Chapter 1 Administration

Chapter 2 Definitions

Chapter 3 General Regulations

Chapter 4 Plumbing Fixtures and Fixture Fittings

Chapter 5 Water Heaters

Chapter 6 Water Supply and Distribution

Chapter 7 Sanitary Drainage

Chapter 8 Indirect Wastes

Chapter 9 Vents

Chapter 10 Traps and Interceptors

Chapter 11 Storm Drainage

Chapter 12 Fuel Gas Piping

Chapter 13 Health Care Facilities and Medical Gas and Medical Vacuum Systems

Chapter 14 Firestop Protection

Chapter 15 Alternate Water Sources for Nonpotable Applications

Chapter 16 Nonpotable Rainwater Catchment Systems

Chapter 16A Non-Potable Water Reuse Systems

Chapter 17 Referenced Standards

Appendices [PDF]

Appendix A Recommended Rules for Sizing the Water Supply System

Appendix B Explanatory Notes on Combination Waste and Vent Systems

Appendix C Alternate Plumbing Systems

Appendix D Sizing Storm Water Drainage Systems

Appendix E Manufactured/Mobile Home Parks and Recreational Vehicle Parks

Appendix F Firefighter Breathing Air Replenishment Systems

Appendix G Sizing of Venting Systems

Appendix H Private Sewage Disposal Systems

Appendix J Combination of Indoor and Outdoor Combustion and Ventilation Opening Design

Appendix K Potable Rainwater Catchment Systems

Appendix L Sustainable Practices

The regulations of this chapter shall govern the construction, location, and installation of fuel-burning and other types of water heaters heating potable water, together with chimneys, vents, and their connectors. The minimum capacity for storage water heaters shall be in accordance with the first hour rating listed in Table 501.1(1). No water heater shall be hereinafter installed that does not comply with the manufacturer's installation instructions and the type and model of each size thereof approved by the Authority Having Jurisdiction. A list of accepted water heater appliance standards are referenced in Table 501.1(2). Listed appliances shall be installed in accordance with the manufacturer's installation instructions. Unlisted water heaters shall be permitted in accordance with Section 504.3.2.

TABLE 501.1(1)
FIRST HOUR RATING1
Number of Bathrooms 1 10 1.5 2 to 2.5 3 to 3.5
Number of Bedrooms 1 2 3 2 3 4 5 3 4 5 6
First Hour Rating2 Gallons 42 54 54 54 67 67 80 67 80 80 80
For SI units: 1 gallon = 3.785 L

Notes:
1   The first hour rating is found on the "Energy Guide" label.
2   Solar water heaters shall be sized to meet the appropriate first hour rating as shown in the table.


TABLE 501.1(2)
WATER HEATERS
TYPE STANDARD
Electricity, Household UL 174
Oil Fired Storage Tank UL 732
Gas, 75000 Btu/h or less CSA Z21.10.1
Gas, Above 75000 Btu/h CSA Z21.10.3
Electric, Commercial UL 1453
Solid Fuel UL 2523
For SI units: 1000 British thermal units per hour = 0.293 kW
It shall be unlawful for a person to install, remove, or replace or cause to be installed, removed, or replaced a water heater without first obtaining a permit from the Authority Having Jurisdiction to do so.
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.
This inspection shall be made after work authorized by the permit has been installed. The Authority Having Jurisdiction will make such inspection as deemed necessary to be assured that the work has been installed in accordance with the intent of this code. No appliance or part thereof shall be covered or concealed until the same has been inspected and approved by the Authority Having Jurisdiction.
Water heater installations in bedrooms and bathrooms shall be in accordance with one of the following [NFPA 54:10.28.1]:
  1. Fuel-burning water heaters shall be permitted to be installed in a closet located in the bedroom or bathroom provided the closet is equipped with a listed, gasketed door assembly and a listed self-closing device. The self-closing door assembly shall meet the requirements of Section 504.1.1. The door assembly shall be installed with a threshold and bottom door seal and shall meet the requirements of Section 504.1.2. Combustion air for such installations shall be obtained from the outdoors in accordance with Section 506.4. The closet shall be for the exclusive use of the water heater.
  2. Water heater shall be of the direct vent type. [NFPA 54:10.28.1(2)]
Self-closing doors shall swing easily and freely, and shall be equipped with a self-closing device to cause the door to close and latch each time it is opened. The closing mechanism shall not have a hold-open feature.
Gasketing on gasketed doors or frames shall be furnished in accordance with the published listings of the door, frame, or gasketing material manufacturer.

Exception: Where acceptable to the Authority Having Jurisdiction, gasketing of non-combustible or limited-combustible material shall be permitted to be applied to the frame, provided closing and latching of the door are not inhibited.
Water heaters of other than the direct-vent type shall be located as close as practical to the chimney or gas vent.
The clearance requirements for water heaters shall comply with Section 504.3.1 or Section 504.3.2.
The clearances shall not be such as to interfere with combustion air, draft hood clearance and relief, and accessibility for servicing. Listed water heaters shall be installed in accordance with their listings and the manufacturer's installation instructions.
Unlisted water heaters shall be installed with a clearance of 12 inches (305 mm) on all sides and rear. Combustible floors under unlisted water heaters shall be protected in an approved manner. [NFPA 54:10.28.2.2]
A water heater installation shall be provided with overpressure protection by means of an approved, listed device installed in accordance with the terms of its listing and the manufacturer's installation instructions.
A water heater installation or a hot water storage vessel installation shall be provided with overtemperature protection by means of an approved, listed device installed in accordance with the terms of its listing and the manufacturer's installation instructions.
Temperature, pressure, and vacuum relief devices or combinations thereof, and automatic gas shutoff devices, shall be installed in accordance with the terms of their listings and the manufacturer's installation instructions. A shutoff valve shall not be placed between the relief valve and the water heater or on discharge pipes between such valves and the atmosphere. The hourly British thermal units (Btu) (kW•h) discharge capacity or the rated steam relief capacity of the device shall be not less than the input rating of the water heater.
Water heaters deriving heat from fuels or types of energy other than gas shall be constructed and installed in accordance with the approved standards referenced in Table 501.1(2), Section 505.3, or Section 505.4. Vents or chimneys for such appliances shall be approved types. An adequate supply of air for combustion and for adequate ventilation of heater rooms or compartments shall be provided. Each such appliance shall be installed in a location approved by the Authority Having Jurisdiction and local and state fire-prevention agencies.
Storage-type water heaters and hot water boilers deriving heat from fuels or types of energy other than gas, shall be provided with, in addition to the primary temperature controls, an overtemperature safety protection device constructed, listed, and installed in accordance with nationally recognized applicable standards for such devices and a combination temperature and pressure-relief valve.
Oil-fired water heaters shall be installed in accordance with NFPA 31.
Indirect-fired water heaters shall comply with the applicable sections of the ASME Boiler and Pressure Vessel Code, or to one of the other applicable standards shown in Table 501.1(2). Each water heater shall bear a label in accordance with ASME requirements, or an approved testing agency, certifying and attesting that such an appliance has been tested, inspected and meets the requirements of the applicable standards or code.
An indirect-fired water heater that incorporates a single-wall heat exchanger shall be in accordance with the following requirements:
  1. The heat transfer medium shall be either potable water or contain fluids recognized as safe by the Food and Drug Administration (FDA) as food grade.
  2. Bear a label with the word "Caution," followed by the following statements:

    1. The heat-transfer medium shall be potable water or other nontoxic fluid recognized as safe by the FDA.
    2. The maximum operating pressure of the heat exchanger shall not exceed the maximum operating pressure of the potable water supply.
  3. The word "Caution" and the statements in letters shall have an uppercase height of not less than 0.120 of an inch (3.048 mm). The vertical spacing between lines of type shall be not less than 0.046 of an inch (1.168 mm). Lowercase letters shall be compatible with the uppercase letter size specification.
Air for combustion, ventilation, and dilution of flue gases for appliances installed in buildings shall be obtained by application of one of the methods covered in Section 506.2 through Section 506.7.3. Where the requirements of Section 506.2 are not met, outdoor air shall be introduced in accordance with methods covered in Section 506.4 through Section 506.7.3.

