93 801.0 Scope. The requirements of this chapter shall govern the venting of fuel-burning appliances. 801.1 Venting of Gas Appliances. Low-heat gas appliances shall be vented in accordance with this chapter. Other gas appliances shall be vented in accordance with NFPA 211 or other applicable stan- dards. 801.2 Appliances Fueled by Other Fuels. Appli- ances fueled by fuels other than gas shall be vented in accordance with NFPA 211 and the appliance manufacturer’s instructions. 802.0 Venting of Appliances. 802.1 General. 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 appliance. 802.1.1 Categories. The operating characteris- tics of vented appliances can be categorized with respect to positive or negative pressure within the venting system and whether or not the appli- ance generates flue or vent gases that can condense in the venting system. See Section 224.0 for the definition of these vented appliance categories. [NFPA 54:12.2.2] 802.1.2 Installation. Listed vents shall be installed in accordance with Chapter 8 and the manufacturer’s installation instructions. [NFPA 54:12.2.3] 802.1.3 Appliance vents shall not discharge into any space enclosed by screens having openings smaller than one-quarter (1/4) inch (6.4 mm) mesh. 802.2 Specification for Venting. 802.2.1 Connection to Venting Systems. Except as permitted in Section 802.2.2 through 802.2.6, all appliances shall be connected to venting systems. [NFPA 54:12.3.1] 802.2.2 Appliances Not Required to Be Vented. The following appliances shall not be required to be vented [NFPA 54:12.3.2]: 802.2.2.1 Listed ranges. [NFPA 54:12.3.2(1)] 802.2.2.2 Built-in domestic cooking units listed and marked for optional venting. [NFPA 54:12.3.2(2)] 802.2.2.3 Listed hot plates and listed laundry stoves. [NFPA 54:12.3.2(3)] 802.2.2.4 Listed Type 1 clothes dryers exhausted in accordance with Section 504.3.2. [NFPA 54:12.3.2(4)] 802.2.2.5 A single listed booster-type (auto- matic instantaneous) water heater, when designed and used solely for the sanitizing rinse requirements of a dishwashing machine, provided that the appliance is installed with the draft hood in place and unaltered, if a draft hood is required, in a commercial kitchen having a mechanical exhaust system; where installed in this manner, the draft hood outlet shall not be less than thirty-six (36) inches (910 mm) vertically and six (6) inches (150 mm) hori- zontally from any surface other than the appliance. [NFPA 54:12.3.2(5)] 802.2.2.6 Listed refrigerators. [NFPA 54:12.3.2(6)] 802.2.2.7 Counter appliances. [NFPA 54:12.3.2(7)] 802.2.2.8 Room heaters listed for unvented use (see Sections 924.1 and 924.2). [NFPA 54:12.3.2(8)] 802.2.2.9 Direct gas-fired makeup air heaters. [NFPA 54:12.3.2(9)] 802.2.2.10 Other appliances listed for unvented use and not provided with flue collars. [NFPA 54:12.3.2(10)] 802.2.2.11 Specialized appliances of limited input such as laboratory burners or gas lights. [NFPA 54:12.3.2(11)] Where any or all of the appliances in Sections 802.2.2.5 through 802.2.2.11 are installed so the aggregate input rating exceeds twenty (20) Btu/h/ft. 3 (207 W/m 3 ) of room or space in which it is installed, one or more shall be provided with venting systems or other approved means for removing the vent gases to the outside atmosphere so the aggregate input rating of the remaining unvented appliances do not exceed twenty (20) Btu/h/ft. 3 (207 W/m 3 ). Where the calculation includes the volume of an adjacent room or space, the room or CHAPTER 8 CHIMNEYS AND VENTS
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801.0 Scope.The requirements of this chapter shall govern theventing of fuel-burning appliances.801.1 Venting of Gas Appliances. Low-heat gasappliances shall be vented in accordance with thischapter. Other gas appliances shall be vented inaccordance with NFPA 211 or other applicable stan-dards.801.2 Appliances Fueled by Other Fuels. Appli-ances fueled by fuels other than gas shall be ventedin accordance with NFPA 211 and the appliancemanufacturer’s instructions.
802.0 Venting of Appliances.802.1 General. This section recognizes that thechoice of venting materials and the methods ofinstallation of venting systems are dependent on theoperating characteristics of the appliance.
802.1.1 Categories. The operating characteris-tics of vented appliances can be categorized withrespect to positive or negative pressure withinthe venting system and whether or not the appli-ance generates flue or vent gases that cancondense in the venting system. See Section224.0 for the definition of these vented appliancecategories. [NFPA 54:12.2.2]802.1.2 Installation. Listed vents shall beinstalled in accordance with Chapter 8 and themanufacturer’s installation instructions. [NFPA54:12.2.3]802.1.3 Appliance vents shall not discharge intoany space enclosed by screens having openingssmaller than one-quarter (1/4) inch (6.4 mm)mesh.
802.2 Specification for Venting.802.2.1 Connection to Venting Systems.Except as permitted in Section 802.2.2 through802.2.6, all appliances shall be connected toventing systems. [NFPA 54:12.3.1]802.2.2 Appliances Not Required to BeVented. The following appliances shall not berequired to be vented [NFPA 54:12.3.2]:
802.2.2.1 Listed ranges. [NFPA 54:12.3.2(1)]802.2.2.2 Built-in domestic cooking unitslisted and marked for optional venting.[NFPA 54:12.3.2(2)]
802.2.2.3 Listed hot plates and listedlaundry stoves. [NFPA 54:12.3.2(3)]802.2.2.4 Listed Type 1 clothes dryersexhausted in accordance with Section504.3.2. [NFPA 54:12.3.2(4)]802.2.2.5 A single listed booster-type (auto-matic instantaneous) water heater, whendesigned and used solely for the sanitizingrinse requirements of a dishwashingmachine, provided that the appliance isinstalled with the draft hood in place andunaltered, if a draft hood is required, in acommercial kitchen having a mechanicalexhaust system; where installed in thismanner, the draft hood outlet shall not beless than thirty-six (36) inches (910 mm)vertically and six (6) inches (150 mm) hori-zontally from any surface other than theappliance. [NFPA 54:12.3.2(5)]802.2.2.6 Listed refrigerators. [NFPA54:12.3.2(6)]802.2.2.7 Counter appliances. [NFPA54:12.3.2(7)]802.2.2.8 Room heaters listed for unventeduse (see Sections 924.1 and 924.2). [NFPA54:12.3.2(8)]802.2.2.9 Direct gas-fired makeup airheaters. [NFPA 54:12.3.2(9)]802.2.2.10 Other appliances listed forunvented use and not provided with fluecollars. [NFPA 54:12.3.2(10)]802.2.2.11 Specialized appliances of limitedinput such as laboratory burners or gaslights. [NFPA 54:12.3.2(11)]
Where any or all of the appliances inSections 802.2.2.5 through 802.2.2.11 areinstalled so the aggregate input ratingexceeds twenty (20) Btu/h/ft.3 (207 W/m3)of room or space in which it is installed, oneor more shall be provided with ventingsystems or other approved means forremoving the vent gases to the outsideatmosphere so the aggregate input rating ofthe remaining unvented appliances do notexceed twenty (20) Btu/h/ft.3 (207 W/m3).Where the calculation includes the volumeof an adjacent room or space, the room or
CHAPTER 8CHIMNEYS AND VENTS
space in which the appliance is installedshall be directly connected to the adjacentroom or space by a doorway, archway, orother opening of comparable size thatcannot be closed. [NFPA 54:12.3.2]
802.2.3 Ventilating Hoods. Ventilating hoodsand exhaust systems shall be permitted to beused to vent appliances installed in commercialapplications (see Section 802.3.5) and to ventindustrial appliance, particularly where theprocess itself requires fume disposal. [NFPA54:12.3.3]802.2.4 Well-Ventilated Spaces. The operationof industrial appliances such that its flue gasesare discharged directly into a large and well-ventilated space shall be permitted. [NFPA54:12.3.4]802.2.5 Direct-Vent Appliance. Listed direct-vent appliances shall be considered properlyvented where installed in accordance with theterms of its listing, the manufacturer’s instruc-tions, and Section 802.8.3. [NFPA 54:12.3.5]802.2.6 Appliances with Integral Vents. Appli-ances incorporating integral venting means shallbe considered properly vented where installedin accordance with its listing, the manufacturer'sinstructions, and Sections 802.8.1 and 802.8.2.[NFPA 54:12.3.6]
802.3 Design and Construction.802.3.1 Minimum Safe Performance. Aventing system shall be designed andconstructed so as to develop a positive flowadequate to remove flue or vent gases to theoutside atmosphere. [NFPA 54:12.1]802.3.2 Appliance Draft Requirements. Aventing system shall satisfy the draft require-ments of the appliance in accordance with themanufacturer's instructions. [NFPA 54:12.4.1]802.3.3 Design and Construction. Appliancesrequired to be vented shall be connected to aventing system designed and installed in accor-dance with the provisions of Sections 802.4through 802.15. [NFPA 54:12.4.2]802.3.4 Mechanical Draft Systems.
802.3.4.1 Mechanical draft systems shall belisted and shall be installed in accordance withthe terms of their listing and both the appli-ance and the mechanical draft system manu-facturer's instructions. [NFPA 54:12.4.3.1]802.3.4.2 Appliances requiring venting shallbe permitted to be vented by means ofmechanical draft systems of either forced orinduced draft design. [NFPA 54:12.4.3.2]
Exception: Incinerators.
