Chapter 1 Administration

Chapter 2 Definitions

Chapter 3 General Regulations

Chapter 4 Gas Piping Installations

Chapter 5 Chimneys and Vents

Chapter 6 Specific Appliances

Chapter 7 Reserved

Chapter 8 Referenced Standards [PDF]

Appendix A Reserved

Appendix B Reserved

Appendix C Reserved

Appendix D Reserved

Appendix E Meters and Gas Service Piping

Appendix F Plastic Fuel Gas Piping

This chapter shall govern the installation, alteration, maintenance, design, minimum safety requirements, repair and approval of factory-built chimneys, chimney liners, vents and connectors, field built chimneys and connectors and the utilization of masonry chimneys serving gas-fired appliances. The requirements for the installation, maintenance, repair and approval of factory-built chimneys, chimney liners, vents and connectors serving appliances burning fuels other than fuel gas shall be regulated by the New York City Mechanical Code. The construction, repair, maintenance and approval of masonry chimneys shall be regulated by the New York City Building Code.
Adjoining chimneys and vents shall be in accordance with Sections 501.1.1.1 to 501.1.1.8.
Whenever a building is erected, enlarged, or increased in height so that any portion of such building, except chimneys or vents, extends higher than the top of any previously constructed chimneys or vents within 100 feet (30 480 mm), the owner of such new or altered building shall have the responsibility of altering such chimneys or vents to make them conform with the requirements of this chapter. A chimney or vent that is no longer connected with a fireplace or combustion or other equipment for which a chimney or vent was required, shall be exempt from this requirement. Such alterations shall be accomplished by one of the following means or a combination thereof:
  1. Carry up the previously constructed chimneys or vents to the height required in this chapter.
  2. Offset such chimneys or vents to a distance beyond that required in Chapter 5 of this code from the new or altered building provided that the new location of the outlet of the offset chimney or vent shall otherwise comply with the requirements of this chapter.
  Such requirements shall not dispense with or modify any additional requirements that may be applicable pursuant to rules of the New York City Department of Environmental Protection.
After the alteration of a chimney or vent as required by this section, it shall be the responsibility of the owner of the new or altered building to provide any mechanical equipment or devices necessary to maintain the proper draft in the equipment.
The owner of the new or altered building shall notify the owner of the building affected in writing at least forty-five days before starting the work required and request written consent to do such work. Such notice shall be accompanied by plans indicating the manner in which the proposed alterations are to be made.
The plans and method of alteration shall be subject to the approval of the commissioner.
If consent is not granted by the owner of the previously constructed building to do the alteration work required by this section, such owner shall signify his or her refusal in writing to the owner of the new or altered building and to the commissioner; and the owner of the new or altered building having submitted plans that conform to the requirements of this section, shall thereupon be released from any responsibility for the proper operation of the equipment due to loss of draft and for any health hazard or nuisance that may occur as a result of the new or altered building. Such responsibilities shall then be assumed by the owner of the previously constructed building. Similarly, should such owner fail to grant consent within forty-five days from the date of written request or fail to signify his or her refusal, he or she shall then assume all responsibilities as prescribed above.
It shall be the obligation of the owner of the new or altered building to:
  1. Schedule this work so as to create a minimum of disturbance to the occupants of the affected building; and
  2. Provide such essential services as are normally supplied by the equipment while it is out of service; and
  3. Where necessary, support such extended chimneys, vents and equipment from this building or to carry up such chimneys or vents within his or her building; and
  4. Provide for the maintenance, repair, and/or replacement of such extensions and added equipment; and
  5. Make such alterations of the same material as the original chimney or vent so as to maintain the same quality and appearance, except where the affected owner of the chimney or vent shall give his or her consent to do otherwise. All work shall be done in such fashion as to maintain the architectural aesthetics of the existing building. Where there is practical difficulty in complying strictly with the provisions of this Item, the commissioner may permit an equally safe alternative.
Any existing violations on the previously constructed equipment shall be corrected by the owner of the equipment before any equipment is added or alterations made at the expense of the owner of the new or altered building.
The commissioner may grant a variance in accordance with the provisions of this code.
Every appliance shall discharge the products of combustion to the outdoors, except for appliances exempted by Section 501.8.
Chimneys and vents shall be designed and constructed so as to provide the necessary draft and capacity for each appliance connected to completely exhaust the products of combustion to the outside air. The temperature on adjacent combustible surfaces shall not be raised above 160°F (71°C). Condensation shall not be developed to an extent that can cause deterioration of the chimney or vent.
The outlet shall be arranged that the flue gases are not directed so that they jeopardize people, overheat combustible structures, or enter building openings in the vicinity of the outlet. Gas fired appliances shall be vented in accordance with this code and NFPA 54.
Chimneys and vents shall not be supported by the equipment they serve unless such equipment has been specifically designed for such loads.
Masonry chimneys shall be constructed in accordance with Section 503.5.3 and the New York City Building Code.
Chimneys and vents shall be sized in accordance with Section 504.
Abandoned inlet openings in chimneys and vents shall be closed by an approved method.
Where an appliance equipped with a mechanical forced draft system creates a positive pressure in the venting system, the venting system shall be designed for positive pressure applications.
Connection of appliances to chimney flues serving fireplaces shall be in accordance with Sections 501.7.1 through 501.7.3.
A noncombustible seal shall be provided below the point of connection to prevent entry of room air into the flue. Means shall be provided for access to the flue for inspection and cleaning.
An appliance shall not be connected to a flue serving a factory-built fireplace unless the appliance is specifically listed for such installation. The connection shall be made in accordance with the appliance manufacturer's installation instructions.
A connector shall extend from the appliance to the flue serving a masonry fireplace such that the flue gases are exhausted directly into the flue. The connector shall be accessible or removable for inspection and cleaning of both the connector and the flue. Listed direct connection devices shall be installed in accordance with their listing.
The following appliances shall not be required to be vented:
  1. Ranges.
  2. Built-in domestic cooking units listed and marked for optional venting.
  3. Hot plates and laundry stoves.
  4. Type 1 clothes dryers (Type 1 clothes dryers shall be exhausted in accordance with the requirements of Section 614).
  5. A single booster-type automatic instantaneous water heater, where designed and used solely for the sanitizing rinse requirements of a dishwashing machine, provided that the heater is installed in a commercial kitchen having a mechanical exhaust system. Where installed in this manner, the draft hood, if required, shall be in place and unaltered and the draft hood outlet shall be not less than 36 inches (914 mm) vertically and 6 inches (152 mm) horizontally from any surface other than the heater.
  6. Refrigerators.
  7. Counter appliances.
  8. Specialized equipment of limited input such as laboratory burners and gas lights.
  9. Recirculating direct-fired industrial air heaters as provided for in Section 612.
  Where the appliances and equipment listed in Items 5 through 9 above are installed so that the aggregate input rating exceeds 20 British thermal units (Btu) per hour per cubic feet (207 watts per m3) of volume of the room or space in which such appliances and equipment are installed, one or more shall be provided with venting systems or other approved means for conveying the vent gases to the outdoor atmosphere so that the aggregate input rating of the remaining unvented appliances and equipment does not exceed the 20 Btu per hour per cubic foot (207 watts per m3) figure. Where the room or space in which the equipment is installed is directly connected to another room or space by a doorway, archway, or other opening of comparable size that cannot be closed, the volume of such adjacent room or space shall be permitted to be included in the calculations.
Connectors shall connect to a masonry chimney flue at a point not less than 12 inches (305 mm) or one chimney diameter above the lowest portion of the interior of the chimney flue.
Appliance connections to a chimney or vent equipped with a power exhauster shall be made on the inlet side of the exhauster. Joints and vent systems on the positive pressure side of the exhauster shall be sealed to prevent flue-gas leakage as specified by the manufacturer's installation instructions for the exhauster.
Masonry chimneys utilized to vent appliances shall be located, constructed and sized as specified in the manufacturer's installation instructions for the appliances being vented and Section 503.
Flue lining systems for use with residential-type and low-heat appliances shall be limited to the following:
  1. Clay flue lining complying with the requirements of ASTM C 315 or equivalent. Clay flue lining shall be installed in accordance with the New York City Building Code.
  2. Listed chimney lining systems complying with UL 1777.
  3. Other approved materials that will resist, without cracking, softening or corrosion, flue gases and condensate at temperatures up to 1,800°F (982°C).
Flue lining systems for use with Category I appliances shall be limited to the following:
  1. Flue lining systems complying with Section 501.12.
  2. Chimney lining systems listed and labeled for use with gas appliances with draft hoods and other Category I gas appliances listed and labeled for use with Type B vents.
The design, sizing and installation of vents for Category II, III and IV appliances shall be in accordance with the appliance manufacturer's installation instructions.
Where an appliance is permanently disconnected from an existing chimney or vent, or where an appliance is connected to an existing chimney or vent during the process of a new installation, the chimney or vent shall comply with Sections 501.15.1 through 501.15.4.
The chimney or vent shall be resized as necessary to control flue gas condensation in the interior of the chimney or vent and to provide the appliance or appliances served with the required draft. For Category I appliances, the resizing shall be in accordance with Section 502.
The flue gas passageway shall be free of obstructions and combustible deposits and shall be cleaned if previously used for venting a solid or liquid fuel-burning appliance or fireplace. The flue liner, chimney inner wall or vent inner wall shall be continuous and shall be free of cracks, gaps, perforations or other damage or deterioration which would allow the escape of combustion products, including gases, moisture and creosote.
Masonry chimney flues shall be provided with a cleanout opening having a minimum height of 6 inches (152 mm). The upper edge of the opening shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The cleanout shall be provided with a tight-fitting, noncombustible cover of a minimum size of 8 inches (203 mm) by 8 inches (203 mm).
Chimneys and vents shall have airspace clearance to combustibles in accordance with the New York City Building Code and the chimney or vent manufacturer's installation instructions. Noncombustible firestopping or fireblocking shall be provided in accordance with the New York City Building Code.
  Exception: Masonry chimneys equipped with a chimney lining system tested and listed for installation in chimneys in contact with combustibles in accordance with UL 1777, and installed in accordance with the manufacturers instructions, shall not be required to have clearance between combustible materials and exterior surfaces of the masonry chimney.
All vents, except as provided in Section 503.7, shall be listed and labeled. Type B and BW vents shall be tested in accordance with UL 441 and labeled or field fabricated in accordance with NFPA 211. Type L vents shall be tested in accordance with UL 641.Vents for Category II and III appliances shall be tested in accordance with UL 1738. Plastic vents for Category IV appliances shall not be required to be listed and labeled where such vents are as specified by the appliance manufacturer and are installed in accordance with the appliance manufacturer's installation instructions.
Connectors shall be used to connect appliances to the vertical chimney or vent, except where the chimney or vent is attached directly to the appliance. Vent connector size, material, construction and installation shall be in accordance with Section 503.
The application of vents shall be in accordance with Table 503.4.

