0 0 0 0 579 1600 
Local 99% winter design temperature: 27°F to 36°F  
6 8 10 15 20 30 50 100 
0 0 0 NA NA NA NA NA 
0 0 51 111 NA NA NA NA 
68 82 97 142 187 NA NA NA 
116 127 141 183 230 330 NA NA 
156 167 183 233 284 319 NA NA 
180 187 201 253 307 419 672 NA 
212 214 225 274 330 445 705 NA 
266 263 265 305 362 485 763 1554 
Local 99% winter design temperature:17°F to 26°F  
6 8 10 15 20 30 50 100 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA 
NA 197 214 NA NA NA NA 
215 226 245 296 352 NA NA 
259 264 278 331 287 507 NA 
349 352 358 398 457 581 NA 
Local 99% winter design temperature: 5°F to 16°F  
6 8 10 15 20 30 50 100 
0 52 NA NA NA NA NA NA 
55 74 90 NA NA NA NA NA 
99 111 125 167 212 NA NA NA 
141 154 169 212 258 262 NA NA 
182 197 214 263 316 429 NA NA 
215 226 245 296 352 470 723 NA 
259 264 278 331 387 507 766 NA 
416 423 430 485 547 682 972 
Local 99% winter design temperature: 10°F to 4°F  
6 8 10 15 20 30 50 100 
NA NA NA NA NA NA NA NA 
NA NA NA NA NA NA NA NA 
145 159 175 NA NA NA NA NA 
196 213 231 283 333 NA NA NA 
249 269 292 351 408 NA NA NA 
296 320 339 404 468 603 NA NA 
349 371 397 457 528 667 955 NA 
484 494 513 586 650 805 1003 NA 
Local 99% winter design temperature: 11°F or lower Not recommended for any vent configurations 
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m^{2}, °C = (°F32)/1.8
Notes:
Notes:
^{1} See Figure 510.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
^{2} NA: Not applicable.The maximum
vent connector horizontal length shall be 18 inches
per inch (18 mm/mm) of connector diameter as shown
in Table 510.2.1, or as permitted by Section 510.2.2.
[NFPA 54:13.2.2]
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
CONNECTOR DIAMETER (inches) 
MAXIMUM CONNECTOR HORIZONTAL LENGTH (feet) 
3  4^{1}/_{2} 
4  6 
5  7^{1}/_{2} 
6  9 
7  10^{1}/_{2} 
8  12 
9  13^{1}/_{2} 
10  15 
12  18 
14  21 
16  24 
18  27 
20  30 
22  33 
24  36 
The vent connector shall be routed to the vent utilizing
the shortest possible route. Connectors with longer horizontal lengths
than those listed in Table 510.2.1 are permitted
under the following conditions:
 The maximum capacity (FAN Max or NAT Max) of the vent connector shall be reduced 10 percent for each additional multiple of the length listed in Table 510.2.1. For example, the length listed for a 4 inch (102 mm) connector shall not exceed 6 feet (1829 mm). With a connector length exceeding 6 feet (1829 mm) but not exceeding 12 feet (3658 mm), the maximum capacity shall be reduced by 10 percent (0.90 x maximum vent connector capacity). With a connector length exceeding 12 feet (3658 mm) but not exceeding 18 feet (5486 mm), the maximum capacity shall be reduced by 20 percent (0.80 x maximum vent capacity).