802.3.4.3 Forced draft systems and allportions of induced draft systems underpositive pressure during operation shall bedesigned and installed so as to preventleakage of flue or vent gases into a building.[NFPA 54:12.4.3.3]802.3.4.4 Vent connectors serving appli-ances vented by natural draft shall not beconnected into any portion of mechanicaldraft systems operating under positive pres-sure. [NFPA 54:12.4.3.4]802.3.4.5 Where a mechanical draft systemis employed, provision shall be made toprevent the flow of gas to the main burnerswhen the draft system is not performing soas to satisfy the operating requirements ofthe appliance for safe performance. [NFPA54:12.4.3.5]802.3.4.6 The exit terminals of mechanicaldraft systems shall be not less than seven (7)feet (2,134 mm) above grade where locatedadjacent to public walkways and shall belocated as specified in Sections 802.8.1 and802.8.2. [NFPA 54:12.4.3.6]
802.3.5 Ventilating Hoods and ExhaustSystems.
802.3.5.1 Ventilating hoods and exhaustsystems shall be permitted to be used tovent appliances installed in commercialapplications. [NFPA 54:12.4.4.1]802.3.5.2 Where automatically operatedappliances are vented through a ventilatinghood or exhaust system equipped with adamper or with a power means of exhaust,provisions shall be made to allow the flow ofgas to the main burners only when thedamper is open to a position to properly ventthe appliance and when the power means ofexhaust is in operation. [NFPA 54:12.4.4.2]
802.3.6 Circulating Air Ducts and FurnacePlenums. No portion of a venting system shallextend into or pass through any circulating airduct or furnace plenum. [NFPA 54:12.4.5.1]
802.4 Type of Venting System to Be Used.802.4.1 The type of venting system to be usedshall be in accordance with Table 8-1. [NFPA54:12.5.1]802.4.2 Plastic Piping. Plastic piping used forventing appliances listed for use with suchventing materials shall be approved. [NFPA54:12.5.2]802.4.3 Plastic Vent Joints. Plastic pipe andfittings used to vent appliances shall be installedin accordance with the appliance manufacturer’s
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installation instructions. Where primer isrequired, it shall be of a contrasting color.[NFPA 54-09:12.5.3]802.4.4 Special Gas Vent. A special gas ventshall be listed and installed in accordance withthe terms of the special gas vent listing and themanufacturer's instructions. [NFPA 54:12.5.3]
802.5 Masonry, Metal, and Factory-Built Chimneys.802.5.1 Listing or Construction.
802.5.1.1 Factory-built chimneys shall beinstalled in accordance with their listing andthe manufacturer's instructions. Factory-builtchimneys used to vent appliances thatoperate at positive vent pressure shall belisted for such application. [NFPA 54:12.6.1.1]802.5.1.2 Metal chimneys shall be built andinstalled in accordance with NFPA 211,Standard for Chimneys, Fireplaces, Vents, andSolid-Fuel-Burning Appliances. [NFPA54:12.6.1.2]802.5.1.3 Masonry chimneys shall be builtand installed in accordance with NFPA 211,Standard for Chimneys, Fireplaces, Vents, andSolid Fuel-Burning Appliances, and lined withan approved clay flue lining, a listedchimney lining system, or other approvedmaterial that will resist corrosion, erosion,softening, or cracking from vent gases attemperatures up to 1,800°F (982°C).
Exception:Masonry chimney flues linedwith a chimney lining system specifi-cally listed for use with listed gas appli-ances with draft hoods, Category Iappliances, and other gas applianceslisted for use with Type B vents shall bepermitted. The liner shall be installed inaccordance with the liner manufactur-er's instructions and the terms of thelisting. A permanent identifying labelshall be attached at the point where theconnection is to be made to the liner.The label shall read: "This chimney lineris for appliances that burn gas only. Donot connect to solid or liquid fuel-burning appliances or incinerators."[NFPA 54:12.6.1.3]
802.5.2 Termination.802.5.2.1 A chimney for residential-type orlow-heat appliances shall extend at leastthree (3) feet (914 mm) above the highestpoint where it passes through a roof of abuilding and at least two (2) feet (610 mm)higher than any portion of a building within
a horizontal distance of ten (10) feet (3,048mm). (See Figure 8-1.) [NFPA 54:12.6.2.1]802.5.2.2 A chimney for medium-heatappliances shall extend at least ten (10) feet(3,048 mm) higher than any portion of anybuilding within twenty-five (25) feet (7,620mm). [NFPA 54:12.6.2.2]802.5.2.3 A chimney shall extend at leastfive (5) feet (1,524 mm) above the highestconnected appliance draft hood outlet orflue collar. [NFPA 54:12.6.2.3]802.5.2.4 Decorative shrouds shall not beinstalled at the termination of factory-builtchimneys except where such shrouds arelisted and labeled for use with the specific
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TABLE 8-1Type of Venting System to Be Used
[NFPA 54: Table 12.5.1]Appliance Type of Venting System
Listed Category I applianceListed appliance equippedwith draft hood
Appliance listed for use withType B gas vent
Type B gas vent (802.6)Chimney (802.5)Single-wall metal pipe(802.7)Listed chimney liningsystem for gas venting(802.5.1.3)Special gas vent listed forthis appliance (802.4.4)
Listed vented wall furnaces Type B-W gas vent(802.6, 928.0)
Category II applianceCategory III applianceCategory IV appliance
As specified or furnishedby manufacturers of listedappliance (802.4.2, 802.4.4)
Incinerators, outdoors
Incinerators, indoorsAppliance that can beconverted to use of solid fuel
Gas-fired toilets Single-wall metal pipe(802.7, 926.3)
Direct-vent appliance See 802.2.5Appliance with integral vent See 802.2.6
factory-built chimney system and areinstalled in accordance with manufacturer' sinstallation instructions. [NFPA 54:12.6.2.4]
802.5.3 Size of Chimneys. The effective area ofa chimney venting system serving listed gasappliances with draft hoods, Category I appli-ances, and other appliances listed for use withType B vents shall be in accordance with one ofthe following methods [NFPA 54:12.6.3.1]:(1) Section 803.0. [NFPA 54:12.6.3.1(1)](2) For sizing an individual chimney venting
system for a single appliance with a drafthood, the effective areas of the ventconnector and chimney flue shall be not lessthan the area of the appliance flue collar ordraft hood outlet or greater than seven timesthe draft hood outlet area. [NFPA54:12.6.3.1(2)]
(3) For sizing a chimney venting systemconnected to two (2) appliances with drafthoods, the effective area of the chimney flueshall be not less than the area of the largerdraft hood outlet plus 50 percent of the areaof the smaller draft hood outlet, or greaterthan seven (7) times the smallest draft hoodoutlet area. [NFPA 54:12.6.3.1(3)]
(4) Other approved engineering methods.[NFPA 54:12.6.3.1(5)]
(5) Chimney venting systems using mechanicaldraft shall be sized in accordance withapproved engineering methods. [NFPA54:12.6.3.1(4)]
802.5.4 Inspection of Chimneys.802.5.4.1 Before replacing an existing appli-ance or connecting a vent connector to achimney, the chimney passageway shall beexamined to ascertain that it is clear and freeof obstructions and shall be cleaned if previ-ously used for venting solid or liquid fuel-burning appliances or fireplaces. [NFPA54:12.6.4.1]802.5.4.2 Chimneys shall be lined in accor-dance with NFPA 211, Standard for Chim-neys, Fireplaces, Vents, and Solid Fuel-BurningAppliances. [NFPA 54:12.6.4.2]
Exception: Existing chimneys shall bepermitted to have their use continuedwhen an appliance is replaced by anappliance or similar type, input rating,and efficiency, where the chimneycomplies with 802.5.4, and the sizing ofthe chimney is in accordance with802.5.3.
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FIGURE 8-1 Typical Termination Locations forChimneys and Single-Wall Metal Pipes ServingResidential-Type and Low-Heat Appliance.[NFPA 54: Figure 12.6.2.1]
802.5.4.3 Cleanouts shall be examined todetermine that they will remain tightlyclosed when not in use. [NFPA 54:12.6.4.3]802.5.4.4 When inspection reveals that anexisting chimney is not safe for the intendedapplication, it shall be repaired, rebuilt,lined, relined, or replaced with a vent orchimney to conform to NFPA 211, Standardfor Chimneys, Fireplaces, Vents, and Solid-Fuel-Burning Appliances, and shall be suitable forthe appliance to be attached. [NFPA54:12.6.4.4]
802.5.5.1 Appliances shall not be connectedto a chimney flue serving a separate appli-ance designed to burn solid fuel. [NFPA54:12.6.5.1]802.5.5.2 Where one (1) chimney serves gasappliances and an appliance burning liquidfuel, the appliances shall be connectedthrough separate openings or shall beconnected through a single opening wherejoined by a suitable fitting located as close aspractical to the chimney. Where two (2) ormore openings are provided into one (1)chimney flue, they shall be at differentlevels. Where the appliance is automaticallycontrolled, it shall be equipped with a safetyshutoff device. [NFPA 54:12.6.5.2]802.5.5.3 A listed combination gas and solidfuel-burning appliance connected to a singlechimney flue shall be equipped with amanual reset device to shut off gas to themain burner in the event of sustained back-draft or flue gas spillage. The chimney flueshall be sized to properly vent the appliance.[NFPA 54: 12.6.5.3]802.5.5.4 A single chimney flue serving alisted combination gas- and oil-burningappliance shall be sized to properly vent theappliance. [NFPA 54:12.6.5.4]
802.5.6 Support of Chimneys. All portions ofchimneys shall be supported for the design andweight of the materials employed. Listedfactory-built chimneys shall be supported andspaced in accordance with their listings and themanufacturers' instructions. [NFPA 54:12.6.6]802.5.7 Cleanouts. Where a chimney thatformerly carried flue products from liquid orsolid fuel-burning appliances is used with anappliance using fuel gas, an accessible cleanoutshall be provided. The cleanout shall have atight-fitting cover and be installed so its upper
edge is at least six (6) inches (150 mm) below thelower edge of the lowest chimney inlet opening.[NFPA 54:12.6.7]802.5.8 Space Surrounding Lining or Vent.The remaining space surrounding a chimneyliner, gas vent, special gas vent, or plastic pipinginstalled within a masonry chimney flue shallnot be used to vent another appliance. [NFPA54:12.6.8.1]
Exception: The insertion of another liner orvent within the chimney as provided in thiscode and the liner or vent manufacturer'sinstructions.The remaining space surrounding a
chimney liner, gas vent, special gas vent, orplastic piping installed within a masonry, metalor factory-built chimney flue shall not be used tosupply combustion air. [NFPA 54:12.6.8.2]
Exception: Direct vent gas-fired appliancesdesigned for installation in a solid-fuel-burning fireplace where installed in accor-dance with the listing and the manufac-turer’s instruction.
802.6 Gas Vents.802.6.1 A gas vent passing through a roof shallextend through the entire roof flashing, roofjack, or roof thimble and be terminated with alisted termination cap. [NFPA 54:12.7.2(6)]
802.6.1.1 Type B or Type L vents shallextend in a generally vertical direction withoffsets not exceeding 45 degrees, except thata vent system having not more than one 60degree offset shall be permitted. Any anglegreater than 45 degrees from the vertical isconsidered horizontal. The total horizontaldistance of a vent plus the horizontal ventconnector serving draft hood equippedappliances shall not be greater than 75percent of the vertical height of the vent.[NFPA 54:12.7.3.2]
Exception: Systems designed and sizedas provided in Section 803.0 or in accor-dance with other approved engineeringmethods.
