509.6 Gas Vents. The installation of gas vents shall meet

the following requirements: (1) Gas vents shall be installed in accordance with the man ufacturer’s installation instructions.

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and are installed in accordance with the manufacturer’s installation instructions. (6) All gas vents shall extend through the roof flashing,

roof jack, or roof thimble and terminate with a listed cap or listed roof assembly. (7) A gas vent shall terminate at least 3 feet (914 mm)

above a forced air inlet located within 10 feet (3048 mm). [NFPA 54:12.7.3]

FIGURE 509.6.1 TERMINATION LOCATIONS FOR GAS VENTS WITH LISTED CAPS 12 INCHES OR LESS IN SIZE

AT LEAST 8 FEET FROM A VERTICAL WALL

[NFPA 54: FIGURE 12.7.3]

TABLE 509.6.1 ROOF SLOPE HEIGHTS

[NFPA 54: TABLE 12.7.3]

For SI Units: 1 inch = 25.4 mm, 1 foot = 304.8 mm

509.6.1.1 Insulation Shield. Where a vent passes through an insulated assembly, an approved metal shield shall be installed between the vent and insulation. The shield shall extend not less than 2 inches (51 mm) above the insulation and be secured to the structure in accordance with the manufacturer’s installation instructions.

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(2) A Type B-W gas vent shall have a listed capacity not less

than that of the listed vented wall furnace to which it is connected. (3) Gas vents installed within masonry chimneys shall be

installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.” (4) Screws, rivets, and other fasteners shall not penetrate the

inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.

[NFPA 54:12.7.2] 509.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements: (1) A gas vent shall terminate in accordance with one

of the following: (a) Gas vents that are 12 inches (300 mm) or less in

size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure 509.6.1 and Table 509.6.1. (b) Gas vents that are over 12 inches (300 mm) in

size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally. (c) Industrial appliances as provided in Section

509.2.5. (d) Direct-vent systems as provided in Section

509.2.6. (e) Appliances with integral vents as provided in

Section 509.2.7. (f) Mechanical draft systems as provided in Section 509.3.3 through Section 509.3.3.5. (g) Ventilating hoods and exhaust systems as pro vided in Section 509.3.4. (2) A Type B or a Type L gas vent shall terminate at least

5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar. (3) A Type B-W gas vent shall terminate at least 12 feet

(3658 mm) in vertical height above the bottom of the wall furnace. (4) A gas vent extending through an exterior wall shall

not terminate adjacent to the wall or below eaves or parapets, except as provided in Section 509.2.6 and Section 509.3.3 through Section 509.3.3.5. (5) Decorative shrouds shall not be installed at the ter mination of gas vents except where such shrouds are listed for use with the specific gas venting system

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509.6.2 Size of Gas Vents. Venting systems shall be sized and constructed in accordance with Section 509.6.2.1 through Section 509.6.2.3 and the appliance manufacturer’s instructions. [NFPA 54:12.7.4]

509.6.2.1 Category I Appliances. The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with a Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following: (1) The provisions of Section 510.0. (2) Vents serving fan-assisted combustion system

appliances, or combinations of fan-assisted combustion system and draft hood-equipped appliances, shall be sized in accordance with Section 510.0 or other approved engineering methods. (3) For sizing an individual gas vent for a single,

draft hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet or greater than seven times the draft hood outlet area. (4) For sizing a gas vent connected to two appli ances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area. (5) Other approved engineering practices. [NFPA

let or greater than seven times the draft hood outlet area. (4) For sizing a gas vent connected to two appli ances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area. (5) Other approved engineering practices. [NFPA

54:12.7.4.1] 509.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 509.6.2.1(3) or Section 509.6.2.1(4) 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 (1.05 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2]

509.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturer’s instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions. [NFPA 54:12.7.4.3] 509.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods. [NFPA 54:12.7.4.4]

509.6.3 Gas Vents Serving Appliances on More than One Floor. A common vent shall be permitted in multistory installations to vent Category I appliances

located on more than one floor level, provided the venting system is designed and installed in accordance with approved engineering methods.

For the purpose of this section, crawl spaces, basements, and attics shall be considered floor levels. [NFPA 54:12.7.5.1] 509.6.3.1 Occupiable Space. All appliances connected to the common vent shall be located in rooms separated from occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation, and dilution air that is not supplied from occupiable space. [NFPA 54:12.7.5.2] (See Figure 509.6.3.1)

FIGURE 509.6.3.1 PLAN VIEW OF PRACTICAL SEPARATION METHOD FOR MULTISTORY GAS VENTING

[NFPA 54: FIGURE A.12.7.5.2]

509.6.3.2 Multistory Venting System. The size of the connectors and common segments of multistory venting systems for appliances listed for use with a Type B double-wall gas vent shall be in accordance with Table 510.2(1), provided all of the following apply: (1) The available total height ( H ) for each segment

of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection tee. (2) The size of the connector for a segment is deter mined from the appliance’s gas input rate and available connector rise and shall not be smaller than the draft hood outlet or flue collar size. (3) The size of the common vertical vent segment,

and of the interconnection tee at the base of that segment, is based on the total appliance’s gas input rate entering that segment and its available total height. [NFPA 54:12.7.5.3]

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509.6.4 Support of Gas Vents. Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.7.6] 509.6.5 Marking. In those localities where solid and liquid fuels are used extensively, gas vents shall be permanently identified by a label attached to the wall or ceiling at a point where the vent connector enters the gas vent. The label shall read: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators.” The Authority Having Jurisdiction shall determine whether its area constitutes such a locality. [NFPA 54:12.7.7]