Exception: This provision shall not apply to direct-vent appliances. [NFPA 54:9.3.1.1]
Appliances of other than natural draft design and other than Category I vented appliances shall be provided with combustion, ventilation, and dilution air in accordance with the appliance manufacturer's instructions. [NFPA 54:9.3.1.2]
Where used, a draft hood or a barometric draft regulator shall be installed in the same room or enclosure as the appliance served so as to prevent a difference in pressure between the hood or regulator and the combustion air supply. [NFPA 54:9.3.1.4]
Where exhaust fans, clothes dryers, and kitchen ventilation systems interfere with the operation of appliances, makeup air shall be provided. [NFPA 54:9.3.1.5]
The required volume of indoor air shall be determined in accordance with Section 506.2.1 or Section 506.2.2, except that where the air infiltration rate is known to be less than 0.40 ACH (air change per hour), Section 506.2.2 shall be used. The total required volume shall be the sum of the required volume calculated for appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section 506.3 are considered a part of the required volume. [NFPA 54:9.3.2]
The required volume shall be not less than 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m3/kW). [NFPA 54:9.3.2.1]
Where the air infiltration rate of a structure is known, the required volume shall be not less than the following [NFPA 54:9.3.2.2]:
  1. For appliances other than fan-assisted, calculate using Equation 506.2.2(1). [NFPA 54:9.3.2.2(1)]
  2. For fan-assisted appliances, calculate using Equation 506.2.2(2). [NFPA 54:9.3.2.2(2)]
  3. For purposes of these calculations, an infiltration rate greater than 0.60 ACH shall not be used in the equations. [NFPA 54:9.3.2.2(3)]
Required columeother ≥(12 ft3/ACH) x (Iother/1000 Btu/h) [Equation 506.2.2(1)]
Required columefan ≥(12 ft3/ACH) x (Ifan/1000 Btu/h)    [Equation 506.2.2(2)]

Where:
Iother = Appliances other than fan-assisted input in Btu/h
Ifan = Fan-assisted appliance input in Btu/h
ACH = Air change per hour (percent of volume of space exchanged per hour, expressed as a decimal)
For SI units: 1 cubic foot = 0.0283 m3, 1000 British thermal units per hour = 0.293 kW
Openings used to connect indoor spaces shall be sized and located in accordance with the following:
  1. Each opening shall have a free area of not less than 1 square inch per 1000 Btu/h (0.002 m2/kW) of the total input rating of appliances in the space, but not less than 100 square inches (0.065 m2). One opening shall commence within 12 inches (305 mm) of the top of the enclosure and one opening shall commence within 12 inches (305 mm) of the bottom of the enclosure (see Figure 506.3). The dimension of air openings shall be not less than 3 inches (76 mm).
  2. The volumes of spaces in different stories shall be considered as communicating spaces where such spaces are connected by one or more openings in doors or floors having a total free area of not less than 2 square inches per 1000 Btu/h (0.004 m2/kW) of total input rating of appliances. [NFPA 54:9.3.2.3]
FIGURE 506.3
COMBUSTION AIR FROM ADJACENT INDOOR SPACES THROUGH INDOOR COMBUSTION AIR OPENINGS [NFPA 54: FIGURE A.9.3.2.3(1)]
Outdoor combustion air shall be provided through opening(s) to the outdoors in accordance with methods in Section 506.4.1 or Section 506.4.2. The dimension of air openings shall be not less than 3 inches (76 mm). [NFPA 54:9.3.3]
Two permanent openings, one commencing within 12 inches (305 mm) of the top of the enclosure and one commencing within 12 inches (305 mm) of the bottom of the enclosure shall be provided. The openings shall communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors as follows:
  1. Where directly communicating with the outdoors or where communicating to the outdoors through vertical ducts, each opening shall have a free area of not less than 1 square inch per 4000 Btu/h (0.0005 m2/kW) of total input rating of appliances in the enclosure. [See Figure 506.4(1) and Figure 506.4(2)]
  2. Where communicating with the outdoors through horizontal ducts, each opening shall have a free area of not less than 1 square inch per 2000 Btu/h (0.001 m2/kW) of total input rating of appliances in the enclosure. [See Figure 506.4(3)] [NFPA 54:9.3.3.1]
FIGURE 506.4(1)
COMBUSTION AIR FROM OUTDOORS INLET AIR FROM VENTILATED CRAWL SPACE AND OUTLET AIR TO VENTILATED ATTIC [NFPA 54: FIGURE A.9.3.3.1(1)(a)]


For SI units: 1 foot = 304.8 mm
FIGURE 506.4(2)
COMBUSTION AIR FROM OUTDOORS THROUGH VENTILATED ATTIC [NFPA 54: FIGURE A.9.3.3.1(1)(b)]

FIGURE 506.4(3)
COMBUSTION AIR FROM OUTDOORS THROUGH HORIZONTAL DUCTS [NFPA 54: FIGURE A.9.3.3.1(2)]
One permanent opening, commencing within 12 inches (305 mm) of the top of the enclosure, shall be provided. The appliance shall have clearances of not less than 1 inch (25.4 mm) from the sides and back and 6 inches (152 mm) from the front of the appliance. The opening shall directly communicate with the outdoors or shall communicate through a vertical or horizontal duct to the outdoors or spaces that freely communicate with the outdoors (see Figure 506.4.2) and shall have a free area not less than the following:
  1. One square inch per 3000 Btu/h (0.0007 m2/kW) of the total input rating of appliances located in the enclosure.
  2. Not less than the sum of the areas of vent connectors in the space. [NFPA 54:9.3.3.2]
FIGURE 506.4.2
COMBUSTION AIR FROM OUTDOORS THROUGH SINGLE COMBUSTION AIR OPENING [NFPA 54: FIGURE A.9.3.3.2]
The use of a combination of indoor and outdoor combustion air shall be in accordance with Section 506.5.1 through Section 506.5.3 (see calculation example in Appendix J). [NFPA 54:9.3.4]
Where used, openings connecting the interior spaces shall be in accordance with Section 506.3. [NFPA 54:9.3.4(1)]
Outdoor openings shall be located in accordance with Section 506.4. [NFPA 54:9.3.4(2)]
The outdoor opening(s) size shall be calculated in accordance with the following:
  1. The ratio of interior spaces shall be the volume of the communicating spaces divided by the required volume.
  2. The outdoor size reduction factor shall be one minus the ratio of interior spaces.
  3. The size of outdoor openings shall be not less than the full size of outdoor openings calculated in accordance with Section 506.4, multiplied by the reduction factor. The dimension of air openings shall be not less than 3 inches (76 mm). [NFPA 54:9.3.4(3)]
Engineered combustion air installations shall provide a supply of combustion, ventilation, and dilution air that is approved by the Authority Having Jurisdiction. [NFPA 54:9.3.5]
Where combustion air is provided by a mechanical air supply system, the combustion air shall be supplied from outdoors at the minimum rate of 0.35 cubic feet per minute per 1000 Btu/h [0.034 (m3/min)/kW] for appliances located within the space. [NFPA 54:9.3.6]
Where exhaust fans are installed, additional air shall be provided to replace the exhausted air. [NFPA 54:9.3.6.1]
Each of the appliances served shall be interlocked to the mechanical air supply system to prevent main burner operation where the mechanical air supply system is not in operation. [NFPA 54:9.3.6.2]
Where combustion air is provided by the building's mechanical ventilation system, the system shall provide the specified combustion air rate in addition to the required ventilation air. [NFPA 54:9.3.6.3]
The required size of openings for combustion, ventilation, and dilution air shall be based on the net free area of each opening. Where the free area through a design of louver, grille, or screen is known, it shall be used in calculating the size opening required to provide the free area specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers have 25 percent free area and metal louvers and grilles have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]
Screens shall be not less than 14 of an inch (6.4 mm) mesh. [NFPA 54:9.3.7.2]
Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to prevent the main burner from igniting where the louver fail to open during burner start-up and to shut down the main burner where the louvers close during burner operation. [NFPA 54:9.3.7.3]
Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:
  1. Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.

    Exception: Within dwelling units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:9.3.8.1]
  2. Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances. [NFPA 54:9.3.8.2]
  3. Ducts shall serve a single space. [NFPA 54:9.3.8.3]
  4. Ducts shall not service both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air. [NFPA 54:9.3.8.4]
  5. Ducts shall not be screened where terminating in an attic space. [NFPA 54:9.3.8.5]
  6. Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located not less than 12 inches (305 mm) vertically from the adjoining finished ground level. [NFPA 54:9.3.8.8]
  7. Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]
  8. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory-built chimney 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 54:9.3.8.7]
The Authority Having Jurisdiction shall have the authority to require the use of an approved dielectric insulator on the water piping connections of water heaters and related water heating appliances.
Water heaters shall be anchored or strapped to resist horizontal displacement due to earthquake motion. Strapping shall be at points within the upper one third (13) and lower one-third (13) of its vertical dimensions. At the lower point, a minimum distance of four (4) inches (102 mm) shall be maintained above the controls with the strapping.

Note: [HCD 1 & HCD 2] Reference Health and Safety Code Section 19211(a) which addresses new, replacement, and existing water heaters.

Note: The applicable subsection of Health and Safety Code Section 19211(a) which addresses new, replacement, and existing water heaters is repeated here for clarity and reads as follows:

    Section 19211(a) Notwithstanding Section 19100, all new and replacement water heaters, and all existing residential water heaters shall be braced, anchored, or strapped to resist falling or horizontal displacement due to earthquake motion. At a minimum, any water heater shall be secured in accordance with the California Plumbing Code, or modifications made thereto by a city, county, or city and county pursuant to Section 17958.5.
Appliances and equipment shall be furnished either with load-distributing bases or with an approved number of supports to prevent damage to either the building structure or the appliance and the equipment. [NFPA 54:9.1.8.1]
At the locations selected for installation of appliances and equipment, the dynamic and static load-carrying capacities of the building structure shall be checked to determine whether they are capable to carry the additional loads, Appliances and equipment shall be supported and shall be connected to the piping so as not to exert undue stress on the connections. [NFPA 54:9.1.8.2]
A water heater supported from the ground shall rest on level concrete or other approved base extending not less than 3 inches (76 mm) above the adjoining ground level.
Where a water heater is located in an attic. in or on an attic-ceiling assembly, floor-ceiling assembly, or floor-subfloor assembly where damage results from a leaking water heater, a watertight pan of corrosion-resistant materials shall be installed beneath the water heater with not less than 34 of an inch (20 mm) diameter drain to an approved location. Such pan shall be not less than 112 inches (38 mm) in depth.
Where additional or replacement equipment or appliances are installed or an appliance is converted to gas from another fuel, the location in which the equipment or appliance is to be operated shall be checked to verify the following:
  1. Air for combustion and ventilation is provided where required, in accordance with the provisions of Section 506.0. Where existing facilities are not adequate, they shall be upgraded to be in accordance with Section 506.0 specifications, [NFPA 54:9.1.2(1)]
  2. The installation components and appliances shall be installed with clearances to combustible material so their operation will not create a hazard to persons or property. Minimum clearances between combustible walls and the back and sides of various conventional types of appliances and their vent connectors are specified in Table 509.7.3(1) and Table 509.7.3(2). [NFPA 54:9.2.2] It shall be determined that the installation and operation of the additional or replacement appliances do not render the remaining appliances unsafe for continued operation.
  3. The venting system is constructed and sized in accordance with the provisions of Section 509.0. Where the existing venting system is not adequate, it shall be upgraded in accordance with Section 509.0. [NFPA 54:9.1.2(3)]
The appliance shall be connected to the fuel gas for which it was designed. No attempt shall be made to convert the appliance from the gas specified on the rating plate for use with a different gas without consulting the installation instructions, the serving gas supplier, or the appliance manufacturer for complete instructions. [NFPA 54:9.1.3]
Unlisted appliances for use with undiluted liquefied petroleum gases and installed indoors, except attended laboratory equipment, shall be equipped with safety shutoff devices of the complete shutoff type. [NFPA 54:9.1.4]
Where air or oxygen under pressure is used in connection with the gas supply, effective means such as a backpressure regulator and relief valve shall be provided to prevent air or oxygen from passing back into the gas piping. Where oxygen is used, installation shall be in accordance with NFPA 51. [NFPA 54:9.1.5]
Nondirect-vent appliances installed in beauty shops, barber shops, or other facilities where chemicals that generate corrosive or flammable products such as aerosol sprays are routinely used shall be located in a mechanical equipment room separate or partitioned off from other areas with provisions for combustion and dilution air from outdoors. Direct-vent appliances in such facilities shall be installed in accordance with the appliance manufacturer's installation instructions. [NFPA 54:9.1.6.2]
In addition to air needed for combustion in commercial or industrial processes, process air shall be provided as required for cooling of appliances, equipment, or material; for controlling dew point, heating, drying, oxidation, dilution, safety exhaust, odor control, air for compressors; and for comfort and proper working conditions for personnel. [NFPA 54:9.1.7]
Appliances shall not be installed in areas where the open use, handling, or dispensing of flammable liquids occurs, unless the design, operation, or installation reduces the potential of ignition of the flammable vapors. Appliances installed in accordance with Section 507.13, Section 507.14, or Section 507.15 shall be considered to be in accordance with the intent of this provision. [NFPA 54:9.1.9]
Appliances in garages and in adjacent spaces that open to the garage and are not part of the living space of a dwelling unit shall be installed so that burners and burner-ignition devices are located not less than 18 inches (457 mm) above the floor unless listed as flammable vapor ignition resistant. [NFPA 54:9.1.10.1]
Appliances installed in garages, warehouses, or other areas subject to mechanical damage shall be guarded against such damage by being installed behind protective barriers or by being elevated or located out of the normal path of vehicles.
Where appliances are installed within a garage and are enclosed in a separate enclosed space having access only from outside of the garage, such appliances shall be permitted to be installed at floor level, provided the required combustion air is taken from the exterior of the garage. [NFPA 54:9.1.10.3]
Appliances installed in commercial garages shall comply with Section 507.14.1 and Section 507.14.2.
Appliances installed in enclosed, basement, and underground parking structures shall be installed in accordance with NFPA 88A. [NFPA 54:9.1.11.1]
Appliances installed in repair garages shall be installed in a detached building or room, separated from repair areas by walls or partitions, floors, or floor-ceiling assemblies that are constructed so as to prohibit the transmission of vapors and having a fire-resistance rating of not less than 1 hour, and that have no openings in the wall separating the repair area within 8 feet (2438 mm) of the floor. Wall penetrations shall be firestopped. Air for combustion purposes shall be obtained from outside the building. The heating room shall not be used for the storage of combustible materials.

Exceptions:
  1. Overhead heaters where installed not less than 8 feet (2438 mm) above the floor shall be permitted.
  2. Heating appliances for vehicle repair areas where there is no dispensing or transferring of Class I or Class II flammable or combustible liquids or liquefied petroleum gas shall be installed in accordance with NFPA 30A. [NFPA 54:9.1.11.2]
Heaters in aircraft hangars shall be installed in accordance with NFPA 409. [NFPA 54:9.1.12]
Appliances shall be vented in accordance with the provisions of this chapter. [NFPA 54:9.1.14]
No device or attachment shall be installed on an appliance that is capable of impairing the combustion of gas. [NFPA 54:9.1.15]
Where additional appliances are being connected to a gas piping system, the existing piping shall be checked to determine where it has adequate capacity. Where inadequate, the existing system shall be enlarged as necessary, or separate gas piping of adequate capacity shall be run from the point of delivery to the appliance. [NFPA 54:9.1.16]
Appliances shall be supported and connected to the piping so as not to exert undue strain on the connections. [NFPA 54:9.1.17]
Where the gas supply pressure is higher than that at which the appliance is designed to operate or varies beyond the design pressure limits of the appliance, a gas appliance pressure regulator shall be installed. [NFPA 54:9.1.18]
Venting of gas appliance pressure regulators shall be in accordance with the following requirements:
  1. Appliance pressure regulators requiring access to the atmosphere for successful operation shall be equipped with vent piping leading outdoors or, where the regulator vent is an integral part of the appliance, into the combustion chamber adjacent to a continuous pilot, unless constructed or equipped with a vent limiting means to limit the escape of gas from the vent opening in the event of diaphragm failure.
  2. Vent limiting means shall be employed on listed gas appliance pressure regulators.
  3. In the case of vents leading outdoors, means shall be employed to prevent water from entering this piping and also to prevent blockage of vents by insects and foreign matter.
  4. Under no circumstances shall a regulator be vented to the appliance flue or exhaust system.
  5. In the case of vents entering the combustion chamber, the vent shall be located so the escaping gas will be readily ignited by the pilot and the heat liberated thereby will not adversely affect the normal operation of the safety shutoff system. The terminus of the vent shall be securely held in a fixed position relative to the pilot. For manufactured gas, the need for a flame arrester in the vent piping shall be determined.
  6. Vent lines from an appliance pressure regulator and bleed lines from a diaphragm-type valve shall not be connected to a common manifold terminating in a combustion chamber. Vent lines shall not terminate in positive-pressure-type combustion chambers. [NFPA 54:9.1.19]
Bleed lines shall comply with the following requirements:
  1. Diaphragm-type valves shall be equipped to convey bleed gas to the outdoors or into the combustion chamber adjacent to a continuous pilot.
  2. In the case of bleed lines leading outdoors, means shall be employed to prevent water from entering this piping and also to prevent blockage of vents by insects and foreign matter.
  3. Bleed lines shall not terminate in the appliance flue or exhaust system.
  4. In the case of bleed lines entering the combustion chamber, the bleed line shall be located so the bleed gas will be readily ignited by the pilot and the heat liberated thereby will not adversely affect the normal operation of the safety shutoff system. The terminus of the bleed line shall be securely held in a fixed position relative to the pilot. For manufactured gas, the need for a flame arrester in the bleed line piping shall be determined.
  5. Bleed lines from a diaphragm-type valve and vent lines from an appliance pressure regulator shall not be connected to a common manifold terminating in a combustion chamber. Bleed lines shall not terminate in positive-pressure-type combustion chambers. [NFPA 54:9.1.20]
A combination of appliances, equipment, attachments, or devices used together in a manner shall be in accordance with the standards that apply to the individual appliance and equipment. [NFPA 54:9.1.21]
The installing agency shall comply with the appliance and equipment manufacturer's installation instructions in completing an installation. The installing agency shall leave the manufacturer's installation, operating, and maintenance instructions in a location on the premises where they will be readily available for reference and guidance for the Authority Having Jurisdiction, service personnel, and the owner or operator. [NFPA 54:9.1.22]
Appliances not listed for outdoor installation but installed outdoors shall be provided with protection to the degree that the environment requires. Appliances listed for outdoor installation shall be permitted to be installed without protection in accordance with the provisions of its listing and the manufacturer's installation instructions.
Appliances shall be located with respect to building construction and other equipment so as to permit access to the appliance. Sufficient clearance shall be maintained to permit cleaning of heating surfaces; the replacement of filters, blowers, motors, burners, controls, and vent connections; the lubrication of moving parts where necessary; the adjustment and cleaning of burners and pilots; and the proper functioning of explosion vents, where provided. For attic installation, the passageway and servicing area adjacent to the appliance shall be floored. [NFPA 54:9.2.1]
Equipment and appliances on roofs shall be designed or enclosed so as to withstand climatic conditions in the area in which they are installed. Where enclosures are provided, each enclosure shall permit easy entry and movement, shall be of reasonable height, and shall have not less than a 30 inch (762 mm) clearance between the entire service access panel(s) of the equipment and appliance and the wall of the enclosure. [NFPA 54:9.4.1.1]
Roofs on which equipment and appliances are to be installed shall be capable of supporting the additional load or shall be reinforced to support the additional load. [NFPA 54:9.4.1.2]
Access locks, screws, and bolts shall be of corrosion-resistant material. [NFPA 54:9.4.1.3]
Equipment and appliances shall be installed in accordance with the manufacturer's installation instructions. [NFPA 54:9.4.2.1]
Equipment and appliances shall be installed on a well-drained surface of the roof. Not less than 6 feet (1829 mm) of clearance shall be between a part of the equipment and appliance and the edge of a roof or similar hazard, or rigidly fixed rails, guards, parapets, or other building structures not less than 42 inches (1067 mm) in height shall be provided on the exposed side. [NFPA 54:9.4.2.2]
Equipment and appliances requiring an external source of electrical power for its operation shall be provided with the following:
  1. A readily accessible electrical disconnecting means within sight of the equipment and appliance that will completely de-energize the equipment and appliance.
  2. A 120-VAC grounding-type receptacle outlet on the roof adjacent to the equipment and appliance. The receptacle outlet shall be on the supply side of the disconnect switch. [NFPA 54:9.4.2.3]
Where water stands on the roof at the equipment and appliance or in the passageways to the equipment and appliance, or where the roof is of a design having a water seal, an approved platform, walkway, or both shall be provided above the waterline. Such platforms or walkways shall be located adjacent to the equipment and appliance and control panels so that the equipment and appliance is capable of being safely serviced where water stands on the roof. [NFPA 54:9.4.2.4]
Equipment and appliances located on roofs or other elevated locations shall be accessible. [NFPA 54:9.4.3.1]
Buildings exceeding 15 feet (4572 mm) in height shall have an inside means of access to the roof, unless other means acceptable to the Authority Having Jurisdiction are used. [NFPA 54:9.4.3.2]
The inside means of access shall be a permanent, or fold-away inside stairway or ladder, terminating in an enclosure, scuttle, or trap door. Such scuttles or trap doors shall be not less than 22 inches by 24 inches (559 mm by 610 mm) in size, shall open easily and safely under all conditions, especially snow; and shall be constructed so as to permit access from the roof side unless deliberately locked on the inside.