Vents serving Category I fan-assisted appliancesshall be installed in accordance with the appli-ance manufacturer's instructions and Section803.0 or other approved engineering methods.[NFPA 54:12.7.1(3)]802.6.2 A gas vent shall terminate in accordancewith one of the following:(1) Above the roof surface with a listed cap or
listed roof assembly. Gas vents twelve (12)inches (300 mm) in size or smaller withlisted caps shall be permitted to be termi-
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nated in accordance with Figure 8-2,provided they are at least eight (8) feet(2,438 mm) from a vertical wall or similarobstruction. All other gas vents shall termi-nate not less than two (2) feet (610 mm)above the highest point where they passthrough the roof and at least two (2) feet(610 mm) higher than any portion of abuilding within ten (10) feet (3,048 mm).[NFPA 54:12.7.2(1)(a) and (b)]
(2) Industrial appliance provided in Section802.2.4. [NFPA 54:12.7.2(1)(c)]
(3) Direct-vent systems as provided in Section802.2.5. [NFPA 54:12.7.2(1)(d)]
(4) Appliance with integral vents as provided inSection 802.2.6. [NFPA 54:12.7.2(1)(e)]
(5) Mechanical draft systems as provided inSection 802.3.4. [NFPA 54:12.7.2(1)(f)]
(6) Ventilating hoods and exhaust systems asprovided in Section 802.3.5. [NFPA54:12.7.2(1)(g)]802.6.2.1 A Type B or a Type L gas ventshall terminate at least five (5) feet (1,524mm) in vertical height above the highestconnected appliances draft hood or fluecollar. [NFPA 54:12.7.2(2)]
802.6.2.2 A Type B-W gas vent shall termi-nate at least twelve (12) feet (3,658 mm) invertical height above the bottom of the wallfurnace. [NFPA 54:12.7.2(3)]802.6.2.3 A gas vent extending through anexterior wall shall not terminate adjacent tothe wall or below eaves or parapets, exceptas provided in Sections 802.2.5 and 802.3.4.[NFPA 54:12.7.2(4)]802.6.2.4 Decorative shrouds shall not beinstalled at the termination of gas ventsexcept where such shrouds are listed for usewith the specific gas venting system and areinstalled in accordance with manufacturers'installation instructions. [NFPA 54:12.7.2(5)]802.6.2.5 Gas vents shall extend through theroof flashing, roof jack, or roof thimble andterminate with a listed cap or listed roofassembly. [NFPA 54:12.7.2(6)]802.6.2.6 A gas vent shall terminate at leastthree (3) feet (914 mm) above a forced airinlet located within ten (10) feet (3,048 mm).[NFPA 54:12.7.2(7)]
802.6.3 Size of Gas Vents. Venting systemsshall be sized and constructed in accordancewith Section 803.0 or other approved engi-neering methods and the gas vent and appliancemanufacturers' instructions. [NFPA 54:12.7.3]
802.6.3.1 Category I Appliances. Thesizing of natural draft venting systemsserving one (1) or more listed appliancesequipped with a draft hood or applianceslisted for use with Type B gas vent, installedin a single story of a building, shall be inaccordance with one of the followingmethods. [NFPA 54:12.7.3.1](1) The provisions of Section 803.0. [NFPA
system appliances, or combinations offan-assisted combustion system anddraft hood-equipped appliances shall besized in accordance with Section 803.0or other approved engineering methods.[NFPA 54:12.7.3.1(2)]
(3) For sizing an individual gas vent for asingle, draft hood-equipped appliance,the effective area of the vent connectorand the gas vent shall be not less than thearea of the appliance draft hood outlet orgreater than seven (7) times the drafthood outlet area. [NFPA 54:12.7.3.1(3)]
(4) For sizing a gas vent connected to two(2) appliances, with draft hoods, the
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FIGURE 8-2 Gas Vent Termination Locations forListed Caps 12 in. (300 mm) or Less in Size atLeast 8 ft. (2.4 m) from a Vertical Wall. [NFPA 54:Figure 12.7.2]
effective area of the vent shall be notless than the area of the larger drafthood outlet plus 50 percent of the areaof the smaller draft hood outlet orgreater than seven (7) times the smallerdraft hood outlet area. [NFPA54:12.7.3.1(4)]
802.6.3.2 Category II, Category III, andCategory IV Appliances. The sizing of gasvents for Category II, Category III, and Cate-gory IV appliances shall be in accordancewith the appliance manufacturer’s instruc-tions. [NFPA 54:12.7.3.3]802.6.3.3 Sizing. Chimney venting systemsusing mechanical draft shall be sized inaccordance with approved engineeringmethods. [NFPA 54:12.7.3.4]
802.6.4 Gas Vents Serving Appliances onMore Than One Floor. A common gas ventshall be permitted in multistory installations tovent Category I appliances located on more thanone floor level, provided the venting system isdesigned and installed in accordance withapproved engineering methods. For the purposeof this section, crawl spaces, basements, andattics shall be considered as floor levels. [NFPA54:12.7.4.1]
All appliances connected to the commonvent shall be located in rooms separated from ahabitable space. Each of these rooms shall haveprovisions for an adequate supply of combus-tion, ventilation, and dilution air that is notsupplied from a habitable space. (See Figure 8-3.) [NFPA 54:12.7.4.2]
The size of the connectors and commonsegments of multistory venting systems forappliances listed for use with Type B double-wall gas vent shall be in accordance with Table8-10, provided [NFPA 54:12.7.4.3]:(1) The available total height (H) for each
segment of a multistory venting system isthe vertical distance between the level of thehighest draft hood outlet or flue collar onthat floor and the centerline of the nexthighest interconnection tee. (See Figure 8-4.)[NFPA 54:12.7.4.3(1)]
(2) The size of the connector for a segment isdetermined from its appliance heat inputand available connector rise, and shall notbe smaller than the draft hood outlet or fluecollar size. [NFPA 54:12.7.4.3(2)]
(3) The size of the common vertical ventsegment, and of the interconnection tee atthe base of that segment, shall be based on
the total appliance heat input entering thatsegment and its available total height.[NFPA 54:12.7.4.3(3)]
802.6.5 Support of Gas Vents. Gas vents shallbe supported and spaced in accordance withtheir listings and the manufacturers' instruc-tions. [NFPA 54:12.7.5]802.6.6 Marking. In those localities where solidand liquid fuels are used extensively, gas ventsshall be permanently identified by a labelattached to the wall or ceiling at a point wherethe vent connector enters the gas vent. The labelshall read: "This gas vent is for appliances thatburn gas. Do not connect to solid or liquid-fuel-burning appliances or incinerators." TheAuthority Having Jurisdiction shall determinewhether its area constitutes such a locality.[NFPA 54:12.7.6]802.6.7 Screws, rivets, and other fasteners shallnot penetrate the inner wall of double wall gasvents, except at the transition from the appliancedraft hood outlet, flue collar or single wall metalconnector to a double wall vent.
802.7 Single-Wall Metal Pipe.802.7.1 Construction. Single-wall metal pipeshall be constructed of galvanized sheet steel notless than 0.0304 inch (0.7 mm) thick or of otherapproved, noncombustible, corrosion-resistantmaterial. [NFPA 54:12.8.1]802.7.2 Cold Climate. Uninsulated single-wallmetal pipe shall not be used outdoors in coldclimates for venting appliances in regions wherethe 99 percent winter design temperature is lessthan 32ºF (0ºC). [NFPA 54:12.8.2]
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FIGURE 8-3 Plan View of Practical SeparationMethod for Multistory Gas Venting. [NFPA 54:Figure 12.7.4.2]
802.7.3 Termination. The termination of single-wall metal pipe shall comply with the followingrequirements: [NFPA 54:12.8.3]
802.7.3.1 Single-wall metal pipe shall termi-nate at least five (5) feet (1,524 mm) in verticalheight above the highest connected appliancedraft hood outlet or flue collar. [NFPA54:12.8.3(1)]802.7.3.2 Single-wall metal pipe shall extendat least two (2) feet (610 mm) above thehighest point where it passes through a roof ofa building and at least two (2) feet (610 mm)higher than any portion of a building within ahorizontal distance of ten (10) feet (3,048 mm).(See Figure 8-1.) [NFPA 54:12.8.3(2)]802.7.3.3 An approved cap or roof assemblyshall be attached to the terminus of a single-wall metal pipe. (Also see Section 802.7.4.4)[NFPA 54:12.8.3(3)]
802.7.4 Installation with Appliances Permittedby Section 802.4.1.
802.7.4.1 Prohibited Use. Single-wall metalpipe shall not be used as a vent in dwellingsand residential occupancies. [NFPA 54-09:12.8.4.1]
802.7.4.2 Single-wall metal pipe shall beused only for runs directly from the space inwhich the appliance is located through theroof or exterior wall to the outer air. A pipepassing through a roof shall extend withoutinterruption through the roof flashing, roofjacket, or roof thimble. [NFPA 54:12.8.4.1]802.7.4.3 Single-wall metal pipe shall notoriginate in any unoccupied attic or concealedspace and shall not pass through any attic,inside wall, concealed space, or floor. For theinstallation of a single-wall metal pipethrough an exterior combustible wall seeSection 802.10.14.2. [NFPA 54:12.8.4.2]802.7.4.4 Single-wall metal pipe used forventing an incinerator shall be exposed andreadily examinable for its full length andshall have suitable clearances maintained.[NFPA 54:12.8.4.3]802.7.4.5 Minimum clearances from single-wall metal pipe to combustible materialshall be in accordance with Table 8-2.Reduced clearances from single-wall metal
UNIFORM MECHANICAL CODETable 8-2 – 802.7
100
TABLE 8-2Clearance for Connectors[NFPA 54: Table 12.8.4.4]
Minimum Distance from Combustible MaterialListed Type B Listed Type L Single-Wall Factory-Built
Appliance Gas Vent Material Vent Material Metal Pipe Chimney Sections
Listed appliance As listed As listed 6 in. As listedwith draft hoods and -appliance listed foruse with Type B gas ventsResidential boilers and 6 in. 6 in. 9 in. As listedfurnaces with listed gasconversion burner andwith draft hoodResidential appliances Not permitted As listed 9 in. As listedlisted for use with TypeL ventsResidential incinerators Not permitted 9 in. 18 in. As listedListed gas-fired toilets Not permitted As listed As listed As listedUnlisted residential Not permitted 6 in. 9 in. As listedappliances with drafthoodResidential and low-heat Not permitted 9 in. 18 in. As listedappliance otherthan those aboveMedium-heat appliance Not permitted Not permitted 36 in. As listedNotes:These clearances shall apply unless the listing of an appliance or connector specifies clearances, in which case the listed clearancesshall apply.1 in.= 25.4 mm
pipe to combustible material shall be asspecified for vent connectors in Table 5-3.[NFPA 54:12.8.4.4]802.7.4.6 Where a single-wall metal pipepasses through a roof constructed ofcombustible material, a noncombustible,nonventilating thimble shall be used at thepoint of passage. The thimble shall extend atleast eighteen (18) inches (460 mm) aboveand six (6) inches (150 mm) below the roof,with the annular space open at the bottomand closed only at the top. The thimble shallbe sized in accordance with Section802.10.14.2. [NFPA 54:12.8.4.5]
802.7.5 Size of Single-Wall Metal Pipe. Single-wall metal piping shall comply with thefollowing requirements: [NFPA 54:12.8.5]
802.7.5.1 A venting system of a single-wallmetal pipe shall be sized in accordance withone of the following methods and the appli-ance manufacturer's instructions: [NFPA54:12.8.5(1)](1) For a draft hood–equipped appliance, in
accordance with Section 803.0. [NFPA54:12.8.5(1)(a)]
(2) For a venting system for a single appli-ance with a draft hood, the areas of theconnector and the pipe each shall not beless than the area of the appliance fluecollar or draft hood outlet, whichever issmaller. The vent area shall not begreater than seven times the draft hoodoutlet area. [NFPA 54:12.8.5(1)(b)]
(3) Other approved engineering methods.[NFPA 54:12.8.5(1)(c)]
802.7.5.2 Where a single-wall metal pipe isused and has a shape other than round, itshall have an equivalent effective area equalto the effective area of the round pipe forwhich it is substituted, and the minimuminternal dimension of the pipe shall be two(2) inches (50 mm). [NFPA 54:12.8.5(2)]802.7.5.3 The vent cap or a roof assemblyshall have a venting capacity not less thanthat of the pipe to which it is attached.[NFPA 54:12.8.5(3)]
802.7.6 Support of Single-Wall Metal Pipe. Allportions of single-wall metal pipe shall besupported for the design and weight of thematerial employed. [NFPA 54:12.8.6]802.7.7 Marking. Single-wall metal pipe shallcomply with the marking provisions of Section802.6.6. [NFPA 54:12.8.7]
802.8 Through-the-Wall Vent Termination.Through the wall vent termination’s shall be inaccordance with the following:
802.8.1 A mechanical draft venting system shallterminate at least three (3) feet (914 mm) aboveany forced air inlet located within ten (10) feet(3,048 mm). [NFPA 54:12.9.1]
Exception 1: This provision shall not applyto the combustion-air intake of a direct-ventappliance.Exception 2: This provision shall not applyto the separation of the integral outdoor-airinlet and flue gas discharge of listed outdoorappliances.