TABLE 503.4
TYPE OF VENTING SYSTEM TO BE USED
GAS UTILIZATION EQUIPMENT TYPE OF VENTING SYSTEM
Listed Category I equipment
Listed equipment equipped with draft hood
Equipment listed for use with Type B gas vent
Type B gas vent (Section 503.6)
Chimney (Section 503.5)
Single-wall metal pipe (Section 503.7)
Listed chimney lining system for gas venting (Section 503.5.3)
Special gas vent listed for this equipment (Section 503.4.2)
Listed vented wall furnaces Type B-W gas vent (Sections 503.6, 608)
Category II equipment As specified or furnished by manufacturers of listed equipment(Sections 503.4.1, 503.4.2)
Category III equipment As specified or furnished by manufacturers of listed equipment(Sections 503.4.1, 503.4.2)
Category IV equipment As specified or furnished by manufacturers of listed equipment(Sections 503.4.1, 503.4.2)
Incinerators, indoors Chimney (Section 503.5)
Incinerators, outdoors Single-wall metal pipe (Sections 503.7, 503.7.6)
Equipment which may be converted to use of solid fuel Chimney (Section 503.5)
Unlisted combination gas and oil-burning equipment Chimney (Section 503.5)
Listed combination gas and oil-burning equipment Type L vent (Section 503.6) or chimney (Section 503.5)
Combination gas and solid fuel-burning equipment Chimney (Section 503.5)
Equipment listed for use with chimneys only Chimney (Section 503.5)
Unlisted equipment Chimney (Section 503.5)
Decorative appliance in vented fireplace Chimney
Direct vent equipment See Section 503.2.2, 503.2.3
Equipment with integral vent See Section 503.2.3, 503.2.4
Where vents pass through insulated assemblies, an insulation shield constructed of not less than 26 gage sheet (0.016 inch) (0.4mm) metal shall be installed to provide clearance between the vent and the insulation material. The clearance shall not be less than the clearance to combustibles specified by the vent manufacturer's installation instructions. Where vents pass through attic space, the shield shall terminate not less than 2 inches (51 mm) above the insulation materials and shall be secured in place to prevent displacement. Insulation shields provided as part of a listed vent system shall be installed in accordance with the manufacturer's installation instructions.
Vent systems shall be sized, installed and terminated in accordance with the vent and appliance manufacturer's installation instructions and Section 503.
All portions of vents shall be adequately supported for the design and weight of the materials employed.
This section recognizes that the choice of venting materials and the methods of installation of venting systems are dependent on the operating characteristics of the equipment being vented. The operating characteristics of vented equipment can be categorized with respect to (1) positive or negative pressure within the venting system; and (2) whether or not the equipment generates flue or vent gases that might condense in the venting system. See Section 202 for the definition of these vented appliance categories.
Except as permitted in Sections 503.2.1 through 503.2.3 and 501.8, all equipment shall be connected to venting systems.
Ventilating hoods and exhaust systems shall be permitted to be used to vent equipment installed in commercial applications (see Section 503.3.4) and to vent industrial equipment, such as where the process itself requires fume disposal.
Listed direct-vent equipment shall be considered properly vented where installed in accordance with the terms of its listing, the manufacturer's instructions, and Section 503.8.
Equipment incorporating integral venting means shall be considered properly vented when installed in accordance with its listing, the manufacturer's instructions, and Section 503.8.
A venting system shall be designed and constructed so as to develop a positive flow adequate to convey flue or vent gases to the outdoor atmosphere.
A venting system shall satisfy the draft requirements of the equipment in accordance with the manufacturer's instructions.
Gas utilization equipment required to be vented shall be connected to a venting system designed and installed in accordance with the provisions of Sections 503.4 through 503.15.
Mechanical draft systems shall comply with the following:
  1. Mechanical draft systems shall be listed and shall be installed in accordance with the terms of their listing and both the appliance and the mechanical draft system manufacturer's instructions.
  2. Equipment, except incinerators, requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design.
  3. Forced draft systems and all 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.
  4. Vent connectors serving equipment vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure.
  5. When a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the equipment for safe performance.
  6. The exit terminals of mechanical draft systems shall be in compliance with Section 503.8.
Ventilating hoods and exhaust systems shall be permitted to be used to vent gas utilization equipment installed in commercial applications. Where automatically operated equipment is 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 only when the damper is open to a position to properly vent the equipment and when the power means of exhaust is in operation.
No portion of a venting system shall extend into or pass through any circulating air duct or furnace plenum.
The type of venting system to be used shall be in accordance with Table 503.4.
Plastic piping used for venting equipment listed for use with such venting materials shall be permitted when approved by the commissioner.
Special gas vent shall be listed and installed in accordance with the terms of the special gas vent listing and the manufacturers' instructions.
Masonry, metal and factory-built chimneys shall comply with Sections 503.5.1 through 503.5.10.
Factory-built chimneys shall be installed in accordance with their listing and the manufacturers' instructions. Factory-built chimneys used to vent appliances that operate at positive vent pressure shall be listed for such application.
Metal chimneys shall be built and installed in accordance with NFPA 211.
Masonry chimneys shall be built and installed in accordance with Chapter 21 of the New York City Building Code and NFPA 211, and shall be lined with approved clay flue lining, a listed chimney lining system, or other approved material that will resist corrosion, erosion, softening, or cracking from vent gases at temperatures up to 1800°F (982°C).
  Exception: Masonry chimney flues serving listed gas appliances with draft hoods, Category I appliances and other gas appliances listed for use with Type B vent shall be permitted to be lined with a chimney lining system specifically listed for use only with such appliances. The liner shall be installed in accordance with the liner manufacturer's instructions and the terms of the listing. A permanent identifying label shall be attached at the point where the connection is to be made to the liner. The label shall read: "This chimney liner is for appliances that burn gas only. Do not connect to solid or liquid fuel-burning appliances or incinerators."
  For information on installation of gas vents in existing masonry chimneys, see Section 503.6.5.
Chimneys serving gas fired equipment shall comply with the appliance listing, the manufacturer's instructions and the following requirements:
  1. Chimneys serving appliances less than 600°F (316°C) shall extend at least 3 feet (914 mm) above the highest construction, such as a roof ridge, parapet wall, or penthouse, within 10 feet (3048 mm) of the chimney outlet, whether the construction is on the same building as the chimney or on another building. However, such constructions do not include other chimneys, vents, or open structural framing. Any chimney located beyond 10 feet (3048 mm) from such construction, but not more than the distance determined by Equation 5-1 shall be at least as high as the construction.
  2. Chimneys serving appliances between 600°F (316°C) and 1000°F (538°C) shall extend at least 10 feet (3048 mm) above the highest construction, such as a roof ridge, or parapet wall or penthouse within 20 feet (6096 mm) of the chimney outlet, whether the construction is on the same building as the chimney or on another building. However, such constructions do not include other chimneys, and vents or open structural framing. Any chimney located beyond 20 feet (6096 mm) from such construction, but not more than the distance determined by Equation 5-1 shall be at least as high as the construction.
  3. Chimneys serving appliances greater than 1000°F shall extend at least 20 feet (6096 mm) above the highest construction, such as roof ridge, parapet wall, penthouse, or other obstruction within 50 feet (15 240 mm) of the chimney outlet, whether the construction is on the same building as the chimney or in another building. However, such constructions do not include other chimneys, vents, or open structural framing. Any chimney located beyond 50 feet (15 240 mm) from such construction but not more than the distance determined by Equation 5-1 shall be at least as high as the construction.
  4. Termination caps shall not be permitted and a 3 inch (76 mm) minimum drain installed to receive collected water shall be required. A positive means shall be provided to prevent water from entering the appliance.
  Exception: Termination caps shall be permitted on listed factory built chimneys,
  5. 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 manufacturers' installation instructions.
  6. The following equation shall be used for determining the distances referred to in Items 1, 2 and 3 of this section.


D = F X √A (Equation 5-1)

where:
D = Distance, in feet, measured from the center of the chimney outlet to the nearest edge of the construction.
F = Value determined from table below.
A = Free area, in square inches, of chimney flue space

“F” FACTOR FOR DETERMINING CHIMNEY DISTANCES
Type of Fuel “F” Factor
600°F (316°C )
and less
600°F (°C ) to
1000°F (538°C)
Greater than
1000°F (538°C)
Gas 2 2 3
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 determined in accordance with one of the following methods:
  1. The provisions of Section 504.
  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, nor greater than seven times the draft hood outlet area.
  3. For sizing a chimney venting system connected to two appliances with draft hoods, the effective area of the chimney flue shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet, nor greater than seven times the smallest draft hood outlet area.
  4. Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.
  5. Other approved engineering methods.
Where an incinerator is vented by a chimney serving other gas utilization equipment, the gas input to the incinerator shall not be included in calculating chimney size, provided the chimney flue diameter is not less than 1 inch (25 mm) larger in equivalent diameter than the diameter of the incinerator flue outlet.
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 it shall be cleaned if previously used for venting solid or liquid fuel-burning appliances or fireplaces.
Chimneys shall be lined in accordance with NFPA 211.
  Exception: Existing chimneys shall be permitted to have their use continued when an appliance is replaced by an appliance of similar type, input rating, and efficiency.
Cleanouts shall be examined to determine if they will remain tightly closed when not in use.
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 to conform to NFPA 211 and it shall be suitable for the equipment to be vented.
All new chimneys shall be test run by the design professional engineer responsible for the testing under operating conditions to demonstrate fire safety and the complete exhausting of smoke and the products of combustion to the outer air. The results of such test run shall be certified as correct by the design professional engineer responsible for the test and shall be submitted in writing to the department.
A smoke test shall be made as outlined below. Any faults or leaks found shall be corrected. Such smoke test shall be witnessed by a representative of the commissioner. In lieu thereof, the commissioner may accept the test report of the design professional engineer responsible for the test which shall be submitted in writing to the department.
To determine the tightness of chimney construction, a smoke test shall be made in accordance with the following conditions and requirements:
  1. The equipment, materials, power and labor necessary for such test shall be furnished by, and at the expense of, the owner or holder of the work permit.
  2. If the test shows any evidence of leakage or other defects, such defects shall be corrected in accordance with the requirement of this chapter and the test shall be repeated until the results are satisfactory.
  3. Method of test. The chimney shall be filled with a thick penetrating smoke produced by one or more smoke machines, or smoke bombs, or other equivalent method. As the smoke appears at the stack opening on the roof, such opening shall be tightly closed and a pressure equivalent to one-half inch (12.7 mm) column of water measured at the base of the stack, shall be applied. The test shall be applied for a length of time sufficient to permit the inspection of the chimney.
Chimneys serving equipment burning other fuels shall comply with Sections 503.5.7.1 through 503.5.7.4.
Gas utilization equipment shall not be connected to a chimney flue serving a separate appliance designed to burn solid fuel.
Where one chimney flue serves gas utilization equipment and equipment burning liquid fuel, the equipment shall be connected through separate openings or shall be connected through a single opening where joined by a suitable 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 utilization equipment is automatically controlled, it shall be equipped with a safety shutoff device.
A combination gas- and solid fuel-burning appliance shall be permitted to be connected to a single chimney flue where equipped with a manual reset device to shut off gas to the main burner in the event of sustained back draft or flue gas spillage. The chimney flue shall be sized to properly vent the appliance.
A listed combination gas- and oil fuel-burning appliance shall be permitted to be connected to a single chimney flue. The chimney flue shall be sized to properly vent the appliance.
All portions of chimneys shall be supported for the design and weight of the materials employed. Factory-built chimneys shall be supported and spaced in accordance with their listings and the manufacturer's instructions.
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 shall be installed at the base of all chimneys in accordance with the rules of the New York City Department of Environmental Protection. The cleanout shall be gas tight if the chimney is to be of positive pressure.
The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney flue shall not be used to vent another appliance. The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer's instructions shall not be prohibited.
  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. Such space shall not be prohibited from supplying combustion air to direct-vent appliances designed for installation in a solid fuel-burning fireplace and installed in accordance with the listing and the manufacturer's instructions.
Gas vents shall comply with Sections 503.6.1 through 503.6.12 (see Section 202, Definitions).
Gas vents shall be installed in accordance with the terms of their listings and the manufacturer's instructions.
A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is connected.
A gas vent passing through a roof shall extend through the roof flashing, roof jack, or roof thimble and shall be terminated by a listed termination cap.
Type B and Type L vents shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60-degree (1.04 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal length of a vent plus the horizontal vent connector length serving draft-hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent.
  Exception: Systems designed and sized as provided in Section 504 or in accordance with other approved engineering methods.
  Vents serving Category I fan-assisted appliances shall be installed in accordance with the appliance manufacturer's instructions and Section 504 or other approved engineering methods.
Gas vents installed within masonry chimneys shall be installed in accordance with the terms of their listing and the manufacturer's installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: "This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators."
A gas vent shall terminate in accordance with one of the following:
  1. Above the roof surface with a listed cap or listed roof assembly. Gas vents 12 inches (305 mm) in size or smaller with listed caps shall be permitted to be terminated in accordance with Figure 503.6.6, provided that such vents are at least 8 feet (2438 mm) from a vertical wall or similar obstruction. All other gas vents shall terminate not less than 2 feet (610mm) above the highest point where they pass through the roof and at least 2 feet (610 mm) higher than any portion of a building within 10 feet (3048 mm).
  2. As provided for direct-vent systems in Section 503.2.2.
  3. As provided for equipment with integral vents in Section 503.2.3.
  4. As provided for mechanical draft systems in Section 503.3.3.
  5. As provided for ventilating hoods and exhaust systems in Section 503.3.4.
  However, such constructions do not include chimneys or other vents, or open structural framing. The vent shall be as high as such construction which is located beyond ten feet from the vent and up to and including the distance determined by the following formula:

D = 2√A (Equation 5-2)

where:
D = Distance in feet, measured from the center of the vent outlet to the nearest edge of the construction.
A = Free area, in square inches, of vent flue space.


ROOF PITCH H (min) ft
Flat to 6/12 1.0
Over 6/12 to 7/12 1.25
Over 7/12 to 8/12 1.5
Over 8/12 to 9/12 2.0
Over 9/12 to 10/12 2.5
Over 10/12 to 11/12 3.25
Over 11/12 to 12/12 4.0
Over 12/12 to 14/12 5.0
Over 14/12 to 16/12 6.0
Over 16/12 to 18/12 7.0
Over 18/12 to 20/12 7.5
Over 20/12 to 21/12 8.0
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
FIGURE 503.6.6
GAS VENT TERMINATION LOCATIONS FOR LISTED CAPS 12 INCHES OR LESS IN SIZE AT LEAST 8 FEET FROM A VERTICAL WALL
Decorative shrouds shall not be installed at the termination of gas vents except where such shrouds are listed for use with the specific gas venting system and are installed in accordance with the manufacturer's installation instructions.
All gas vents shall terminate in an approved vent or cowl, which shall prevent downdrafts and prevent rain and debris from entering the vent.
A Type B or a Type L gas vent shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected equipment draft hood or flue collar. A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace.
A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Sections 503.2.3 and 503.3.3.
Venting systems shall be sized and constructed in accordance with Section 504 or other approved engineering methods acceptable to the commissioner. Gas vents shall also comply with the manufacturers' instructions.
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 methods:
  1. The provisions of Section 504.
  2. 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, nor greater than seven times the draft hood outlet area.
  3. 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, nor greater than seven times the smaller draft hood outlet area.
  4. Engineering practices acceptable to the commissioner.
The sizing of gas vents for Category II, III, and IV equipment shall be in accordance with the equipment manufacturer's instructions.
Chimney venting systems using mechanical draft shall be designed and sized to develop a positive flow adequate to carry all products of combustion to the outside atmosphere.
A single or common gas vent shall be permitted in multistory installations to vent Category I equipment located on more than one floor level, provided the venting system is designed and installed in accordance with this section and approved engineering methods.
All equipment connected to the common vent shall be located in rooms that do not communicate with occupiable and or habitable spaces. habitable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation, and dilution air that is not supplied from habitable space (see Figure 503.6.10.1).
The size of the connectors and common segments of multistory venting systems for equipment listed for use with Type B double-wall gas vent shall be in accordance with Table 504.3(1) and Figures 503.6.10.2(1) and 503.6.10.2(2), provided:
  1. The available total height (H) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection tee (see Figure 503.6.10.2(1)).
  2. The size of the connector for a segment is determined from its gas utilization equipment heat input and available connector rise, and shall not be smaller than the draft hood outlet or flue collar size.
  3. The size of the common vertical segment, and of the interconnection tee at the base of that segment, shall be based on the total gas utilization equipment heat input entering that segment and its available total height.
FIGURE 503.6.10.1
PLAIN VIEW OF PRACTICAL SEPARATION METHOD FOR MULTISTORY GAS VENTING
FIGURE 503.6.10.2(1)
MULTISTORY GAS VENT DESIGN PROCDEDURE FOR EACH SEGMENT SYSTEM
FIGURE 503.6.10.2(2)
MULTISTORY VENT SYSETMS

TABLE 504.3(1)
TYPE B DOUBLE-WALL VENT




VENT CONNECTOR CAPACITY
Number of Appliances Two or more
Appliance Type Category I
Appliance Vent Connection Type B double-wall connector






VENT
HEIGHT
(H)
(feet)






CONNECTOR
RISE
(R)
(feet)
TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER—(D) inches
3 4 5 6 7 8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H
FAN NAT FAN NAT FAN NAT 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 Min Max Max Min Max Max Min Max Max
6 1 22 37 26 35 66 46 46 106 72 58 164 104 77 225 142 92 296 185 109 376 237 128 466 289
2 23 41 31 37 75 55 48 121 86 60 183 124 79 253 168 95 333 220 112 424 282 131 526 345
3 24 44 35 38 81 62 49 132 96 62 199 139 82 275 189 97 363 248 114 463 317 134 575 386
8 1 22 40 27 35 72 48 49 114 76 64 176 109 84 243 148 100 320 194 118 408 248 138 507 303
2 23 44 32 36 80 57 51 128 90 66 195 129 86 269 175 103 356 230 121 454 294 141 564 358
3 24 47 36 37 87 64 53 139 101 67 210 145 88 290 198 105 384 258 123 492 330 143 612 402
10 1 22 43 28 34 78 50 49 123 78 65 189 113 89 157 154 106 341 200 125 436 257 146 542 314
2 23 47 33 36 86 59 51 136 93 67 206 134 91 282 182 109 374 238 128 479 305 149 596 372
3 24 50 37 37 92 67 52 146 104 69 220 150 94 303 205 111 402 268 131 515 342 152 642 417
15 1 21 50 30 33 89 53 47 142 83 64 220 120 88 298 163 110 389 214 134 493 273 162 609 333
2 22 53 35 35 96 63 49 153 99 66 235 142 91 320 193 112 419 253 137 532 323 165 658 394
3 24 55 40 36 102 71 51 163 111 68 248 160 93 339 218 115 445 286 140 565 365 167 700 444



20
1 21 54 31 33 99 56 46 157 87 62 246 125 86 334 171 107 436 224 131 552 285 158 681 347
2 22 57 37 34 105 66 48 167 104 64 259 149 89 354 202 110 463 265 134 587 339 161 725 414
3 23 60 42 35 110 74 50 176 116 66 271 168 91 371 228 113 486 300 137 618 383 164 764 466



30
1 20 62 33 31 113 59 45 181 93 60 288 134 83 391 182 103 512 238 125 649 305 151 802 372
2 21 64 39 33 118 70 47 190 110 62 299 158 85 408 215 105 535 282 129 679 360 155 840 439
3 22 66 44 36 123 79 48 198 124 64 309 178 88 423 242 108 555 317 132 706 405 158 874 494



50
1 19 71 36 30 133 64 43 216 101 57 349 145 78 477 197 97 627 257 120 797 330 144 984 403
2 21 73 43 32 137 76 45 223 119 59 358 172 81 490 243 100 645 306 123 820 392 148 1,014 478
3 22 75 48 33 141 86 46 229 134 61 366 194 83 502 263 103 661 343 126 842 441 151 1,043 538



100
1 18 82 37 28 158 66 40 262 104 53 442 150 73 611 204 91 810 266 112 1,038 341 135 1,285 417
2 19 83 44 30 161 79 42 267 123 55 447 178 75 619 242 94 822 316 115 1,054 405 139 1,306 494
3 20 84 50 31 163 89 44 272 138 57 452 109 78 627 272 97 834 355 118 1,069 455 142 1,327 555

COMMON VENT CAPACITY




VENT
HEIGHT
(H)
(feet
TYPE B DOUBLE-WALL COMMON VENT DIAMETER (D)—inches
4 5 6 7 8 9 10
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 92 81 65 140 116 103 204 161 147 309 248 200 404 314 260 547 434 335 672 520 410
8 101 90 73 155 129 114 224 178 163 339 275 223 444 348 290 602 480 378 740 577 465
10 110 97 79 169 141 124 243 194 178 367 299 242 477 377 315 649 522 405 800 627 495
15 125 112 91 195 164 144 283 228 206 427 352 280 556 444 365 753 612 465 924 733 565
20 136 123 102 215 183 160 314 255 229 475 394 310 621 499 405 842 688 523 1,035 826 640
30 152 138 118 244 210 185 361 297 266 547 459 360 720 585 470 989 808 605 1,209 975 740
50 167 153 134 279 244 214 421 353 310 641 547 423 854 706 550 1,164 977 705 1,451 1,188 860
100 175 163 NA 311 277 NA 489 421 NA 751 658 479 1,025 873 625 1,408 1,215 800 1,784 1,502 975


TABLE 504.3(1)—continued
TYPE B DOUBLE-WALL VENT




VENT CONNECTOR CAPACITY
Number of Appliances Two or more
Appliance Type Category I
Appliance Vent Connection Type B double-wall connector






VENT
HEIGHT
(H)
(feet)