    Not less than 6 feet (1829 mm) of clearance shall be between the access opening and the edge of the roof or similar hazard, or rigidly fixed rails or guards not less than 42 inches (1067 mm) in height shall be provided on the exposed side. Where parapets or other building structures are utilized in lieu of guards or rails, they shall be not less than 42 inches (l067 mm) in height. [NFPA 54:9.4.3.3]
Permanent lighting shall be provided at the roof access. The switch for such lighting shall be located inside the building near the access means leading to the roof. [NFPA 54:9.4.3.4]
An attic or under-floor space in which an appliance is installed shall be accessible through an opening and passageway not less than as large as the largest component of the appliance, and not less than 22 inches by 30 inches (559 mm by 762 mm).
Where the height of the passageway is less than 6 feet (1829 mm), the distance from the passageway access to the appliance shall not exceed 20 feet (6096 mm) measured along the centerline of the passageway. [NFPA 54:9.5.1.1]
The passageway shall be unobstructed and shall have solid flooring not less than 24 inches (610 mm) wide from the entrance opening to the appliance. [NFPA 54:9.5.1.2]
A level working platform not less than 30 inches by 30 inches (762 mm by 762 mm) shall be provided in front of the service side of the appliance. [NFPA 54:9.5.2]
A permanent 120-volt receptacle outlet and a lighting fixture shall be installed near the appliance. The switch controlling the lighting fixture shall be located at the entrance to the passageway. [NFPA 54:9.5.3]
Type B and Type B-W gas vents shall comply WIth UL 441 and 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 14 of an inch (6.4 mm) mesh.
Except as permitted in Section 509.2.1 through Section 509.2.5, appliances shall be connected to venting systems. [NFPA 54:12.3.1]
The following appliances shall not be required to be vented [NFPA 54:12.3.2]:
  1. A single listed booster-type (automatic instantaneous) water heater, where 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 where a draft hood is required, in a commercial kitchen having a mechanical exhaust system; where installed in this manner, the draft hood outlet shall be not less than 36 inches (914 mm) vertically and 6 inches (152 mm) horizontally from a surface other than the appliance. [NFPA 54:12.3.2(5)]
  2. Other appliances listed for unvented use and not provided with flue collars. [NFPA 54:12.3.2(10)]
    Where appliances in Section 509.2.1(1) and Section 509.2.1(2) are installed so the aggregate input rating exceeds 20 British thermal units per hour per cubic foot [(Btu/h)/ft3] (0.21 kW/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 appliance does not exceed 20 [(Btu/h)/ft3] (0.21 kW/m3). Where the calculation includes the volume of an adjacent room or space, the room or space in which the appliance is 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 54:12.3.2.1, 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 509.8.2. [NFPA 54:12.3.5]
Appliances incorporating integral venting means shall be installed in accordance with the manufacturer's installation instructions, Section 509.8, and Section 509.8.1. [NFPA 54:12.3.6]
Venting systems shall be designed and constructed to convey flue, vent, or both 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 509.4 through Section 509.14 of this code. [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]

Exception: Incinerators.
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 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 509.8 and Section 509.8.1 of this code. [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]
The type of venting system to be used shall be in accordance with Table 509.4. [NFPA 54:12.5.1]

TABLE 509.4
TYPE OF VENTING SYSTEM TO BE USED
[NFPA 54: TABLE 12.5.1]
APPLIANCES TYPE OF VENTING SYSTEM
Listed Category I appliances Type B gas vent(Section 509.6)
Listed appliances equipped
with draft hood
Chimney (Section 509.5)
Appliances listed for
Type B gas vent
Single-wall metal pipe
(Section 509.7)
Listed Chimney lining system for
gas venting (Section 509.5.3)
Special gas vent listed for this
appliance (Section 509.4.3)
Listed vented wall furnaces Type B-W gas vent
(Section 509.6, Section 509.6.2.2)
Category II appliances
Category III appliances
Category IV appliances
As specified or furnished by
manufacturers of listed appliance.
(Section 509.4.1, Section 509.4.3)
Incinerators, outdoors Single-wall metal pipe
(Section 509.7, Section 509.7.2)
Incinerators, indoors

Appliances that are capable of being 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 509.5)
Listed combination gas- and
oil-burning appliances
Type L vent (Section 509.6) or
chimney (Section 509.5)
Decorative appliance in
vented fireplace
Chimney (UMC Section 911.2)
Direct-vent appliance See Sections 509.2.4
Appliances with integral vent See Section 509.2.5
Plastic piping used for venting appliances listed for use with such venting materials shall be approved. [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 509.5.1 through Section 509.5.3.
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 509.5.4.3 shall be listed or labeled in accordance with UL 103 for factory-built residential chimneys.
Factory-built chimneys shall comply with the requirements of UL 103 or 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 tor 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 the 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 509.5.4) [NFPA 54:12.6.2.1]


For SI units: 1 foot = 304.8 mm
FIGURE 509.5.4
TYPICAL TERMINATION LOCATIONS FOR CHIMNEYS AND SINGLE-WALL METAL PIPES SERVING RESIDENTIAL-TYPE AND LOW-HEAT APPLIANCE [NFPA 54: FIGURE A.12.602.1]
A chimney for a medium-heat appliance shall extend not less than 10 feet (3048 mm) above a portion of a 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 [NFPA 54:12.6.3.1]:
  1. Section 510.0. [NFPA 54:12.6.3.1(1)]
  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 exceeding seven times the draft hood outlet area. [NFPA 54:12.6.3.1(2)]
  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 exceeding seven times the smallest draft hood outlet area. [NFPA 54:12.6.3.1(3)]
  4. Other approved engineering methods. [NFPA 54:12.6.3.1(5)]
  5. Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods. [NFPA 54:12.6.3.1(4)]
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 where an appliance is replaced by an appliance of similar type, input rating, and efficiency, where the chimney is in accordance with Section 509.5.6, and the sizing of the chimney is in accordance with Section 509.5.5. [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]
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 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]
Gas vents shall be installed in accordance with the manufacturer's installation instructions. [NFPA 54:12.7.1(1)]
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(4)]
A gas vent shall terminate in accordance with one of the following:
  1. Gas vents that are 12 inches (305 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 509.6.2 and Table 509.6.2. Gas vents that are over 12 inches (305 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.
  2. Industrial appliances as provided in Section 509.2.3.
  3. Direct-vent systems as provided in Section 509.2.4.
  4. Appliances with integral vents as provided in Section 509.2.5.
  5. Mechanical draft systems as provided in Section 509.3.3.
  6. Ventilating hoods and exhaust systems as provided in Section 509.3.4. [NFPA 54:12.7.2(1)]

FIGURE 509.6.2
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 509.6.2
ROOF PITCH HEIGHT
[NFPA 54: TABLE 12.7.2]
ROOF PITCH H (minimum) (feet)
Flat to 612 1.0
Over 612 to 712 1.25
Over 712 to 812 1.5
Over 812 to 912 2
Over 912 to 1012 2.5
Over 1012 to 1112 3.25
Over 1112 to 1212 4.0
Over 1212 to 1412 5.0
Over 1412 to 1612 6.0
Over 1612 to 1812 7.0
Over 1812 to 2012 7.5
Over 2012 to 2112 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 509.2.4 and Section 509.3.3. [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 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 510.0 or other approved engineering methods and the gas vent and gas 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 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 510.0.
  2. Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion systems and draft hood-equipped appliances, shall be sized in accordance with Section 510.0 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 or Type L vents shall extend in a vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60 degree (1.05 rad) offset shall be permitted. An angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall be not greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.3.2]
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 509.6.4.1) [NFPA 54:12.7.4.2]
FIGURE 509.6.4.1
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 510.2(1), provided the following apply:
  1. The 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 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, shall be based on the total appliance's gas input rate entering that segment and its total height. [NFPA 54:12.7.4.3]
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 bum 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. 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 comply with the following requirements:
  1. Single-wall metal pipe shall terminate not less than 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 not less than 2 feet (610 mm) above the highest point where it passes through the roof of a building and not less than 2 feet (610 mm) exceeding a portion ofa building within a horizontal distance of 10 feet (3048 mm). (See Figure 509.5.4)
  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]