802.8.2 A mechanical draft venting system ofother than direct-vent type shall terminate at leastfour (4) feet (1,219 mm) below, four (4) feet (1,219mm) horizontally from, or one (1) foot (300 mm)above any door, operable window, or gravity airinlet into any building. The bottom of the ventterminal shall be located at least twelve (12)inches (300 mm) above grade. [NFPA 54:12.9.2]802.8.3 The vent terminal of a direct-vent appli-ance with an input of 10,000 Btu/h (3 kW) or lessshall be located at least six (6) inches (150 mm)from any air opening into a building, and suchan appliance with an input over 10,000 Btu/h (3kW) but not over 50,000 Btu/h (14.7 kW) shall beinstalled with a nine (9) inches (230 mm) venttermination clearance, and an appliance with aninput over 50,000 Btu/h (14.7 kW) shall have atleast a twelve (12) inches (300 mm) vent termina-tion clearance. The bottom of the vent terminaland the air intake shall be located at least twelve(12) inches (300 mm) above grade. [NFPA54:12.9.3]802.8.4 Through-the-wall vents for Category IIand Category IV appliances and noncategorizedcondensing appliances shall not terminate overpublic walkways or over an area where conden-sate or vapor could create a nuisance or hazardor could be detrimental to the operation of regu-lators, relief valves, or other equipment. Wherelocal experience indicates that condensate is aproblem with Category I and Category III appli-ances, this provision shall also apply. Drains forcondensate shall be installed in accordance withthe manufacturer’s installation instructions.[NFPA 54-09:12.9.4]802.8.5 Where vents, including those for direct-vent appliances, penetrate outside walls ofbuildings, the annular spaces around such pene-trations shall be permanently sealed usingapproved materials to prevent entry of combus-tion products into the building. [NFPA 54-09:12.9.6]
CHIMNEYS AND VENTS 802.7 – 802.8
101
802.9 Condensation Drain.802.9.1 Provision shall be made to collect anddispose of condensate from venting systemsserving Category II and Category IV appliancesand noncategorized condensing appliances inaccordance with Section 802.8.4. [NFPA54:12.10.1]802.9.2 Where local experience indicates thatcondensation is a problem, provision shall bemade to drain off and dispose of condensatefrom venting systems serving Category I andCategory III appliances in accordance withSection 802.8.4. [NFPA 54:12.10.2]
802.10 Vent Connectors for Category I Appli-ances.
802.10.1 Where Required. A vent connectorshall be used to connect appliances to a gas vent,chimney, or single-wall metal pipe, exceptwhere the gas vent, chimney, or single-wallmetal pipe is directly connected to the appliance.[NFPA 54:12.11.1]802.10.2 Materials.
802.10.2.1 A vent connector shall be made ofnoncombustible, corrosion-resistant materialcapable of withstanding the vent gas temper-ature produced by the appliance and of suffi-cient thickness to withstand physicaldamage. [NFPA 54:12.11.2.1]802.10.2.2 Where the vent connector usedfor appliances having a draft hood or aCategory I appliance is located in or passesthrough an unconditioned area, that portionof the vent connector shall be listed Type B,Type L, or listed vent material having equiv-alent insulation qualities. [NFPA54:12.11.2.2]
Exception: Single-wall metal pipelocated within the exterior walls of thebuilding and located in areas having alocal 99 percent winter design tempera-ture of 5ºF (-15ºC) or higher.
802.10.2.3 Where the vent connector usedfor appliances having a draft hood or aCategory I appliance is located in or passesthrough attics and crawl spaces, that portionof the vent connector shall be listed Type B,Type L, or listed vent material having equiv-alent insulation qualities. [NFPA54:12.11.2.3]802.10.2.4 Vent connectors for residential-type appliances shall comply with thefollowing: [NFPA 54:12.11.2.4](1) Vent connectors for listed gas appli-
ances having draft hoods and for appli-
ances having draft hoods and equippedwith listed conversion burners that arenot installed in attics, crawl spaces, orother unconditioned areas shall be oneof the following: [NFPA 54:12.11.2.4(1)](a) Type B or Type L vent material.(b) Galvanized sheet steel not less than
0.018 in. (0.46 mm) thick.(c) Aluminum (1100 or 3003 alloy or
equivalent) sheet not less than 0.027in. (0.69 mm) thick.
(d) Stainless steel sheet not less than0.012 in. (0.31 mm) thick.
(e) Smooth-interior-wall metal pipehaving resistance to heat andcorrosion equal to or greater thanthat of b, c, or d above.
(f) A listed vent connector.(2) Vent connectors shall not be covered
with insulation. [NFPA 54:12.11.2.4(2)]Exception: Listed insulated ventconnectors shall be installedaccording to the terms of theirlisting in accordance with themanufacturer’s installation instruc-tions.
802.10.2.5 A vent connector for non-residen-tial low-heat appliance shall be a factory-built chimney section or steel pipe havingresistance to heat and corrosion equivalent tothat for the appropriate galvanized pipe asspecified in Table 8-3. Factory-built chimneysections shall be joined together in accor-dance with the chimney manufacturer'sinstructions. [NFPA 54:12.11.2.5]802.10.2.6 Vent connectors for medium-heat appliances, commercial and industrialincinerators shall be constructed of factory-built, medium-heat chimney sections orsteel of a thickness not less than that speci-
UNIFORM MECHANICAL CODE802.9 – Table 8-3
102
TABLE 8-3Minimum Thickness for Galvanized Steel Vent
Connectors for Low-Heat Appliances[NFPA 54: Table 12.11.2.5]
Diameter of Connector (in.) Minimum Thickness (in.)Less than 66 to less than 1010 to 12 inclusive14 to 16 inclusiveOver 16
0.0190.0230.0290.0340.056
Notes: 1 in. = 25.4 mm, 1 in.2 = 645 mm2
fied in Table 8-4, and shall comply with thefollowing: [NFPA 54:12.11.2.6](1) A steel vent connector for appliances
with a vent gas temperature in excess of1,000°F (538°C) measured at theentrance to the connector shall be linedwith medium-duty fire brick (ASTM C64, Specification for Refractories for Incin-erators and Boilers, Type F) or the equiva-lent.
(2) The lining shall be at least two and one-half (2-1/2) inches (64 mm) thick for avent connector having a diameter orgreatest cross-sectional dimension ofeighteen (18) inches (460 mm) or less.
(3) The lining shall be at least four and one-half (4-1/2) inches (110 mm) thick laidon the four and one-half (4-1/2) inches(110 mm) bed for a vent connectorhaving diameter or greatest cross-sectional dimension greater than eigh-teen (18) inches (460 mm).
(4) Factory-built chimney sections, ifemployed, shall be joined together inaccordance with the chimney manufac-turer's instructions.
802.10.3 Size of Vent Connector.802.10.3.1 A vent connector for gas utiliza-tion appliances with a single draft hood orfor a Category I fan-assisted combustionsystem appliance shall be sized and installedin accordance with Section 803.0 or otherapproved engineering methods. [NFPA54:12.11.3.1]802.10.3.2 For a single appliance havingmore than one (1) draft hood outlet or fluecollar, the manifold shall be constructedaccording to the instructions of the appli-ance manufacturer. Where there are noinstructions, the manifold shall be designedand constructed in accordance withapproved engineering practices. As an alter-
nate method, the effective area of the mani-fold shall equal the combined area of theflue collars or draft hood outlets and thevent connectors shall have a minimum one(1) foot (305 mm) rise. [NFPA 54:12.11.3.2]802.10.3.3 Where two or more gas appli-ances are connected to a common vent orchimney, each vent connector shall be sizedin accordance with Section 803.0 or otherapproved engineering methods. As an alter-native method applicable only when all ofthe appliances are draft hood equipped,each vent connector shall have an effectivearea not less than the area of the draft hoodoutlet of the appliance to which it isconnected. [NFPA 54:12.11.3.3, 12.11.3.4]802.10.3.4Where two (2) or more gas appli-ances are vented through a common ventconnector or vent manifold, the commonvent connector or vent manifold shall belocated at the highest level consistent withavailable head-room and clearance tocombustible material and shall be sized inaccordance with Section 803.0 or otherapproved engineering methods. [NFPA54:12.11.3.5]
As an alternate method applicable onlywhere there are two (2) draft hood–equippedappliances, the effective area of the commonvent connector or vent manifold and all junc-tion fittings shall be not less than the area ofthe larger vent connector plus 50 percent ofthe areas of smaller flue collar outlets.[NFPA 54:12.11.3.6]802.10.3.5 Where the size of a ventconnector is increased to overcome installa-tion limitations and obtain connectorcapacity equal to the appliance input, thesize increase shall be made at the appliancedraft hood outlet. [NFPA 54:12.11.3.7]
802.10.4 Two or More Appliances Connectedto a Single Vent.
802.10.4.1 Where two (2) or more openingsare provided into one (1) chimney flue orvent, the openings shall either be at differentlevels, or the connectors shall be attached tothe vertical portion of the chimney or vent atan angle of 45 degrees or less relative to thevertical. [NFPA 54-09:12.11.4.1]802.10.4.2 Where two (2) or more ventconnectors enter a common gas vent,chimney flue, or single-wall metal pipe, thesmaller connector shall enter at the highestlevel consistent with the available headroomor clearance to combustible material. [NFPA54:12.11.4.1]
CHIMNEYS AND VENTS 802.10
103
TABLE 8-4Minimum Thickness for Steel Vent Connectorsfor Medium-Heat Appliances and Commercial
and Industrial Incinerators[NFPA 54: Table 12.11.2.6]
Vent Connector Size
Diameter (in.) Area (in.2)Minimum
Thickness (in.)Up to 14
Over 14 to 16Over 16 to 18Over 18
Up to 154154 to 201201 to 254
Larger than 254
0.0530.0670.0930.123
Notes: 1 in. = 25.4 mm, 1 in.2 = 645 mm2
802.10.4.3 Vent connectors serving Cate-gory I appliances shall not be connected toany portion of a mechanical draft systemoperating under positive static pressure,such as those serving Category III or Cate-gory IV appliances. [NFPA 54:12.11.4.2]
802.10.5 Clearance. Minimum clearances fromvent connectors to combustible material shall bein accordance with Table 8-2. [NFPA 54:12.11.5]
Exception: The clearance between a ventconnector and combustible material shall bepermitted to be reduced where thecombustible material is protected as speci-fied for vent connectors in Table 5-3.