CONNECTOR
RISE
(R)
(feet)
TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER—(D) inches
12 14 16 18 20 22 24
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H
FAN NAT FAN NAT 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 Min Max Max Min Max Max
6 2 174 764 496 223 1,046 623 281 1,371 853 346 1,772 1,080 NA NA NA NA NA NA NA NA NA
4 180 897 616 230 1,231 827 287 1,617 1,081 352 2,069 1,370 NA NA NA NA NA NA NA NA NA
6 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
8 2 186 822 516 238 1,126 696 298 1,478 910 365 1,920 1,150 NA NA NA NA NA NA NA NA NA
4 192 952 644 244 1,307 884 305 1,719 1,150 372 2,211 1,460 471 2,737 1,800 560 3,319 2,180 662 3,957 2,590
6 198 1,050 772 252 1,445 1,072 313 1,902 1,390 380 2,434 1,770 478 3,018 2,180 568 3,665 2,640 669 4,373 3,130
10 2 196 870 536 249 1,195 730 311 1,570 955 379 2,049 1,205 NA NA NA NA NA NA NA NA NA
4 201 997 664 256 1,371 924 318 1,804 1,205 387 2,332 1,535 486 2,887 1,890 581 3,502 2,280 686 4,175 2,710
6 207 1,095 792 263 1,509 1,118 325 1,989 1,455 395 2,556 1,865 494 3,169 2,290 589 3,849 2,760 694 4,593 3,270
15 2 214 967 568 272 1,334 790 336 1,760 1,030 408 2,317 1,317 1,305 NA NA NA NA NA NA NA NA
4 221 1,085 712 279 1,499 1,006 344 1,978 1,320 416 2,579 1,665 523 3,197 2,060 624 3,881 2,490 734 4,631 2,960
6 228 1,181 856 286 1,632 1,222 351 2,157 1,610 424 2,796 2,025 533 3,470 2,510 634 4,216 3,030 743 5,035 3,600



20
2 223 1,051 596 291 1,443 840 357 1,911 1,095 430 2,533 1,385 NA NA NA NA NA NA NA NA NA
4 230 1,162 748 298 1,597 1,064 365 2,116 1,395 438 2,778 1,765 554 3,447 2,180 661 4,190 2,630 772 5,005 3,130
6 237 1,253 900 307 1,726 1,288 373 2,287 1,695 450 2,984 2,145 567 3,708 2,650 671 4,511 3,190 785 5,392 3,790



30
2 216 1,127 632 286 1,664 910 367 2,183 1,190 461 2,891 1,540 NA NA NA NA NA NA NA NA NA
4 223 1,316 792 294 1,802 1,160 376 2,366 1,510 474 3,110 1,920 619 3,840 2,365 728 4,861 2,860 847 5,606 3,410
6 231 1,400 952 303 1,920 1,410 384 2,524 1,830 485 3,299 2,340 632 4,080 2,875 741 4,976 3,480 860 5,961 4,150



50
2 206 1,479 689 273 2,023 1,007 350 2,659 1,315 435 3,548 1,665 NA NA NA NA NA NA NA NA NA
4 213 1,561 860 281 2,139 1,291 259 2,814 1,685 447 3,730 2,135 580 4,601 2,633 709 5,569 3,185 851 6,633 3,790
6 221 1,631 1,031 290 2,242 1,575 369 2,951 2,055 461 3,893 2,605 594 4,808 3,208 424 5,826 3,885 867 6,943 4,620



100
2 192 1,923 712 254 2,644 1,050 326 3,490 1,370 402 4,707 1,740 NA NA NA NA NA NA NA NA NA
4 200 1,984 888 263 2,731 1,346 336 3,606 1,760 414 4,842 2,220 523 5,982 2,750 639 7,254 3,330 769 8,650 3,950
6 208 2,035 1,064 272 2,811 1,642 346 3,714 2,150 426 4,968 2,700 539 6,143 3,350 654 7,453 4,070 786 8,892 4,810

COMMON VENT CAPACITY




VENT
HEIGHT
(H)
(feet
TYPE B DOUBLE-WALL COMMON VENT DIAMETER (D)—inches
12 14 16 18 20 22 24
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 900 696 588 1,284 990 815 1,735 1,336 1,065 2,253 1,732 1,345 2,838 2,180 1,660 3,488 2,677 1970 4,206 3,226 2,390
8 994 773 652 1,423 1,103 912 1,927 1,491 1,190 2,507 1,936 1,510 3,162 2,439 1,860 3,890 2,998 2,200 4,695 3,616 2,680
10 1,076 841 712 1,542 1,200 955 2,093 1,625 1,300 2,727 2,113 1,645 3,444 2,665 2,030 4,241 3,278 2,400 5,123 3,957 2,920
15 1,247 986 825 1,794 1,410 1,158 2,440 1,910 1,510 3,184 2,484 1,910 4,026 3,133 2,360 4,971 3,862 2,790 6,016 4,670 3,400
20 1,405 1,116 916 2,006 1,588 1,290 2,722 2,147 1,690 3,561 2,798 2,140 4,548 3,552 2,640 5,573 4,352 3,120 6,749 5,261 3,800
30 1,658 1,327 1,025 2,373 1,892 1,525 3,220 2,558 1,990 4,197 3,326 2,520 5,303 4,190 3,110 6,539 5,157 3,680 7,940 6,247 4,480
50 2,024 1,640 1,280 2,911 2,347 1,863 3,964 3,183 2,430 5,184 4,149 3,075 6,567 5,240 3,800 8,116 6,458 4,500 9,837 7,813 5,475
100 2,569 2,131 1,670 3,732 3,076 2,450 5,225 4,202 3,200 6,749 5,509 4,050 8,597 6,986 5,000 10,681 8,648 5,920 13,004 10,499 7,200
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.293 1 W.

Gas vents shall be supported and spaced in accordance with their listings and the manufacturer's instructions.
Gas vents shall be permanently identified by a label attached to the wall or ceiling at a point where the vent connector enters the gas vent. The label shall read:
  "This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel- burning appliances or incinerators."
Single-wall metal pipe vents shall comply with Sections 503.7.1 through 503.7.12.
Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 inch (0.7 mm) thick or other approved, noncombustible, corrosion- resistant material.
Uninsulated single-wall metal pipe shall not be used outdoors for venting gas utilization equipment.
Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected equipment draft hood outlet or flue collar. Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm) (see Figure 503.5.4). An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe (see also Section 503.7.8, Item 3). However, such constructions do not include chimneys or other vents, or open structural framing. The single wall metal pipe shall be as high as such construction which is located beyond ten feet from the vent and up to and including the distance determined by Equation 5-2.
Single-wall metal pipe shall be used only for runs directly from the space in which the equipment is located through the roof or exterior wall to the outdoor atmosphere.
A pipe passing through a roof shall extend without interruption through the roof flashing, roof jack, or roof thimble. Where a single-wall metal pipe passes through a roof constructed of combustible material, a noncombustible, non-ventilating thimble shall be used at the point of passage. The thimble shall extend at least 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed only at the top. The thimble shall be sized in accordance with Section 503.10.16.
Single-wall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space, or floor. The installation of a single-wall metal pipe through an exterior combustible wall shall comply with Section 503.10.15. Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have suitable clearances maintained.
Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 503.7.7. The clearance from single-wall metal pipe to combustible material shall be permitted to be reduced where the combustible material is protected as specified for vent connectors in Table 308.2.

TABLE 503.7.7a
CLEARANCES FOR CONNECTORS



EQUIPMENT
MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL
Listed Type B gas
vent material
Listed Type L
vent material
Single-wall
metal pipe
Factory-built
chimney sections
Listed equipment with draft hoods and equipment listed for use with Type B gas vents As listed As listed 6 inches As listed
Residential boilers and furnaces with listed gas conversion burner and with draft hood 6 inches 6 inches 6 inches As listed
Residential appliances listed for use with Type L vents Not permitted As listed 9 inches As listed
Listed gas-fired toilets Not permitted As listed As listed As listed
Unlisted residential appliances with draft hood Not permitted 6 inches 9 inches As listed
Residential and low-heat equipment other than above Not permitted 9 inches 18 inches As listed
Medium-heat equipment Not permitted Not permitted 36 inches As listed
For SI: 1 inch = 25.4 mm.
  1. These clearances shall apply unless the listing of an appliance or connector specifies different clearances, in which case the listed clearances shall apply.
A venting system constructed of single-wall metal pipe shall be sized in accordance with one of the following methods and the equipment manufacturer's instructions:
  1. For a draft-hood-equipped appliance, in accordance with Section 504.
  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 be greater than seven times the draft hood outlet area.
  3. Other approved engineering methods.
Any shaped single-wall metal pipe shall be permitted to be used, provided that its equivalent effective area is equal to the effective area of the round pipe for which it is substituted, and provided that the minimum internal dimension of the pipe is not less than 2 inches (51 mm).
The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached.
All portions of single-wall metal pipe shall be supported for the design and weight of the material employed.
Single-wall metal pipe shall comply with the marking provisions of Section 503.6.12.
The location of venting system terminations shall comply with the following:
  1. Gas venting systems shall be extended at least 2 feet (610 mm) above the highest construction, such as a roof ridge, parapet wall, or penthouse, within 10 feet (3048 mm) of the vent outlet whether the construction is on the same building as the chimney or on another building. However, such constructions do not include chimneys or other vents, or open structural framing. The vent shall be as high as such construction which is located beyond 10 feet (3048 mm) from the vent and up to and including the distance determined by Equation 5-2.
  Exception: Direct vent appliances approved by the commissioner and installed in accordance with the manufacturer's instructions.
  2. Where permitted, through-the-wall vents for Category II and IV appliances and non-categorized condensing appliances shall not terminate over public walkways or over an area where condensate or vapor could create a nuisance or hazard or could be detrimental to the operation of regulators, relief valves or other equipment. Where local experience indicates that condensate is a problem with Category I and III appliances, this provision shall also apply.
  3. A mechanical draft venting system shall terminate at least 3 feet (914 mm) above any 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.
Provision shall be made to collect and dispose of condensate from venting systems serving Category II and IV equipment and noncategorized condensing appliances in accordance with Section 503.8, Item 2.
Vent connectors for Category I equipment shall comply with Sections 503.10.1 through 503.10.16.
A vent connector shall be used to connect equipment 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 equipment.
Vent connectors shall be constructed in accordance with Sections 503.10.2.1 through 503.10.2.5.
A vent connector shall be made of noncombustible corrosion-resistant material capable of withstanding the vent gas temperature produced by the equipment and of sufficient thickness to withstand physical damage.
Where the vent connector used for equipment having a draft hood or a Category I appliance is located in or passes through attics, crawl spaces or other unconditioned spaces, that portion of the vent connector shall be listed Type B or Type L or listed vent material or listed material having equivalent insulation properties.
Where vent connectors for residential-type appliances are not installed in attics or other unconditioned spaces, connectors for listed appliances having draft hoods and for appliances having draft hoods and equipped with listed conversion burners shall be one of the following:
  1. Type B or Type L vent material;
  2. Galvanized sheet steel not less than 0.018 inch (0.46 mm) thick;
  3. Aluminum (1100 or 3003 alloy or equivalent) sheet not less than 0.027 inch (0.69 mm) thick;
  4. Stainless steel sheet not less than 0.012 inch (0.31 mm) thick;
  5. Smooth interior wall metal pipe having resistance to heat and corrosion equal to or greater than that of Item 2, 3 or 4 above; or
  6. A listed vent connector.
  Vent connectors shall not be covered with insulation.
  Exception: Listed insulated vent connectors shall be installed according to the terms of their listing.
A vent connector for low-heat equipment shall be a factory-built chimney section or steel pipe having resistance to heat and corrosion equivalent to that for the appropriate galvanized pipe as specified in Table 503.10.2.4. Factory-built chimney sections shall be joined together in accordance with the chimney manufacturers' instructions.

