CODES

ADOPTS WITH AMENDMENTS:

2018 Uniform Mechanical Code

Chapter 1 ADMINISTRATION

Chapter 2 DEFINITIONS

Chapter 3 GENERAL REGULATIONS

Chapter 4 VENTILATION AIR

Chapter 5 EXHAUST SYSTEMS

Chapter 6 DUCT SYSTEMS

Chapter 7 COMBUSTION AIR

Chapter 8 CHIMNEYS AND VENTS

Chapter 9 INSTALLATION OF SPECIFIC APPLIANCES

Chapter 10 BOILERS AND PRESSURE VESSELS

Chapter 11 REFRIGERATION

Chapter 12 HYDRONICS

Chapter 13 FUEL GAS PIPING

Chapter 14 PROCESS PIPING

Chapter 15 SOLAR ENERGY SYSTEMS

Chapter 16 STATIONARY POWER PLANTS

Chapter 17 REFERENCED STANDARDS

Appendix A RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SYSTEM DESIGN
(Loads, Equipment, Ducts) [ACCA]

Appendix B PROCEDURES TO BE FOLLOWED TO PLACE GAS EQUIPMENT IN OPERATION

Appendix C INSTALLATION AND TESTING OF OIL (LIQUID) FUEL-FIRED EQUIPMENT

Appendix D FUEL SUPPLY: MANUFACTURED/MOBILE HOME PARKS AND RECREATIONAL VEHICLE PARKS

Appendix E SUSTAINABLE PRACTICES

Appendix F SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION AND VENTILATION OPENING DESIGN

Appendix G EXAMPLE CALCULATION OF OUTDOOR AIR RATE

CALIFORNIA MECHANICAL CODE - MATRIX ADOPTION TABLE
CHAPTER 8 - CHIMNEYS AND VENTS
(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
Adopting agency BSC BSC-CG SFM HCD DSA OSHPD BSCC DPH AGR DWR CEC CA SL SLC
1 2 1-AC AC SS SS/CC 1 1R 2 3 4 5
Adopt entire chapter X X X X X X X X X X X X
Adopt entire chapter as
amended (amended
sections listed below)
Adopt only those sections
that are listed below
Chapter / Section
This state agency does not adopt sections identified with the following symbol:
The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
The requirements of this chapter shall govern the venting of fuel-burning appliances.
Low-heat and medium-heat gas appliances shall be vented in accordance with this chapter. Other gas appliances shall be vented in accordance with NFPA 211 or other applicable standards.
Appliances fueled by fuels other than gas shall be vented in accordance with NFPA 211 and the appliance manufacturer's instructions.
Type B and Type B-W gas vents shall comply with UL 441, Type L gas vents shall comply with UL 641.
Listed vents shall be installed in accordance with this chapter and the manufacturer's installation instructions. [NFPA 54:12.2.1]
Appliance vents shall not discharge into a space enclosed by screens having openings less than 1/4 of an inch (6.4 mm) mesh.
Except as permitted in Section 802.2.1 through Section 802.2.8, all appliances shall be connected to venting systems. [NFPA 54:12.3.1]
The following appliances shall not be required to be vented:
  1. Listed ranges.
  2. Built-in domestic cooking units listed and marked for optional venting.
  3. Listed hot plates and listed laundry stoves.
  4. Listed Type 1 clothes dryers exhausted in accordance with Section 504.4.
  5. A single listed booster-type (automatic instantaneous) water heater, when designed and used solely for the sanitizing rinse requirements of a dishwashing machine, provided that the appliance is installed with the draft hood in place and unaltered, if a draft hood is required, in a commercial kitchen having a mechanical exhaust system; where installed in this manner, the draft hood outlet shall not be less than 36 inches (914 mm) vertically and 6 inches (152 mm) horizontally from any surface other than the appliance.
  6. Listed refrigerators.
  7. Counter appliances.
  8. Room heaters listed for unvented use.
  9. Direct gas-fired makeup air heaters.
  10. Other appliances listed for unvented use and not provided with flue collars.
  11. Specialized appliances of limited input such as laboratory burners or gas lights. [NFPA 54:12.3.2]
Where any or all of the appliances in Section 802.2.1(5) through Section 802.2.1(11) are installed so the aggregate input rating exceeds 20 Btu/hr/ft3 (207 W/m3) of room or space in which it is installed, one or more shall be provided with venting systems or other approved means for conveying the vent gases to the outdoors so the aggregate input rating of the remaining unvented appliances does not exceed 20 Btu/hr/ft3 (207 W/m3). [NFPA 54:12.3.2.1]
Where the calculation includes the volume of an adjacent room or space, the room or space in which the appliances are installed shall be directly connected to the adjacent room or space by a doorway, archway, or other opening of comparable size that cannot be closed. [NFPA 54:12.3.2.2]
Ventilating hoods and exhaust systems shall be permitted to be used to vent appliances installed in commercial applications and to vent industrial appliances, particularly where the process itself requires fume disposal. [NFPA 54:12.3.3]
The operation of industrial appliances such that its flue gases are discharged directly into a large and well-ventilated space shall be permitted. [NFPA 54:12.3.4]
Listed direct-vent appliances shall be installed in accordance with the manufacturer's installation instructions and Section 802.8.2. [NFPA 54:12.3.5]
Appliances incorporating integral venting means shall be installed in accordance with the manufacturer's installation instructions, Section 802.8, and Section 802.8.1. [NFPA 54:12.3.6]
Commercial industrial-type incinerators shall be vented in accordance with NFPA 82. [NFPA 54:12.3.7]
Venting systems shall be designed and constructed to convey flue and vent gases to the outdoors. [NFPA 54:12.1]
A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer's instructions. [NFPA 54:12.4.1]
Appliances required to be vented shall be connected to a venting system designed and installed in accordance with the provisions of Section 802.4 through Section 802.15.1. [NFPA 54:12.4.2]
Mechanical draft systems shall be listed and installed in accordance with both the appliance and the mechanical draft system manufacturer's installation instructions. [NFPA 54:12.4.3.1]
Appliances requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design. [NFPA 54:12.4.3.2]
Forced draft systems and portions of induced draft systems under positive pressure during operation shall be designed and installed so as to prevent leakage of flue or vent gases into a building. [NFPA 54:12.4.3.3]
Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure. [NFPA 54:12.4.3.4]
Where a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners where the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance. [NFPA 54:12.4.3.5]
The exit terminals of mechanical draft systems shall be not less than 7 feet (2134 mm) above finished ground level where located adjacent to public walkways and shall be located as specified in Section 802.8 and Section 802.8.1. [NFPA 54:12.4.3.6]
Ventilating hoods and exhaust systems shall be permitted to be used to vent appliances installed in commercial applications. [NFPA 54:12.4.4.1]
Where automatically operated appliances, other than commercial cooking appliances, are vented through a ventilating hood or exhaust system equipped with a damper or with a power means of exhaust, provisions shall be made to allow the flow of gas to the main burners where the damper is open to a position to properly vent the appliance and where the power means of exhaust is in operation. [NFPA 54:12.4.4.2]
Venting systems shall not extend into or pass through a fabricated air duct or furnace plenum. [NFPA 54:12.4.5.1]
Where a venting system passes through an above-ceiling air space or other nonducted portion of an air-handling system, it shall conform to one of the following requirements:
  1. The venting system shall be a listed special gas vent, other system serving a Category III or Category IV appliance, or other positive pressure vent, with joints sealed in accordance with the appliance or vent manufacturer's instructions.
  2. The vent system shall be installed such that no fittings or joints between sections are installed in the above-ceiling space.
  3. The venting system shall be installed in a conduit or enclosure with joints between the interior of the enclosure and the ceiling space sealed. [NFPA 54:12.4.5.2]
The type of venting system to be used shall be in accordance with Table 802.4. [NFPA 54:12.5.1]

TABLE 802.4
TYPE OF VENTING SYSTEM TO BE USED
[NFPA 54: TABLE 12.5.1]
APPLIANCES TYPE OF VENTING SYSTEM LOCATION OF REQUIREMENTS
Listed Category I appliances Type B gas vent Section 802.6
Listed appliances equipped with draft hood Chimney Section 802.5
Appliances listed for use with Type B gas vent
Single-wall metal pipe

Listed chimney lining system for gas
venting

Special gas vent listed for these appliances
Section 802.7

Section 802.5.3

Section 802.4.3
Listed vented wall furnaces Type B-W gas vent Section 802.6, Section 907.0
Category II appliances
Category Ill appliances
Category IV appliances


As specified or furnished by manufacturers
of listed appliances


Section 802.4.1 and Section 802.4.3
Incinerators Single-wall metal pipe NFPA 82
Appliances that can be converted to use of solid fuel

Unlisted combination gas- and oil-burning appliances

Combination gas- and solid-fuel-burning appliances

Appliances listed for use with chimneys only

Unlisted appliances
Chimney Section 802.5
Listed combination gas- and oil-burning appliances Type L vent

Chimney
Section 802.6

Section 802.5
Decorative appliances in vented fireplace Chimney Section 911.2
Gas-fired toilets Single-wall metal pipe Section 802.7, Section 929.3
Direct-vent appliances - Section 802.2.6
Appliances with integral vents - Section 802.2.7
Where plastic piping is used to vent an appliance, the appliance shall be listed for use with such venting materials and the appliance manufacturer's installation instructions shall identify the specific plastic piping material. [NFPA 54:12.5.2]
Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer's installation instructions. Where primer is required, it shall be of a contrasting color. [NFPA 54:12.5.3]
Special gas vents shall be listed and installed in accordance with the special gas vent manufacturer's installation instructions. [NFPA 54:12.5.4]
Chimneys shall be installed in accordance with Section 802.5.1 through Section 802.5.3.
Factory-built chimneys shall be installed in accordance with the manufacturer's installation instructions. Factory-built chimneys used to vent appliances that operate at positive vent pressure shall be listed for such application. [NFPA 54:12.6.1.1]
Decorative shrouds addressed in Section 802.5.4.3 shall be listed or labeled in accordance with UL 103 for factory-built residential chimneys, UL 127 for factory-built fireplaces, or UL 1482 for solid-fuel room heaters.
Factory-built chimneys shall comply with the requirements of UL 103 or of UL 959. Factory-built chimneys for use with wood-burning appliances shall comply with the Type HT requirements of UL 103. [NFPA 211:6.1.3.1, 6.1.3.2]
Metal chimneys shall be built and installed in accordance with NFPA 211. [NFPA 54:12.6.1.2]
Masonry chimneys shall be built and installed in accordance with NFPA 211 and lined with approved clay flue lining, a listed chimney lining system, or other approved material that resists corrosion, erosion, softening, or cracking from vent gases at temperatures not exceeding 1800°F (982°C).

Exception: Masonry chimney flues lined with a chimney lining system specifically listed for use with listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be permitted. The liner shall be installed in accordance with the liner manufacturer's installation instructions. A permanent identifying label shall be attached at the point where the connection is to be made to the liner. The label shall read: "This chimney liner is for appliances that burn gas only. Do not connect to solid-or liquid-fuel-burning appliances or incinerators." [NFPA 54:12.6.1.3]
A chimney for a residential-type or low-heat appliance shall extend not less than 3 feet (914 mm) above the highest point where it passes through a roof of a building and not less than 2 feet (610 mm) higher than a portion of a building within a horizontal distance of 10 feet (3048 mm). (See Figure 802.5.4) [NFPA 54:12.6.2.1]

  1. Termination 10 ft.(3.0 m) or Less from Ridge, Wall, or Parapet
  2. Termination More Than 10 ft.(3.0 m) from Ridge, Wall, or Parapet
FIGURE 802.5.4
TYPICAL TERMINATION LOCATIONS FOR CHIMNEYS AND SINGLE-WALL METAL PIPES SERVING RESIDENTIAL-TYPE AND LOW-HEAT APPLIANCE [NFPA 54: FIGURE A.12.6.2.1]
A chimney for medium-heat appliance shall extend at least less than 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm). [NFPA 54:12.6.2.2]
A chimney shall extend not less than 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar. [NFPA 54:12.6.2.3]
Decorative shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are listed and labeled for use with the specific factory-built chimney system and are installed in accordance with the manufacturer's installation instructions. [NFPA 54:12.6.2.4]
The effective area of a chimney venting system serving listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be in accordance with one of the following methods:
  1. Those listed in Section 803.0.
  2. For sizing an individual chimney venting system for a single appliance with a draft hood, the effective areas of the vent connector and chimney flue shall be not less than the area of the appliance flue collar or draft hood outlet or greater than seven times the draft hood outlet area.
  3. For sizing a chimney venting system connected to two appliances with draft hoods, the effective area of the chimney flue shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.
  4. Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.
  5. Other approved engineering methods. [NFPA 54:12.6.3.1]
This inspection shall be made after chimneys, vents, or parts thereof, authorized by the permit, have been installed and before such vent or part thereof has been covered or concealed.
Before replacing an existing appliance or connecting a vent connector to a chimney, the chimney passageway shall be examined to ascertain that it is clear and free of obstructions and shall be cleaned where previously used for venting solid- or liquid-fuel-burning appliances or fireplaces. [NFPA 54:12.6.4.1]
Chimneys shall be lined in accordance with NFPA 211.

Exception: Existing chimneys shall be permitted to have their use continued when an appliance is replaced by an appliance of similar type, input rating, and efficiency, where the chimney complies with Section 802.5.7 through Section 802.5.7.3 and the sizing of the chimney is in accordance with Section 802.5.5. [NFPA 54:12.6.4.2]
Cleanouts shall be examined to determine that they will remain tightly closed where not in use. [NFPA 54:12.6.4.3]
Where inspection reveals that an existing chimney is not safe for the intended application, it shall be repaired, rebuilt, lined, relined, or replaced with a vent or chimney in accordance with NFPA 211, and shall be approved for the appliances to be attached. [NFPA 54:12.6.4.4]
An appliance shall not be connected to a chimney flue serving a separate appliance designed to burn solid fuel. [NFPA 54:12.6.5.1]
Where one chimney serves gas appliances and liquid fuel-burning appliances, the appliances shall be connected through separate openings or shall be connected through a single opening where joined by a fitting located as close as practical to the chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels. Where the gas appliance is automatically controlled, it shall be equipped with a safety shutoff device. [NFPA 54:12.6.5.2]
A listed combination gas-and solid-fuel-burning appliance connected to a single chimney flue shall be equipped with a manual reset device to shut off gas to the main burner in the event of sustained backdraft or flue gas spillage. The chimney flue shall be sized to properly vent the appliance. [NFPA 54:12.6.5.3]
A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized to properly vent the appliance. [NFPA 54:12.6.5.4]
All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer's installation instructions. [NFPA 54:12.6.6]
Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is not less than 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7]
The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appliance.

Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer's instructions. [NFPA 54:12.6.8.1]
The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal or factory-built chimney flue shall not be used to supply combustion air.

Exception: Direct-vent appliances designed for installation in a solid-fuel-burning fireplace where installed in accordance with the manufacturer's installation instructions. [NFPA 54:12.6.8.2]
The installation of gas vents shall meet the following requirements:
  1. Gas vents shall be installed in accordance with the manufacturer's installation instructions.
  2. A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is connected.
  3. Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer's installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: "This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators."
  4. Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent. [NFPA 54:12.7.1]
A gas vent shall terminate in accordance with one of the following:
  1. Gas vents that are 12 inches (300 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure 802.6.1 and Table 802.6.1.
  2. Gas vents that are over 12 inches (300 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above a portion of a building within 10 feet (3048 mm) horizontally.
  3. Industrial appliances as provided in Section 802.2.5.
  4. Direct-vent systems as provided in Section 802.2.6.
  5. Appliance with integral vents as provided in Section 802.2.7.
  6. Mechanical draft systems as provided in Section 802.3.3 through Section 802.3.3.5.
  7. Ventilating hoods and exhaust systems as provided in Section 802.3.4 and Section 802.3.4.1. [NFPA 54:12.7.2(1)]
FIGURE 802.6.1
GAS VENT TERMINATION LOCATIONS FOR LISTED CAPS 12 INCHES OR LESS IN SIZE NOT LESS THAN 8 FEET FROM A VERTICAL WALL [NFPA 54: FIGURE 12.7.2]


TABLE 802.6.1
ROOF PITCH HEIGHT
[NFPA 54: TABLE 12.7.2]
ROOF PITCH H (minimum) (feet)
Flat to 6/12 1.0
Over 6/12 to 7/12 1.25
Over 7/12 to 8/12 1.5
Over 8/12 to 9/12 2.0
Over 9/12 to 10/12 2.5
Over 10/12 to 11/12 3.25
Over 11/12 to 12/12 4.0
Over 12/12 to 14/12 5.0
Over 14/12 to 16/12 6.0
Over 16/12 to 18/12 7.0
Over 18/12 to 20/12 7.5
Over 20/12 to 21/12 8.0
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
A Type B or a Type L gas vent shall terminate not less than 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar. [NFPA 54:12.7.2(2)]
A Type B-W gas vent shall terminate not less than 12 feet (3658 mm) in vertical height above the bottom of the wall furnace. [NFPA 54:12.7.2(3)]
A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Section 802.2.6 and Section 802.3.3 through Section 802.3.3.5. [NFPA 54:12.7.2(4)]
Decorative shrouds shall not be installed at the termination of gas vents except where such shrouds are listed for use with the specific gas venting system and are installed in accordance with the manufacturer's installation instructions. [NFPA 54:12.7.2(5)]
A gas vent shall extend through the roof flashing, roof jack, or roof thimble and terminate with a listed cap or listed roof assembly. [NFPA 54:12.7.2(6)]
A gas vent shall terminate not less than 3 feet (914 mm) above a forced air inlet located within 10 feet (3048 mm). [NFPA 54:12.7.2(7)]
Where a vent passes through an insulated assembly, an approved metal shield shall be installed between the vent and insulation. The shield shall extend not less than 2 inches (51 mm) above the insulation and be secured to the structure in accordance with the manufacturer's installation instructions.
Venting systems shall be sized and constructed in accordance with Section 803.0 or other approved engineering methods and the gas vent and the appliance manufacturer's instructions. [NFPA 54:12.7.3]
The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with a Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following:
  1. The provisions of Section 803.0.
  2. Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion system and draft hood-equipped appliances shall be sized in accordance with Section 803.0 or other approved engineering methods.
  3. For sizing an individual gas vent for a single, draft hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet or exceeding seven times the draft hood outlet area.
  4. For sizing a gas vent connected to two appliances, with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or exceeding seven times the smaller draft hood outlet area.
  5. Approved engineering practices. [NFPA 54:12.7.3.1]
Type B and Type L vents sized in accordance with Section 802.6.2.1(3) or Section 802.6.2.1(4) shall extend in a generally vertical direction with offsets not exceeding 45 degrees except that a vent system having not more than one 60 degree offset shall be permitted. Any angle greater than 45 degrees from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.3.2]
The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturer's instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers' instructions. [NFPA 54:12.7.3.3]
Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods. [NFPA 54:12.7.3.4]
A common vent shall be permitted in multistory installations to vent Category I appliances located on more than one floor level, provided the venting system is designed and installed in accordance with approved engineering methods.

     For the purpose of this section, crawl spaces, basements, and attics shall be considered as floor levels. [NFPA 54:12.7.4.1]
Appliances connected to the common vent shall be located in rooms separated from an occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation, and dilution air that is not supplied from an occupiable space. (See Figure 802.6.3.1) [NFPA 54:12.7.4.2]

FIGURE 802.6.3.1
PLAN VIEW OF PRACTICAL SEPARATION METHOD FOR MULTISTORY GAS VENTING [NFPA 54: FIGURE A.12.7.4.2]
The size of the connectors and common segments of multistory venting systems for appliances listed for use with a Type B double-wall gas vent shall be in accordance with Table 803.2(1), provided all of the following apply:
  1. The available total height (H) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection tee.
  2. The size of the connector for a segment is determined from the appliance's gas input rate and available connector rise, and shall not be smaller than the draft hood outlet or flue collar size.
  3. The size of the common vertical vent segment, and of the interconnection tee at the base of that segment, is based on the total appliance's gas input rate entering that segment and its available total height. [NFPA 54:12.7.4.3]
FIGURE 802.6.3.2
USE OF MANIFOLDED COMMON VENT CONNECTOR
[NFPA 54:FIGURE F.1(k)]
Gas vents shall be supported and spaced in accordance with the manufacturer's installation instructions. [NFPA 54:12.7.5]
In those localities where solid and liquid fuels are used extensively, gas vents shall be permanently identified by a label attached to the wall or ceiling at a point where the vent connector enters the gas vent. The label shall read: "This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators. "The Authority Having Jurisdiction shall determine whether its area constitutes such a locality. [NFPA 54:12.7.6]
Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 of an inch (0.7722 mm) thick or of other approved, noncombustible, corrosion-resistant material. [NFPA 54:12.8.1]
Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99 percent winter design temperature is below 32°F (0°C). [NFPA 54:12.8.2]
The termination of single-wall metal pipe shall meet the following requirements:
  1. Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood outlet or flue collar.
  2. Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). (See Figure 802.5.4)
  3. An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe. [NFPA 54:12.8.3]
Single-wall metal pipe shall not be used as a vent in dwellings and residential occupancies. [NFPA 54:12.8.4.1]
Single-wall metal pipe shall be used for runs directly from the space in which the appliance is located through the roof or exterior wall to the outer air. A pipe passing through a roof shall extend without interruption through the roof flashing, roof jacket, or roof thimble. [NFPA 54:12.8.4.2]
Single-wall metal pipe shall not originate in an unoccupied attic or concealed space and shall not pass through an attic, inside wall, concealed space, or floor. [NFPA 54:12.8.4.3]
Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 802.7.3.3. Reduced clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors in Table 303.10.1. [NFPA 54:12.8.4.4]

TABLE 802.7.3.3
CLEARANCE FOR CONNECTORS*
[NFPA 54: TABLE 12.8.4.4]
MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches)
APPLIANCE LISTED TYPE B GAS
VENT MATERIAL
LISTED TYPE L
VENT MATERIAL
SINGLE-WALL
METAL PIPE
FACTORY-BUILT
CHIMNEY SECTIONS
Listed appliance with draft hoods and appliance listed for use
with Type B gas vents
As listed As listed 6 As listed
Residential boilers and furnaces with listed gas conversion
burner and with draft hood
6 6 9 As listed
Residential appliances listed for use with Type L vents Not permitted As listed 9 As listed
Listed gas-fired toilets Not permitted As listed As listed As listed
Unlisted residential appliances with draft hood Not permitted 6 9 As listed
Residential and low-heat appliance other than those above Not permitted 9 18 As listed
Medium-heat appliance Not permitted Not permitted 36 As listed
For SI units: 1 inch= 25.4 mm
* These clearances shall apply unless the installation instructions of a listed appliance or connector specify different clearances, in which case the listed clearances shall apply.
Single-wall metal pipe shall not pass through a combustible exterior wall unless guarded at the point of passage by a ventilated metal thimble not smaller than the following:
  1. For listed appliances with draft hoods and appliances listed for use with Type B gas vents, the thimble shall be a minimum of 4 inches (102 mm) larger in diameter than the metal pipe. Where there is a run of not less than 6 feet (1829 mm) of metal pipe in the opening between the draft hood outlet and the thimble, the thimble shall be a minimum of 2 inches (51 mm) larger in diameter than the metal pipe.
  2. For unlisted appliances having draft hoods, the thimble shall be a minimum of 6 inches (152 mm) larger in diameter than the metal pipe.
  3. For residential and low-heat appliances, the thimble shall be a minimum of 12 inches (305 mm) larger in diameter than the metal pipe.
Exception: In lieu of thimble protection, combustible material in the wall shall be removed a sufficient distance from the metal pipe to provide the specified clearance from such metal pipe to combustible material. Any material used to close up such opening shall be noncombustible. [NFPA 54:12.8.4.6]
Where a single-wall metal pipe passes through a roof constructed of combustible material, a noncombustible, nonventilating thimble shall be used at the point of passage. The thimble shall extend not less than 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed at the top. The thimble shall be sized in accordance with Section 802.7.3.4. [NFPA 54:12.8.4.5]
Single-wall metal piping shall comply with Section 802.7.4.1 through Section 802.7.4.3. [NFPA 54:12.8.5]
A venting system of a single-wall metal pipe shall be sized in accordance with one of the following methods and the appliance manufacturer's instructions:
  1. For a draft hood-equipped appliance, in accordance with Section 803.0.
  2. For a venting system for a single appliance with a draft hood, the areas of the connector and the pipe each shall not be less than the area of the appliance flue collar or draft hood outlet, whichever is smaller. The vent area shall not exceed seven times the draft hood outlet area.
  3. Other approved engineering methods. [NFPA 54:12.8.5(1)]
Where a single-wall metal pipe is used and has a shape other than round, it shall have an effective area equal to the effective area of the round pipe for which it is substituted, and the internal dimension of the pipe shall be not less than 2 inches (51 mm). [NFPA 54:12.8.5(2)]
The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached. [NFPA 54:12.8.5(3)]
Portions of single-wall metal pipe shall be supported for the design and weight of the material employed. [NFPA 54:12.8.6]
Single-wall metal pipe shall comply with the marking provisions of Section 802.6.5. [NFPA 54:12.8.7]
A mechanical draft venting system shall terminate at least 3 feet (914 mm) above any forced air inlet located within 10 feet (3048 mm). (See Figure 802.8)

Exceptions:
  1. This provision shall not apply to the combustion-air intake of a direct-vent appliance.
  2. This provision shall not apply to the separation of the integral outdoor-air inlet and flue gas discharge of listed outdoor appliances. [NFPA 54:12.9.1]


FIGURE 802.8
EXIT TERMINALS OF MECHANICAL DRAFT AND DIRECT-VENT VENTING SYSTEMS
[NFPA 54:FIGURE A.12.9]
A mechanical draft venting system of other than direct-vent type shall terminate not less than 4 feet (1219 mm) below, 4 feet (1219 mm) horizontally from, or 1 foot (305 mm) above a door, operable window, or gravity air inlet into a building. The bottom of the vent terminal shall be located not less than 12 inches (305 mm) above finished ground level. [NFPA 54:12.9.2]
The vent terminal of a direct-vent appliance with an input of 10000 Btu/h (3 kW) or less shall be located at least 6 inches (152 mm) from any air opening into a building, an appliance with an input over 10000 Btu/h (3 kW) but not over 50000 Btu/h (14.7 kW) shall be installed with a 9 inch (229 mm) vent termination clearance, and an appliance with an input exceeding 50000 Btu/h (14.7 kW) shall have at least a 12 inch (305 mm) vent termination clearance. The bottom of the vent terminal and the air intake shall be located at least 12 inches (305 mm) above finished ground level. [NFPA 54:12.9.3]
Through-the-wall vents for Category II and Category IV appliances and noncategorized condensing appliances shall not terminate over public walkways or over an area where condensate or vapor could create a nuisance or hazard or could be detrimental to the operation of regulators, relief valves, or other equipment. Where local experience indicates that condensate is a problem with Category I and Category III appliances, this provision shall also apply.

     Drains for condensate shall be installed in accordance with the appliance and the vent manufacturer's installation instructions. [NFPA 54:12.9.4]
Where vents, including those for direct-vent appliances or combustion air intake pipes, penetrate outside walls of buildings, the annular spaces around such penetrations shall be permanently sealed using approved materials to prevent entry of combustion products into the building. [NFPA 54:12.9.5]
Vent systems for Category IV appliances that terminate through an outside wall of a building and discharge flue gases perpendicular to the adjacent wall shall be located not less than 10 feet (3048 mm) horizontally from an operable opening in an adjacent building.

Exception: This shall not apply to vent terminals that are 2 feet (610 mm) or more above or 25 feet (7620 mm) or more below operable openings. [NFPA 54:12.9.6]
Provision shall be made to collect and dispose of condensate from venting systems serving Category II and Category IV appliances and noncategorized condensing appliances in accordance with Section 802.8.3. [NFPA 54:12.10.1]
Where local experience indicates that condensation is a problem, provision shall be made to drain off and dispose of condensate from venting systems serving Category I and Category III appliances in accordance with Section 802.8.3. [NFPA 54:12.10.2]
A vent connector shall be used to connect an appliance to a gas vent, chimney, or single-wall metal pipe, except where the gas vent, chimney, or single-wall metal pipe is directly connected to the appliance. [NFPA 54:12.11.1]
A vent connector shall be made of noncombustible, corrosion resistant material capable of withstanding the vent gas temperature produced by the appliance and of a thickness to withstand physical damage. [NFPA 54:12.11.2.1]
Where the vent connector used for an appliance having a draft hood or a Category I appliance is located in or passes through an unconditioned area, attic or crawl space, that portion of the vent connector shall be listed Type B, Type L, or listed vent material having equivalent insulation qualities.