802.10.6 Avoid Unnecessary Bends. A ventconnector shall be installed so as to avoid turnsor other construction features that create exces-sive resistance to flow of vent gases. [NFPA54:12.11.6]802.10.7 Joints. Joints between sections ofconnector piping and connections to flue collarsor draft hood outlets shall be fastened in accor-dance with one of the following methods:[NFPA 54:12.11.7](1) By sheet metal screws.(2) Vent connectors of listed vent material shall
be assembled and connected to flue collarsor draft hood outlets in accordance with themanufacturers' instructions.
(3) Other approved means.802.10.8 Slope. A vent connector shall beinstalled without any dips or sags and shallslope upward toward the vent or chimney atleast one-quarter (1/4) in./ft. (20 mm/m).[NFPA 54:12.11.8]
Exception: Vent connectors attached to amechanical draft system installed in accor-dance with the draft system manufacturers'instructions.
802.10.9 Length of Vent Connector.802.10.9.1 A vent connector shall be asshort as practical, and the appliance locatedas close as practical to the chimney or vent.[NFPA 54:12.11.9.1]802.10.9.2 The maximum horizontal lengthof a single-wall connector shall be 75 percentof the height of the chimney or vent exceptfor engineered systems. [NFPA 54:12.11.9.2]802.10.9.3 The maximum horizontal lengthof a Type B double-wall connector shall be100 percent of the height of the chimney orvent, except for engineered systems. Themaximum length of an individual connector
for a chimney or vent system servingmultiple appliances, from the applianceoutlet to the junction with the common ventor another connector, shall be 100 percent ofthe height of the chimney or vent. [NFPA 54:12.11.9.3]
802.10.10 Support. A vent connector shall besupported for the design and weight of thematerial employed to maintain clearances andprevent physical damage and separation ofjoints. [NFPA 54:12.11.10]802.10.11 Chimney Connection. Whereentering a flue in a masonry or metal chimney,the vent connector shall be installed above theextreme bottom to avoid stoppage. Where athimble or slip joint is used to facilitate removalof the connector, the connector shall be firmlyattached to or inserted into the thimble or slipjoint to prevent the connector from falling out.Means shall be employed to prevent theconnector from entering so far as to restrict thespace between its end and the opposite wall ofthe chimney flue. [NFPA 54:12.11.11]802.10.12 Inspection. The entire length of avent connector shall be readily accessible forinspection, cleaning, and replacement. [NFPA54:12.11.12]802.10.13 Fireplaces. A vent connector shallnot be connected to a chimney flue serving afireplace unless the fireplace flue opening ispermanently sealed. [NFPA 54:12.11.13]802.10.14 Passage Through Ceilings, Floors,or Walls.
802.10.14.1 A vent connector shall not passthrough any ceiling, floor, or fire-resistancerated wall. A single-wall metal pipeconnector shall not pass through any inte-rior wall.
Exception: Vent connectors made oflisted Type B or Type L vent materialand serving listed appliances with drafthoods and other appliances listed foruse with Type B gas vents that passthrough walls or partitions constructedof combustible material shall beinstalled with not less than the listedclearance to combustible material.
802.10.14.2 A vent connector made of asingle-wall metal pipe shall not passthrough a combustible exterior wall unlessguarded at the point of passage by a venti-lated metal thimble not smaller than thefollowing: [NFPA 54:12.11.14.2](1) For listed appliances equipped with
draft hoods and appliances listed for
UNIFORM MECHANICAL CODE802.10
104
use with Type B gas vents, the thimbleshall be a minimum of four (4) inches(100 mm) larger in diameter than thevent connector. Where there is a run ofnot less than six (6) feet (305 mm) ofvent connector in the opening betweenthe draft hood outlet and the thimble,the thimble shall be a minimum of two(2) inches (50 mm) larger in diameterthan the vent connector.
(2) For unlisted appliances having drafthoods, the thimble shall be a minimumof six (6) inches (150 mm) larger indiameter than the vent connector.
(3) For residential and low-heat appliances,the thimble shall be a minimum oftwelve (12) inches (300 mm) larger indiameter than the vent connector.
Exception: In lieu of thimble protec-tion, all combustible material in thewall shall be removed from the ventconnector a sufficient distance toprovide the specified clearancefrom such vent connector tocombustible material. Any materialused to close up such opening shallbe noncombustible.
802.10.14.3 Vent connectors for medium-heat appliances shall not pass through wallsor partitions constructed of combustiblematerial. [NFPA 54:12.11.14.3]
802.11 Vent Connectors for Category II, CategoryIII, and Category IV Appliances. (See Section 802.4.)[NFPA 54:12.12]802.12 Draft Hoods and Draft Controls.
802.12.1 Appliances Requiring Draft Hoods.Vented appliances shall be installed with drafthoods. [NFPA 54:12.13.1]
Exception: Dual oven–type combinationranges; incinerators; direct-vent appliances;fan-assisted combustion system appliances;appliances requiring chimney draft for oper-ation; single-firebox boilers equipped withconversion burners with inputs greater than400,000 Btu/h (117 kW); appliancesequipped with blast, power, or pressureburners that are not listed for use with drafthoods; and appliances designed for forcedventing.
802.12.2 Installation. A draft hood suppliedwith or forming a part of listed vented applianceshall be installed without alteration, exactly asfurnished and specified by the appliance manu-facturer. If a draft hood is not supplied by the
appliance manufacturer where one (1) is required,a draft hood shall be installed, be of a listed orapproved type, and, in the absence of otherinstructions, be of the same size as the applianceflue collar. Where a draft hood is required with aconversion burner, it shall be of a listed orapproved type. Where it is determined that adraft hood of special design is needed or prefer-able for a particular installation, the installationshall be in accordance with the recommenda-tions of the appliance manufacturer and shall bewith the approval of the Authority Having Juris-diction. [NFPA 54:12.13.2, 12.13.2.1, 12.13.2.2]802.12.3 Draft Control Devices. Where a draftcontrol device is part of the appliance or issupplied by the appliance manufacturer, it shallbe installed in accordance with the manufactur-er's instructions. In the absence of manufactur-er's instructions, the device shall be attached tothe flue collar of the appliance or as near to theappliance as practical. [NFPA 54:12.13.3]802.12.4 Additional Devices. Appliances(except incinerators) requiring controlledchimney draft shall be permitted to be equippedwith a listed double-acting barometric draftregulator installed and adjusted in accordancewith the manufacturers' instructions. [NFPA54:12.13.4]802.12.5 Location. Draft hoods and barometricdraft regulators shall be installed in the sameroom or enclosure as the appliance in such amanner as to prevent any difference in pressurebetween the hood or regulator and the combus-tion air supply. [NFPA 54:12.13.5]802.12.6 Positioning. Draft hoods and draftregulators shall be installed in the position forthat they were designed with reference to thehorizontal and vertical planes and shall belocated so that the relief opening is notobstructed by any part of the appliance or adja-cent construction. The appliance and its drafthood shall be located so that the relief opening isaccessible for checking vent operation. [NFPA54:12.13.6]802.12.7 Clearance. A draft hood shall belocated so that its relief opening is not less thansix (6) inches (150 mm) from any surface exceptthat of the appliance it serves and the ventingsystem to which the draft hood is connected.Where a greater or lesser clearance is indicatedon the appliance label, the clearance shall not beless than that specified on the label. Such clear-ances shall not be reduced. [NFPA 54:12.13.7]
CHIMNEYS AND VENTS 802.10 – 802.12
105
802.13 Manually Operated Dampers. A manuallyoperated damper shall not be placed in any appli-ance vent connector. Fixed baffles shall not be classi-fied as manually operated dampers. [NFPA 54:12.14]802.14 Automatically Operated Vent Dampers. Anautomatically operated vent damper shall be of alisted type. [NFPA 54:12.15]802.15 Obstructions. Devices that retard the flow ofvent gases shall not be installed in a vent connector,chimney, or vent. The following shall not be consid-ered as obstructions:(1) Draft regulators and safety controls specifically
listed for installation in venting systems andinstalled in accordance with the terms of theirlisting.
(2) Approved draft regulators and safety controlsdesigned and installed in accordance withapproved engineering methods.
(3) Listed heat reclaimers and automatically oper-ated vent dampers installed in accordance withthe terms of their listing.
(4) Vent dampers serving listed appliances installedin accordance with Sections 803.1 and 803.2.1 orother approved engineering methods.
(5) Approved economizers, heat reclaimers, andrecuperators installed in venting systems ofappliances not required to be equipped withdraft hoods, provided the appliance manufactur-er's instructions cover the installation of such adevice in the venting system and performance inaccordance with Sections 802.3.1 and 802.3.2 isobtained. [NFPA 54:12.16]
803.0 Sizing of Category I Venting Systems.803.1 These venting tables shall not be used whereobstructions (see Section 802.15) are installed in theventing system. The installation of vents servinglisted appliances with vent dampers shall be inaccordance with the appliance manufacturer’sinstructions or in accordance with the following:[NFPA 54:13.1.1](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 theminimum capacity of the vent system. Wherethe corresponding FAN Min is NA, the ventconfiguration shall not be permitted and analternative venting configuration shall beutilized.803.1.1 Where the vent size determined fromthe tables is smaller than the appliance draft
hood outlet or flue collar, the use of the smallersize shall be permitted provided that the instal-lation complies with all of the following require-ments: [NFPA 54:13.1.2](1) The total vent height (H) is at least ten (10)
feet (3,048 mm).(2) Vents for appliance draft hood outlets or
flue collars twelve (12) inches (300 mm) indiameter or smaller are not reduced morethan one table size.
(3) Vents for appliance draft hood outlets orflue collars larger than twelve (12) inches(300 mm) in diameter are not reduced morethan two table sizes.