TABLE 503.10.2.4
MINIMUM THICKNESS FOR GALVANIZED STEEL VENT
CONNECTORS FOR LOW-HEAT APPLIANCES
DIAMETER OF CONNECTOR
(inches)
MINIMUM THICKNESS
(inch)
Less than 6 0.019
6 to less than 10 0.023
10 to 12 inclusive 0.029
14 to 16 inclusive 0.034
Over 16 0.056
For SI: 1 inch = 25.4 mm.
Vent connectors for medium-heat equipment 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 503.10.2.5 and shall comply with the following:
  1. A steel vent connector for equipment 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 (ASTM C 64, Type F), or the equivalent.
  2. The lining shall be at least 21/2 inches (64 mm) thick for a vent connector having a diameter or greatest cross-sectional dimension of 18 inches (457 mm) or less.
  3. The lining shall be at least 41/2 inches (114 mm) thick laid on the 41/2-inch (114 mm) bed for a vent connector having a diameter or greatest cross-sectional dimension greater than 18 inches (457 mm).
  4. Factory-built chimney sections, if employed, shall be joined together in accordance with the chimney manufacturers' instructions.

TABLE 503.10.2.5
MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FORM
EDIUM-HEAT EQUIPMENT AND COMMERCIAL AND
INDUSTRIAL INCINERATORS VENT CONNECTOR SIZE
DIAMETER
(inches)
AREA
(square inches)
MINIMUM THICKNESS
(inch)
Up to 14 Up to 154 0.053
Over 14 to 16 154 to 201 0.067
Over 16 to 18 201 to 254 0.093
Over 18 Larger than 254 0.123
For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2.
Vent connectors shall be sized in accordance with Sections 503.10.3.1 through 503.10.3.5.
A vent connector for equipment with a single draft hood or for a Category I fan-assisted combustion system appliance shall be sized and installed in accordance with Section 504 or other approved engineering methods.
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 a minimum 1-foot (305 mm) rise.
Where two or more appliances are connected to a common vent or chimney, each vent connector shall be sized in accordance with Section 504 or other approved engineering methods.
  As an alternative method applicable only when all of 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.
Where two or more gas 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 the required clearance to combustible materials and shall be sized in accordance with Section 504 or other approved engineering methods.
  As an alternate method applicable only where there are two draft hood equipped appliances, the effective area of the common vent connector or vent manifold and all junction fittings shall be not less than the area of the larger vent connector plus 50 percent of the area of the smaller flue collar outlet.
Where the size of a vent connector is increased to overcome installation limitations and obtain connector capacity equal to the equipment input, the size increase shall be made at the equipment draft hood outlet.
Where two or more vent connectors enter a common gas 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. Vent connectors serving Category I appliances shall not be connected to any portion of a mechanical draft system operating under positive static pressure, such as those serving Category III or IV appliances.
Minimum clearances from vent connectors to combustible material shall be in accordance with Table 503.7.7.
  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 308.2.
A vent connector shall be installed so as to avoid turns or other construction features that create excessive resistance to flow of vent gases.
Joints between sections of connector piping and connections to flue collars and hood outlets shall be fastened by one of the following methods:
  1. Sheet metal screws.
  2. Vent connectors of listed vent material assembled and connected to flue collars or draft hood outlets in accordance with the manufacturers' instructions.
  3. Welding.
A vent connector shall be installed without dips or sags and shall slope upward toward the vent or chimney at least 1/4 inch per foot (21 mm/m).
  Exception: Vent connectors attached to a mechanical draft system installed in accordance with the manufacturers' instructions.
A vent connector shall be as short as practical and the equipment located as close as practical to the chimney or vent. Except as provided for in Section 503.10.3, the maximum horizontal length of a single- wall connector shall be 75 percent of the height of the chimney or vent. Except as provided for in Section 503.10.3, the maximum horizontal length of a Type B double-wall connector shall be 100 percent of the height of the chimney or vent. For a chimney or vent system serving multiple appliances, the maximum length of an individual connector, 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.
A vent connector shall be supported in accordance with the manufacturer's recommendations for the design and weight of the material employed to maintain clearances and prevent physical damage and separation of joints.
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 firmly 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 (see Section 501.9).
The entire length of a vent connector shall be provided with ready access for inspection, cleaning, and replacement.
A vent connector shall not be connected to a chimney flue serving a fireplace.
A vent connector shall not pass through any ceiling, floor or fire-resistance-rated wall. A single-wall metal pipe connector shall not pass through any interior wall.
  Exception: Vent connectors made of listed Type B or Type L vent material and serving listed equipment with draft hoods and other equipment listed for use with Type B gas vents shall be permitted to pass through walls or partitions constructed of combustible material if the connectors are installed with not less than the listed clearance to combustible material.
A vent connector made of 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 equipped 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 vent connector. Where there is a run of not less than 6 feet (1829 mm) of vent connector in the open between the draft hood outlet and the thimble, the thimble shall be permitted to be not less than 2 inches (51 mm) larger in diameter than the vent connector.
  2. For unlisted appliances having draft hoods, the thimble shall be not less than 6 inches (152 mm) larger in diameter than the vent connector.
  3. For residential and low-heat appliances, the thimble shall be not less than 12 inches (305 mm) larger in diameter than the vent connector.
  Exception: In lieu of thimble protection, all combustible material in the wall shall be removed from the vent connector a sufficient distance to provide the specified clearance from such vent connector to combustible material. Any material used to close up such opening shall be noncombustible.
Vent connectors for medium-heat equipment shall not pass through walls or partitions constructed of combustible material.
Vent connectors for Category II, III and IV appliances shall be as specified for the venting systems in accordance with Section 503.4.
The installation of draft hoods and draft controls shall comply with Sections 503.12.1 through 503.12.7.
Vented equipment shall be installed with draft hoods.
  Exception: Incinerators, direct-vent equipment, fan-assisted combustion system appliances, equipment requiring chimney draft for operation, equipment equipped with blast, power, or pressure burners that are not listed for use with draft hoods, and equipment designed for forced venting.
A draft hood supplied with or forming a part of listed vented equipment shall be installed without alteration, exactly as furnished and specified by the equipment manufacturer.
If a draft hood is not supplied by the equipment manufacturer where one is required, a draft hood shall be installed, shall be of a listed or approved type and, in the absence of other instructions, shall be of the same size as the equipment flue collar. Where a draft hood is required with a conversion burner, it shall be of a listed or approved type.
Where it is determined that a draft hood of special design is needed or preferable for a particular installation, the installation shall be in accordance with the recommendations of the equipment manufacturer and shall be approved by the department.
Where a draft control device is part of the equipment or is supplied by the equipment manufacturer, it shall be installed in accordance with the manufacturers' instructions. In the absence of manufacturers' instructions, the device shall be attached to the flue collar of the equipment or as near to the equipment as practical.
Equipment requiring controlled chimney draft shall be permitted to be equipped with a listed double-acting barometric-draft regulator installed and adjusted in accordance with the manufacturers' instructions.
Draft hoods and barometric draft regulators shall be installed in the same room or enclosure as the equipment in such a manner as to prevent any difference in pressure between the hood or regulator and the combustion air supply.
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 any part of the equipment or adjacent construction. The equipment and its draft hood shall be located so that the relief opening is accessible for checking vent operation.
A draft hood shall be located so its relief opening is not less than 6 inches (152 mm) from any surface except that of the equipment it serves and the venting system to which the draft hood is connected. Where a greater or lesser clearance is indicated on the equipment label, the clearance shall be not less than that specified on the label. Such clearances shall not be reduced.
A manually operated damper shall not be placed in the vent connector for any equipment. Fixed baffles shall not be classified as manually operated dampers.
An automatically operated vent damper shall be of a listed type complete with safety controls to prove open position of the damper before equipment operation.
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 terms of their listing.
  2. Approved draft regulators and safety controls that are designed and installed in accordance with approved engineering methods.
  3. Listed heat reclaimers and automatically operated vent dampers installed in accordance with the terms of their listing.
  4. Approved economizers, heat reclaimers, and recuperators installed in venting systems of equipment not required to be equipped with draft hoods, provided that the gas utilization equipment manufacturer's instructions cover the installation of such a device in the venting system and performance in accordance with Sections 503.3 and 503.3.1 is obtained.
  5. Vent dampers serving listed appliances installed in accordance with Sections 504.2.1 and 504.3.1 or other approved engineering methods.
The following definitions apply to the tables in this section.
  APPLIANCE CATEGORIZED VENT DIAMETER/ AREA. The minimum vent area/diameter permissible for Category I appliances to maintain a non-positive vent static pressure when tested in accordance with nationally recognized standards.
  FAN-ASSISTED COMBUSTION SYSTEM. An appliance equipped with an integral mechanical means to either draw or force products of combustion through the combustion chamber or heat exchanger.
  FAN Min. The minimum input rating of a Category I fan-assisted appliance attached to a vent or connector.
  FAN Max. The maximum input rating of a Category I fan-assisted appliance attached to a vent or connector.
  NAT Max. The maximum input rating of a Category I draft-hood-equipped appliance attached to a vent or connector.
  FAN FAN. The maximum combined appliance input rating of two or more Category I fan-assisted appliances attached to the common vent.
  FAN NAT. The maximum combined appliance input rating of one or more Category I fan-assisted appliances and one or more Category I draft-hood-equipped appliances attached to the common vent.
  NA. Vent configuration is not allowed due to potential for condensate formation or pressurization of the venting system, or not applicable due to physical or geometric restraints.
  NAT NAT. The maximum combined appliance input rating of two or more Category I draft-hood-equipped appliances attached to the common vent.
The application of Tables 504.2(1) through 504.2(5) shall be subject to the requirements of Sections 504.2.1 through 504.2.15.