Exception: Single-wall metal pipe located within the exterior walls of the building and located in an unconditioned area other than an attic or a crawl space having a local 99 percent winter design temperature of 5°F (-15°C) or higher. [NFPA 54:12.11.2.2]
Vent connectors for residential-type appliances shall comply with the following:
  1. Vent connectors for listed appliances having draft hoods, appliances having draft hoods and equipped with listed conversion burners, and Category I appliances that are not installed in attics, crawl spaces, or other unconditioned areas shall be one of the following:
    1. Type B or Type L vent material.
    2. Galvanized sheet steel not less than 0.018 of an inch (0.457 mm) thick.
    3. Aluminum (1100 or 3003 alloy or equivalent) sheet not less than 0.027 of an inch (0.686 mm) thick.
    4. Stainless steel sheet not less than 0.012 of an inch (0.305 mm) thick.
    5. Smooth interior wall metal pipe having resistance to heat and corrosion equal to or greater than that of Section 802.10.1.2(1)(b), Section 802.10.1.2(1)(c), or Section 802.10.1.2(1)(d).
    6. A listed vent connector.
  2. Vent connectors shall not be covered with insulation.
Exception: Listed insulated vent connectors shall be installed in accordance with the manufacturer's installation instructions. [NFPA 54:12.11.2.3]
A vent connector for a nonresidential low-heat appliance shall be a factory-built chimney section or steel pipe having resistance to heat and corrosion equivalent to that for the appropriate galvanized pipe as specified in Table 802.10.1.3. Factory-built chimney sections shall be joined together in accordance with the chimney manufacturer's instructions. [NFPA 54:12.11.2.4]

TABLE 802.10.1.3
MINIMUM THICKNESS FOR GALVANIZED STEEL VENT CONNECTORS FOR LOW-HEAT APPLIANCES
[NFPA 54: TABLE 12.11.2.4]
DIAMETER OF CONNECTOR
(inches)
MINIMUM THICKNESS
(inches)
Less than 6 0.019
6 to less than 10 0.023
10 to 12 inclusive 0.029
14 to 16 inclusive 0.034
Over 16 0.056
For SI units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m2
Vent connectors for medium-heat appliances shall be constructed of factory-built, medium-heat chimney sections or steel of a thickness not less than that specified in Table 802.10.1.4 and shall comply with the following:
  1. A steel vent connector for an appliance with a vent gas temperature in excess of 1000°F (538°C) measured at the entrance to the connector shall be lined with medium-duty fire brick or the equivalent.
  2. The lining shall be at least 21/2 inches (64 mm) thick for a vent connector having a diameter or greatest cross-sectional dimension of 18 inches (457 mm) or less.
  3. The lining shall be at least 41/2 inches (114 mm) thick laid on the 41/2 inches (114 mm) bed for a vent connector having a diameter or greatest cross-sectional dimension greater than 18 inches (457 mm).
  4. Factory-built chimney sections, if employed, shall be joined together in accordance with the chimney manufacturer's instructions. [NFPA 54:12.11.2.5]
TABLE 802.10.1.4
MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR MEDIUM-HEAT APPLIANCES
[NFPA 54:TABLE 12.11.2.5]
VENT CONNECTOR SIZE
DIAMETER
(inches)
AREA
(square inches)
MINIMUM THICKNESS
(inches)
Up to 14 Up to 154 0.053
Over 14 to 16 154 to 201 0.067
Over 16 to 18 201 to 254 0.093
Over 18 Larger than 254 0.123
For SI units: 1 inch= 25.4 mm, 1 square inch= 0.000645 m2
A vent connector for an appliance with a single draft hood or for a Category I fan-assisted combustion system appliance shall be sized and installed in accordance with Section 803.0 or other approved engineering methods. [NFPA 54:12.11.3.1]
For a single appliance having more than one draft hood outlet or flue collar, the manifold shall be constructed according to the instructions of the appliance manufacturer. Where there are no instructions, the manifold shall be designed and constructed in accordance with approved engineering practices. As an alternative method, the effective area of the manifold shall equal the combined area of the flue collars or draft hood outlets, and the vent connectors shall have a minimum 1 foot (305 mm) rise. [NFPA 54:12.11.3.2]
Where two or more appliances are connected to a common vent or chimney, each vent connector shall be sized in accordance with Section 803.0 or other approved engineering methods. [NFPA 54:12.11.3.3]

     As an alternative method applicable where the appliances are draft hood-equipped, each vent connector shall have an effective area not less than the area of the draft hood outlet of the appliance to which it is connected. [NFPA 54:12.11.3.4]
Where two or more appliances are vented through a common vent connector or vent manifold, the common vent connector or vent manifold shall be located at the highest level consistent with available headroom and clearance to combustible material and sized in accordance with Section 803.0 or other approved engineering methods. [NFPA 54:12.11.3.5]

     As an alternative method applicable only where there are two draft hood-equipped appliances, the effective area of the common vent connector or vent manifold and all junction fittings shall be not less than the area of the larger vent connector plus 50 percent of the area of the smaller flue collar outlet [NFPA 54:12.11.3.6]
Where the size of a vent connector is increased to overcome installation limitations and obtain connector capacity equal to the appliance input, the size increase shall be made at the appliance draft hood outlet. [NFPA 54:12.11.3.7]
Where two or more openings are provided into one chimney flue or vent, either of the following shall apply:
  1. The openings shall be at different levels.
  2. The connectors shall be attached to the vertical portion of the chimney or vent at an angle of 45 degrees or less relative to the vertical. [NFPA 54:12.11.4.1]
Where two or more vent connectors enter a common vent, chimney flue, or single-wall metal pipe, the smaller connector shall enter at the highest level consistent with the available headroom or clearance to combustible material. [NFPA 54:12.11.4.2]
Vent connectors serving Category I appliances shall not be connected to a portion of a mechanical draft system operating under positive static pressure, such as those serving Category III or Category IV appliances. [NFPA 54:12.11.4.3]
Minimum clearances from vent connectors to combustible material shall comply with Table 802.7.3.3.

Exception: The clearance between a vent connector and combustible material shall be permitted to be reduced where the combustible material is protected as specified for vent connectors in Table 303.10.1. [NFPA 54:12.11.5]
Joints between sections of connector piping and connections to flue collars or draft hood outlets shall be fastened in accordance with one of the following methods:
  1. Sheet metal screws.
  2. Vent connectors of listed vent material assembled and connected to flue collars or draft hood outlets in accordance with the manufacturer's instructions.
  3. Other approved means. [NFPA 54:12.11.6]
A vent connector shall be installed without any dips or sags and shall slope upward toward the vent or chimney at least 1/4 inch per foot (20.8 mm/m).

Exception: Vent connectors attached to a mechanical draft system installed in accordance with appliance and the draft system manufacturers' instructions. [NFPA 54:12.11.7]
The length of vent connectors shall comply with Section 802.10.7.1 or Section 802.10.7.2.
The maximum horizontal length of a single-wall connector shall be 75 percent of the height of the chimney or vent except for engineered systems. [NFPA 54:12.11.8.1]
The maximum horizontal length of a Type B double-wall connector shall be 100 percent of the height of the chimney or vent, except for engineered systems. The maximum length of an individual connector for a chimney or vent system serving multiple appliances, from the appliance outlet to the junction with the common vent or another connector, shall be 100 percent of the height of the chimney or vent. [NFPA 54:12.11.8.2]
A vent connector shall be supported for the design and weight of the material employed to maintain clearances and prevent physical damage and separation of joints. [NFPA 54:12.11.9]
Where entering a flue in a masonry or metal chimney, the vent connector shall be installed above the extreme bottom to avoid stoppage. Where a thimble or slip joint is used to facilitate removal of the connector, the connector shall be attached to or inserted into the thimble or slip joint to prevent the connector from falling out. Means shall be employed to prevent the connector from entering so far as to restrict the space between its end and the opposite wall of the chimney flue. [NFPA 54:12.11.10]
The entire length of a vent connector shall be readily accessible for inspection, cleaning, and replacement. [NFPA 54:12.11.11]
A vent connector shall not be connected to a chimney flue serving a fireplace unless the fireplace flue opening is permanently sealed. [NFPA 54:12.11.12]
A vent connector shall not pass through a ceiling, floor, or fire-resistance-rated wall. A single-wall metal pipe connector shall not pass through an interior wall.

Exception: Vent connectors made of listed Type B or Type L vent material and serving listed appliances with draft hoods and other appliances listed for use with Type B gas vents that pass through walls or partitions constructed of combustible material shall be installed with not less than the listed clearance to combustible material.
Vent connectors for medium-heat appliances shall not pass through walls or partitions constructed of combustible material. [NFPA 54:12.11.13.2]
The vent connectors for Category II, Category III, and Category IV appliances shall be in accordance with Section 802.4 through Section 802.4.3. [NFPA 54:12.12]
Vented appliances shall be installed with draft hoods.

Exception: Dual oven-type combination ranges; incinerators; direct-vent appliances; fan-assisted combustion system appliances; appliances requiring chimney draft for operation; single firebox boilers equipped with conversion burners with inputs exceeding 400 000 Btu/h (117 kW); appliances equipped with blast, power, or pressure burners that are not listed for use with draft hoods; and appliances designed for forced venting.
A draft hood supplied with or forming a part of listed vented appliances shall be installed without alteration, exactly as furnished and specified by the appliance manufacturer. [NFPA 54:12.13.2]

     Where a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, be of a listed or approved type, and, in the absence of other instructions, be of the same size as the appliance flue collar. Where a draft hood is required with a conversion burner, it shall be of a listed or approved type. [NFPA 54:12.13.2.1]

     Where a draft hood of special design is needed or preferable, the installation shall be approved and in accordance with the recommendations of the appliance manufacturer. [NFPA 54:12.13.2.2]
Where a draft control device is part of the appliance or is supplied by the appliance manufacturer, it shall be installed in accordance with the manufacturer's instructions. In the absence of manufacturer's instructions, the device shall be attached to the flue collar of the appliance or as near to the appliance as practical. [NFPA 54:12.13.3]
Appliances requiring controlled chimney draft shall be permitted to be equipped with listed double-acting barometric draft regulators installed and adjusted in accordance with the manufacturer's installation instructions. [NFPA 54:12.13.4]
Draft hoods and barometric draft regulators shall be installed in the same room or enclosure as the appliance in such a manner as to prevent a difference in pressure between the hood or regulator and the combustion air supply. [NFPA 54:12.13.5]
Draft hoods and draft regulators shall be installed in the position for which they were designed with reference to the horizontal and vertical planes and shall be located so that the relief opening is not obstructed by a part of the appliance or adjacent construction. The appliance and its draft hood shall be located so that the relief opening is accessible for checking vent operation. [NFPA 54:12.13.6]
A draft hood shall be located so that its relief opening is not less than 6 inches (152 mm) from a surface except that of the appliance it serves and the venting system to which the draft hood is connected. Where a greater or lesser clearance is indicated on the appliance label, the clearance shall not be less than that specified on the label. Such clearances shall not be reduced. [NFPA 54:12.13.7]
A manually operated damper shall not be placed in an appliance vent connector. Fixed baffles shall not be classified as manually operated dampers. [NFPA 54:12.14]
Devices that retard the flow of vent gases shall not be installed in a vent connector, chimney, or vent. The following shall not be considered as obstructions:
  1. Draft regulators and safety controls specifically listed for installation in venting systems and installed in accordance with the manufacturer's installation instructions.
  2. Approved draft regulators and safety controls designed and installed in accordance with approved engineering methods.
  3. Listed heat reclaimers and automatically operated vent dampers installed in accordance with the manufacturer's installation instructions.
  4. Vent dampers serving listed appliances installed in accordance with Section 803.1 or Section 803.2 or other approved engineering methods.
  5. Approved economizers, heat reclaimers, and recuperators installed in venting systems of appliances not required to be equipped with draft hoods, provided the appliance manufacturer's installation instructions cover the installation of such a device in the venting system and performance in accordance with Section 802.3 and Section 802.3.1 is obtained. [NFPA 54:12.16]
An automatically operated vent damper shall be of a listed type. [NFPA 54:12.15]
Automatically operated vent dampers for oil-fired appliances shall comply with UL 17. The automatic damper control shall comply with UL 378.
Table 803.1.2(1) through Table 803.1.2(6) 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:
  1. The maximum capacity of the vent system shall be determined using the NAT Max column.
  2. 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]
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:
  1. The total vent height (H) is not less than 10 feet (3048 mm).
  2. 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.
  3. Vents for appliance draft hood outlets or flue collars exceeding 12 inches (305 mm) in diameter are not reduced more than two table sizes.
  4. The maximum capacity listed in the tables for a fan-assisted appliance is reduced by 10 percent (0.90 x maximum table capacity).
  5. 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]
Single-appliance venting configurations with zero (0) lateral lengths in Table 803.1.2(1), Table 803.1.2(2), and Table 803.1.2(5) shall not have elbows in the venting system. Single-appliance venting with lateral length, include two 90 degree elbows. For each additional elbow up to and including 45 degrees, the maximum capacity listed in the venting tables shall be reduced by 5 percent. For each additional elbow greater than 45 degrees up to and including 90 degrees, 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 all offsets combined shall not exceed that specified in Table 803.1.2(1) through Table 803.1.2(5). [NFPA 54:13.1.3]

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)/1.8
FIGURE 803.1.2(6)
RANGE OF WINTER DESIGN TEMPERATURES USED IN ANALYZING EXTERIOR MASONRY CHIMNEYS IN THE UNITED STATES
[NFPA 54: FIGURE F.2.4]