(4) The maximum capacity listed in the tablesfor a fan-assisted appliance is reduced byten (10) percent (0.90 maximum tablecapacity).
(5) The draft hood outlet is greater than four (4)inches (100 mm) in diameter. Do not connecta three (3) inches (80 mm) diameter vent to afour (4) inches (100 mm) diameter drafthood outlet. This provision shall not applyto fan-assisted appliances.
803.1.2 Single-appliance venting configurationswith zero (0) lateral lengths in Tables 8-5, 8-6,and 8-9 shall not have elbows in the ventingsystem. For vent configurations with laterallengths, the venting tables include allowance fortwo (2) 90 degree turns. For each additionalelbow up to and including 45 degrees, themaximum capacity listed in the venting tablesshall be reduced by 5 percent. For each elbowgreater than 45 degrees up to and including 90degrees, the maximum capacity listed in theventing tables shall be reduced by 10 percent.Where multiple offsets occur in a vent, the totallateral length of all offsets combined shall notexceed that specified in Tables 8-5 through 8-9.[NFPA 54-09:13.1.3]803.1.3 Zero (0) lateral (L) shall apply only to astraight vertical vent attached to a top-outletdraft hood or flue collar. [NFPA 54:13.1.4]803.1.4 Sea level input ratings shall be usedwhen determining maximum capacity for high-altitude installation. Actual input (derated foraltitude) shall be used for determining minimumcapacity for high-altitude installation. [NFPA54:13.1.5]803.1.5 For appliances with more than one (1)input rate, the minimum vent capacity (FANMin) determined from the tables shall be lessthan the lowest appliance input rating, and themaximum vent capacity (FAN Max/NAT Max)determined from the tables shall be greater than
UNIFORM MECHANICAL CODE802.13 – 803.1
106
the highest appliance rating input. [NFPA54:13.1.6]803.1.6 Listed corrugated metallic chimney linersystems in masonry chimneys shall be sized byusing Table 8-5 or 8-6 for Type B vents, with themaximum capacity reduced by 20 percent (0.80maximum capacity) and the minimum capacityas shown in Table 8-5 or 8-6. Corrugated metallicliner systems installed with bends or offsets shallhave their maximum capacity further reduced inaccordance with Section 803.1.2. The 20 percentreduction for corrugated metallic chimney linersystems includes an allowance for one (1) longradius 90 degree turn at the bottom of the liner.[NFPA 54:13.1.7]803.1.7 Where the vertical vent has a largerdiameter than the vent connector, the verticalvent diameter shall be used to determine theminimum vent capacity, and the connectordiameter shall be used to determine themaximum vent capacity. The flow area of thevertical vent shall not exceed seven (7) times theflow area of the listed appliance categorized ventarea, flue collar area, or draft hood outlet areaunless designed in accordance with approvedengineering methods. [NFPA 54:13.1.9]803.1.8 Connection to Chimney Liners.Connections between chimney liners and listeddouble-wall connectors shall be made with listedadapters designed for such purpose. [NFPA54:13.1.8]
803.1.8.1 Tables 8-5 through 8-9 shall beused for chimneys and vents not exposed tothe outdoors below the roof line. A Type Bvent or listed chimney lining system passingthrough an unused masonry chimney flueshall not be considered to be exposed to theoutdoors. A Type B vent passing through anunventilated enclosure or chase insulated toa value of not less than R8 shall not beconsidered to be exposed to the outdoors.Table 8-7 in combination with Table 8-15shall be used for clay-tile-lined exteriormasonry chimneys, provided all of thefollowing are met:(1) The vent connector is Type B double wall.(2) The vent connector length is limited to
one and one-half (1-1/2) feet for eachinch (18 mm/mm) of vent connectordiameter.
(3) The appliance is draft hood equipped.(4) The input rating is less than the
maximum capacity given in Table 8-7.(5) For a water heater, the outdoor design
temperature shall not be less than 5°F(-15°C).
(6) For a space-heating appliance, the inputrating is greater than the minimumcapacity given by Table 8-15. [NFPA54:13.1.11]
803.1.9 Corrugated vent connectors shall not besmaller than the listed appliance categorizedvent diameter, flue collar diameter, or drafthood outlet diameter. [NFPA 54:13.1.12]803.1.10 Vent connectors shall not be upsizedmore than two (2) sizes greater than the listedappliance categorized vent diameter, flue collardiameter, or draft hood outlet diameter. [NFPA54:13.1.13]803.1.11 In a single run of vent or ventconnector, more than one diameter and typeshall be permitted to be used, provided that allthe sizes and types are permitted by the tables.[NFPA 54:13.1.14]803.1.12 Interpolation shall be permitted incalculating capacities for vent dimensions thatfall between table entries. (See Example 8-1 inSection 803.2.23.) [NFPA 54:13.1.15]803.1.13 Extrapolation beyond the table entriesshall not be permitted. [NFPA 54:13.1.16]803.1.14 For vent heights lower than six (6) feet(1,829 mm) and higher than shown in the tables,engineering methods shall be used to calculatevent capacities. [NFPA 54:13.1.17]803.1.15 Draft Hood Conversion Accessories.Draft hood conversion accessories for use withmasonry chimneys venting listed Category I fan-assisted appliances shall be listed and installedin accordance with the listed accessory manufac-turer’s installation instructions. [NFPA54:13.1.10]
803.2 Additional Requirements to Multiple Appli-ance Vent Tables 8-10 through 8-14 and Tables 8-16 through 8-19.
803.2.1 These venting tables shall not be usedwhere obstructions (see Section 802.15) areinstalled in the venting system. The installationof vents serving listed appliances with ventdampers shall be in accordance with the appli-ance manufacturer’s instructions or in accor-dance with the following:(1) The maximum capacity of the vent
connector shall be determined using theNAT Max column.
(2) The maximum capacity of the vertical ventor chimney shall be determined using theFAN+NAT column when the second appli-ance is a fan-assisted appliance, or the
CHIMNEYS AND VENTS 803.1 – 803.2
107
NAT+NAT column when the second appli-ance is equipped with a draft hood.
(3) The minimum capacity shall be determinedas if the appliance were a fan-assisted appli-ance.(a) The minimum capacity of the vent
connector shall be determined using theFANMin column.
(b) The FAN+FAN column shall be usedwhen the second appliance is a fan-assisted appliance, and the FAN+NATcolumn shall be used when the secondappliance is equipped with a drafthood, to determine whether the verticalvent or chimney configuration is notpermitted (NA). Where the vent config-uration is NA, the vent configurationshall not be permitted, and an alterna-tive venting configuration shall beutilized. [NFPA 54:13.2.1]
803.2.2 The maximum vent connector horizontallength shall be 18 in./in. (18 mm/mm) ofconnector diameter (see the Vent ConnectorMaximum Length Table). [NFPA 54:13.2.2]
803.2.3 The vent connector shall be routed to thevent utilizing the shortest possible route.Connectors with longer horizontal lengths thanthose listed in Section 803.2.2 are permittedunder the following conditions: [NFPA 54:13.2.3]
(A) The maximum capacity (FAN Max or NATMax) of the vent connector shall be reduced10 percent for each additional multiple ofthe length listed in 803.2.2. For example, themaximum length listed for a four (4) inches(100 mm) connector is six (6) feet (1,829mm). With a connector length greater thansix (6) feet (1,829 mm) but not exceedingtwelve (12) feet (3,658 mm), the maximumcapacity must be reduced by 10 percent(0.90 maximum vent connector capacity).With connector length greater than twelve(12) feet (3,658 mm) but not exceeding eigh-teen (18) feet (5,486 mm), the maximumcapacity must be reduced by 20 percent(0.80 maximum vent capacity). [NFPA54:13.2.3(1)]
(B) For a connector serving a fan-assisted appli-ance, the minimum capacity (FAN Min) ofthe connector shall be determined by refer-ring to the corresponding single-appliancetable. For Type B double-wall connectors,Table 8-5 shall be used. For single-wallconnectors, Table 8-6 shall be used. Theheight (H) and lateral (L) shall be measuredaccording to the procedures for a single-appliance vent, as if the other applianceswere not present. [NFPA 54:13.2.3(2)]
803.2.4Where the vent connectors are combinedprior to entering the vertical portion of thecommon vent to form a common vent manifold,the size of the common vent manifold and thecommon vent shall be determined by applying a10 percent reduction (0.90 x maximum commonvent capacity) to the Common Vent Capacitypart of the common vent tables. The length ofthe common vent connector manifold (LM) shallnot exceed 18 in./in. (18 mm/mm) of commonvent connector manifold diameter (D). (SeeFigure 8-4.) [NFPA 54:13.2.4]803.2.5 Where the common vertical vent isoffset, the maximum capacity of the commonvent shall be reduced in accordance with Section803.2.6, and the horizontal length of the commonvent offset shall not exceed 18 in./in. (18mm/mm) of common vent diameter. Wheremultiple offsets occur in a common vent, thetotal horizontal length of all offsets combinedshall not exceed 18 in./in. (18 mm/mm) ofcommon vent diameter. [NFPA 54-09:13.2.5]803.2.6 For each elbow up to and including 45degrees in the common vent, the maximumcommon vent capacity listed in the ventingtables shall be reduced by 5 percent. For each
UNIFORM MECHANICAL CODE803.2
108
Vent Connector Maximum Length[NFPA 54: Table 13.2.2]
Connector Connector HorizontalDiameter Maximum Length
elbow exceeding 45 degrees up to and including90 degrees, the maximum common vent capacitylisted in the venting tables shall be reduced by10 percent. [NFPA 54:13.2.6]803.2.7 Common Vent Minimum Size. Thecross-sectional area of the common vent shall beequal to or greater than the cross-sectional areaof the largest connector. [NFPA 54:13.2.8]803.2.8 Tee and Wye Fittings. Tee and wyefittings connected to a common gas vent shall beconsidered as part of the common gas vent andconstructed of materials consistent with that ofthe common gas vent. [NFPA 54-09:13.2.9]
803.2.8.1 At the point where tee or wyefittings connect to a common vent, theopening size of the fitting shall be equal tothe size of the common vent. Such fittingsshall not be prohibited from having reducedsize openings at the point of connection ofappliance vent connectors. [NFPA 54:13.2.10]
803.2.9 Sea level input ratings shall be usedwhen determining maximum capacity for high-altitude installation. Actual input (derated foraltitude) shall be used for determining minimumcapacity for high-altitude installation. [NFPA54:13.2.11]803.2.10 The connector rise (R) for each appli-ance connector shall be measured from the drafthood outlet or flue collar to the centerline wherethe vent gas streams come together. [NFPA54:13.2.12]803.2.11 For multiple units of appliances alllocated on one (1) floor, available total height (H)shall be measured from the highest draft hoodoutlet or flue collar up to the level of the outletof the common vent. [NFPA 54:13.2.13]
803.2.12 For multistory installations, availabletotal height (H) for each segment of the systemshall be the vertical distance between the highestdraft hood outlet or flue collar entering thatsegment and the centerline of the next higherinterconnection tee. (See Figure 8-5.) [NFPA54:13.2.14]
803.2.13 The size of the lowest connector and ofthe vertical vent leading to the lowest intercon-nection of a multistory system shall be in accor-dance with Table 8-5 or 8-6 for available totalheight (H) up to the lowest interconnection. (SeeFigure 8-6.) [NFPA 54:13.2.15]803.2.14 Where used in multistory systems,vertical common vents shall be Type B double-wall and shall be installed with a listed vent cap.[NFPA 54:13.2.16]803.2.15 Offsets in multistory common ventsystems shall be limited to a single offset in eachsystem, and systems with an offset shall complywith all of the following:(1) The offset angle shall not exceed 45 degrees
from vertical.