TABLE 504.2(5)
SINGLE-WALL METAL PIPE OR TYPE B
ASBESTOS CEMENT VENT
Number of Appliances Single
Appliance Type Draft hood equipped
Appliance Vent Connection Connected directly to pipe or vent
HEIGHT
(H)
(feet)
LATERAL
(L)
(feet)
VENT DIAMETER—(D) inches
3 4 5 6 7 8 10 12
MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H


6
0 39 70 116 170 232 312 500 750
2 31 55 94 141 194 260 425 620
5 28 51 88 128 177 242 390 600



8
0 42 76 126 185 252 340 542 815
2 32 61 102 154 210 284 451 680
5 29 56 95 141 194 264 430 648
10 24 49 86 131 180 250 406 912




10
0 45 84 138 202 279 372 606 912
2 35 67 111 168 233 311 505 760
5 32 61 104 153 215 289 480 724
10 27 54 94 143 200 274 455 700
15 NA 46 84 130 186 258 432 666





15
0 49 91 151 223 312 420 684 1,040
2 39 72 122 186 260 350 570 865
5 35 67 110 170 240 325 540 825
10 30 58 103 158 223 308 514 795
15 NA 50 93 144 207 291 488 760
20 NA NA 82 132 195 273 466 726






20
0 53 101 163 252 342 470 770 1,190
2 42 80 136 210 286 392 641 990
5 38 74 123 192 264 364 610 945
10 32 65 115 178 246 345 571 910
15 NA 55 104 163 228 326 550 870
20 NA NA 91 149 214 306 525 832







30
0 56 108 183 276 384 529 878 1,370
2 44 84 148 230 320 441 730 1,140
5 NA 78 137 210 296 410 694 1,080
10 NA 68 125 196 274 388 626 1,050
15 NA NA 113 177 258 366 625 1,000
20 NA NA 99 163 240 344 596 960
30 NA NA NA NA 192 295 540 890







50
0 NA 120 210 310 443 590 980 1,550
2 NA 95 171 260 370 492 820 1,290
5 NA NA 159 234 374 474 780 1,230
10 NA NA 146 221 318 456 730 1,190
15 NA NA NA 200 292 407 705 1,130
20 NA NA NA 185 276 384 670 1,080
30 NA NA NA NA 222 330 605 1,010
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.293 1 W.
These venting tables shall not be used where obstructions, as described in Section 503.15, are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer's instructions or in accordance with the following:
  1. The maximum capacity of the vent system shall be determined using the "NAT Max" column.
  2. The minimum capacity shall be determined as if 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.
Where the vent size determined from the tables is smaller than the appliance draft hood outlet or flue collar, the smaller size shall be permitted to be used provided that all of the following requirements are met:
  1. The total vent height (H) is at least 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 larger than 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 × maximum table capacity).
  5. The draft hood outlet is greater than 4 inches (102 mm) in diameter. Do not connect a 3-inch-diameter (76 mm) vent to a 4-inch-diameter (102 mm) draft hood outlet. This provision shall not apply to fan-assisted appliances.
Single-appliance venting configurations with zero (0) lateral lengths in Tables 504.2(1), 504.2(2), and 504.2(5) shall not have elbows in the venting system. For vent configurations with lateral lengths, the venting tables include allowance for two 90-degree (1.57rad) turns. For each 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 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.
Zero (0) lateral (L) shall apply only to a straight vertical vent attached to a top outlet draft hood or flue collar.
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 be greater than the highest appliance rating input.
Listed corrugated metallic chimney liner systems in masonry chimneys shall be sized by using Table 504.2(1) or 504.2(2) for Type B vents with the maximum capacity reduced by 20 percent (0.80 × maximum capacity) and the minimum capacity as shown in Table 504.2(1) or 504.2(2). Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 504.2.3. The 20-percent reduction for corrugated metallic chimney liner systems includes an allowance for one long-radius 90-degree (157 rad) turn at the bottom of the liner.

TABLE 504.3(2)
TYPE B DOUBLE-WALL VENT



VENT CONNECTOR CAPACITY
Number of Appliances Two or more
Appliance Type Category I
Appliance Vent Connection Single-wall metal connector






VENT
HEIGHT
(H)
(feet)






CONNECTOR
RISE
(R)
(feet)
SINGLE-WALL METAL VENT CONNECTOR DIAMETER—(D) inches
3 4 5 6 7 8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H
FAN NAT FAN NAT FAN NAT 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 Min Max Max Min Max Max Min Max Max
6 1 NA NA 26 NA NA 46 NA NA 71 NA NA 102 207 223 140 262 293 183 325 373 234 447 463 286
2 NA NA 31 NA NA 55 NA NA 85 168 182 123 215 251 167 271 331 219 334 422 281 458 524 344
3 NA NA 34 NA NA 62 121 131 95 175 198 138 222 273 188 279 361 247 344 462 316 468 574 385
8 1 NA NA 27 NA NA 48 NA NA 75 NA NA 106 226 240 145 285 316 191 352 403 244 481 502 299
2 NA NA 35 NA NA 57 125 126 89 184 193 127 234 266 173 293 353 228 360 450 292 492 560 355
3 NA NA 35 NA NA 64 130 138 100 191 208 144 241 287 197 302 381 256 370 489 328 501 609 400
10 1 NA NA 28 NA NA 50 119 121 77 182 186 110 240 253 150 302 335 196 372 429 252 506 534 308
2 NA NA 33 84 85 59 124 134 91 189 203 132 248 278 183 311 369 235 381 473 302 517 589 368
3 NA NA 33 89 91 67 129 144 102 197 217 148 257 299 203 320 398 265 391 511 339 528 637 413
15 1 NA NA 29 79 87 52 116 138 81 177 214 116 238 291 158 312 380 208 397 482 266 556 596 324
2 NA NA 34 83 94 62 121 150 97 185 230 138 246 314 189 321 411 248 407 522 317 568 646 387
3 NA NA 39 87 100 70 127 160 109 193 243 157 255 333 215 331 438 281 418 557 360 579 690 437



20
1 49 56 30 78 97 54 115 152 84 175 238 120 233 325 165 306 425 217 390 538 276 546 664 336
2 52 59 36 82 103 64 120 163 101 182 252 144 243 346 197 317 453 259 400 574 331 558 709 403
3 55 62 40 87 107 72 125 172 113 190 264 164 252 363 223 326 476 294 412 607 375 570 750 457



30
1 47 60 31 77 110 57 112 175 89 169 278 129 226 380 175 296 497 230 378 630 294 528 779 358
2 51 62 37 81 115 67 117 185 106 177 290 152 236 397 208 307 521 274 389 662 349 541 819 425
3 54 64 42 85 119 76 122 193 120 185 300 172 244 412 235 316 542 309 400 690 394 555 855 482



50
1 46 69 34 75 128 60 109 207 96 162 336 137 217 460 188 284 604 245 364 768 314 507 951 384
2 49 71 40 79 132 72 114 215 113 170 345 164 226 473 223 294 623 293 376 793 375 520 983 458
3 52 72 45 83 136 82 119 221 123 178 353 186 235 486 252 304 640 331 387 816 423 535 1,013 518



100
1 45 79 34 71 150 61 104 249 98 153 424 140 205 585 192 269 774 249 345 993 321 476 1,236 393
2 48 80 4 75 153 73 110 255 115 160 428 167 212 593 228 279 788 299 358 1,011 383 490 1,259 469
3 51 81 46 79 157 85 114 260 129 168 433 190 222 603 256 289 801 339 368 1,027 431 506 1,280 527

COMMON VENT CAPACITY




VENT
HEIGHT
(H)
(feet
TYPE B DOUBLE-WALL COMMON VENT DIAMETER (D)—inches
4 5 6 7 8 9 10
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA 78 64 NA 113 99 200 158 144 304 244 196 398 310 257 541 429 332 665 515 407
8 NA 87 71 NA 126 111 218 173 159 331 269 218 436 342 285 592 473 373 730 569 460
10 NA 94 76 163 137 120 237 189 174 357 292 236 467 369 309 638 512 398 787 617 487
15 121 108 88 189 159 140 275 221 200 416 343 274 544 434 357 738 599 456 905 718 553
20 131 118 98 208 177 156 305 247 223 463 383 302 606 487 395 824 673 512 1,013 808 626
30 145 132 113 236 202 180 350 286 257 533 446 349 703 570 459 958 790 593 1,183 852 723
50 159 145 128 268 233 208 406 337 296 622 529 410 833 686 535 1,139 954 689 1,418 1,157 838
100 166 153 NA 297 263 NA 469 398 NA 726 633 464 999 846 606 1,378 1,185 780 1,741 1,459 948
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.293 1 W.
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.
Tables 504.2(1), 504.2(2), 504.2(3), 504.2(4) and 504.2(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. Table 504.2(3) in combination with Table 504.3(6) shall be used for clay-tile-lined exterior masonry chimneys, provided all of the following are met:
  1. Vent connector is Type B double-wall.
  2. Vent connector length is limited to 11 feet for each inch (18 mm per mm) of vent connector diameter.
  3. The appliance is draft hood equipped.
  4. The input rating is less than the maximum capacity given by Table 504.2(3).
  5. For a water heater, the outdoor design temperature is not less than 5°F (-15°C).
  6. For a space-heating appliance, the input rating is greater than the minimum capacity given by Table 504.3(6).
  Where these conditions cannot be met, an alternative venting design shall be used, such as a listed chimney lining system.
  Exception: The installation of vents serving listed appliances shall be permitted to be in accordance with the appliance manufacturer's instructions and the terms of the listing.

TABLE 504.3(6)
EXTERIOR MASONRY CHIMNEY
Number of Appliances One
Appliance Type NAT
Appliance Vent Connection Type B double-wall connector
MINIMUM ALLOWABLE INPUT RATING OF SPACE-HEATING APPLIANCE
IN THOUSANDS OF BTU PER HOUR


VENT HEIGHT
(feet)
Internal area of chimney (square inches)
12 19 28 38 50 63 78 113
37°F or Greater
Local 99% Winter Design Temperature: 37°F or Greater
6
8
10
15
20
30
50
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
27 to 36°F
Local 99% Winter Design Temperature:27 to 36°F
6
8
10
15
20
30
50
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
17 to 26°F
Local 99% Winter Design Temperature: 17 to 26°F
6
8
10
15
20
30
50
NA
NA
NA
NA
NA
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
387
507
NA
349
352
358
398
457
581
NA
5 to 16°F
Local 99% Winter Design Temperature: 5 to 16°F
6
8
10
15
20
30
50
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
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
-10 to 4°F
Local 99% Winter Design Temperature: -10 to 4°F
6
8
10
15
20
30
50
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
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
1,003
-11°F or Lower
Local 99% Winter Design Temperature: -1 1°F or Lower
Not recommended for any vent configurations
Note: See Figure B-19 in Appendix B for a map showing local 99 percent winter design temperatures in the United States.
For SI: °C = [(°F -32]/1.8, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.
Corrugated vent connectors shall be not smaller than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter.
Vent connectors shall not be increased in size more than two sizes greater than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter.
In a single run of vent or vent connector, different diameters and types of vent and connector components shall be permitted to be used, provided that all such sizes and types are permitted by the tables.
Interpolation shall be permitted in calculating capacities for vent dimensions that fall between the table entries.
Extrapolation beyond the table entries shall not be permitted.
For vent heights less than 6 feet (1829 mm) and greater than shown in the tables, engineering methods shall be used to calculate vent capacities. Signed and sealed calculations shall be submitted with filing application.
3(1) through 504.3(8). The application of Tables 504.3(1) through 504.3(8) shall be subject to the requirements of Sections 504.3.1 through 504.3.2.5.
These venting tables shall not be used where obstructions, as described in Section 503.15, are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer's instructions or in accordance with the following:
  1. The maximum capacity of the vent connector shall be determined using the NAT Max column.
  2. The maximum capacity of the vertical vent or chimney shall be determined using the FANNAT column when the second appliance is a fan-assisted appliance, or the NATNAT column when the second appliance is equipped with a draft hood.
  3. The minimum capacity shall be determined as if the appliance were a fan-assisted appliance.
  3.1. The minimum capacity of the vent connector shall be determined using the FAN Min column.
  3.2. The FANFAN column shall be used where the second appliance is a fan-assisted appliance, and the FANNAT 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.
The vent connector shall be routed to the vent utilizing the shortest possible route. Except as provided in Section 504.3.3, the maximum vent connector horizontal length shall be 11/2 feet for each inch (18 mm per mm) of connector diameter as shown in Table 504.3.2.