 For a connector serving a fanassisted appliance, the minimum capacity (FAN Min) of the connector shall be determined by referring to the corresponding single appliance table. For Type B doublewall connectors, Table 510.1.2(1) shall be used. For singlewall connectors, Table 510.1.2(2) shall be used. The height (H) and lateral (L) shall be measured according to the procedures for a single appliance vent, as if the other appliances were not present. [NFPA 54:13.2.3]
Where the vent connectors
are combined prior to entering the vertical portion
of the common vent to form a common vent manifold, the
size of the common vent manifold and the common vent
shall be determined by applying a 10 percent reduction
(0.90 x maximum common vent capacity) to the common
vent capacity part of the common vent tables. The length
of the common vent manifold (LM) shall not exceed 18 inches per inch (18 mm/mm) of common vent diameter (D). [NFPA 54:13.2.4]
Where the common vertical vent is
offset, the maximum capacity of the common vent shall
be reduced in accordance with Section 510.2.5, and the
horizontal length of the common vent offset shall not
exceed 18 inches per inch (18 mm/mm) of common vent
diameter (D). Where multiple offsets occur in a common
vent, the total horizontal length of offsets combined shall
not exceed 18 inches per inch (18 mm/mm) of the common
vent diameter. [NFPA 54:13.2.5]
For each elbow up to and
including 45 degrees (0.79 rad) in the common vent, the
maximum common vent capacity listed in the venting
tables shall be reduced by 5 percent. For each elbow
exceeding 45 degrees (0.79 rad) up to and including 90
degrees (1.57 rad), the maximum common vent capacity
listed in the venting tables shall be reduced by 10 percent.
[NFPA 54:13.2.6]
The crosssectional
area of the common vent shall be equal to or exceeding the crosssectional area of the largest connector.
[NFPA 54:13.2.8]
Tee and wye fittings connected
to a common gas vent shall be considered as part of
the common gas vent and constructed of materials consistent
with that of the common gas vent. [NFPA 54:13.2.9]
At the point where tee or wye
fittings connect to a common gas vent, the opening size
of the fitting sha1l be equal to the size of the common
vent. Such fittings shall not be prohibited from having
reduced size openings at the point of connection of appliance
gas vent connectors. [NFPA 54:13.2.10]
Sea level input ratings
shall be used where determining maximum capacity
for highaltitude installation. Actual input (derated for
altitude) shall be used for determining minimum capacity
for highaltitude installation. [NFPA 54:13.2.11]
The connector rise (R) for
each appliance connector shall be measured from the
draft hood outlet or flue collar to the centerline where the
vent gas streams come together. [NFPA 54:13.2.12]
For multiple appliances located
on one floor, the total height (H) shall be measured from
the highest draft hood outlet or flue collar up to the level
of the outlet of the common vent. [NFPA 54:13.2.13]
For multistory
installations, the total height (H) for each segment of the
system shall be the vertical distance between the highest draft hood outlet or flue collar entering that segment and
the centerline of the next higher interconnection tee.
[NFPA 54:13.2.14]
The
size of the lowest connector and of the vertical vent leading
to the lowest interconnection of a multistory system
shall be in accordance with Table 510.1.2(1) or Table
510.1.2(2) for available total height (H) up to the lowest
interconnection. [NFPA 54:13.2.15]
Where
used in multistory systems, vertical common vents shall
be Type B doublewall and shall be installed with a listed
vent cap. [NFPA 54:13.2.16]
Offsets in
multistory common vent systems shall be limited to a
single offset in each system, and systems with an offset
shall comply with the following:
 The offset angle shall not exceed 45 degrees (0.79 rad) from vertical.
 The horizontal length of the offset shall not exceed 18 inches per inch (18 mm/mm) of common vent diameter of the segment in which the offset is located.
 For the segment of the common vertical vent containing the offset, the common vent capacity listed in the common venting tables shall be reduced by 20 percent (0.80 x maximum common vent capacity).