CHIMNEYS AND VENTS Figure 8-4 – 803.2
109
FIGURE 8-4 Use of Manifolded Common VentConnector. [NFPA 54: Figure G.1(k)]
FIGURE 8-5 Multistory Gas Vent Design Proce-dure for Each Segment of System.[NFPA 54: Figure G.1(m)]
(2) The horizontal length of the offset shall notexceed eighteen (18) inches for each inch(180 mm/mm) of common vent diameter ofthe segment in that the offset is located.
(3) For the segment of the common vertical ventcontaining the offset, the common ventcapacity listed in the common venting tablesshall be reduced by 20 percent (0.80 xmaximum common vent capacity).
(4) A multistory common vent shall not bereduced in size above the offset. [NFPA54:13.2.17]
803.2.16 Where two or more appliances areconnected to a vertical vent or chimney, the flowarea of the largest section of vertical vent orchimney shall not exceed seven times thesmallest listed appliance categorized vent areas,flue collar area, or draft hood outlet area, unlessdesigned in accordance with approved engi-neering methods. [NFPA 54:13.2.18]
803.2.17 For appliances with more than oneinput rate, the minimum vent connector capacity(FAN Min) determined from the tables shall beless than the lowest appliance input rating, andthe maximum vent connector capacity (FANMax or NAT Max) determined from the tablesshall be greater than the highest appliance inputrating. [NFPA 54:13.2.19]803.2.18 Listed, corrugated metallic chimneyliner systems in masonry chimneys shall besized by using Table 8-10 or 8-11 for Type Bvents, with the maximum capacity reduced by20 percent (0.80 maximum capacity) and theminimum capacity as shown in Table 8-10 or 8-11. Corrugated metallic liner systems installedwith bends or offsets shall have their maximumcapacity further reduced in accordance withSections 803.2.5 and 803.2.6. The 20 percentreduction for corrugated metallic chimney linersystems includes an allowance for one longradius 90 degree turn at the bottom of the liner.[NFPA 54:13.2.20]803.2.19 Tables 8-10 and 8-11 shall be used forchimneys and vents not exposed to the outdoorsbelow the roof line. A Type B vent passingthrough an unventilated enclosure or chase insu-lated to a value of not less than R 8 shall not beconsidered to be exposed to the outdoors. Tables8-16 through 8-19 shall be used for clay-tile-linedexterior masonry chimneys, provided all of thefollowing 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 Table8-16 (for NAT+NAT) or Table 8-18 (forFAN+NAT).
(4) The input rating of each space-heatingappliance is greater than the minimuminput rating given by Table 8-17 (forNAT+NAT) or Table 8-19 (for FAN+NAT).
(5) The vent connector sizing is in accordancewith Table 8-12. [NFPA 54:13.2.22]
803.2.20 Vent connectors shall not be increasedmore than two sizes greater than the listed appli-ance categorized vent diameter, flue collar diam-eter, or draft hood outlet diameter. Vent connec-tors for draft hood-equipped appliances shallnot be smaller than the draft hood outlet diam-eter. Where a vent connector size(s) determinedfrom the tables for a fan-assisted appliance(s) issmaller than the flue collar diameter, the use ofthe smaller size(s) shall be permitted provided
UNIFORM MECHANICAL CODE803.2
110
FIGURE 8-6 Principle of Design of MultistoryVents Using Vent Connector and Common VentDesign Tables. [NFPA 54: Figure G.1(n)]
that the installation complies with all of thefollowing:(1) Vent connectors for fan-assisted appliance
flue collars twelve (12) inches (300 mm) indiameter or smaller are not reduced by morethan one table size [e.g., 12 in. to 10 in. (300mm to 250 mm) is a one-size reduction] andthose larger than twelve (12) inches (300mm) in diameter are not reduced more thantwo table sizes [e.g., 24 in. to 20 in. (610 mmto 510 mm) is a two-size reduction].
(2) The fan-assisted appliance(s) is commonvented with a draft hood equipped appli-ance(s).
(3) The vent connector has a smooth interiorwall. [NFPA 54:13.2.24]
803.2.21 All combinations of pipe sizes andsingle-wall and double-wall metal pipe shall beallowed within any connector run(s) or withinthe common vent provided ALL of the appro-priate tables permit ALL of the desired sizes andtypes of pipe, as if they were used for the entirelength of the subject connector or vent. Wheresingle-wall and Type B double-wall metal pipesare used for vent connectors within the sameventing system, the common vent must be sizedusing Table 8-11 or 8-13, as appropriate. [NFPA54:13.2.25]803.2.22 Where a table permits more than one(1) diameter of pipe to be used for a connector orvent, all the permitted sizes shall be permitted tobe used. [NFPA 54:13.2.26]803.2.23 Interpolation shall be permitted incalculating capacities for vent dimensions thatfall between table entries. (See Example 8-1.)[NFPA 54:13.2.27]Example 8-1: Interpolating between TableValues. An installer has an 80,000 Btu/h. inputappliance with a four (4) inch diameter drafthood outlet that needs to be vented into a twelve(12) foot high Type B vent. The vent connectorhas a five (5) foot lateral length and is also TypeB. Can this appliance be vented using a four (4)inch diameter vent?SolutionTable 8-5 is used in the case of an all Type B ventsystem. However, since there is no entry inTable 8-5 for a height of 12 ft., interpolation mustbe used. Read down the 4 in. diameter NAT Maxcolumn to the row associated with 10 ft. heightand 5 ft. lateral to find the capacity value of77,000 Btu/h. Read further down to the 15 ft.height, 5 ft. lateral row to find the capacity valueof 87,000 Btu/h. The difference between the 15
ft. height capacity value and the 10 ft. heightcapacity value is 10,000 Btu/h. The capacity for avent system with a 12 ft. height is equal to thecapacity for a 10 ft. height plus 2/5 of the differ-ence between the 10 ft. and 15 ft. height values,or 77,000 + 2/5 x 10,000 = 81,000 Btu/h. There-fore, a 4 in. diameter vent can be used in theinstallation.803.2.24 Extrapolation beyond the table entriesshall not be permitted. [NFPA 54:13.2.28]803.2.25 For vent heights lower than six (6) feetand higher than shown in the tables, engineeringmethods shall be used to calculate vent capaci-ties. [NFPA 54:13.2.29]
CHIMNEYS AND VENTS 803.2
111
UNIFORM MECHANICAL CODETable 8-5
112
Number of Appliances: SingleAppliance Type: Category I
Appliance Vent Connection: Connected Directly to VentVent Diameter – D (in.)
3 4 5 6 7Appliance Input Rating in Thousands of Btu per Hour
HeightH(ft)
LateralL(ft)
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
0132125
78514946
46363452
0183036
152979491
86676461
0273947
251157153149
141105103100
0325059
375232227223
205157153149
0446678
524321316310
285217211205
8 0258
0122328
84575349
50403835
0163239
16510910398
94757166
0254251
276178171164
155120115109
0285364
415263255247
235180173165
0427084
583365356347
320247237227
10 02510
0122330
88615751
53424036
0173241
175118113104
100817770
0234154
295194187176
166129124115
0265267
447289280267
255195188175
0406888
631402392376
345273263245
15 0251015
011222935
9469655953
5848454137
015304048
191136130121112
11293878276
020395161
327226219206195
187150142135128
022496476
502339330315301
285225217208198
038648498
716475463445429
390316300288275
20 025101520
01021283448
977571645852
615148444035
01429384655
202149143133124116
11910096898478
01838505969
349250242229217206
202166160150142134
02047627384
540377367351337322
307249241228217206
033628194107
776531519499481464
430346337321308295
30 02510152030
0921273356NA
1008177706458NA
64565450NANANA
0132837445373
213166160150141132113
1281121081029690NA
0143648576688
374283275262249237214
220185176171163154NA
01845597080104
587432421405389374346
336280273261249237219
027587790102131
853613600580560542507
475394385371357343321
50 02510152030
08202659NANA
10186827670NANA
6761NANANANANA
0112735425069
216183177168158149131
134122119114NANANA
0143545546384
397320312299287275250
232206200190180169NA
0154356667699
633497487471455440410
363314308298288278259
02255738597123
932715702681662642605
518445438426413401376
100 0251015203050
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
01026334047NANA
218194189182174166NANA
NANANANANANANANA
0123343505978NA
407354347335321311290NA
NANANANANANANANA
0134053627192147
665566557542528513483428
400375369361353344NANA
01852688090115180
997831820801782763726651
560510504493482471449405
Table 8-5Type B Double-Wall Gas Vent [NFPA 54: Table 13.1(a)]
CHIMNEYS AND VENTS Table 8-5 continued
113
Number of Appliances: SingleAppliance Type: Category I
Appliance Vent Connection: Connected Directly to VentVent Diameter – D (in.)