TABLE 504.3.2
MAXIMUM VENT CONNECTOR LENGTH
CONNECTOR DIAMETER MAXIMUM
(inches)
CONNECTOR HORIZONTAL
LENGTH (feet)
3
4 6
5
6 9
7 10½
8 12
9 13½
10 15
12 18
14 21
16 24
18 27
20 30
22 33
24 36
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
Connectors with longer horizontal lengths than those listed in Section 504.3.2 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 above. For example, the maximum length listed above for a 4-inch (102 mm) connector is 6 feet (1829 mm).With a connector length greater than 6 feet (1829 mm) but not exceeding 12 feet (3658 mm), the maximum capacity must be reduced by 10 percent (0.90 ?maximum vent connector capacity). With a connector length greater than 12 feet (3658 mm) but not exceeding 18 feet (5486 mm), the maximum capacity must be reduced by 20 percent (0.80 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 504.2(1) shall be used. For single-wall connectors, Table 504.2(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.
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 maximum common vent capacity) to the common vent capacity part of the common vent tables. The length of the common vent connector manifold (L M ) shall not exceed 112 feet for each inch (457 mm for each 25.4 mm) of common vent connector manifold diameter (D) (see Figure B-11).
Where the common vertical vent is offset, the maximum capacity of the common vent shall be reduced in accordance with Section 504.3.6. The horizontal length of the common vent offset (Lo) shall not exceed 112 feet for each inch (457 mm for each 25.4 mm) of common vent diameter.
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 greater than 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.
The vent connector capacities listed in the common vent sizing tables include allowance for two 90-degree (1.57 rad) elbows. For each additional elbow up to and including 45 degrees (0.79 rad), the maximum vent connector capacity listed in the venting tables shall be reduced by 5 percent. For each elbow greater than 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum vent connector capacity listed in the venting tables shall be reduced by 10 percent.
The cross-sectional area of the common vent shall be equal to or greater than the cross-sectional area of the largest connector.
At the point where tee or wye fittings connect to a common vent, the opening size of the fitting shall be equal to the size of the common vent. Such fittings shall not be prohibited from having reduced size openings at the point of connection of appliance vent connectors.
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.
For multiple units of equipment all located on one floor, available 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.
For multistory installations, available 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.
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 504.2(1) or 504.2(2) for available total height (H) up to the lowest interconnection.
Where used in multistory systems, vertical common vents shall be Type B double wall and shall be installed with a listed vent cap.
Offsets in multistory common vent systems shall be limited to a single offset in each system, and systems with an offset shall comply with all of 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 11/2 feet for each inch (457 mm for each 25.4 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 × maximum common vent capacity).
  4. A multi-story common vent shall not be reduced in size above the offset.
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.
For appliances with more than one input rate, the minimum vent connector capacity (FAN Min) determined from the tables shall be less than the lowest appliance input rating, and the maximum vent connector capacity (FAN Max or NAT Max) determined from the tables shall be greater than the highest appliance input rating.
Listed, corrugated metallic chimney liner systems in masonry chimneys shall be sized by using Table 504.3(1) or 504.3(2) for Type B vents, with the maximum capacity reduced by 20 percent (0.80 × maximum capacity) and the minimum capacity as shown in Table 504.3(1) or 504.3(2). Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Sections 504.3.5 and 504.3.6. The 20-percent reduction for corrugated metallic chimney liner systems includes an allowance for one long-radius 90-degree (1.57 rad) turn at the bottom of the liner.
Tables 504.3(1), 504.3(2), 504.3(3), 504.3(4), and 504.3(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. Tables 504.3(7) and 504.3(8) shall be used for clay-tile-lined exterior masonry chimneys, provided all of the following conditions are met:
  1. Vent connector is Type B double-wall.
  2. At least one appliance is draft hood equipped.
  3. The combined appliance input rating is less than the maximum capacity given by Table 504.3(7a) for NATNAT or Table 504.3(8a) for FANNAT.
  4. The input rating of each space-heating appliance is greater than the minimum input rating given by Table 504.3(7b) for NATNAT or Table 504.3(8b) for FANNAT.
  5. The vent connector sizing is in accordance with Table 504.3(3).
  Where these conditions cannot be met, an alternative venting design shall be used, such as a listed chimney lining system.
  Exception: Vents serving listed appliances installed in accordance with the appliance manufacturer's instructions and the terms of the listing.

TABLE 504.3(3)
MASONRY CHIMNEY




VENT CONNECTOR CAPACITY
Number of Appliances Two or more
Appliance Type Category I
Appliance Vent Connection Type B double-wall connector






VENT
HEIGHT
(H)
(feet)






CONNECTOR
RISE
(R)
(feet)
TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER—(D) inches
3 4 5 6 7 8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H
FAN NAT FAN NAT FAN NAT 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 Min Max Max Min Max Max Min Max Max
6 1 24 33 21 39 62 40 52 106 67 65 194 101 87 274 141 104 370 201 124 479 253 145 599 319
2 26 43 28 41 79 52 53 133 85 67 230 124 89 324 173 107 436 232 127 562 300 148 694 378
3 27 49 34 42 92 61 55 155 97 69 262 143 91 369 203 109 491 270 129 633 249 151 795 439
8 1 24 39 22 39 72 41 55 117 69 71 213 105 94 304 148 113 414 210 134 539 267 156 682 335
2 26 47 29 40 87 53 57 140 56 73 246 127 97 350 179 116 473 240 137 615 311 160 776 394
3 27 52 34 42 98 62 59 159 98 75 269 145 99 383 206 119 517 276 139 672 358 163 848 452
10 1 24 42 22 38 80 42 55 130 71 74 232 108 101 324 153 120 444 216 142 582 277 165 739 348
2 26 50 29 40 93 54 57 153 87 76 261 129 103 366 184 123 498 247 145 652 321 168 814 407
3 27 55 35 41 105 63 58 170 100 78 284 148 106 397 209 126 540 281 147 705 366 171 893 436
15 1 24 48 23 35 93 44 54 154 74 72 277 114 100 384 464 125 511 229 153 658 297 184 824 375
2 25 55 31 39 105 55 56 174 9+ 74 299 134 103 419 192 128 558 260 156 718 339 187 900 432
3 26 59 35 41 115 64 57 189 102 76 319 153 105 448 215 131 597 292 159 760 382 190 960 486



20
1 24 52 24 37 102 46 53 172 77 71 312 119 98 437 193 123 584 239 150 752 312 180 943 397
2 25 58 31 39 114 56 55 190 91 73 335 138 101 467 199 126 625 270 153 805 354 184 1,011 452
3 26 63 35 40 123 65 57 204 104 75 353 157 104 493 222 129 661 301 156 851 396 187 1,067 505



30
1 24 54 25 37 111 48 52 192 82 69 357 127 96 504 187 119 680 225 145 883 337 175 1,115 432
2 25 60 32 35 122 58 54 208 95 72 376 145 99 532 209 122 715 287 149 928 378 178 1,171 484
3 26 64 36 40 131 66 56 221 107 74 392 163 101 554 233 125 746 317 152 968 418 182 1,220 535



50
1 23 51 25 36 116 51 51 209 89 67 405 143 92 582 213 115 798 294 140 1,049 392 168 1,334 506
2 24 59 32 37 127 61 53 225 102 70 421 161 95 604 235 118 827 326 143 1,085 433 172 1,379 588
3 26 64 35 39 135 69 55 237 115 72 435 80 98 624 2260 121 854 357 147 1,118 474 176 1,421 611



100
1 23 46 24 35 108 50 49 208 92 65 428 155 88 640 237 109 907 334 134 1,222 454 161 1,589 596
2 24 53 31 37 120 60 51 224 105 67 444 174 92 660 260 113 933 367 138 1,253 497 165 1,626 651
3 25 59 35 38 130 68 53 237 118 69 458 193 94 679 285 116 956 399 141 1,282 540 169 1,661 705

COMMON VENT CAPACITY




VENT
HEIGHT
(H)
(feet
MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)
12 19 28 38 50 63 78 113
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA 74 25 NA 119 46 NA 178 71 NA 257 103 NA 351 143 NA 458 188 NA 582 246 1,041 853 NA
8 NA 80 28 NA 130 53 NA 193 82 NA 279 119 NA 384 163 NA 501 218 724 636 278 1,144 937 408
10 NA 84 31 NA 138 56 NA 207 90 NA 299 131 NA 409 177 606 538 236 776 686 305 1,226 1,010 454
15 NA NA 36 NA 152 67 NA 233 106 NA 334 152 523 467 212 682 611 283 874 781 365 1,374 1,156 546
20 NA NA 41 NA NA 75 NA 250 122 NA 368 172 565 508 243 74 668 325 955 858 419 1,513 1,286 648
30 NA NA NA NA NA NA NA 270 137 NA 404 198 615 564 278 816 747 381 1,062 969 496 1,702 1,473 749
50 NA NA NA NA NA NA NA NA NA NA NA NA NA 620 328 879 831 461 1,165 1,089 606 1,905 1,692 922
100 NA NA NA NA NA NA NA NA NA NA NA NA NA NA 348 NA NA 499 NA NA 669 2,053 1,921 1,058
For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.3(4)
MASONRY CHIMNEY




VENT CONNECTOR CAPACITY
Number of Appliances Two or more
Appliance Type Category I
Appliance Vent Connection Single-wall metal connector






VENT
HEIGHT
(H)
(feet)






CONNECTOR
RISE
(R)
(feet)
SINGLE-WALL METAL VENT CONNECTOR DIAMETER (D)—inches
3 4 5 6 7 8 9 10
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H
FAN NAT FAN NAT FAN NAT 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 Min Max Max Min Max Max Min Max Max
6 1 NA NA 21 NA NA 39 NA NA 66 179 191 100 231 271 140 292 366 200 362 474 252 499 594 316
2 NA NA 28 NA NA 52 NA NA 84 186 227 123 239 321 172 301 432 231 373 557 299 509 696 376
3 NA NA 34 NA NA 61 134 153 97 193 258 142 247 365 202 309 491 269 381 634 348 519 793 437
8 1 NA NA 21 NA NA 40 NA NA 68 195 208 103 250 298 146 313 407 207 387 530 263 529 672 331
2 NA NA 28 NA NA 52 137 139 85 202 240 125 258 343 177 323 465 238 397 607 309 540 766 391
3 NA NA 34 NA NA 62 143 156 98 210 264 145 266 376 205 332 509 274 407 663 356 551 838 450
10 1 NA NA 22 NA NA 41 130 151 70 202 225 106 267 316 151 333 434 213 410 571 273 558 727 343
2 NA NA 29 NA NA 53 136 150 86 210 255 128 276 358 181 343 489 244 420 640 317 569 813 403
3 NA NA 34 97 102 62 143 166 99 217 277 147 284 389 207 352 530 278 430 694 363 580 880 459
15 1 NA NA 23 NA NA 43 129 151 73 199 271 112 268 376 161 349 502 225 445 646 291 623 808 366
2 NA NA 30 92 103 54 135 170 88 207 295 132 277 411 18 359 548 256 456 706 334 634 884 424
3 NA NA 34 96 112 63 141 185 101 215 315 151 286 439 213 368 586 289 466 755 378 646 945 479