 A multistory common vent shall not be reduced in size above the offset. [NFPA 54:13.2.17]
Where two or
more appliances are connected to a vertical vent or chimney,
the flow area of the largest section of vertical vent or
chimney shall not exceed seven times the smallest listed
appliance categorized vent areas, flue collar area, or draft
hood outlet area unless designed in accordance with
approved engineering methods. [NFPA 54:13.2.18]
For appliances with
more than one input rate, the minimum vent connector
capacity (FAN Min) determined from the tables shall be
less than the lowest appliance input rating, and the maximum
vent connector capacity (FAN Max or NAT Max)
determined from the table shall exceed the highest appliance
input rating. [NFPA 54:13.2.19]
Listed corrugated metallic chimney liner systems
in masonry chimneys shall be sized by using Table
510.2(1) or Table 510.2(2) for Type B vents, with the
maximum capacity reduced by 20 percent (0.80 x maximum
capacity) and the minimum capacity as shown in
Table 510.2(1) or Table 510.2(2). Corrugated metallic
liner systems installed with bends or offsets shall have
their maximum capacity further reduced in accordance
with Section 510.2.5. The 20 percent reduction for corrugated
metallic chimney liner systems includes an
allowance for one long radius 90 degree (1.57 rad) turn
at the bottom of the liner. [NFPA 54:13.2.20]
Table 510.2(1)
through Table 510.2(5) shall be used for chimneys and
vents not exposed to the outdoors below the roof line. A
Type B vent or listed chimney lining system passing
through an unused masonry chimney flue shall not be
considered to be exposed to the outdoors. A Type B vent
passing through an unventilated enclosure or chase insulated
to a value of not less than R8 shall not be considered
to be exposed to the outdoors. Where vents extend
outdoors above the roof more than 5 feet (1524 mm)
higher than required by Table 509.6.2, and where vents
terminate in accordance with Section 509.6.2(1), the outdoor
portion of the vent shall be enclosed as required by
this section for vents not considered to be exposed to the
outdoors, or such venting system shall be engineered.
Table 510.2(6) through Table 510.2(9) shall be used for
claytilelined exterior masonry chimneys, provided the
following conditions are met:
 The vent connector is Type B doublewall.
 Not less than one appliance is draft hoodequipped.
 The combined appliance input rating is less than the maximum capacity given by Table 510.2(6) (for NAT + NAT) or Table 510.2(8) (for FAN + NAT).
 The input rating of each spaceheating appliance exceeds the minimum input rating given by Table 510.2(7) (for NAT + NAT) or Table 510.2(9) (for FAN + NAT).
 The vent connector sizing is in accordance with Table 510.2(3). [NFPA 54:13.2.22]
Vent connectors shall
not be increased more than two sizes exceeding the listed
appliance categorized vent diameter, flue collar diameter,
or draft hood outlet diameter. Vent connectors for draft
hoodequipped appliances shall not be smaller than the
draft hood outlet diameter. Where vent connector sizes
determined from the tables for fanassisted appliances
are smaller than the flue collar diameter, the use of the
smaller sizes shall be permitted provided that the installation
is in accordance with the following conditions:
 Vent connectors for fanassisted appliance flue collars 12 inches (305 mm) in diameter or smaller are not reduced by more than one table size [e.g., 12 inches to 10 inches (305 mm to 254 mm) is a one size reduction] and those exceeding 12 inches (305 mm) in diameter are not reduced exceeding two table sizes [e.g., 24 inches to 20 inches (610 mm to 508 mm) is a two size reduction].
 The fanassisted appliance is common vented with a draft hoodequipped appliance.
 The vent connector has a smooth interior wall. [NFPA 54:13.2.24]
Combinations of pipe sizes, singlewall metal pipe, and
doublewall metal pipe shall be allowed within a connector
run or within the common vent, provided the appropriate
tables permit the desired sizes and types of pipe,
where they were used for the entire length of the subject
connector or vent. Where singlewall and Type B doublewall
metal pipes are used for vent connectors within the
same venting system, the common vent shall be sized in
accordance with Table 510.2(2) or Table 510.2(4). [NFPA 54:13.2.25]
Where a table permits more than one diameter of pipe to be used for a connector or vent, the permitted sizes shall be permitted to be used. [NFPA 54:13.2.26]
Interpolation shall be permitted
in calculating capacities for vent dimensions that fall
between table entries. [NFPA 54:13.2.27]
Extrapolation beyond the table
entries shall not bc permitted. [NFPA 54:13.2.28]
For vent heights lower
than 6 feet (1829 mm) and exceeding vent heights shown
in the tables, engineering methods shall be used to calculate
vent capacities. [NFPA 54:13.2.29]
Where the actual height of a
vent falls between entries in the height column of the
applicable table in Table 510.2(1) through Table
510.2(9), one of the following shall be used:
 Interpolation.
 The lower appliance input rating shown in the table entries for FAN Max and NAT Max column values; and the higher appliance input rating for the FAN Min column values. [NFPA 54:13.2.30]