Notes:
1   A - Equals the clearance with no protection specified in Table 509.7.3(1) and Table 509.7.3(2) and in the sections applying to various types of appliances.
2   B - Equals the reduced clearance permitted in accordance with Table 509.7.3(2)
3   The protection applied to the construction using combustible material shall extend far enough in each direction to make C equal to A.
FIGURE 509.7.3(1)1, 2, 3
EXTENT OF PROTECTION NECESSARY TO REDUCE CLEARANCES FROM GAS APPLIANCES OR VENT CONNECTORS
[NFPA 54: FIGURE 10.3.2.3(a)]
For SI units: 1 inch = 25.4 mm
Note: Masonry walls shall be attached to combustible walls using wall ties. Spacers shall not be used directly behind appliance or connector.
FIGURE 509.7.3(2)
WALL PROTECTION REDUCTION SYSTEM
[NFPA 54: FIGURE 10.3.2.3(b)]

For SI units: 1 inch = 25.4 mm
FIGURE 509.7.3(3)
MASONRY CLEARANCE REDUCTION SYSTEM
[NFPA 54: FIGURE 10.3.2.3(c)]



TABLE 509.7.3(1)
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 appliances with draft hoods and appliances 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
Unlisted residential appliances with draft hood Not permitted 6 9 As listed
Residential an low-heat appliances other than those
above
Not permitted 9 18 As listed
Medium-heat appliances 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.



TABLE 509.7.3(2)
REDUCTION OF CLEARANCES WITH SPECIFIED FORMS OF PROTECTION1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
[NFPA 54: TABLE 10.2.3]
TYPE OF PROTECTION APPLIED
TO AND COVERING SURFACES
OF COMBUSTIBLE MATERIAL
WITHIN THE DISTANCE SPECIFIED
AS THE REQUIRED CLEARANCE
WITH NO PROTECTION [SEE
FIGURE 509.7.3(1) THROUGH
FIGURE 509.7.3(3)]
WHERE THE REQUIRED CLEARANCE WITH NO PROTECTION FROM APPLIANCE,
VENT CONNECTOR, OR SINGLE-WALL METAL PIPE IS:
36 (inches) 18 (inches) 12 (inches) 9 (inches) 6 (inches)
ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)
USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE
COLUMN 2 FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.
ABOVE
COLUMN 1
SIDES AND
REAR
COLUMN 2
ABOVE
COLUMN 1
SIDES AND
REAR
COLUMN 2
ABOVE
COLUMN 1
SIDES AND
REAR
COLUMN 2
ABOVE
COLUMN 1
SIDES AND
REAR
COLUMN 2
ABOVE
COLUMN 1
SIDES AND
REAR
COLUMN 2
(1)    312 inch thick masonry wall without ventilated air space
- 24 - 12 - 9 - 6 - 5
(2)    12 of an inch insulation board over 1 inch glass fiber or mineral woll batts
24 18 12 9 9 6 6 5 4 3
(3)    0.024 inch sheet metal over 1 inch glass fiber or mineral woll batts reinforced with wire on rear face with ventilated air space
18 12 9 6 6 4 5 3 3 3
(4)    312 inch thick masonry wall with ventilated air space
- 12 - 6 - 6 - 6 - 6
(5)    0.024 inch sheet metal with ventilated air space
18 12 9 6 6 4 5 3 3 2
(6)    12 of an inch thick insulation board with ventilated air space
18 12 9 6 6 4 5 3 3 3
(7)    0.024 inch sheet metal with ventilated air space over 0.024 inch sheet metal with ventilated air space
18 12 9 6 6 4 5 3 3 3
(8)    1 inch glass fiber or mineral wool batts sandwiched between two sheets 0.024 inch sheet metal with ventilated air space
18 12 9 6 6 4 5 3 3 3
For SI units: 1 inch = 25.4 mm, °C = (°F-32)/1.8

Notes:
1   Reduction of clearances from combustible materials shall not interfere with combustion air, draft hood clearance and relief, and accessibility of servicing.
2   Clearances shall be measured from the outer surface of the combustible material to the nearest point on the surface of the appliance, disregarding an intervening protection applied to the combustible material.
3   Spacers and ties shall be of noncombustible material. No spacer or tie shall be used directly opposite the appliance or connector.
4   Where clearance reduction systems use a ventilated air space, adequate provision for air circulation shall be provided as described. [See Figure 509.7.3(2) and Figure 509.7.3(3)]
5   There shall be not less than 1 inch (25.4 mm) between clearance reduction systems and combustible walls and ceilings for reduction systems using a ventilated air space.
6   Where a wall protector is mounted on a single flat wall away from comers, it shall have a minimum 1 inch (25.4 mm) air gap. To provide air circulation, the bottom and top edges, or only the side and top edges, or edges shall be left open.
7   Mineral wool batts (blanket or board) shall have a minimum density of 8 pounds per cubic foot (lb/ft3) (128 kg/m3) and a minimum melting point of 1500°F (816°C).
8   Insulation material used as part of a clearance reduction system shall have a thermal conductivity of 1 British thermal unit inch per hour square foot degree Fahrenheit [Btu•in/(h•ft2•°F)] [0.1 W/(m•K)) or less.
9   There shall be not less than 1 inch (25.4 mm) between the appliance and the protector. In no case shall the clearance between the appliance and the combustible surface be reduced below that allowed in this table.
10 Clearances and thicknesses are minimum; larger clearances and thicknesses are acceptable.
11 Listed single-wall connectors shall be installed in accordance with the terms of their listing and the manufacturer's installation instructions.
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]
Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have required clearances maintained.
Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 509.7.3(1). Reduced clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors in Table 509.7.3(2). [NFPA 54:12.8.4.4]
A 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 not less than 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 not less than 2 inches (51 mm) larger in diameter than the metal pipe.
  2. For unlisted appliances having draft hoods, the thimble shall be not less than 6 inches (152 mm) larger in diameter than the metal pipe.
  3. For residential and low-heat appliances, the thimble shall be not less than 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 from the metal pipe to provide the specified clearance from combustible material. 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 509.7.3.5. [NFPA 54:12.8.4.5]
Single-wall metal piping shall comply with the Section 509.7.4.1 through Section 509.7.4.3. [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 510.0.
  2. For a venting system for a single appliance with a draft hood, the areas of the connector and the pipe each shall be not 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 509.6.6. [NFPA 54:12.8.7]
(See Figure 509.8) A mechanical draft venting system shall terminate not less than 3 feet (914 mm) above a forced air inlet located within 10 feet (3048 mm).

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 509.8
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 not less than 6 inches (152 mm) from an air opening into a building, and such an appliance with an input exceeding 10000 Btu/h (3 kW) but not exceeding 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 not less than a 12 inch (305 mm) vent termination clearance. The bottom of the vent terminal and the air intake shall be located not less than 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 is capable of creating a nuisance or hazard 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 terminals 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 509.8.3. [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 509.8.3. [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 exceeding that of Section 509.10.1.2(1)(b). Section 509.10.1.2(1)(c), or Section 509.10.1.2(1)(d) above.
    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 non-residential low-heat appliance shall be a factory-built chimney section or steel pipe having resistance to heat and corrosion equivalent to the galvanized pipe specified in Table 509.10.1.3. Factory-built chimney sections shall be installed in accordance with the chimney manufacturer's installation instructions. [NFPA 54:12.11.2.4]

TABLE 509.10.1.3
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
to 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, and commercial and industrial incinerators, shall be constructed of factory-built, medium-heat chimney sections or steel of a thickness not less than that specified in Table 509.10.1.4 and shall comply with the following:
  1. A steel vent connector for appliances 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 not less than 21&fral;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 not less than 41&fral;2 inches (114 mm) thick laid on the 41&fral;2 inch (114 mm) bed for a vent connector having a diameter or cross-sectional dimension exceeding 18 inches (457 mm).
  4. Factory-built chimney sections, where employed, shall be installed in accordance with the chimney manufacturer's installation instructions. [NFPA 54:12.11.2.5]

TABLE 509.10.1.4
MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR MEDIUM-HEAT APPLIANCES AND COMMERCIAL AND INDUSTRIAL INCINERATORS
[NFPA 54: TABLE 12.11.2.5]
VENT CONNECTOR SIZE
DIAMETER (inches) AREA
(square inches)
MINIMUM
THICKNESS (inches)
Up to 14 Up to 154 0.53
Over 14 to 16 154 to 201 0.067
Over 16 to 18 201 to 254 0.093
Over 18 Exceeding 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 510.0 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 alternate 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 not less than 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 510.0 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 shall be sized in accordance with Section 510.0 or other approved engineering methods. [NFPA 54:12.11.3.5]

    As an alternate method applicable where there are two draft hood-equipped appliances, the effective area of the common vent connector or vent manifold and junction fittings shall be not less than the area of the larger vent connector plus 50 percent of the areas of smaller flue collar outlets. [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 Hue or vent, the openings shall be at different levels, or the connectors shall be attached to the vertical portion of the chimney or vent at an angle of 45 degrees (0.79 rad) 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 509.7.3(1).

