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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 fan-assisted 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]
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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 fan-assisted 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 fan-assisted
appliances. [NFPA 54:13.1.2]
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Single-appliance 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. Single-appliance 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(1)
TYPE B DOUBLE-WALL 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 m2
* NA: Not applicable.
TABLE 510.1.2(1)
TYPE B DOUBLE-WALL 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 m2
TABLE 510.1.2(1)
TYPE B DOUBLE-WALL 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 m2
TABLE 510.1.2(2)
TYPE B DOUBLE-WALL 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 m2
* NA: Not applicable.
TABLE 510.1.2(2)
TYPE B DOUBLE-WALL 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 m2
* NA: Not applicable.
MINIMUM ALLOWABLE INPUT RATING OF SPACE-HEATING 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
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 m2, °C = (°F-32)/1.8
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 = (°F-32)/1.8FIGURE 510.1.2(6)
RANGE OF WINTER DESIGN TEMPERATURES USED IN ANALYZING EXTERIOR MASONRY CHIMNEYS IN THE UNITED STATES
[NFPA 54: FIGURE F.2.4]
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Sea level input ratings shall be used where determining maximum capacity for high-altitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for high-altitude installation. [NFPA 54:13.1.5]
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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]
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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]
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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]
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Draft hood conversion accessories for use with masonry
chimneys venting listed Category I fan-assisted appliances
shall be listed and installed in accordance with the listed accessory manufacturer's installation instructions. [NFPA 54:13.1.10]
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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 R-8 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 clay-tile-lined 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 hood-equipped.
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 space-heating appliance, the input rating
exceeds the minimum capacity given by Table
510.1.2(6). [NFPA 54:13.1.11]
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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]
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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]
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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]
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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]
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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]
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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:
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 fan-assisted 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 fan-assisted 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 fan-assisted 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 DOUBLE-WALL 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 m2
* NA: Not applicable.
TABLE 510.2(1)
TYPE B DOUBLE-WALL 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 m2
TABLE 510.2(1)
TYPE B DOUBLE-WALL 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 m2
* NA: Not applicable.
TABLE 510.2(1)
TYPE B DOUBLE-WALL 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 m2
* NA: Not applicable.
TABLE 510.2(2)
TYPE B DOUBLE-WALL 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 m2
* NA: Not applicable.
TABLE 510.2(2)
TYPE B DOUBLE-WALL 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 m2
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 m2
* 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 m2
* 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 m2
* 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 m2
* NA: Not applicable.
TABLE 510.2(5)
SINGLE-WALL METAL PIPE ORTYPE B ASBESTOS-CEMENT VENT [NFPA 54: TABLE 13.2(e)]*
NUMBER OF APPLIANCES:
TWO OR MORE
APPLIANCE TYPE:
DRAFT HOOD-EQUIPMENT
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
6-8
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 m2
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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]
TABLE 510.2.1
VENT CONNECTOR MAXIMUM LENGTH
[NFPA 54: TABLE 13.2.2]
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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 fan-assisted appliance, the
minimum capacity (FAN Min) of the connector shall
be determined by referring to the corresponding single
appliance table. For Type B double-wall connectors, Table 510.1.2(1) shall be used. For single-wall
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]
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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]
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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]
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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]
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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]
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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]
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Sea level input ratings
shall be used where determining maximum capacity
for high-altitude installation. Actual input (derated for
altitude) shall be used for determining minimum capacity
for high-altitude installation. [NFPA 54:13.2.11]
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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]
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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]
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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]
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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]
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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]
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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]
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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]
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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]
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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 R-8 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
clay-tile-lined exterior masonry chimneys, provided the
following conditions are met:
The vent connector is Type B double-wall.
Not less than one appliance is draft hood-equipped.
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 space-heating 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]
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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
hood-equipped appliances shall not be smaller than the
draft hood outlet diameter. Where vent connector sizes
determined from the tables for fan-assisted 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 fan-assisted 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 fan-assisted appliance is common vented with a
draft hood-equipped appliance.
The vent connector has a smooth interior wall.
[NFPA 54:13.2.24]
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Combinations of pipe sizes, single-wall metal pipe, and
double-wall 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 single-wall and Type B double-wall
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]
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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]
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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]
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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]