TABLE 803.1.2(1)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(a)]*
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: CONNECTED DIRECTLY TO VENT
VENT DIAMETER - D (inch)
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 0 0 78 46 0 152 86 0 251 141 0 375 205 0 524 285
2 13 51 36 18 97 67 27 157 105 32 232 157 44 321 217
4 21 49 34 30 94 64 39 153 103 50 227 153 66 316 211
6 25 46 32 36 91 61 47 149 100 59 223 149 78 310 205
8 0 0 84 50 0 165 94 0 276 155 0 415 235 0 583 320
2 12 57 40 16 109 75 25 178 120 28 263 180 42 365 247
5 23 53 38 32 103 71 42 171 115 53 255 173 70 356 237
8 28 49 35 39 98 66 51 164 109 64 247 165 84 347 227
10 0 0 88 53 0 175 100 0 295 166 0 447 255 0 631 345
2 12 61 42 17 118 81 23 194 129 26 289 195 40 402 273
5 23 57 40 32 113 77 41 187 124 52 280 188 68 392 263
10 30 51 36 41 104 70 54 176 115 67 267 175 88 376 245
15 0 0 94 58 0 191 112 0 327 187 0 502 285 0 716 390
2 11 69 48 15 136 93 20 226 150 22 339 225 38 475 316
5 22 65 45 30 130 87 39 219 142 49 330 217 64 463 300
10 29 59 41 40 121 82 51 206 135 64 315 208 84 445 288
15 35 53 37 48 112 76 61 195 128 76 301 198 98 429 275
20 0 0 97 61 0 202 119 0 349 202 0 540 307 0 776 430
2 10 75 51 14 149 100 18 250 166 20 377 249 33 531 346
5 21 71 48 29 143 96 38 242 160 47 367 241 62 519 337
10 28 64 44 38 133 89 50 229 150 62 351 228 81 499 321
15 34 58 40 46 124 84 59 217 142 73 337 217 94 481 308
20 48 52 35 55 116 78 69 206 134 84 322 206 107 464 295
30 0 0 100 64 0 213 128 0 374 220 0 587 336 0 853 475
2 9 81 56 13 166 112 14 283 185 18 432 280 27 613 394
5 21 77 54 28 160 108 36 275 176 45 421 273 58 600 385
10 27 70 50 37 150 102 48 262 171 59 405 261 77 580 371
15 33 64 NA 44 141 96 57 249 163 70 389 249 90 560 357
20 56 58 NA 53 132 90 66 237 154 80 374 237 102 542 343
30 NA NA NA 73 113 NA 88 214 NA 104 346 219 131 507 321
50 0 0 101 67 0 216 134 0 397 232 0 633 363 0 932 518
2 8 86 61 11 183 122 14 320 206 15 497 314 22 715 445
5 20 82 NA 27 177 119 35 312 200 43 487 308 55 702 438
10 26 76 NA 35 168 114 45 299 190 56 471 298 73 681 426
15 59 70 NA 42 158 NA 54 287 180 66 455 288 85 662 413
20 NA NA NA 50 149 NA 63 275 169 76 440 278 97 642 401
30 NA NA NA 69 131 NA 84 250 NA 99 410 259 123 605 376
100 0 NA NA NA 0 218 NA 0 407 NA 0 665 400 0 997 560
2 NA NA NA 10 194 NA 12 354 NA 13 566 375 18 831 510
5 NA NA NA 26 189 NA 33 347 NA 40 557 369 52 820 504
10 NA NA NA 33 182 NA 43 335 NA 53 542 361 68 801 493
15 NA NA NA 40 174 NA 50 321 NA 62 528 353 80 782 482
20 NA NA NA 47 166 NA 59 311 NA 71 513 344 90 763 471
30 NA NA NA NA NA NA 78 290 NA 92 483 NA 115 726 449
50 NA NA NA NA NA NA NA NA NA 147 428 NA 180 651 405
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.


NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: CONNECTED DIRECTLY TO VENT
VENT DIAMETER - D (inch)
8 9 10 12 14
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 0 0 698 370 0 897 470 0 1121 570 0 1645 850 0 2267 1170
2 53 425 285 63 543 370 75 675 455 103 982 650 138 1346 890
4 79 419 279 93 536 362 110 668 445 147 975 640 191 1338 880
6 93 413 273 110 530 354 128 661 435 171 967 630 219 1330 870
8 0 0 780 415 0 1006 537 0 1261 660 0 1858 970 0 2571 1320
2 50 483 322 60 619 418 71 770 515 98 1124 745 130 1543 1020
5 83 473 313 99 607 407 115 758 503 154 1110 733 199 1528 1010
8 99 463 303 117 596 396 137 746 490 180 1097 720 231 1514 1000
10 0 0 847 450 0 1096 585 0 1377 720 0 2036 1060 0 2825 1450
2 48 533 355 57 684 457 68 852 560 93 1244 850 124 1713 1130
5 81 522 346 95 671 446 112 839 547 149 1229 829 192 1696 1105
10 104 504 330 122 651 427 142 817 525 187 1204 795 238 1669 1080
15 0 0 970 525 0 1263 682 0 1596 840 0 2380 1240 0 3323 1720
2 45 633 414 53 815 544 63 1019 675 86 1495 985 114 2062 1350
5 76 620 403 90 800 529 105 1003 660 140 1476 967 182 2041 1327
10 99 600 386 116 777 507 135 977 635 177 1446 936 227 2009 1289
15 115 580 373 134 755 491 155 953 610 202 1418 905 257 1976 1250
20 0 0 1057 575 0 1384 752 0 1756 930 0 2637 1350 0 3701 1900
2 41 711 470 50 917 612 59 1150 755 81 1694 1100 107 2343 1520
5 73 697 460 86 902 599 101 1133 738 135 1674 1079 174 2320 1498
10 95 675 443 112 877 576 130 1105 710 172 1641 1045 220 2282 1460
15 111 654 427 129 853 557 150 1078 688 195 1609 1018 248 2245 1425
20 125 634 410 145 830 537 167 1052 665 217 1578 990 273 2210 1390
30 0 0 1173 650 0 1548 855 0 1977 1060 0 3004 1550 0 4252 2170
2 33 826 535 42 1072 700 54 1351 865 74 2004 1310 98 2786 1800
5 69 811 524 82 1055 688 96 1332 851 127 1981 1289 164 2759 1775
10 91 788 507 107 1028 668 125 1301 829 164 1944 1254 209 2716 1733
15 105 765 490 124 1002 648 143 1272 807 187 1908 1220 237 2674 1692
20 119 743 473 139 977 628 160 1243 784 207 1873 1185 260 2633 1650
30 149 702 444 171 929 594 195 1189 745 246 1807 1130 305 2555 1585
50 0 0 1297 708 0 1730 952 0 2231 1195 0 3441 1825 0 4934 2550
2 26 975 615 33 1276 813 41 1620 1010 66 2431 1513 86 3409 2125
5 65 960 605 77 1259 798 90 1600 996 118 2406 1495 151 3380 2102
10 86 935 589 101 1230 773 118 1567 972 154 2366 1466 196 3332 2064
15 100 911 572 117 1203 747 136 1536 948 177 2327 1437 222 3285 2026
20 113 888 556 131 1176 722 151 1505 924 195 2288 1408 244 3239 1987
30 141 844 522 161 1125 670 183 1446 876 232 2214 1349 287 3150 1910
100 0 0 1411 770 0 1908 1040 0 2491 1310 0 3925 2050 0 5729 2950
2 21 1155 700 25 1536 935 30 1975 1170 44 3027 1820 72 4313 2550
5 60 1141 692 71 1519 926 82 1955 1159 107 3002 1803 136 4282 2531
10 80 1118 679 94 1492 910 108 1923 1142 142 2961 1775 180 4231 2500
15 93 1095 666 109 1465 895 126 1892 1124 163 2920 1747 206 4182 2469
20 105 1073 653 122 1438 880 141 1861 1107 181 2880 1719 226 4133 2438
30 131 1029 627 149 1387 849 170 1802 1071 215 2803 1663 265 4037 2375
50 197 944 575 217 1288 787 241 1688 1000 292 2657 1550 350 3856 2250
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


NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: CONNECTED DIRECTLY TO VENT
VENT DIAMETER - D (inch)
16 18 20 22 24
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 0 0 2983 1530 0 3802 1960 0 4721 2430 0 5737 2950 0 6853 3520
2 178 1769 1170 225 2250 1480 296 2782 1850 360 3377 2220 426 4030 2670
4 242 1761 1160 300 2242 1475 390 2774 1835 469 3370 2215 555 4023 2660
6 276 1753 1150 341 2235 1470 437 2767 1820 523 3363 2210 618 4017 2650
8 0 0 3399 1740 0 4333 2220 0 5387 2750 0 6555 3360 0 7838 4010
2 168 2030 1340 212 2584 1700 278 3196 2110 336 3882 2560 401 4634 3050
5 251 2013 1330 311 2563 1685 398 3180 2090 476 3863 2545 562 4612 3040
8 289 2000 1320 354 2552 1670 450 3163 2070 537 3850 2530 630 4602 3030
10 0 0 3742 1925 0 4782 2450 0 5955 3050 0 7254 3710 0 8682 4450
2 161 2256 1480 202 2868 1890 264 3556 2340 319 4322 2840 378 5153 3390
5 243 2238 1461 300 2849 1871 382 3536 2318 458 4301 2818 540 5132 3371
10 298 2209 1430 364 2818 1840 459 3504 2280 546 4268 2780 641 5099 3340
15 0 0 4423 2270 0 5678 2900 0 7099 3620 0 8665 4410 0 10393 5300
2 147 2719 1770 186 3467 2260 239 4304 2800 290 5232 3410 346 6251 4080
5 229 2696 1748 283 3442 2235 355 4278 2777 426 5204 3385 501 6222 4057
10 283 2659 1712 346 3402 2193 432 4234 2739 510 5159 3343 599 6175 4019
15 318 2623 1675 385 3363 2150 479 4192 2700 564 5115 3300 665 6129 3980
20 0 0 4948 2520 0 6376 3250 0 7988 4060 0 9785 4980 0 11753 6000
2 139 3097 2000 175 3955 2570 220 4916 3200 269 5983 3910 321 7154 4700
5 219 3071 1978 270 3926 2544 337 4885 3174 403 5950 3880 475 7119 4662
10 273 3029 1940 334 3880 2500 413 4835 3130 489 5896 3830 573 7063 4600
15 306 2988 1910 372 3835 2465 459 4786 3090 541 5844 3795 631 7007 4575
20 335 2948 1880 404 3791 2430 495 4737 3050 585 5792 3760 689 6953 4550
30 0 0 5725 2920 0 7420 3770 0 9341 4750 0 11483 5850 0 13848 7060
2 127 3696 2380 159 4734 3050 199 5900 3810 241 7194 4650 285 8617 5600
5 206 3666 2350 252 4701 3020 312 5863 3783 373 7155 4622 439 8574 5552
10 259 3617 2300 316 4647 2970 386 5803 3739 456 7090 4574 535 8505 5471
15 292 3570 2250 354 4594 2920 431 5744 3695 507 7026 4527 590 8437 5391
20 319 3523 2200 384 4542 2870 467 5686 3650 548 6964 4480 639 8370 5310
30 369 3433 2130 440 4442 2785 540 5574 3565 635 6842 4375 739 8239 5225
50 0 0 6711 3440 0 8774 4460 0 11129 5635 0 13767 6940 0 16694 8430
2 113 4554 2840 141 5864 3670 171 7339 4630 209 8980 5695 251 10788 6860
5 191 4520 2813 234 5826 3639 283 7295 4597 336 8933 5654 394 10737 6818
10 243 4464 2767 295 5763 3585 355 7224 4542 419 8855 5585 491 10652 6749
15 274 4409 2721 330 5701 3534 396 7155 4511 465 8779 5546 542 10570 6710
20 300 4356 2675 361 5641 3481 433 7086 4479 506 8704 5506 586 10488 6670
30 347 4253 2631 412 5523 3431 494 6953 4421 577 8557 5444 672 10328 6603
100 0 0 7914 4050 0 10485 5300 0 13454 6700 0 16817 8600 0 20578 10300
2 95 5834 3500 120 7591 4600 138 9577 5800 169 11803 7200 204 14264 8800
5 172 5797 3475 208 7548 4566 245 9528 5769 293 11748 7162 341 14204 8756
10 223 5737 3434 268 7478 4509 318 9447 5717 374 11658 7100 436 14105 8683
15 252 5678 3392 304 7409 4451 358 9367 5665 418 11569 7037 487 14007 8610
20 277 5619 3351 330 7341 4394 387 9289 5613 452 11482 6975 523 13910 8537
30 319 5505 3267 378 7209 4279 446 9136 5509 514 11310 6850 592 13720 8391
50 415 5289 3100 486 6956 4050 572 8841 5300 659 10979 6600 752 13354 8100
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 803.1.2(2)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(b)]*
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
VENT DIAMETER - D (inch)
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 0 38 77 45 59 151 85 85 249 140 126 373 204 165 522 284
2 39 51 36 60 96 66 85 156 104 123 231 156 159 320 213
4 NA NA 33 74 92 63 102 152 102 146 225 152 187 313 208
6 NA NA 31 83 89 60 114 147 99 163 220 148 207 307 203
8 0 37 83 50 58 164 93 83 273 154 123 412 234 161 580 319
2 39 56 39 59 108 75 83 176 119 121 261 179 155 263 246
5 NA NA 37 77 102 69 107 168 114 151 252 171 193 352 235
8 NA NA 33 90 95 64 122 161 107 175 243 163 223 342 225
10 0 37 87 53 57 174 99 82 293 165 120 444 254 158 628 344
2 39 61 41 59 117 80 82 193 128 119 287 194 153 400 272
5 52 56 39 76 111 76 105 185 122 148 277 186 190 388 261
10 NA NA 34 97 100 68 132 171 112 188 261 171 237 369 241
15 0 36 93 57 56 190 111 80 325 186 116 499 283 153 713 388
2 38 69 47 57 136 93 80 225 149 115 337 224 148 473 314
5 51 63 44 75 128 86 102 216 140 144 326 217 182 459 298
10 NA NA 39 95 116 79 128 201 131 182 308 203 228 438 284
15 NA NA NA NA NA 72 158 186 124 220 290 192 272 418 269
20 0 35 96 60 54 200 118 78 346 201 114 537 306 149 772 428
2 37 74 50 56 148 99 78 248 165 113 375 248 144 528 344
5 50 68 47 73 140 94 100 239 158 141 363 239 178 514 334
10 NA NA 41 93 129 86 125 223 146 177 344 224 222 491 316
15 NA NA NA NA NA 80 155 208 136 216 325 210 264 469 301
20 NA NA NA NA NA NA 186 192 126 254 306 196 309 448 285
30 0 34 99 63 53 211 127 76 372 219 110 584 334 144 849 472
2 37 80 56 55 164 111 76 281 183 109 429 279 139 610 392
5 49 74 52 72 157 106 98 271 173 136 417 271 171 595 382
10 NA NA NA 91 144 98 122 255 168 171 397 257 213 570 367
15 NA NA NA 115 131 NA 151 239 157 208 377 242 255 547 349
20 NA NA NA NA NA NA 181 223 NA 246 357 228 298 524 333
30 NA NA NA NA NA NA NA NA NA NA NA NA 389 477 305
50 0 33 99 66 51 213 133 73 394 230 105 629 361 138 928 515
2 36 84 61 53 181 121 73 318 205 104 495 312 133 712 443
5 48 80 NA 70 174 117 94 308 198 131 482 305 164 696 435
10 NA NA NA 89 160 NA 118 292 186 162 461 292 203 671 420
15 NA NA NA 112 148 NA 145 275 174 199 441 280 244 646 405
20 NA NA NA NA NA NA 176 257 NA 236 420 267 285 622 389
30 NA NA NA NA NA NA NA NA NA 315 376 NA 373 573 NA
100 0 NA NA NA 49 214 NA 69 403 NA 100 659 395 131 991 555
2 NA NA NA 51 192 NA 70 351 NA 98 563 373 125 828 508
5 NA NA NA 67 186 NA 90 342 NA 125 551 366 156 813 501
10 NA NA NA 85 175 NA 113 324 NA 153 532 354 191 789 486
15 NA NA NA 132 162 NA 138 310 NA 188 511 343 230 764 473
20 NA NA NA NA NA NA 168 295 NA 224 487 NA 270 739 458
30 NA NA NA NA NA NA 231 264 NA 301 448 NA 355 685 NA
50 NA NA NA NA NA NA NA NA NA NA NA NA 540 584 NA
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.


NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
VENT DIAMETER - D (inch)
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 0 211 695 369 267 894 469 371 1118 569 537 1639 849
2 201 423 284 251 541 368 347 673 453 498 979 648
4 237 416 277 295 533 360 409 664 443 584 971 638
6 263 409 271 327 526 352 449 656 433 638 962 627
8 0 206 777 141 258 1002 536 360 1257 658 521 1852 967
2 197 482 321 246 617 417 339 768 513 486 1120 743
5 245 470 311 305 604 404 418 754 500 598 1104 730
8 280 458 300 344 591 392 470 740 486 665 1089 715
10 0 202 844 449 253 1093 584 351 1373 718 507 2031 1057
2 193 531 354 242 681 456 332 849 559 475 1242 848
5 241 518 344 299 667 443 409 834 544 584 1224 825
10 296 497 325 363 643 423 492 808 520 688 1194 788
15 0 195 966 523 244 1259 681 336 1591 838 488 2374 1237
2 187 631 413 232 812 543 319 1015 673 457 1491 983
5 231 616 400 287 795 526 392 997 657 562 1469 963
10 284 592 381 349 768 501 470 966 628 664 1433 928
15 334 568 367 404 742 484 540 937 601 750 1399 894
20 0 190 1053 573 238 1379 750 326 1751 927 473 2631 1346
2 182 708 468 227 914 611 309 1146 754 443 1689 1098
5 224 692 457 279 896 596 381 1126 734 547 1665 1074
10 277 666 437 339 866 570 457 1092 702 646 1626 1037
15 325 640 419 393 838 549 526 1060 677 730 1587 1005
20 374 616 400 448 810 526 592 1028 651 808 1550 973
30 0 184 1168 647 229 1542 852 312 1971 1056 454 2996 1545
2 175 823 533 219 1069 698 296 1346 863 424 1999 1308
5 215 806 521 269 1049 684 366 1324 846 524 1971 1283
10 265 777 501 327 1017 662 440 1287 821 620 1927 1243
15 312 750 481 379 985 638 507 1251 794 702 1884 1205
20 360 723 461 433 955 615 570 1216 768 780 1841 1166
30 461 670 426 541 895 574 704 1147 720 937 1759 1101
50 0 176 1292 704 220 1724 948 295 2223 1189 428 3432 1818
2 168 971 613 209 1273 811 280 1615 1007 401 2426 1509
5 204 953 602 257 1252 795 347 1591 991 496 2396 1490
10 253 923 583 313 1217 765 418 1551 963 589 2347 1455
15 299 894 562 363 1183 736 481 1512 934 668 2299 1421
20 345 866 543 415 1150 708 544 1473 906 741 2251 1387
30 442 809 502 521 1086 649 674 1399 848 892 2159 1318
100 0 166 1404 765 207 1900 1033 273 2479 1300 395 3912 2042
2 158 1152 698 196 1532 933 259 1970 1168 371 3021 1817
5 194 1134 688 240 1511 921 322 1945 1153 460 2990 1796
10 238 1104 672 293 1477 902 389 1905 1133 547 2938 1763
15 281 1075 656 342 1443 884 447 1865 1110 618 2888 1730
20 325 1046 639 391 1410 864 507 1825 1087 690 2838 1696
30 418 988 NA 491 1343 824 631 1747 1041 834 2739 1627
50 617 866 NA 711 1205 NA 895 1591 NA 1138 2547 1489
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 803.1.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(c)]*
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
TYPE B DOUBLE-WALL 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 NA NA 28 NA NA 52 NA NA 86 NA NA 130 NA NA 180
5 NA NA 25 NA NA 49 NA NA 82 NA NA 117 NA NA 165
8 2 NA NA 29 NA NA 55 NA NA 93 NA NA 145 NA NA 198
5 NA NA 26 NA NA 52 NA NA 88 NA NA 134 NA NA 183
8 NA NA 24 NA NA 48 NA NA 83 NA NA 127 NA NA 175
10 2 NA NA 31 NA NA 61 NA NA 103 NA NA 162 NA NA 221
5 NA NA 28 NA NA 57 NA NA 96 NA NA 148 NA NA 204
10 NA NA 25 NA NA 50 NA NA 87 NA NA 139 NA NA 191
15 2 NA NA 35 NA NA 67 NA NA 114 NA NA 179 53 475 250
5 NA NA 35 NA NA 62 NA NA 107 NA NA 164 NA NA 231
10 NA NA 28 NA NA 55 NA NA 97 NA NA 153 NA NA 216
15 NA NA NA NA NA 48 NA NA 89 NA NA 141 NA NA 201
20 2 NA NA 38 NA NA 74 NA NA 124 NA NA 201 51 522 274
5 NA NA 36 NA NA 68 NA NA 116 NA NA 184 80 503 254
10 NA NA NA NA NA 60 NA NA 107 NA NA 172 NA NA 237
15 NA NA NA NA NA NA NA NA 97 NA NA 159 NA NA 220
20 NA NA NA NA NA NA NA NA 83 NA NA 148 NA NA 206
30 2 NA NA 41 NA NA 82 NA NA 137 NA NA 216 47 581 303
5 NA NA NA NA NA 76 NA NA 128 NA NA 198 75 561 281
10 NA NA NA NA NA 67 NA NA 115 NA NA 184 NA NA 263
15 NA NA NA NA NA NA NA NA 107 NA NA 171 NA NA 243
20 NA NA NA NA NA NA NA NA 91 NA NA 159 NA NA 227
30 NA NA NA NA NA NA NA NA NA NA NA NA NA NA 188
50 2 NA NA NA NA NA 92 NA NA 161 NA NA 251 NA NA 351
5 NA NA NA NA NA NA NA NA 151 NA NA 230 NA NA 323
10 NA NA NA NA NA NA NA NA 138 NA NA 215 NA NA 304
15 NA NA NA NA NA NA NA NA 127 NA NA 199 NA NA 282
20 NA NA NA NA NA NA NA NA NA NA NA 185 NA NA 264
30 NA NA NA NA NA NA NA NA NA NA NA NA NA NA 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.
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.


NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
TYPE B DOUBLE-WALL 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 NA NA 247 NA NA 320 NA NA 401 NA NA 581
5 NA NA 231 NA NA 298 NA NA 376 NA NA 561
8 2 NA NA 266 84 590 350 100 728 446 139 1024 651
5 NA NA 247 NA NA 328 149 711 423 201 1007 640
8 NA NA 239 NA NA 318 173 695 410 231 990 623
10 2 68 519 298 82 655 388 98 810 491 136 1144 724
5 NA NA 277 124 638 365 146 791 466 196 1124 712
10 NA NA 263 155 610 347 182 762 444 240 1093 668
15 2 64 613 336 77 779 441 92 968 562 127 1376 841
5 99 594 313 118 759 416 139 946 533 186 1352 828
10 126 565 296 148 727 394 173 912 567 229 1315 777
15 NA NA 281 171 698 375 198 880 485 259 1280 742
20 2 61 678 375 73 867 491 87 1083 627 121 1548 953
5 95 658 350 113 845 463 133 1059 597 179 1523 933
10 122 627 332 143 811 440 167 1022 566 221 1482 879
15 NA NA 314 165 780 418 191 987 541 251 1443 840
20 NA NA 296 186 750 397 214 955 513 277 1406 807
30 2 57 762 421 68 985 558 81 1240 717 111 1793 1112
5 90 741 393 106 962 526 125 1216 683 169 1766 1094
10 115 709 373 135 927 500 158 1176 648 210 1721 1025
15 NA NA 353 156 893 476 181 1139 621 239 1679 981
20 NA NA 332 176 860 450 203 1103 592 264 1638 940
30 NA NA 288 NA NA 416 249 1035 555 318 1560 877
50 2 51 840 477 61 1106 633 72 1413 812 99 2080 1243
5 83 819 445 98 1083 596 116 1387 774 155 2052 1225
10 NA NA 424 126 1047 567 147 1347 733 195 2006 1147
15 NA NA 400 146 1010 539 170 1307 702 222 1961 1099
20 NA NA 376 165 977 511 190 1269 669 246 1916 1050
30 NA NA 327 NA NA 468 233 1196 623 295 1832 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.
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 803.1.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(d)]*
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
TYPE B DOUBLE-WALL 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 NA NA 28 NA NA 52 NA NA 86 NA NA 130 NA NA 180
5 NA NA 25 NA NA 48 NA NA 81 NA NA 116 NA NA 164
8 2 NA NA 29 NA NA 55 NA NA 93 NA NA 145 NA NA 197
5 NA NA 26 NA NA 51 NA NA 87 NA NA 133 NA NA 182
8 NA NA 23 NA NA 47 NA NA 82 NA NA 126 NA NA 174
10 2 NA NA 31 NA NA 61 NA NA 102 NA NA 161 NA NA 220
5 NA NA 28 NA NA 56 NA NA 95 NA NA 147 NA NA 203
10 NA NA 24 NA NA 49 NA NA 86 NA NA 137 NA NA 189
15 2 NA NA 35 NA NA 67 NA NA 113 NA NA 178 166 473 249
5 NA NA 32 NA NA 61 NA NA 106 NA NA 163 NA NA 230
10 NA NA 27 NA NA 54 NA NA 96 NA NA 151 NA NA 214
15 NA NA NA NA NA 46 NA NA 87 NA NA 138 NA NA 198
20 2 NA NA 38 NA NA 73 NA NA 123 NA NA 200 163 520 273
5 NA NA 35 NA NA 67 NA NA 115 NA NA 183 NA NA 252
10 NA NA NA NA NA 59 NA NA 105 NA NA 170 NA NA 235
15 NA NA NA NA NA NA NA NA 95 NA NA 156 NA NA 217
20 NA NA NA NA NA NA NA NA 80 NA NA 144 NA NA 202
30 2 NA NA 41 NA NA 81 NA NA 136 NA NA 215 158 578 302
5 NA NA NA NA NA 75 NA NA 127 NA NA 196 NA NA 279
10 NA NA NA NA NA 66 NA NA 113 NA NA 182 NA NA 260
15 NA NA NA NA NA NA NA NA 105 NA NA 168 NA NA 240
20 NA NA NA NA NA NA NA NA 88 NA NA 155 NA NA 223
30 NA NA NA NA NA NA NA NA NA NA NA NA NA NA 182
50 2 NA NA NA NA NA 91 NA NA 160 NA NA 250 NA NA 350
5 NA NA NA NA NA NA NA NA 149 NA NA 228 NA NA 321
10 NA NA NA NA NA NA NA NA 136 NA NA 212 NA NA 301
15 NA NA NA NA NA NA NA NA 124 NA NA 195 NA NA 278
20 NA NA NA NA NA NA NA NA NA NA NA 180 NA NA 258
30 NA NA NA NA NA NA NA NA NA NA NA NA NA NA 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.
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.


NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
SINGLE-WALL METAL 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 NA NA 247 NA NA 319 NA NA 400 NA NA 580
5 NA NA 230 NA NA 297 NA NA 375 NA NA 560
8 2 NA NA 265 NA NA 349 382 725 445 549 1021 650
5 NA NA 246 NA NA 327 NA NA 422 673 1003 638
8 NA NA 237 NA NA 317 NA NA 408 747 985 621
10 2 216 518 297 271 654 387 373 808 490 536 1142 722
5 NA NA 276 334 635 364 459 789 465 657 1121 710
10 NA NA 261 NA NA 345 547 758 441 771 1088 665
15 2 211 611 335 264 776 440 362 965 560 520 1373 840
5 261 591 312 325 755 414 444 942 531 637 1348 825
10 NA NA 294 392 722 392 531 907 504 749 1309 774
15 NA NA 278 452 692 372 606 873 481 841 1272 738
20 2 206 675 374 258 864 490 252 1079 625 508 1544 950
5 255 655 348 317 842 461 433 1055 594 623 1518 930
10 312 622 330 382 806 437 517 1016 562 733 1475 875
15 NA NA 311 442 773 414 591 979 539 823 1434 835
20 NA NA 292 NA NA 392 663 944 510 911 1394 800
30 2 200 759 420 249 982 556 340 1237 715 489 1789 1110
5 245 737 391 306 958 524 417 1210 680 600 1760 1090
10 300 703 370 370 920 496 500 1168 644 708 1713 1020
15 NA NA 349 428 884 471 572 1128 615 798 1668 975
20 NA NA 327 NA NA 445 643 1089 585 883 1624 932
30 NA NA 281 NA NA 408 NA NA 544 1055 1539 865
50 2 191 837 475 238 1103 631 323 1408 810 463 2076 1240
5 NA NA 442 293 1078 593 398 1381 770 571 2044 1220
10 NA NA 420 355 1038 562 447 1337 728 674 1994 1140
15 NA NA 395 NA NA 533 546 1294 695 761 1945 1090
20 NA NA 370 NA NA 504 616 1251 660 844 1898 1040
30 NA NA 318 NA NA 458 NA NA 610 1009 1805 970
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.
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 803.1.2(5)
SINGLE-WALL METAL PIPE OR TYPE B ASBESTOSCEMENT VENT [NFPA 54: TABLE 13.1 (e)]*
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: DRAFT HOOD-EQUIPPED
APPLIANCE VENT CONNECTION: CONNECTED DIRECTLY TO PIPE OR VENT
DIAMETER - D (inch)
TO BE USED WITH CHIMNEY AREAS WITHIN THE SIZE LIMITS AT BOTTOM
3 4 5 6 7 8 10 12
HEIGHT
H
(feet)
LATERAL
L
(feet)
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
6 0 39 70 116 170 232 312 500 750
2 31 55 94 141 194 260 415 620
5 28 51 88 128 177 242 390 600
8 0 42 76 126 185 252 340 542 815
2 32 61 102 154 210 284 451 680
5 29 56 95 141 194 264 430 648
10 24 49 86 131 180 250 406 625
10 0 45 84 138 202 279 372 606 912
2 35 67 111 168 233 311 505 760
5 32 61 104 153 215 289 480 724
10 27 54 94 143 200 274 455 700
15 NA 46 84 130 186 258 432 666
15 0 49 91 151 223 312 420 684 1040
2 39 72 122 186 260 350 570 865
5 35 67 110 170 240 325 540 825
10 30 58 103 158 223 308 514 795
15 NA 50 93 144 207 291 488 760
20 NA NA 82 132 195 273 466 726
20 0 53 101 163 252 342 470 770 1190
2 42 80 136 210 286 392 641 990
5 38 74 123 192 264 364 610 945
10 32 65 115 178 246 345 571 910
15 NA 55 104 163 228 326 550 870
20 NA NA 91 149 214 306 525 832
30 0 56 108 183 276 384 529 878 1370
2 44 84 148 230 320 441 730 1140
5 NA 78 137 210 296 410 694 1080
10 NA 68 125 196 274 388 656 1050
15 NA NA 113 177 258 366 625 1000
20 NA NA 99 163 240 344 596 960
30 NA NA NA NA 192 295 540 890
50 0 NA 120 210 310 443 590 980 1550
2 NA 95 171 260 370 492 820 1290
5 NA NA 159 234 342 474 780 1230
10 NA NA 146 221 318 456 730 1190
15 NA NA NA 200 292 407 705 1130
20 NA NA NA 185 276 384 670 1080
30 NA NA NA NA 222 330 605 1010
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 803. 1.2(6)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.1(f)]1, 2
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: NAT
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
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
Local 99% winter design temperature: 37°F or greater
6 0 0 0 0 0 0 0 0
8 0 0 0 0 0 0 0 0
10 0 0 0 0 0 0 0 0
15 NA 0 0 0 0 0 0 0
20 NA NA 123 190 249 184 0 0
30 NA NA NA NA NA 393 334 0
50 NA NA NA NA NA NA NA 579
Local 99% winter design temperature: 27°F to 36°F
6 0 0 68 116 156 180 212 266
8 0 0 82 127 167 187 214 263
10 0 51 97 141 183 201 225 265
15 NA NA NA NA 233 253 274 305
20 NA NA NA NA NA 307 330 362
30 NA NA NA NA NA 419 445 485
50 NA NA NA NA NA NA NA 763
Local 99% winter design temperature: 17°F to 26°F
6 NA NA NA NA NA 215 259 349
8 NA NA NA NA 197 226 264 352
10 NA NA NA NA 214 245 278 358
15 NA NA NA NA NA 296 331 398
20 NA NA NA NA NA 352 387 457
30 NA NA NA NA NA NA 507 581
50 NA NA NA NA NA NA NA NA
Local 99% winter design temperature: 5°F to 16°F
6 NA NA NA NA NA NA NA 416
8 NA NA NA NA NA NA 312 423
10 NA NA NA NA NA 289 331 430
15 NA NA NA NA NA NA 393 485
20 NA NA NA NA NA NA 450 547
30 NA NA NA NA NA NA NA 682
50 NA NA NA NA NA NA NA 972
Local 99% winter design temperature: -10°F to 4°F
6 NA NA NA NA NA NA NA 484
8 NA NA NA NA NA NA NA 494
10 NA NA NA NA NA NA NA 513
15 NA NA NA NA NA NA NA 586
20 NA NA NA NA NA NA NA 650
30 NA NA NA NA NA NA NA 805
50 NA NA NA NA NA NA NA 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. 1 See Figure 803.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
  2. 2 NA: Not applicable.
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 high-altitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for high-altitude 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 803.1.2(1) or Table 803.1.2(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 803.1.2(1) or Table 803.1.2(2).

     Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 803.1.2. 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 double-wall connectors shall be made with listed adapters designed for such purpose. [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 fan-assisted appliances shall be listed and installed in accordance with the listed accessory manufacturer's installation instructions. [NFPA 54:13.1.10]
Table 803.1.2(1) through Table 803.1.2(5) shall be used only 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 802.6.1, and where vents terminate in accordance with Section 802.6.1(2), the outdoor portion of the vent shall be enclosed as required by this paragraph 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 803.1.2(3) in combination with Table 803.1.2(6) shall be used for clay tile-lined exterior masonry chimneys, provided all of the following requirements are met:
  1. The vent connector is Type B double wall.
  2. The vent connector length is limited to 18 in./in. (18 mm/mm) of vent connector diameter.
  3. The appliance is draft hood equipped.
  4. The input rating is less than the maximum capacity given in Table 803.1.2(3).
  5. For a water heater, the outdoor design temperature shall be not less than 5°F (-15°C).
  6. For a space-heating appliance, the input rating is greater than the minimum capacity given by Table 803.1.2(6). [NFPA 54:13.1.11]
Flue lining system for residential and low heat appliance shall be in accordance with Section 803.1.11.1 and Section 803.1.11.2.
Clay flue lining shall be manufactured in accordance with ASTM C315 or other approved standard.
Chimney lining shall be listed in accordance with UL 1777.
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 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 803.1.2(1) through Table 803.1.2(6), either of the following shall be used:
  1. Interpolation.
  2. 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]
Venting Table 803.2(1) through Table 803.2(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 instructions or in accordance with the following:
  1. The maximum capacity of the vent connector shall be determined using the NAT Max column.
  2. The maximum capacity of the vertical vent or chimney shall be determined using the FAN+ NAT column when the second appliance is a fan-assisted appliance, or the NAT + NAT column when the second appliance is equipped with a draft hood.
  3. The minimum capacity shall be determined as if the appliance were a fan-assisted appliance, as follows:
    1. The minimum capacity of the vent connector shall be determined using the FAN Min column.
    2. The FAN+ FAN column shall be used when the second appliance is a fan-assisted appliance, and the FAN+ NAT column shall be used when 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]
Venting Table 803.2(1) through Table 803.2(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 instructions or in accordance with the following:
  1. The maximum capacity of the vent connector shall be determined using the NAT Max column.
  2. The maximum capacity of the vertical vent or chimney shall be determined using the FAN+ NAT column when the second appliance is a fan-assisted appliance, or the NAT + NAT column when the second appliance is equipped with a draft hood.
  3. The minimum capacity shall be determined as if the appliance were a fan-assisted appliance, as follows:
    1. The minimum capacity of the vent connector shall be determined using the FAN Min column.
    2. The FAN+ FAN column shall be used when the second appliance is a fan-assisted appliance, and the FAN+ NAT column shall be used when 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 803.2(1)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)]*
NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
VENT CONNECTOR CAPACITY
TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER - D (inch)
3 4 5 6 7
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(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 1 22 37 26 35 66 46 46 106 72 58 164 104 77 225 142
2 23 41 31 37 75 55 48 121 86 60 183 124 79 253 168
3 24 44 35 38 81 62 49 132 96 62 199 139 82 275 189
8 1 22 40 27 35 72 48 49 114 76 64 176 109 84 243 148
2 23 44 32 36 80 57 51 128 90 66 195 129 86 269 175
3 24 47 36 37 87 64 53 139 101 67 210 145 88 290 198
10 1 22 43 28 34 78 50 49 123 78 65 189 113 89 257 154
2 23 47 33 36 86 59 51 136 93 67 206 134 91 282 182
3 24 50 37 37 92 67 52 146 104 69 220 150 94 303 205
15 1 21 50 30 33 89 53 47 142 83 64 220 120 88 298 163
2 22 53 35 35 96 63 49 153 99 66 235 142 91 320 193
3 24 55 40 36 102 71 51 163 111 68 248 160 93 339 218
20 1 21 54 31 33 99 56 46 157 87 62 246 125 86 334 171
2 22 57 37 34 105 66 48 167 104 64 259 149 89 354 202
3 23 60 42 35 110 74 50 176 116 66 271 168 91 371 228
30 1 20 62 33 31 113 59 45 181 93 60 288 134 83 391 182
2 21 64 39 33 118 70 47 190 110 62 299 158 85 408 215
3 22 66 44 34 123 79 48 198 124 64 309 178 88 423 242
50 1 19 71 36 30 133 64 43 216 101 57 349 145 78 477 197
2 21 73 43 32 137 76 45 223 119 59 358 172 81 490 234
3 22 75 48 33 141 86 46 229 134 61 366 194 83 502 263
100 1 18 82 37 28 158 66 40 262 104 53 442 150 73 611 204
2 19 83 44 30 161 79 42 267 123 55 447 178 75 619 242
3 20 84 50 31 163 89 44 272 138 57 452 200 78 627 272

COMMON VENT CAPACITY
TYPE B DOUBLE-WALL COMMON VENT DIAMETER - D (inch)
4 5 6 7
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 92 81 65 140 116 103 204 161 147 309 248 200
8 101 90 73 155 129 114 224 178 163 339 275 223
10 110 97 79 169 141 124 243 194 178 367 299 242
15 125 112 91 195 164 144 283 228 206 427 352 280
20 136 123 102 215 183 160 314 255 229 475 394 310
30 152 138 118 244 210 185 361 297 266 547 459 360
50 167 153 134 279 244 214 421 353 310 641 547 423
100 175 163 NA 311 277 NA 489 421 NA 751 658 479
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.


NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
VENT CONNECTOR CAPACITY
TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER - D (inch)
8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(feet)
FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max
6 1 92 296 185 109 376 237 128 466 289
2 95 333 220 112 424 282 131 526 345
3 97 363 248 114 463 317 134 575 386
8 1 100 320 194 118 408 248 138 507 303
2 103 356 230 121 454 294 141 564 358
3 105 384 258 123 492 330 143 612 402
10 1 106 341 200 125 436 257 146 542 314
2 109 374 238 128 479 305 149 596 372
3 111 402 268 131 515 342 152 642 417
15 1 110 389 214 134 493 273 162 609 333
2 112 419 253 137 532 323 165 658 394
3 115 445 286 140 565 365 167 700 444
20 1 107 436 224 131 552 285 158 681 347
2 110 463 265 134 587 339 161 725 414
3 113 486 300 137 618 383 164 764 466
30 1 103 512 238 125 649 305 151 802 372
2 105 535 282 129 679 360 155 840 439
3 108 555 317 132 706 405 158 874 494
50 1 97 627 257 120 797 330 144 984 403
2 100 645 306 123 820 392 148 1014 478
3 103 661 343 126 842 441 151 1043 538
100 1 91 810 266 112 1038 341 135 1285 417
2 94 822 316 115 1054 405 139 1306 494
3 97 834 355 118 1069 455 142 1327 555

COMMON VENT CAPACITY
TYPE B DOUBLE-WALL COMMON VENT DIAMETER - D (inch)
8 9 10
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 404 314 260 547 434 335 672 520 410
8 444 348 290 602 480 378 740 577 465
10 477 377 315 649 522 405 800 627 495
15 556 444 365 753 612 465 924 733 565
20 621 499 405 842 688 523 1035 826 640
30 720 585 470 979 808 605 1209 975 740
50 854 706 550 1164 977 705 1451 1188 860
100 1025 873 625 1408 1215 800 1784 1502 975
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

NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
VENT CONNECTOR CAPACITY
TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER - D (inch)
12 14 16 18
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(feet)
FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max
6 2 174 764 496 223 1046 653 281 1371 853 346 1772 1080
4 180 897 616 230 1231 827 287 1617 1081 352 2069 1370
6 NA NA NA NA NA NA NA NA NA NA NA NA
8 2 186 822 516 238 1126 696 298 1478 910 365 1920 1150
4 192 952 644 244 1307 884 305 1719 1150 372 2211 1460
6 198 1050 772 252 1445 1072 313 1902 1390 380 2434 1770
10 2 196 870 536 249 1195 730 311 1570 955 379 2049 1205
4 201 997 664 256 1371 924 318 1804 1205 387 2332 1535
6 207 1095 792 263 1509 1118 325 1989 1455 395 2556 1865
15 2 214 967 568 272 1334 790 336 1760 1030 408 2317 1305
4 221 1085 712 279 1499 1006 344 1978 1320 416 2579 1665
6 228 1181 856 286 1632 1222 351 2157 1610 424 2796 2025
20 2 223 1051 596 291 1443 840 357 1911 1095 430 2533 1385
4 230 1162 748 298 1597 1064 365 2116 1395 438 2778 1765
6 237 1253 900 307 1726 1288 373 2287 1695 450 2984 2145
30 2 216 1217 632 286 1664 910 367 2183 1190 461 2891 1540
4 223 1316 792 294 1802 1160 376 2366 1510 474 3110 1920
6 231 1400 952 303 1920 1410 384 2524 1830 485 3299 2340
50 2 206 1479 689 273 2023 1007 350 2659 1315 435 3548 1665
4 213 1561 860 281 2139 1291 359 2814 1685 447 3730 2135
6 221 1631 1031 290 2242 1575 369 2951 2055 461 3893 2605
100 2 192 1923 712 254 2644 1050 326 3490 1370 402 4707 1740
4 200 1984 888 263 2731 1346 336 3606 1760 414 4842 2220
6 208 2035 1064 272 2811 1642 346 3714 2150 426 4968 2700

COMMON VENT CAPACITY
TYPE B DOUBLE-WALL COMMON VENT DIAMETER - D (inch)
12 14 16 18
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 900 696 588 1284 990 815 1735 1336 1065 2253 1732 1345
8 994 773 652 1423 1103 912 1927 1491 1190 2507 1936 1510
10 1076 841 712 1542 1200 995 2093 1625 1300 2727 2113 1645
15 1247 986 825 1794 1410 1158 2440 1910 1510 3184 2484 1910
20 1405 1116 916 2006 1588 1290 2722 2147 1690 3561 2798 2140
30 1658 1327 1025 2373 1892 1525 3220 2558 1990 4197 3326 2520
50 2024 1640 1280 2911 2347 1863 3964 3183 2430 5184 4149 3075
100 2569 2131 1670 3732 3076 2450 5125 4202 3200 6749 5509 4050
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.

NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
VENT CONNECTOR CAPACITY
TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER - D (inch)
20 22 24
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(feet)
FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max
6 2 NA NA NA NA NA NA NA NA NA
4 NA NA NA NA NA NA NA NA NA
6 NA NA NA NA NA NA NA NA NA
8 2 NA NA NA NA NA NA NA NA NA
4 471 2737 1800 560 3319 2180 662 3957 2590
6 478 3018 2180 568 3665 2640 669 4373 3130
10 2 NA NA NA NA NA NA NA NA NA
4 486 2887 1890 581 3502 2280 686 4175 2710
6 494 3169 2290 589 3849 2760 694 4593 3270
15 2 NA NA NA NA NA NA NA NA NA
4 523 3197 2060 624 3881 2490 734 4631 2960
6 533 3470 2510 634 4216 3030 743 5035 3600
20 2 NA NA NA NA NA NA NA NA NA
4 554 3447 2180 661 4190 2630 772 5005 3130
6 567 3708 2650 671 4511 3190 785 5392 3790
30 2 NA NA NA NA NA NA NA NA NA
4 619 3840 2365 728 4861 2860 847 5606 3410
6 632 4080 2875 741 4976 3480 860 5961 4150
50 2 NA NA NA NA NA NA NA NA NA
4 580 4601 2633 709 5569 3185 851 6633 3790
6 594 4808 3208 724 5826 3885 867 6943 4620
100 2 NA NA NA NA NA NA NA NA NA
4 523 5982 2750 639 7254 3330 769 8650 3950
6 539 6143 3350 654 7453 4070 786 8892 4810

COMMON VENT CAPACITY
TYPE B DOUBLE-WALL COMMON VENT DIAMETER - D (inch)
20 22 24
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 2838 2180 1660 3488 2677 1970 4206 3226 2390
8 3162 2439 1860 3890 2998 2200 4695 3616 2680
10 3444 2665 2030 4241 3278 2400 5123 3957 2920
15 4026 3133 2360 4971 3862 2790 6016 4670 3400
20 4548 3552 2640 5573 4352 3120 6749 5261 3800
30 5303 4193 3110 6539 5157 3680 7940 6247 4480
50 6567 5240 3800 8116 6458 4500 9837 7813 5475
100 8597 6986 5000 10681 8648 5920 13004 10499 7200
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 803.2(2)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(b)]*
NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
VENT CONNECTOR CAPACITY
SINGLE-WALL METAL VENT CONNECTOR DIAMETER - D (inch)
3 4 5 6 7
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(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 1 NA NA 26 NA NA 46 NA NA 71 NA NA 102 207 223 140
2 NA NA 31 NA NA 55 NA NA 85 168 182 123 215 251 167
3 NA NA 34 NA NA 62 121 131 95 175 198 138 222 273 188
8 1 NA NA 27 NA NA 48 NA NA 75 NA NA 106 226 240 145
2 NA NA 32 NA NA 57 125 126 89 184 193 127 234 266 173
3 NA NA 35 NA NA 64 130 138 100 191 208 144 241 287 197
10 1 NA NA 28 NA NA 50 119 121 77 182 186 110 240 253 150
2 NA NA 33 84 85 59 124 134 91 189 203 132 248 278 183
3 NA NA 36 89 91 67 129 144 102 197 217 148 257 299 203
15 1 NA NA 29 79 87 52 116 138 81 177 214 116 238 291 158
2 NA NA 34 83 94 62 121 150 97 185 230 138 246 314 189
3 NA NA 39 87 100 70 127 160 109 193 243 157 255 333 215
20 1 49 56 30 78 97 54 115 152 84 175 238 120 233 325 165
2 52 59 36 82 103 64 120 163 101 182 252 144 243 346 197
3 55 62 40 87 107 72 125 172 113 190 264 164 252 363 223
30 1 47 60 31 77 110 57 112 175 89 169 278 129 226 380 175
2 51 62 37 81 115 67 117 185 106 177 290 152 236 397 208
3 54 64 42 85 119 76 122 193 120 185 300 172 244 412 235
50 1 46 69 34 75 128 60 109 207 96 162 336 137 217 460 188
2 49 71 40 79 132 72 114 215 113 170 345 164 226 473 223
3 52 72 45 83 136 82 119 221 123 178 353 186 235 486 252
100 1 45 79 34 71 150 61 104 249 98 153 424 140 205 585 192
2 48 80 41 75 153 73 110 255 115 160 428 167 212 593 228
3 51 81 46 79 157 85 114 260 129 168 433 190 222 603 256

COMMON VENT CAPACITY
TYPE B DOUBLE-WALL COMMON VENT DIAMETER - D (inch)
4 5 6 7
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA 78 64 NA 113 99 200 158 144 304 244 196
8 NA 87 71 NA 126 111 218 173 159 331 269 218
10 NA 94 76 163 137 120 237 189 174 357 292 236
15 121 108 88 189 159 140 275 221 200 416 343 274
20 131 118 98 208 177 156 305 247 223 463 383 302
30 145 132 113 236 202 180 350 286 257 533 446 349
50 159 145 128 268 233 208 406 337 296 622 529 410
100 166 153 NA 297 263 NA 469 398 NA 726 633 464
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.


NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
VENT CONNECTOR CAPACITY
SINGLE-WALL METAL VENT CONNECTOR DIAMETER - D (inch)
8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(feet)
FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max
6 1 262 293 183 325 373 234 447 463 286
2 271 331 219 334 422 281 458 524 344
3 279 361 247 344 462 316 468 574 385
8 1 285 316 191 352 403 244 481 502 299
2 293 353 228 360 450 292 492 560 355
3 302 381 256 370 489 328 501 609 400
10 1 302 335 196 372 429 252 506 534 308
2 311 369 235 381 473 302 517 589 368
3 320 398 265 391 511 339 528 637 413
15 1 312 380 208 397 482 266 556 596 324
2 321 411 248 407 522 317 568 646 387
3 331 438 281 418 557 360 579 690 437
20 1 306 425 217 390 538 276 546 664 336
2 317 453 259 400 574 331 558 709 403
3 326 476 294 412 607 375 570 750 457
30 1 296 497 230 378 630 294 528 779 358
2 307 521 274 389 662 349 541 819 425
3 316 542 309 400 690 394 555 855 482
50 1 284 604 245 364 768 314 507 951 384
2 294 623 293 376 793 375 520 983 458
3 304 640 331 387 816 423 535 1013 518
100 1 269 774 249 345 993 321 476 1236 393
2 279 788 299 358 1011 383 490 1259 469
3 289 801 339 368 1027 431 506 1280 527

COMMON VENT CAPACITY
TYPE B DOUBLE-WALL COMMON VENT DIAMETER - D (inch)
8 9 10
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 398 310 257 541 429 332 665 515 407
8 436 342 285 592 473 373 730 569 460
10 467 369 309 638 512 398 787 617 487
15 544 434 357 738 599 456 905 718 553
20 606 487 395 824 673 512 1013 808 626
30 703 570 459 958 790 593 1183 952 723
50 833 686 535 1139 954 689 1418 1157 838
100 999 846 606 1378 1185 780 1741 1459 948
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 803.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)]*
NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
VENT CONNECTOR CAPACITY
TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER - D (inch)
3 4 5 6 7
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(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 1 24 33 21 39 62 40 52 106 67 65 194 101 87 274 141
2 26 43 28 41 79 52 53 133 85 67 230 124 89 324 173
3 27 49 34 42 92 61 55 155 97 69 262 143 91 369 203
8 1 24 39 22 39 72 41 55 117 69 71 213 105 94 304 148
2 26 47 29 40 87 53 57 140 86 73 246 127 97 350 179
3 27 52 34 42 97 62 59 159 98 75 269 145 99 383 206
10 1 24 42 22 38 80 42 55 130 71 74 232 108 101 324 153
2 26 50 29 40 93 54 57 153 87 76 261 129 103 366 184
3 27 55 35 41 105 63 58 170 100 78 284 148 106 397 209
15 1 24 48 23 38 93 44 54 154 74 72 277 114 100 384 164
2 25 55 31 39 105 55 56 174 89 74 299 134 103 419 192
3 26 59 35 41 115 64 57 189 102 76 319 153 105 448 215
20 1 24 52 24 37 102 46 53 172 77 71 313 119 98 437 173
2 25 58 31 39 114 56 55 190 91 73 335 138 101 467 199
3 26 63 35 40 123 65 57 204 104 75 353 157 104 493 222
30 1 24 54 25 37 111 48 52 192 82 69 357 127 96 504 187
2 25 60 32 38 122 58 54 208 95 72 376 145 99 531 209
3 26 64 36 40 131 66 56 221 107 74 392 163 101 554 233
50 1 23 51 25 36 116 51 51 209 89 67 405 143 92 582 213
2 24 59 32 37 127 61 53 225 102 70 421 161 95 604 235
3 26 64 36 39 135 69 55 237 115 72 435 180 98 624 260
100 1 23 46 24 35 108 50 49 208 92 65 428 155 88 640 237
2 24 53 31 37 120 60 51 224 105 67 444 174 92 660 260
3 25 59 35 38 130 68 53 237 118 69 458 193 94 679 285

COMMON VENT CAPACITY
MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)
12 19 28 38 50
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA 74 25 NA 119 46 NA 178 71 NA 257 103 NA 351 143
8 NA 80 28 NA 130 53 NA 193 82 NA 279 119 NA 384 163
10 NA 84 31 NA 138 56 NA 207 90 NA 299 131 NA 409 177
15 NA NA 36 NA 152 67 NA 233 106 NA 334 152 523 467 212
20 NA NA 41 NA NA 75 NA 250 122 NA 368 172 565 508 243
30 NA NA NA NA NA NA NA 270 137 NA 404 198 615 564 278
50 NA NA NA NA NA NA NA NA NA NA NA NA NA 620 328
100 NA NA NA NA NA NA NA NA NA NA NA NA NA NA 348
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.


NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B DOUBLE-WALL CONNECTOR
VENT CONNECTOR CAPACITY
TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER - D (inch)
8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(feet)
FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max
6 1 104 370 201 124 479 253 145 599 319
2 107 436 232 127 562 300 148 694 378
3 109 491 270 129 633 349 151 795 439
8 1 113 414 210 134 539 267 156 682 335
2 116 473 240 137 615 311 160 776 394
3 119 517 276 139 672 358 163 848 452
10 1 120 444 216 142 582 277 165 739 348
2 123 498 247 145 652 321 168 825 407
3 126 540 281 147 705 366 171 893 463
15 1 125 511 229 153 658 297 184 824 375
2 128 558 260 156 718 339 187 900 432
3 131 597 292 159 760 382 190 960 486
20 1 123 584 239 150 752 312 180 943 397
2 126 625 270 153 805 354 184 1011 452
3 129 661 301 156 851 396 187 1067 505
30 1 119 680 255 145 883 337 175 1115 432
2 122 715 287 149 928 378 179 1171 484
3 125 746 317 152 968 418 182 1220 535
50 1 115 798 294 140 1049 392 168 1334 506
2 118 827 326 143 1085 433 172 1379 558
3 121 854 357 147 1118 474 176 1421 611
100 1 109 907 334 134 1222 454 161 1589 596
2 113 933 368 138 1253 497 165 1626 651
3 116 956 399 141 1282 540 169 1661 705

COMMON VENT CAPACITY
MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)
63 78 113
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA 458 188 NA 582 246 1041 853 NA
8 NA 501 218 724 636 278 1144 937 408
10 606 538 236 776 686 302 1226 1010 454
15 682 611 283 874 781 365 1374 1156 546
20 742 668 325 955 858 419 1513 1286 648
30 816 747 381 1062 969 496 1702 1473 749
50 879 831 461 1165 1089 606 1905 1692 922
100 NA NA 499 NA NA 669 2053 1921 1058
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 803.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(d)]*
NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
VENT CONNECTOR CAPACITY
SINGLE-WALL METAL VENT CONNECTOR DIAMETER - D (inch)
3 4 5 6 7
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(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 1 NA NA 21 NA NA 39 NA NA 66 179 191 100 231 271 140
2 NA NA 28 NA NA 52 NA NA 84 186 227 123 239 321 172
3 NA NA 34 NA NA 61 134 153 97 193 258 142 247 365 202
8 1 NA NA 21 NA NA 40 NA NA 68 195 208 103 250 298 146
2 NA NA 28 NA NA 52 137 139 85 202 240 125 258 343 177
3 NA NA 34 NA NA 62 143 156 98 210 264 145 266 376 205
10 1 NA NA 22 NA NA 41 130 151 70 202 225 106 267 316 151
2 NA NA 29 NA NA 53 136 150 86 210 255 128 276 358 181
3 NA NA 34 97 102 62 143 166 99 217 277 147 284 389 207
15 1 NA NA 23 NA NA 43 129 151 73 199 271 112 268 376 161
2 NA NA 30 92 103 54 135 170 88 207 295 132 277 411 189
3 NA NA 34 96 112 63 141 185 101 215 315 151 286 439 213
20 1 NA NA 23 87 99 45 128 167 76 197 303 117 265 425 169
2 NA NA 30 91 111 55 134 185 90 205 325 136 274 455 195
3 NA NA 35 96 119 64 140 199 103 213 343 154 282 481 219
30 1 NA NA 24 86 108 47 126 187 80 193 347 124 259 492 183
2 NA NA 31 91 119 57 132 203 93 201 366 142 269 518 205
3 NA NA 35 95 127 65 138 216 105 209 381 160 277 540 229
50 1 NA NA 24 85 113 50 124 204 87 188 392 139 252 567 208
2 NA NA 31 89 123 60 130 218 100 196 408 158 262 588 230
3 NA NA 35 94 131 68 136 231 112 205 422 176 271 607 255
100 1 NA NA 23 84 104 49 122 200 89 182 410 151 243 617 232
2 NA NA 30 88 115 59 127 215 102 190 425 169 253 636 254
3 NA NA 34 93 124 67 133 228 115 199 438 188 262 654 279

COMMON VENT CAPACITY
MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)
12 19 28 38 50
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA NA 25 NA 118 45 NA 176 71 NA 255 102 NA 348 142
8 NA NA 28 NA 128 52 NA 190 81 NA 276 118 NA 380 162
10 NA NA 31 NA 136 56 NA 205 89 NA 295 129 NA 405 175
15 NA NA 36 NA NA 66 NA 230 105 NA 335 150 NA 400 210
20 NA NA NA NA NA 74 NA 247 120 NA 362 170 NA 503 240
30 NA NA NA NA NA NA NA NA 135 NA 398 195 NA 558 275
50 NA NA NA NA NA NA NA NA NA NA NA NA NA 612 325
100 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
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.


NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
VENT CONNECTOR CAPACITY
SINGLE-WALL METAL VENT CONNECTOR DIAMETER - D (inch)
8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(feet)
FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max
6 1 292 366 200 362 474 252 499 594 316
2 301 432 231 373 557 299 509 696 376
3 309 491 269 381 634 348 519 793 437
8 1 313 407 207 387 530 263 529 672 331
2 323 465 238 397 607 309 540 766 391
3 332 509 274 407 663 356 551 838 450
10 1 333 434 213 410 571 273 558 727 343
2 343 489 244 420 640 317 569 813 403
3 352 530 279 430 694 363 580 880 459
15 1 349 502 225 445 646 291 623 808 366
2 359 548 256 456 706 334 634 884 424
3 368 586 289 466 755 378 646 945 479
20 1 345 569 235 439 734 306 614 921 387
2 355 610 266 450 787 348 627 986 443
3 365 644 298 461 831 391 639 1042 496
30 1 338 665 250 430 864 330 600 1089 421
2 348 699 282 442 908 372 613 1145 473
3 358 729 312 452 946 412 626 1193 524
50 1 328 778 287 417 1022 383 582 1302 492
2 339 806 320 429 1058 425 596 1346 545
3 349 831 351 440 1090 466 610 1386 597
100 1 315 875 328 402 1181 444 560 1537 580
2 326 899 361 415 1210 488 575 1570 634
3 337 921 392 427 1238 529 589 1604 687

COMMON VENT CAPACITY
MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)
63 78 113
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
VENT
HEIGHT
H
(feet)
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA 455 187 NA 579 245 NA 846 NA
8 NA 497 217 NA 633 277 1136 928 405
10 NA 532 234 771 680 300 1216 1000 450
15 677 602 280 866 772 360 1359 1139 540
20 765 661 321 947 849 415 1495 1264 640
30 808 739 377 1052 957 490 1682 1447 740
50 NA 821 456 1152 1076 600 1879 1672 910
100 NA NA 494 NA NA 663 2006 1885 1046
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 803.2(5)
SINGLE-WALL METAL PIPE OR TYPE B ASBESTOS-CEMENT VENT [NFPA 54: TABLE 13.2(e)]*
NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: DRAFT HOOD-EQUIPMENT
APPLIANCE VENT CONNECTION: DIRECTTO 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 21 40 68 102 146 205
2 28 53 86 124 178 235
3 34 61 98 147 204 275
15 1 23 44 77 117 179 240
2 30 56 92 134 194 265
3 35 64 102 155 216 298
30
and up
1 25 49 84 129 190 270
2 31 58 97 145 211 295
3 36 68 107 164 232 321

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 48 78 111 155 205 320 NA
8 55 89 128 175 234 365 505
10 59 95 136 190 250 395 560
15 71 115 168 228 305 480 690
20 80 129 186 260 340 550 790
30 NA 147 215 300 400 650 940
50 NA NA NA 360 490 810 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
* NA: Not applicable.


TABLE 803.2(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 DOUBLE-WALL 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 25 46 71 103 143 188 246 NA
8 28 53 82 119 163 218 278 408
10 31 56 90 131 177 236 302 454
15 NA 67 106 152 212 283 365 546
20 NA NA NA NA NA 325 419 648
30 NA NA NA NA NA NA 496 749
50 NA NA NA NA NA NA NA 922
100 NA NA NA NA NA NA NA NA
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 803.2(7)
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 DOUBLE-WALL CONNECTOR
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
Local 99% winter design temperature: 37°F or greater
6 0 0 0 0 0 0 0 NA
8 0 0 0 0 0 0 0 0
10 0 0 0 0 0 0 0 0
15 NA 0 0 0 0 0 0 0
20 NA NA NA NA NA 184 0 0
30 NA NA NA NA NA 393 334 0
50 NA NA NA NA NA NA NA 579
100 NA NA NA NA NA NA NA NA
Local 99% winter design temperature: 27°F to 36°F
6 0 0 68 NA NA 180 212 NA
8 0 0 82 NA NA 187 214 263
10 0 51 NA NA NA 201 225 265
15 NA NA NA NA NA 253 274 305
20 NA NA NA NA NA 307 330 362
30 NA NA NA NA NA NA 445 485
50 NA NA NA NA NA NA NA 763
100 NA NA NA NA NA NA NA NA
Local 99% winter design temperature: 17°F to 26°F
6 NA NA NA NA NA NA NA NA
8 NA NA NA NA NA NA 264 352
10 NA NA NA NA NA NA 278 358
15 NA NA NA NA NA NA 331 398
20 NA NA NA NA NA NA 387 457
30 NA NA NA NA NA NA NA 581
50 NA NA NA NA NA NA NA 862
100 NA NA NA NA NA NA NA NA
Local 99% winter design temperature: 5°F to 16°F
6 NA NA NA NA NA NA NA NA
8 NA NA NA NA NA NA NA NA
10 NA NA NA NA NA NA NA 430
15 NA NA NA NA NA NA NA 485
20 NA NA NA NA NA NA NA 547
30 NA NA NA NA NA NA NA 682
50 NA NA NA NA NA NA NA NA
100 NA NA NA NA NA NA 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 m2, °C = (°F-32)/1.8
Notes:
  1. 1 See Figure 803.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
  2. 2 NA: Not applicable.
TABLE 803.2(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 DOUBLE-WALL 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 74 119 178 257 351 458 582 853
8 80 130 193 279 384 501 636 937
10 84 138 207 299 409 538 686 1010
15 NA 152 233 334 467 611 781 1156
20 NA NA 250 368 508 668 858 1286
30 NA NA NA 404 564 747 969 1473
50 NA NA NA NA NA 831 1089 1692
100 NA NA NA NA NA NA NA 1921
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 803.2(9)
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 DOUBLE-WALL CONNECTOR
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
Local 99% winter design temperature: 37°F or greater
6 0 0 0 0 0 0 0 0
8 0 0 0 0 0 0 0 0
10 0 0 0 0 0 0 0 0
15 NA 0 0 0 0 0 0 0
20 NA NA 123 190 249 184 0 0
30 NA NA NA 334 398 393 334 0
50 NA NA NA NA NA 714 707 579
100 NA NA NA NA NA NA NA 1600
Local 99% winter design temperature: 27°F to 36°F
6 0 0 68 116 156 180 212 266
8 0 0 82 127 167 187 214 263
10 0 51 97 141 183 201 225 265
15 NA 111 142 183 233 253 274 305
20 NA NA 187 230 284 307 330 362
30 NA NA NA 330 319 419 445 485
50 NA NA NA NA NA 672 705 763
100 NA NA NA NA NA NA NA 1554
Local 99% winter design temperature: 17°F to 26°F
6 0 55 99 141 182 215 259 349
8 52 74 111 154 197 226 264 352
10 NA 90 125 169 214 245 278 358
15 NA NA 167 212 263 296 331 398
20 NA NA 212 258 316 352 387 457
30 NA NA NA 362 429 470 507 581
50 NA NA NA NA NA 723 766 862
100 NA NA NA NA NA NA NA 1669
Local 99% winter design temperature: 5°F to 16°F
6 NA 78 121 166 214 252 301 416
8 NA 94 135 182 230 269 312 423
10 NA 111 149 198 250 289 331 430
15 NA NA 193 247 305 346 393 485
20 NA NA NA 293 360 408 450 547
30 NA NA NA 377 450 531 580 682
50 NA NA NA NA NA 797 853 972
100 NA NA NA NA NA NA NA 1833
Local 99% winter design temperature: -10°F to 4°F
6 NA NA 145 196 249 296 349 484
8 NA NA 159 213 269 320 371 494
10 NA NA 175 231 292 339 397 513
15 NA NA NA 283 351 404 457 586
20 NA NA NA 333 408 468 528 650
30 NA NA NA NA NA 603 667 805
50 NA NA NA NA NA NA 955 1003
100 NA NA NA NA NA NA NA 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 m2, °C = (°F-32)/1.8
Notes:
  1. 1 See Figure 803.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
  2. 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 803.2.1, or as permitted by Section 803.2.2. [NFPA 54:13.2.2]

TABLE 803.2.1
VENT CONNECTOR MAXIMUM LENGTH
[NFPA 54: TABLE 13.2.2]
CONNECTOR
DIAMETER
(inches)
MAXIMUM CONNECTOR
HORIZONTAL LENGTH
(feet)
3 41/2
4 6
5 71/2
6 9
7 101/2
8 12
9 131/2
10 15
12 18
14 21
16 24
18 27
20 30
22 33
24 36
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
The vent connector shall be routed to the vent utilizing the shortest possible route. Connectors with longer horizontal lengths than those listed in Table 803.2.1 are permitted under the following conditions:
  1. 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 803.2.1. For example, the maximum length listed for a 4 inch (100 mm) connector is 6 feet (1829 mm) With a connector length greater than 6 feet (1829 mm) but not exceeding 12 feet (3658 mm), the maximum capacity must be reduced by 10 percent (0.90 x maximum vent connector capacity). With a connector length greater than 12 feet (3658 mm) but not exceeding 18 feet (5486 mm), the maximum capacity must be reduced by 20 percent (0.80 x maximum vent capacity).
  2. 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 803.1.2(1) shall be used. For single-wall connectors, Table 803.1.2(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). (See Figure 802.6.3.2) [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 803.2.5, 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 vent connector capacities listed in the common vent sizing tables include allowance for two 90 degree elbows. For each additional elbow up to and including 45 degrees, the maximum vent connector capacity listed in the venting tables shall be reduced by 5 percent. For each elbow greater than 45 degrees up to and including 90 degrees, the maximum vent connector capacity listed in the venting tables shall be reduced by 10 percent. [NFPA 54:13.2.7]
The cross-sectional area of the common vent shall be equal to or greater than the cross-sectional 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 shall 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 high-altitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for high-altitude 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. (See Figure 803.2.13) [NFPA 54:13.2.14]


Multistory gas vent design procedure for each
segment of system
Vent connector size
depends on:
Common vent size
depends on:
• Input • Combined imputs
• Rise • Available total height H
• Available total height H Table 803.2(1)
  common vent
Table 803.2(1)
  connectors
FIGURE 803.2.13
MULTISTORY GAS VENT DESIGN PROCEDURE FOR EACH SEGMENT OF SYSTEM
[NFPA 54: FIGURE F.1(m)]
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 803.1.2(1) or Table 803.1.2(2) for available total height (H) up to the lowest interconnection. (See Figure 803.2.13) [NFPA 54:13.2.15]

FIGURE 803.2.14
PRINCIPLES OF DESIGN OF MULTISTORY VENTS USING VENT CONNECTOR AND COMMON VENT DESIGN TABLES
[NFPA 54: FIGURE F.1(n)]
Where used in multistory systems, vertical common vents shall be Type B double-wall 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:
  1. The offset angle shall not exceed 45 degrees (0.79 rad) from vertical.
  2. 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.
  3. 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).
  4. 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 tables 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 803.2(1) or Table 803.2(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 803.2(1) or Table 803.2(2). Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 803.2.5 and Section 803.2.6. 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 803.2(1) through Table 803.2(5) shall be used only 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 802.6.1, and where vents terminate in accordance with Section 802.6.1(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 803.2(6) through Table 803.2(9) shall be used for clay-tile-lined exterior masonry chimneys, provided all the following conditions are met:
  1. The vent connector is Type B double-wall.
  2. At least one appliance is draft hood-equipped.
  3. The combined appliance input rating is less than the maximum capacity given by Table 803.2(6) (for NAT+NAT) or Table 803.2(8) (for FAN+NAT).
  4. The input rating of each space-heating appliance is greater than the minimum input rating given by Table 803.2(7) (for NAT+NAT) or Table 803.2(9) (for FAN+NAT).
  5. The vent connector sizing is in accordance with Table 803.2(3). [NFPA 54:13.2.22]
Vent connectors shall not be increased more than two sizes greater than 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 a vent connector sizes determined from the tables for a fan-assisted appliance(s) is smaller than the flue collar diameter, the use of the smaller size(s) shall be permitted, provided that the installation complies with all of the following conditions:
  1. Vent connectors for fan-assisted appliance flue collars 12 inches (300 mm) in diameter or smaller are not reduced by more than one table size [e.g., 12 inches to 10 inches (300 mm to 250 mm) is a one-size reduction] and those larger than 12 inches (300 mm) in diameter are not reduced more than two table sizes [e.g., 24 inches to 20 inches (600 mm to 500 mm) is a two-size reduction].
  2. The fan-assisted appliance(s) is common vented with a draft hood-equipped appliance(s).
  3. The vent connector has a smooth interior wall. [NFPA 54:13.2.24]
All combinations of pipe sizes, single-wall metal pipe, and double-wall metal pipe shall be allowed within any connector run(s) or within the common vent, provided ALL of the appropriate tables permit ALL of the desired sizes and types of pipe, as if 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 using Table 803.2(2) or Table 803.2(4) as appropriate. [NFPA 54:13.2.25]
Where a table permits more than one diameter of pipe to be used for a connector or vent, all 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 be permitted. [NFPA 54:13.2.28]
For vent heights lower than 6 feet (1829 mm) and higher than 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 803.2(1) through Table 803.2(9), one of the following shall be used:
  1. Interpolation.
  2. 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]
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