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 509.7.3(2). [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. By sheet metal screws.
  2. Vent connectors of listed vent material shall be assembled and connected to flue collars or draft hood outlets in accordance with the manufacturer's installation instructions.
  3. Other approved means. [NFPA 54:12.11.6]
A vent connector shall be installed without dips or sags and shall slope upward toward the vent or chimney not less than 14 inch per foot (20.8 mm/m).

Exception: Vent connectors attached to a mechanical draft system installed in accordance with the appliance and draft system manufacturer's installation instructions. [NFPA 54:12.11.7]
The length of vent connectors shall comply with Section 509.10.7.1 or Section 509.10.7.2.
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]
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 400000 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 installation instructions. In the absence of manufacturer's installation 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 cheeking 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]
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.
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 510.1 or Section 510.2 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 509.3 and Section 509.3.1 is obtained. [NFPA 54:12.16]
Table 510.1.2(1) through Table 510.1.2(6) shall not be used where obstructions arc installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer's installation instructions or in accordance with the following:
  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 lateral lengths in Table 510.1.2(1), Table 510.1.2(2), and Table 510.1.2(5) shall not have elbows in the venting system. Single-appliance venting with lateral lengths, include two 90 degree (1.57 rad) elbows. For each additional elbow up to and including 45 degrees (0.79 rad), the maximum capacity listed in the venting tables shall be reduced by 5 percent. For each additional elbow greater than 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum capacity listed in the venting tables shall be reduced by 10 percent. Where multiple offsets occur in a vent, the total lateral length of offsets combined shall not exceed that specified in Table 510.1.2(1) through Table 510.1.2(5). [NFPA 54:13.1.3]


TABLE 510.1.2(1)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(a)]*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2
* NA: Not applicable.



TABLE 510.1.2(1)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54:TABLE 13.1(a)] (continued)
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2



TABLE 510.1.2(1)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54:TABLE 13.1(a)] (continued)
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2



TABLE 510.1.2(2)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(b)]*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2
* NA: Not applicable.



TABLE 510.1.2(2)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(b)] (continued)*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2
* NA: Not applicable.



TABLE 510.1.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(c)]*
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B 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
5
NA
NA
NA
NA
28
25
NA
NA
NA
NA
52
49
NA
NA
NA
NA
86
82
NA
NA
NA
NA
130
117
NA
NA
NA
NA
180
165
8 2
5
8
NA
NA
NA
NA
NA
NA
29
26
24
NA
NA
NA
NA
NA
NA
55
52
48
NA
NA
NA
NA
NA
NA
93
88
83
NA
NA
NA
NA
NA
NA
145
134
127
NA
NA
NA
NA
NA
NA
198
183
175
10 2
5
10
NA
NA
NA
NA
NA
NA
31
28
25
NA
NA
NA
NA
NA
NA
61
57
50
NA
NA
NA
NA
NA
NA
103
96
87
NA
NA
NA
NA
NA
NA
162
148
139
NA
NA
NA
NA
NA
NA
221
204
191
15 2
5
10
15
NA
NA
NA
NA
NA
NA
NA
NA
35
35
28
NA
NA
NA
NA
NA
NA
NA
NA
NA
67
62
55
48
NA
NA
NA
NA
NA
NA
NA
NA
114
107
97
89
NA
NA
NA
NA
NA
NA
NA
NA
179
164
153
141
53
NA
NA
NA
475
NA
NA
NA
250
231
216
201
20 2
5
10
15
20
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
38
36
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
74
68
60
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
124
116
107
97
83
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
201
184
172
159
148
51
80
NA
NA
NA
522
503
NA
NA
NA
274
254
237
220
206
30 2
5
10
15
20
30
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
41
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
82
76
67
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
137
128
115
107
91
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
216
198
184
171
159
NA
47
75
NA
NA
NA
NA
581
561
NA
NA
NA
NA
303
281
263
243
227
188
50 2
5
10
15
20
30
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
92
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
161
151
138
127
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
251
230
215
199
185
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
351
323
304
282
264
NA
Minimum
internal area of
chimney
(square inches)
12 19 28 38 50
Maximum
internal area of
chimney
(square inches)
Seven times the listed appliance categorized vent area, flue collar area, or draft hood outlet areas.
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.1.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(c)] (continued)*
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
5
NA
NA
NA
NA
247
231
NA
NA
NA
NA
320
298
NA
NA
NA
NA
401
376
NA
NA
NA
NA
581
561
8 2
5
8
NA
NA
NA
NA
NA
NA
266
247
239
84
NA
NA
590
NA
NA
350
328
318
100
149
173
728
711
695
446
423
410
139
201
231
1024
1007
990
651
640
623
10 2
5
10
68
NA
NA
519
NA
NA
298
277
263
82
124
155
655
638
610
388
365
347
98
146
182
810
791
762
491
466
444
136
196
240
1144
1124
1093
724
712
668
15 2
5
10
15
64
99
NA
NA
613
594
565
NA
336
313
296
281
77
118
148
171
779
759
727
698
441
416
394
375
92
139
173
198
968
946
912
880
562
533
567
485
127
186
229
259
1376
1352
1315
1280
841
828
777
742
20 2
5
10
15
20
61
95
122
NA
NA
687
658
627
NA
NA
375
350
332
314
296
73
113
143
165
186
867
845
811
780
750
491
463
440
418
397
87
133
167
191
214
1083
1059
1022
987
955
627
597
566
541
513
121
179
221
251
277
1548
1523
1482
1443
1406
953
933
879
840
807
30 2
5
10
15
20
30
57
90
115
NA
NA
NA
762
741
709
NA
NA
NA
421
393
373
353
332
288
68
106
135
156
176
NA
985
962
927
893
860
NA
558
526
500
476
450
416
81
125
158
181
203
249
1240
1216
1176
1139
1103
1035
717
683
648
621
592
555
111
169
210
239
264
318
1793
1766
1721
1679
1638
1560
1112
1094
1025
981
940
877
50 2
5
10
15
20
30
51
83
NA
NA
NA
NA
840
819
NA
NA
NA
NA
477
445
424
400
376
327
61
98
126
146
165
NA
1106
1083
1047
1010
977
NA
633
596
567
539
511
468
72
116
147
170
190
233
1413
1387
1347
1307
1269
1196
812
774
733
702
669
623
99
155
195
222
246
295
2080
2052
2006
1961
1916
1832
1243
1225
1147
1099
1050
984
Minimum
internal area of
chimney
(square inches)
63 78 95 132
Maximum
internal area of
chimney
(square inches)
Seven times the listed appliance categorized vent area, flue collar area, or draft hood outlet areas.
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.1.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(d)]*

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
5
NA
NA
NA
NA
28
25
NA
NA
NA
NA
52
48
NA
NA
NA
NA
86
81
NA
NA
NA
NA
130
116
NA
NA
NA
NA
180
164
8 2
5
8
NA
NA
NA
NA
NA
NA
29
26
23
NA
NA
NA
NA
NA
NA
55
51
47
NA
NA
NA
NA
NA
NA
93
87
82
NA
NA
NA
NA
NA
NA
145
133
126
NA
NA
NA
NA
NA
NA
197
182
174
10 2
5
10
NA
NA
NA
NA
NA
NA
31
28
24
NA
NA
NA
NA
NA
NA
61
56
49
NA
NA
NA
NA
NA
NA
102
95
86
NA
NA
NA
NA
NA
NA
161
147
137
NA
NA
NA
NA
NA
NA
220
203
189
15 2
5
10
15
NA
NA
NA
NA
NA
NA
NA
NA
35
32
27
NA
NA
NA
NA
NA
NA
NA
NA
NA
67
61
54
46
NA
NA
NA
NA
NA
NA
NA
NA
113
106
96
87
NA
NA
NA
NA
NA
NA
NA
NA
178
163
151
138
166
NA
NA
NA
473
NA
NA
NA
249
230
214
198
20 2
5
10
15
20
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
38
35
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
73
67
59
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
123
115
105
95
80
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
200
183
170
156
144
163
NA
NA
NA
NA
520
NA
NA
NA
NA
273
252
235
217
202
30 2
5
10
15
20
30
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
41
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
81
75
66
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
136
127
113
105
88
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
215
196
182
168
155
NA
158
NA
NA
NA
NA
NA
578
NA
NA
NA
NA
NA
302
279
260
240
223
182
50 2
5
10
15
20
30
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
91
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
160
149
136
124
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
250
228
212
195
180
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
350
321
301
278
258
NA
Minimum
internal area of
chimney
(square inches)
12 19 28 38 50
Maximum
internal area of
chimney
(square inches)
Seven times the listed appliance categorized vent area, flue collar area, or draft hood outlet areas.
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thelmal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.1.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.1(d)] (continued)*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2
* NA: Not applicable.



TABLE 510.1.2(5)
SINGLE-WALL METAL PIPE OR TYPE B ASBESTOS-CEMENT VENT [NFPA 54: TABLE 13.1(e)]*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2
* NA: Not applicable.