20
1 NA NA 23 87 99 45 125 167 76 197 303 117 265 425 169 345 569 235 439 734 306 614 921 347
2 NA NA 30 91 111 55 134 185 90 205 325 136 274 455 195 355 610 266 450 787 348 627 986 443
3 NA NA 35 96 119 64 140 199 103 213 343 154 282 481 249 365 644 298 461 831 391 639 1,042 496



30
1 NA NA 24 86 108 47 126 187 80 193 347 124 259 492 183 338 665 250 430 864 330 600 1,089 421
2 NA NA 31 91 119 57 132 203 93 201 366 142 269 518 205 348 699 282 442 908 372 613 1,145 473
3 NA NA 35 95 127 65 138 216 105 209 38 160 277 540 229 358 729 312 452 946 412 626 1,193 524



50
1 NA NA 24 85 113 50 124 204 8 188 392 193 252 567 208 328 778 278 417 1,022 383 582 1,302 492
2 NA NA 31 89 123 60 130 218 100 196 408 158 262 588 230 339 806 320 429 1,058 425 596 1,346 545
3 NA NA 35 94 131 68 136 231 112 205 422 176 271 607 255 349 831 351 440 1,090 466 610 1,386 597



100
1 NA NA 23 84 104 49 122 200 89 182 410 151 243 617 232 315 875 328 402 1,181 444 560 1,537 580
2 NA NA 30 88 115 59 127 215 102 190 425 169 253 636 254 326 899 361 415 1,210 488 575 1,570 634
3 NA NA 34 93 124 67 133 228 115 199 438 188 262 654 279 337 921 392 427 1,238 529 589 1,604 687

COMMON VENT CAPACITY




VENT
HEIGHT
(H)
(feet
MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)
12 19 28 38 50 63 78 113
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
FAN
+FAN
FAN
+NAT
NAT
+NAT
6 NA NA 25 NA 118 45 NA 176 71 NA 255 102 NA 348 142 NA 455 187 NA 579 245 NA 846 NA
8 NA NA 28 NA 128 52 NA 190 81 NA 276 118 NA 380 162 NA 497 217 NA 633 277 1,136 928 405
10 NA NA 31 NA 136 56 NA 205 89 NA 295 129 NA 405 175 NA 532 234 171 680 300 1,216 1,000 450
15 NA NA 36 NA NA 66 NA 230 105 NA 335 150 NA 400 210 677 602 280 866 772 360 1,359 1,139 540
20 NA NA NA NA NA 74 NA 247 120 NA 362 170 NA 503 240 765 661 321 947 849 415 1,495 1,264 640
30 NA NA NA NA NA NA NA NA 135 NA 398 195 NA 558 275 808 739 377 1,052 957 490 1,682 1,447 740
50 NA NA NA NA NA NA NA NA NA NA NA NA NA 612 325 NA 821 456 1,152 1,076 600 1,879 1,672 910
100 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 494 NA NA 663 2,006 1,885 1,046
For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.293 1 W.

TABLE 504.3(5)
SINGLE-WALL METAL PIPE OR TYPE ASBESTOS CEMENT VENT



VENT CONNECTOR CAPACITY
Number of Appliances Two or more
Appliance Type Draft hood-equipped
Appliance Vent Connection Direct to pipe or vent

TOTAL VENT
HEIGHT
(H)
(feet)


CONNECTOR
RISE
(R)
(feet)
VENT CONNECTOR DIAMETER—(D) inches
3 4 5 6 7 8
MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
6-8 1 21 40 68 102 146 205
2 28 53 86 124 178 235
3 34 61 98 147 204 275
15 1 23 44 77 117 179 240
2 30 56 92 134 194 265
3 35 64 102 155 216 298



30 and up
1 25 49 84 129 190 270
2 31 58 97 145 211 295
3 36 68 107 164 232 321

COMMON VENT CAPACITY

TOTAL VENT
HEIGHT
(H)
(feet)
COMMON VENT DIAMETER—(D) inches
4 5 6 7 8 10 12
COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
6 48 78 111 155 205 320 NA
8 55 89 128 175 234 365 505
10 59 95 136 190 250 395 560
15 71 115 168 228 305 480 690
20 80 129 186 260 340 550 790
30 NA 147 215 300 400 650 940
50 NA NA NA 360 490 810 1,190
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.293 1 W.

TABLE 504.3(7a)
EXTERIOR MASONRY CHIMNEY


Combined Appliance Maximum
Input Rating in Thousands of Btu per Hour
Number of Appliances Two or more
ApplianceType NAT + NAT
Appliance Vent Connection Type B double-wall connector
VENT
HEIGHT
(feet)
INTERNAL AREA OF CHIMNEY (square inches)
12 19 28 38 50 63 78 113
6
8
10
15
20
30
25
28
31
NA
NA
NA
46
53
56
67
NA
NA
71
82
90
106
NA
NA
103
119
131
152
NA
NA
143
163
177
213
NA
NA
188
218
236
283
325
NA
246
278
302
365
419
496
NA
408
454
546
648
749
50 NA NA NA NA NA NA NA 922
100 NA NA NA NA NA NA NA NA


TABLE 504.3(7b)
EXTERIOR MASONRY CHIMNEY



Minimum Allowable Input Rating of
Space-Heating Appliance in Thousands of Btu per Hour
Number of Appliances Two or more
ApplianceType FAT + NAT
Appliance Vent Connection Type B double-wall connector

VENT
HEIGHT
(feet)
INTERNAL AREA OF CHIMNEY (square inches)
12 19 28 38 50 63 78 113
37°F or
Greater
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
NA
NA
0
0
0
0
0
334
NA
NA
NA
0
0
0
0
0
579
NA
27 to
36°F
Local 99% Winter Design Temperature: 27 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
17 to
26°F
Local 99% Winter Design Temperature: 17 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
387
NA
NA
NA
NA
352
358
398
457
581
862
NA
5 to
16°F
Local 99% Winter Design Temperature: 5 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
4°F or
Lower
Local 99% Winter Design Temperature: 4°F or Lower
Not recommended for any vent configurations
Note: See Figure B-19 in Appendix B for a map showing local 99 percent winter design temperatures in the United States.
For SI: °C = [(°F -32]/1.8, 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.293 1 W.


TABLE 504.3(8a)
EXTERIOR MASONRY CHIMNEY



Combined Appliance Maximum
Input Rating in Thousands of Btu per Hour
Number of Appliances Two or more
ApplianceType FAT + NAT
Appliance Vent Connection Type B double-wall connector

VENT
HEIGHT
(feet)
INTERNAL AREA OF CHIMNEY (square inches)
12 19 28 38 50 63 78 113
6 74 119 178 257 351 458 582 853
8 80 130 193 279 384 501 636 937
10 84 138 207 299 409 538 686 1,010
15 NA 152 233 334 467 611 781 1,156
20 NA NA 250 368 508 668 858 1,286
30 NA NA NA 404 564 747 969 1,473
50 NA NA NA NA NA 831 1,089 1,692
100 NA NA NA NA NA NA NA 1,921


TABLE 504.3(8b)
EXTERIOR MASONRY CHIMNEY



Minimum Allowable Input Rating of
Space-Heating Appliance in Thousands of Btu per Hour
Number of Appliances Two or more
ApplianceType FAT + NAT
Appliance Vent Connection Type B double-wall connector

VENT
HEIGHT
(feet)
INTERNAL AREA OF CHIMNEY (square inches)
12 19 28 38 50 63 78 113
37°F or
Greater
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
1,600
27 to
36°F
Local 99% Winter Design Temperature: 27 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
210
253
307
419
672
NA
2112
214
225
274
330
445
705
NA
266
263
265
305
362
485
763
1,554
17 to
26°F
Local 99% Winter Design Temperature: 17 to 26°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
362
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
349
352
358
457
581
862
1,669
5 to
16°F
Local 99% Winter Design Temperature: 5 to 16°F
6
8
10
15
20
30
50
100
NA
NA
NA
NA
NA
NA
NA
NA
78
94
111
NA
NA
NA
NA
NA
121
135
149
193
NA
NA
NA
NA
166
182
198
247
293
377
NA
NA
214
230
250
305
360
450
NA
NA
252
269
289
346
408
531
797
NA
301
312
331
393
450
580
853
NA
416
423
430
485
547
682
972
1,833
-10 to
4°F
Local 99% Winter Design Temperature: -10 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
249
371
397
457
528
667
995
NA
484
494
513
586
650
805
1,003
NA
-11°F or
Lower
Local 99% Winter Design Temperature: -11°F or Lower
Not recommended for any vent configurations
Note: See Figure B-19 in Appendix B for a map showing local 99 percent winter design temperatures in the United States.
For SI: °C = [(°F -32]/1.8, 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.293 1
Vent connectors shall not be increased in size more than two sizes greater than the listed appliance categorized vent diameter, flue collar diameter, or draft hood outlet diameter. Vent connectors for draft hood-equipped appliances shall not be smaller than the draft hood outlet diameter. Where a vent connector size(s) determined from the tables for a fan-assisted appliance(s) is smaller than the flue collar diameter, the use of the smaller size(s) shall be permitted provided that the installation complies with all of the following conditions:
  1. Vent connectors for fan-assisted appliance flue collars 12 inches (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 larger than 12 inches (305 mm) in diameter are not reduced more than 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(s) is common vented with a draft-hood-equipped appliances(s).
  3. The vent connector has a smooth interior wall.
All combinations of pipe sizes, single-wall, and double-wall metal pipe shall be allowed within any connector run(s) or within the common vent, provided all of the appropriate tables permit all of the desired sizes and types of pipe, as if they were used for the entire length of the subject connector or vent. Where single-wall and Type B double-wall metal pipes are used for vent connectors within the same venting system, the common vent must be sized using Table 504.3(2) or 504.3(4), as appropriate.
Where a table permits more than one diameter of pipe to be used for a connector or vent, all the permitted sizes shall be permitted to be used.
Interpolation shall be permitted in calculating capacities for vent dimensions that fall between table entries.
Extrapolation beyond the table entries shall not be permitted.
For vent heights less than 6 feet (1829 mm) and greater than shown in the tables, engineering methods shall be used to calculate vent capacities.
The installation of direct-vent and integral vent appliances shall be in accordance with Section 503. Mechanical venting systems and exhaust hood venting systems shall be designed and installed in accordance with Section 503.
Factory-built chimneys for building heating appliances producing flue gases having a temperature not greater than 1,000°F (538°C), measured at the entrance to the chimney, shall be listed and labeled in accordance with UL 103 and shall be installed and terminated in accordance with the manufacturer's installation instructions and this code.
Where factory-built chimneys are supported by structural members, such as joists and rafters, such members shall be designed to support the additional load.
Factory-built chimneys for medium-heat appliances producing flue gases having a temperature above 1,000°F (538°C), measured at the entrance to the chimney, shall be listed and labeled in accordance with UL 959 and shall be installed and terminated in accordance with the manufacturer's installation instructions and this code.
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