TABLE 510.1.2(6)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.1(f)]1, 2
NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: TYPE B 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
6
8
10
15
20
30
50
Local 99% winter design temperature: 37°F or greater
0
0
0
NA
NA
NA
NA
0
0
0
0
NA
NA
NA
0
0
0
0
123
NA
NA
0
0
0
0
190
NA
NA
0
0
0
0
249
NA
NA
0
0
0
0
184
393
NA
0
0
0
0
0
334
NA
0
0
0
0
0
0
579
6
8
10
15
20
30
50
Local 99% winter design temperature: 27°F to 36°F
0
0
0
NA
NA
NA
NA
0
0
51
NA
NA
NA
NA
68
82
97
NA
NA
NA
NA
116
127
141
NA
NA
NA
NA
156
167
183
233
NA
NA
NA
180
187
201
253
307
419
NA
212
214
225
274
330
445
NA
266
263
265
305
362
485
763
6
8
10
15
20
30
50
Local 99% winter design temperature:17°F to 26°F
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
197
214
NA
NA
NA
NA
215
226
245
296
352
NA
NA
259
264
278
331
287
507
NA
349
352
358
398
457
581
NA
6
8
10
15
20
30
50
Local 99% winter design temperature: 5°F to 16°F
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
289
NA
NA
NA
NA
NA
312
331
393
450
NA
NA
416
423
430
485
547
682
972
6
8
10
15
20
30
50
Local 99% winter design temperature: -10°F to 4°F
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
484
494
513
586
650
805
1003
Local 99% winter design temperature: -11°F or lower
Not recommended for any vent configurations
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2, °C = (°F-32)/1.8

Notes:
1   See Figure 510.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
2   NA: Not applicable.



99% Winter Design Temperatures for the Contiguous United States

This map is a necessarily generalized guide to temperatures in the contiguous United States, Temperatures shown for areas such as mountainous regions and large urban centers may not be accurate. The data used to develop this map are from the 1993 ASHRAE Handbook - Fundamentals (Chapter 24, Table 1: Climate Conditions for the United States).

For 99% winter design temperatures in Alaska, consult the ASHRAE Handbook - Fundamentals.

99% winter design temperatures for Hawaii are greater than 37°F.

For SI units: °C = (°F-32)/1.8
FIGURE 510.1.2(6)
RANGE OF WINTER DESIGN TEMPERATURES USED IN ANALYZING EXTERIOR MASONRY CHIMNEYS IN THE UNITED STATES
[NFPA 54: FIGURE F.2.4]
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 510.1.2(1) or Table 510.1.2(2) for Type B vents with the maximum capacity reduced by 20 percent (0.80 x maximum capacity) and the minimum capacity as shown in Table 510.1.2(1) or Table 510.1.2(2).

    Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 510.1.2. The 20 percent reduction for corrugated metallic chimney liner systems includes an allowance for one long radius 90 degree (1.57 rad) turn at the bottom of the liner. [NFPA 54:13.1.7]
Connections between chimney liners and listed double-wall connectors shall be made with listed adapters designed for such purposes. [NFPA 54:13.1.8]
Where the vertical vent has a larger diameter than the vent connector the vertical vent diameter shall be used to determine the minimum vent capacity, and the connector diameter shall be used to determine the maximum vent capacity. The flow area of the vertical vent shall not exceed seven times the flow area of the listed appliance categorized vent area, flue collar area, or draft hood outlet area unless designed in accordance with approved engineering methods. [NFPA 54:13.1.9]
Draft hood conversion accessories for use with masonry chimneys venting listed Category I fan-assisted appliances shall be listed and installed in accordance with the listed accessory manufacturer's installation instructions. [NFPA 54:13.1.10]
Table 510.1.2(1) through Table 510.1.2(5) shall be used for chimneys and vents not exposed to the outdoors below the roof line. A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Table 509.6.2, and where vents terminate in accordance with Section 509.6.2(1), the outdoor portion of the vent shall be enclosed as required by this section for vents not considered to be exposed to the outdoors or such venting system shall be engineered. A Type B vent passing through an unventilated enclosure or chase insulated to a value of not less than R-8 shall not be considered to be exposed to the outdoors. Table 510.1.2(3) in combination with Table 510.1.2(6) shall be used for clay-tile-lined exterior masonry chimneys, provided the following requirements are met:
  1. The vent connector is Type B double wall.
  2. The vent connector length is limited to 18 inches per inch (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 510.1.2(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 exceeds the minimum capacity given by Table 510.1.2(6). [NFPA 54:13.1.11]
Corrugated vent connectors shall not be smaller than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.12]
Vent connectors shall not be upsized more than two sizes exceeding the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. [NFPA 54:13.1.13]
In a single run of vent or vent connector, more than one diameter and type shall be permitted to be used, provided that the sizes and types are permitted by the tables. [NFPA 54:13.1.14]
Interpolation shall be permitted in calculating capacities for vent dimensions that fall between table entries. [NFPA 54:13.1.15]
Extrapolation beyond the table entries shall not be permitted. [NFPA 54:13.1.16]
For vent heights lower than 6 feet (1829 mm) and higher than vent heights shown in the tables, engineering methods shall be used to calculate vent capacities. [NFPA 54:13.1.17]
Where the actual height of a vent falls between entries in the height column of the applicable table in Table 510.1.2(1) through Table 510.1.2(6), one of the following shall be used:
  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]
Table 510.2(1) through Table 510.2(9) shall not be used where obstructions are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer's installation instructions or in accordance with the following:
  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 where the second appliance is a fan-assisted appliance, or the NAT + NAT column where 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 where the second appliance is a fan-assisted appliance, and the FAN + NAT column shall be used where the second appliance is equipped with a draft hood, to determine whether the vertical vent or chimney configuration is not permitted (NA). Where the vent configuration is NA, the vent configuration shall not be permitted and an alternative venting configuration shall be utilized. [NFPA 54:13.2.1]

TABLE 510.2(1)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)]*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(1)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)] (continued)
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2


TABLE 510.2(1)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)] (continued)*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(1)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(a)] (continued)*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(2)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(b)]*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(2)
TYPE B DOUBLE-WALL VENT [NFPA 54: TABLE 13.2(b)] (continued)
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2


TABLE 510.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)]*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(3)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(c)] (continued)*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(d)]*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(4)
MASONRY CHIMNEY [NFPA 54: TABLE 13.2(d)) (continued)*
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(5)
SINGLE-WALL METAL PIPE ORTYPE B ASBESTOS-CEMENT VENT [NFPA 54: TABLE 13.2(e)]*
NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: DRAFT HOOD-EQUIPMENT
APPLIANCE VENT CONNECTION: DIRECT TO PIPE OR VENT
VENT CONNECTOR CAPACITY
VENT CONNECTOR DIAMETER - D (inch)
TOTAL VENT
HEIGHT
H
(feet)
CONNECTOR
RISE
R
(feet)
3 4 5 6 7 8
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
6-8 1
2
3
21
28
34
40
53
61
68
86
98
102
124
147
146
178
204
205
235
275
15 1
2
3
23
30
35
44
56
64
77
92
102
117
134
155
179
194
216
240
265
298
30
and up
1
2
3
25
31
36
49
58
68
84
97
107
129
145
164
190
211
232

270
295
321

COMMON VENT CAPACITY
COMMON VENT DIAMETER - D (inch)
TOTAL VENT
HEIGHT
H
(feet)
4 5 6 7 8 10 12
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
6
8
10
15
20
30
50
48
55
59
71
80
NA
NA
78
89
95
115
129
147
NA
111
128
136
168
186
215
NA
155
175
190
228
260
300
360
205
234
250
305
340
400
490
320
365
395
480
550
650
810
NA
505
560
590
790
940
1190
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(6)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(f)]*

NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: NAT + NAT
APPLIANCE VENT CONNECTION TYPE B 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
8
10
15
20
30
50
100
25
28
31
NA
NA
NA
NA
NA
46
53
56
67
NA
NA
NA
NA
71
82
90
106
NA
NA
NA
NA
103
119
131
152
NA
NA
NA
NA
143
163
177
212
NA
NA
NA
NA
188
218
236
283
325
NA
NA
NA
246
278
302
365
419
496
NA
NA
NA
408
454
546
648
749
922
NA
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(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
8
10
15
20
30
50
100
0
0
0
NA
NA
NA
NA
NA
0
0
0
0
NA
NA
NA
NA
0
0
0
0
NA
NA
NA
NA
0
0
0
0
NA
NA
NA
NA
0
0
0
0
NA
NA
NA
NA
0
0
0
0
184
393
N A
NA
0
0
0
0
0
334
NA
NA
NA
0
0
0
0
0
579
NA
Local 99% winter design temperature: 27°F to 36°F
6
8
10
15
20
30
50
100
0
0
0
NA
NA
NA
NA
NA
0
0
51
NA
NA
NA
NA
NA
68
82
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
180
187
201
253
307
NA
NA
NA
212
214
225
274
330
445
NA
NA

NA
263
265
305
362
485
763
NA
Local 99% winter design temperature:17°F to 26°F
6
8
10
15
20
30
50
100
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
264
278
331
287
NA
NA
NA
NA
352
358
398
457
581
862
NA
Local 99% winter design temperature: 5°F to 16°F
6
8
10
15
20
30
50
100
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
430
485
547
682
NA
NA
Local 99% winter design temperature: 4°F or lower
Not recommended for any vent configurations
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2, °C = (°F-32)/1.8

Notes:
1   See Figure 510.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
2   NA: Not applicable.



TABLE 510.2(8)
EXTERIOR MASONRY CHIMNEY [NFPA 54: TABLE 13.2(h)]*

NUMBER OF APPLIANCES: TWO OR MORE
APPLIANCE TYPE: FAN + NAT
APPLIANCE VENT CONNECTION TYPE B 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
8
10
15
20
30
50
100
74
80
84
NA
NA
NA
NA
NA
119
130
138
152
NA
NA
NA
NA
178
193
207
233
250
NA
NA
NA
257
279
299
334
368
404
NA
NA
351
384
409
467
508
564
NA
NA
458
501
538
611
668
747
831
NA
582
636
686
781
858
969
1089
NA
853
937
1010
1156
1286
1473
1692
1921
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.



TABLE 510.2(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
8
10
15
20
30
50
100
0
0
0
NA
NA
NA
NA
NA
0
0
0
0
NA
NA
NA
NA
0
0
0
0
123
NA
NA
NA
0
0
0
0
190
334
NA
NA
0
0
0
0
249
398
NA
NA
0
0
0
0
184
393
714
NA
0
0
0
0
0
334
707
NA
0
0
0
0
0
0
579
1600
Local 99% winter design temperature: 27°F to 36°F
6
8
10
15
20
30
50
100
0
0
0
NA
NA
NA
NA
NA
0
0
51
111
NA
NA
NA
NA
68
82
97
142
187
NA
NA
NA
116
127
141
183
230
330
NA
NA
156
167
183
233
284
319
NA
NA
180
187
201
253
307
419
672
NA
212
214
225
274
330
445
705
NA
266
263
265
305
362
485
763
1554
Local 99% winter design temperature:17°F to 26°F
6
8
10
15
20
30
50
100
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
197
214
NA
NA
NA
NA
215
226
245
296
352
NA
NA
259
264
278
331
287
507
NA
349
352
358
398
457
581
NA
Local 99% winter design temperature: 5°F to 16°F
6
8
10
15
20
30
50
100
0
52
NA
NA
NA
NA
NA
NA
55
74
90
NA
NA
NA
NA
NA
99
111
125
167
212
NA
NA
NA
141
154
169
212
258
262
NA
NA
182
197
214
263
316
429
NA
NA
215
226
245
296
352
470
723
NA
259
264
278
331
387
507
766
NA
416
423
430
485
547
682
972
Local 99% winter design temperature: -10°F to 4°F
6
8
10
15
20
30
50
100
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
145
159
175
NA
NA
NA
NA
NA
196
213
231
283
333
NA
NA
NA
249
269
292
351
408
NA
NA
NA
296
320
339
404
468
603
NA
NA
349
371
397
457
528
667
955
NA
484
494
513
586
650
805
1003
NA
Local 99% winter design temperature: -11°F or lower
Not recommended for any vent configurations
For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2, °C = (°F-32)/1.8

Notes:
1   See Figure 510.1.2(6) for a map showing local 99 percent winter design temperatures in the United States.
2   NA: Not applicable.
The maximum vent connector horizontal length shall be 18 inches per inch (18 mm/mm) of connector diameter as shown in Table 510.2.1, or as permitted by Section 510.2.2. [NFPA 54:13.2.2]

TABLE 510.2.1
VENT CONNECTOR MAXIMUM LENGTH
[NFPA 54: TABLE 13.2.2]
CONNECTOR DIAMETER
(inches)
MAXIMUM CONNECTOR
HORIZONTAL LENGTH (feet)
3 412
4 6
5 712
6 9
7 1012
8 12
9 1312
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 510.2.1 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 510.2.1. For example, the length listed for a 4 inch (102 mm) connector shall not exceed 6 feet (1829 mm). With a connector length exceeding 6 feet (1829 mm) but not exceeding 12 feet (3658 mm), the maximum capacity shall be reduced by 10 percent (0.90 x maximum vent connector capacity). With a connector length exceeding 12 feet (3658 mm) but not exceeding 18 feet (5486 mm), the maximum capacity shall be reduced by 20 percent (0.80 x maximum vent capacity).
  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 510.1.2(1) shall be used. For single-wall connectors, Table 510.1.2(2) shall be used. The height (H) and lateral (L) shall be measured according to the procedures for a single appliance vent, as if the other appliances were not present. [NFPA 54:13.2.3]
Where the vent connectors are combined prior to entering the vertical portion of the common vent to form a common vent manifold, the size of the common vent manifold and the common vent shall be determined by applying a 10 percent reduction (0.90 x maximum common vent capacity) to the common vent capacity part of the common vent tables. The length of the common vent manifold (LM) shall not exceed 18 inches per inch (18 mm/mm) of common vent diameter (D). [NFPA 54:13.2.4]
Where the common vertical vent is offset, the maximum capacity of the common vent shall be reduced in accordance with Section 510.2.5, and the horizontal length of the common vent offset shall not exceed 18 inches per inch (18 mm/mm) of common vent diameter (D). Where multiple offsets occur in a common vent, the total horizontal length of offsets combined shall not exceed 18 inches per inch (18 mm/mm) of the common vent diameter. [NFPA 54:13.2.5]
For each elbow up to and including 45 degrees (0.79 rad) in the common vent, the maximum common vent capacity listed in the venting tables shall be reduced by 5 percent. For each elbow exceeding 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum common vent capacity listed in the venting tables shall be reduced by 10 percent. [NFPA 54:13.2.6]
The cross-sectional area of the common vent shall be equal to or exceeding 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 sha1l be equal to the size of the common vent. Such fittings shall not be prohibited from having reduced size openings at the point of connection of appliance gas vent connectors. [NFPA 54:13.2.10]
Sea level input ratings shall be used where determining maximum capacity for 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. [NFPA 54:13.2.14]
The size of the lowest connector and of the vertical vent leading to the lowest interconnection of a multistory system shall be in accordance with Table 510.1.2(1) or Table 510.1.2(2) for available total height (H) up to the lowest interconnection. [NFPA 54:13.2.15]
Where used in multistory systems, vertical common vents shall be Type B 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 table shall exceed the highest appliance input rating. [NFPA 54:13.2.19]
Listed corrugated metallic chimney liner systems in masonry chimneys shall be sized by using Table 510.2(1) or Table 510.2(2) for Type B vents, with the maximum capacity reduced by 20 percent (0.80 x maximum capacity) and the minimum capacity as shown in Table 510.2(1) or Table 510.2(2). Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 510.2.5. The 20 percent reduction for corrugated metallic chimney liner systems includes an allowance for one long radius 90 degree (1.57 rad) turn at the bottom of the liner. [NFPA 54:13.2.20]
Table 510.2(1) through Table 510.2(5) shall be used for chimneys and vents not exposed to the outdoors below the roof line. A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. A Type B vent passing through an unventilated enclosure or chase insulated to a value of not less than R-8 shall not be considered to be exposed to the outdoors. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Table 509.6.2, and where vents terminate in accordance with Section 509.6.2(1), the outdoor portion of the vent shall be enclosed as required by this section for vents not considered to be exposed to the outdoors, or such venting system shall be engineered. Table 510.2(6) through Table 510.2(9) shall be used for clay-tile-lined exterior masonry chimneys, provided the following conditions are met:
  1. The vent connector is Type B double-wall.
  2. Not less than one appliance is draft hood-equipped.
  3. The combined appliance input rating is less than the maximum capacity given by Table 510.2(6) (for NAT + NAT) or Table 510.2(8) (for FAN + NAT).
  4. The input rating of each space-heating appliance exceeds the minimum input rating given by Table 510.2(7) (for NAT + NAT) or Table 510.2(9) (for FAN + NAT).
  5. The vent connector sizing is in accordance with Table 510.2(3). [NFPA 54:13.2.22]
Vent connectors shall not be increased more than two sizes exceeding the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. Vent connectors for draft hood-equipped appliances shall not be smaller than the draft hood outlet diameter. Where vent connector sizes determined from the tables for fan-assisted appliances are smaller than the flue collar diameter, the use of the smaller sizes shall be permitted provided that the installation is in accordance with the following conditions:
  1. Vent connectors for fan-assisted appliance flue collars 12 inches (305 mm) in diameter or smaller are not reduced by more than one table size [e.g., 12 inches to 10 inches (305 mm to 254 mm) is a one size reduction] and those exceeding 12 inches (305 mm) in diameter are not reduced exceeding two table sizes [e.g., 24 inches to 20 inches (610 mm to 508 mm) is a two size reduction].
  2. The fan-assisted appliance is common vented with a draft hood-equipped appliance.
  3. The vent connector has a smooth interior wall. [NFPA 54:13.2.24]
Combinations of pipe sizes, single-wall metal pipe, and double-wall metal pipe shall be allowed within a connector run or within the common vent, provided the appropriate tables permit the desired sizes and types of pipe, where they were used for the entire length of the subject connector or vent. Where single-wall and Type B double-wall metal pipes are used for vent connectors within the same venting system, the common vent shall be sized in accordance with Table 510.2(2) or Table 510.2(4). [NFPA 54:13.2.25]
Where a table permits more than one diameter of pipe to be used for a connector or vent, the permitted sizes shall be permitted to be used. [NFPA 54:13.2.26]
Interpolation shall be permitted in calculating capacities for vent dimensions that fall between table entries. [NFPA 54:13.2.27]
Extrapolation beyond the table entries shall not bc permitted. [NFPA 54:13.2.28]
For vent heights lower than 6 feet (1829 mm) and exceeding vent heights shown in the tables, engineering methods shall be used to calculate vent capacities. [NFPA 54:13.2.29]
Where the actual height of a vent falls between entries in the height column of the applicable table in Table 510.2(1) through Table 510.2(9), one of the following shall be used:
  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]
Resources