8 9 10 12 14Appliance Input Rating in Thousands of Btu per Hour
HeightH(ft)
LateralL(ft)
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
0537993
698425419413
370285279273
06393110
897543536530
470370862354
075110128
1121675668661
570455445435
0103147171
1645982975967
850650640630
0138191219
2267134613381330
1170890880870
8 0258
0508399
780483473463
415322313303
06099117
1006619607596
537418407396
071115137
1261770758746
660515503490
098154180
1858112411101097
970745733720
0130199231
2571154315281514
1320102010101000
10 02510
04881104
847533522504
450355346330
05795122
1096684671651
585457446427
068112142
1377852839817
720560547525
093149187
2036124412291204
1060850829795
0124192238
2825171316961669
1450113011051080
15 0251015
0457699115
970633620600580
525414403386373
05390116134
1263815800777755
682544529507491
063105135155
159610191003977953
840675660635610
086140177202
23801495147614461418
1240985967936905
0114182227257
33232062204120091976
17201350132712891250
20 025101520
0417395111125
1057711697675654634
575470460443427410
05086112129145
1384917902877853830
752612599576557537
059101130150167
175611501133110510781052
930755738710688665
081135172195217
263716941674164116091578
13501100107910451018990
0107174220248273
370123432320228222452210
190015201498146014251390
30 02510152030
0336991105119149
1173826811788765743702
650535524507490473444
04282107124139171
15481072105510281002977929
855700688668648628594
05496125143160195
1977135113321301127212431189
1060865851829807784745
074127164187207246
3004200419811944190818731807
1550131012891254122011851130
098164209237260305
4252278627592716267426332555
2170180017751733169216501585
50 02510152030
0266586100113141
1297975960935911888844
708615605589572556522
03377101117131161
1730127612591230120311761125
952813798773747722670
04190118136151183
2231162016001567153615051446
11951010996972948924876
066118154177195232
3441243124062366232722882214
1825151314951466143714081349
086151196222244287
4034340933803332328532393150
2550212521022064202619871910
100 0251015203050
021608093105131197
1411115511411118109510731029944
770700692679666653627575
0257194109122149217
19081536151914921465143813871288
1040935926910895880849787
03082108126141170241
24911975195519231892186118021688
13101170115911421124110710711000
044107142163181215292
39253027300229612920288028032657
20501820180317751747171916631550
072136180206226265350
57294313428242314182413340373856
29502550253125002469243823752250
Table 8-5Type B Double-Wall Gas Vent [NFPA 54: Table 13.1(a)] (continued)
UNIFORM MECHANICAL CODETable 8-5 continued
114
Number of Appliances: SingleAppliance Type: Category I
Appliance Vent Connection: Connected Directly to VentVent Diameter – D (in.)
16 18 20 22 24Appliance Input Rating in Thousands of Btu per Hour
HeightH(ft)
LateralL(ft)
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
0178242276
2983176917611753
1530117011601150
0225300341
3802225022422235
1960148014751470
0296390437
4721278227742767
2430185018351820
0360469523
5737337733703363
2950222022152210
0426555618
6853403040234017
3520267026602650
8 0258
0168251289
3399203020132000
1740134013301320
0212311354
4333258425632552
2220170016851670
0278398450
5387319631803163
2750211020902070
0336476537
6555388238633850
3360256025452530
0401562630
7838463446124602
4010305030403030
10 02510
0161243298
3742225622382209
1925148014611430
0202300364
4782286828492818
2450189018711840
0264382459
5955355635363504
3050234023182280
0319458546
7254432243014268
3710284028182780
0378540641
8682515351325099
4450339033713340
15 0251015
0147229283318
44232719269626592623
22701770174817121675
0186283346385
56783467344234023363
29002260223521932150
0239355432479
70994304427842344192
36202800277727392700
0290426510564
86655232520451595115
44103410338533433300
0346501599665
10,3936251622261756129
53004080405740193980
20 025101520
0139219273306335
494830973071302929882948
252020001978194019101880
0175270334372404
637639553926388038353791
325025702544250024652430
0220337413459495
798849164885483547864737
406032003174313030903050
0269403489541585
978559835950589658445792
498039103880383037953760
0321475573631689
11,75371547119706370076953
600047004662460045754550
30 02510152030
0127206259292319369
5725369636663617357035233433
2920238023502300225022002130
0159252316354384440
7420473447014647459445424442
3770305030202970292028702785
0199312386431467540
9341590058635803574456865574
4750381037833739369536503565
0241373456507548635
11,483719471557090702669646842
5850465046224574452744804375
0285439535590639739
13,848861785748505843783708239
7060560055525471539153105225
50 02510152030
0113191243274300347
6711455445204464440943564253
3440284028132767272126752631
0141234295330361412
8774586458265763570156415523
4460367036393585353434813431
0171283355396433494
11,129733972957224715570866953
5635463045974542451144794421
0209336419465506577
13,767898089338855877987048557
6940569556545585554655065444
0251394491542586672
16,69410,78810,73710,65210,57010,48810,328
8430686068186749671066706603
100 0251015203050
095172223252277319415
79145834579757375678561955055289
40503500347534343392335132673100
0120208268304330378486
10,4857591754874787409734172096956
53004600456645094451439442794050
0138245318358387446572
13,4549577952894479367928991368841
67005800576957175665561355095300
0169293374418452514659
16,81711,80311,74811,65811,56911,48211,31010,979
86007200716271007037697568506600
0204341436487523592752
20,57814,26414,20414,10514,00713,91013,72013,354
10,3008800875686838610853783918100
Table 8-5Type B Double-Wall Gas Vent [NFPA 54: Table 13.1(a)] (continued)
For SI units, 1 in. = 25.4 mm, 1 ft. = 0.305 m, 1 in.2 = 645 mm2, 1,000 Btu/hr = 0.293 kW
CHIMNEYS AND VENTS Table 8-6
115
Number of Appliances: SingleAppliance Type: Category I
Appliance Vent Connection: Single-Wall Metal ConnectorVent Diameter – D (in.)
3 4 5 6 7Appliance Input Rating in Thousands of Btu per Hour
HeightH(ft)
LateralL(ft)
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
3839NANA
7751NANA
45363331
59607483
151969289
85666360
8585102114
249156152147
14010410299
126123146163
373231225220
204156152148
165159187207
522320313307
284213208203
8 0258
3739NANA
8356NANA
50393733
58597790
16410810295
93756964
8383107122
273176168161
154119114107
123121151175
412261252243
234179171163
161155193223
580363352342
319246235225
10 02510
373952NA
876156NA
53413934
57597697
174117111100
99807668
8282105132
293193185171
165128122112
120119148188
444287277261
254194186171
158153190237
628400388369
344272261241
15 0251015
363851NANA
936963NANA
57474439NA
56577595NA
190136128116NA
11193867972
8080102128158
325225216201186
186149140131124
116115144182220
499337326308290
283224217203192
153148182228272
713473459438418
388314298284269
20 025101520
353750NANANA
967468NANANA
60504741NANA
54567393NANA
200148140129NANA
11899948680NA
7878100125155186
346248239223208192
201165158146136126
114113141177216254
537375363344325306
306248239224210196
149144178222264309
772528514491469448
428344334316301285
30 02510152030
343749NANANANA
998074NANANANA
635652NANANANA
53557291115NANA
211164157144131NANA
12711110698NANANA
767698122151181NA
372281271255239223NA
219183173168157NANA
110109136171208246NA
584429417397377357NA
334279271257242228NA
144139171213255298389
849610595570547524477
472392382367349333305
50 02510152030
333648NANANANA
998480NANANANA
6661NANANANANA
51537089112NANA
213181174160148NANA
133121117NANANANA
737394118145176NA
394318308292275257NA
230205198186174NANA
105104131136199236315
629495482461441420376
361312305292280267NA
138133164203244285373
928712696671646622573
515443435420405389NA
100 0251015203050
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
49516785132NANANA
214192186175162NANANA
NANANANANANANANA
697090113138168231NA
403351342324310295264NA
NANANANANANANANA
10098125153188224301NA
659563551532511487448NA
395373366354343NANANA
131125156191230270355540
991828813789764739685584
555508501486473458NANA
Table 8-6Type B Double-Wall Gas Vent [NFPA 54: Table 13.1(b)]
UNIFORM MECHANICAL CODETable 8-6 continued
116
Number of Appliances: SingleAppliance Type: Category I
Appliance Vent Connection: Single-Wall Metal ConnectorVent Diameter – D (in.)
8 9 10 12Appliance Input Rating in Thousands of Btu per Hour
HeightH(ft)
LateralL(ft)
FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max
6 0246
211201237263
695423416409
369284277271
267251295327
894541533526
469368360352
371347409449
1118673664656
569453443433
537498584638
1639979971962
849648638627
8 0258
206197245280
777482470458
414321311300
258246305344
1002617604591
536417404392
360339418470
1257768754740
658513500486
521486598665
1852112011041080
967743730715
10 02510
202193241296
844531518497
449354344325
253242299363
1093681667643
584456443423
351332409492
1373849834808
718559544520
507475584688
2031124212241194
1057848825788
15 0251015
195187231284334
966631616592568
523413400381367
244232287349404
1259812795768742
681543526501484
336319392470540
15911015997966937
838673657628601
488457562664750
23741491146914331399
1237983963928894
20 025101520
190182224277325374
1053708692666640616
573468457437419400
238227279339393448
1379914896866838810
750611596570549526
326309381457526592
175111461126109210601028
927754734702677651
473443547646730808
263116891665162615871550
13461098107410371005973
30 02510152030
184175215265312360461
1168823806777750723670
647533521501481461426
229219269327379433541
1542106910491017985955895
852698684662638615574
312296366440507570704
1971134613241287125112161147
1056863846821794768720
454424524620702780937
2996199919711927188418411759
1545130812831243120511661101
50 02510152030
176168204253299345442
1292971953923894866809
704613602583562543502
220209257313363415521
1724127312521217118311501086
948811795765736708649
295280347418481544674
2223161515911551151214731399
11891007991963934906848
428401496589668741892
3432242623962347229922512159
1818150914901455142113871318
100 0251015203050
166158194238281325418617
140411521134110410751046988866
765698688672656639NANA
207196240293342391491711
19001532151114771443141013431205
1033933921902884864824NA
273259322389447507631895
24791970194519051865182517471591
1300116811531133111010871041NA
3953714605476186908341138
39123021299029382888283827392547
20421817179617631730169616271489
Table 8-6Type B Double-Wall Gas Vent [NFPA 54: Table 13.1(b)] (continued)
For SI units, 1 in. = 25.4 mm, 1 ft. = 0.305 m, 1 in.2 = 645 mm2, 1,000 Btu/hr = 0.293 kW
CHIMNEYS AND VENTS Table 8-7
117
Number of Appliances: SingleAppliance Type: Category I
Appliance Vent Connection: Type B Double-Wall ConnectorType B Double-Wall Connector Diameter – D (in.)
To be used with chimney areas within the size limits at bottom3 4 5 6 7
Appliance Input Rating in Thousands of Btu per HourHeight
H(ft)
LateralL(ft)
FAN NAT FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max Min Max Max
6 25
NANA
NANA
2825
NANA
NANA
5249
NANA
NANA
8682
NANA
NANA
130117
NANA
NANA
180165
8 258
NANANA
NANANA
292624
NANANA
NANANA
555248
NANANA
NANANA
938883
NANANA
NANANA
145134127
NANANA
NANANA
198183175
10 2510
NANANA
NANANA
312825
NANANA
NANANA
615730
NANANA
NANANA
1039687
NANANA
NANANA
162148139
NANANA
NANANA
221204191
15 251015
NANANANA
NANANANA
353528NA
NANANANA
NANANANA
67625548
NANANANA
NANANANA
1141079789
NANANANA
NANANANA
179164153141
53NANANA
475NANANA
250231216201
20 25101520
NANANANANA
NANANANANA
3836NANANA
NANANANANA
NANANANANA
746860NANA
NANANANANA
NANANANANA
1241161079783
NANANANANA
NANANANANA
201184172159148
5180NANANA
522503NANANA
274254237220206
30 2510152030
NANANANANANA
NANANANANANA
41NANANANANA
NANANANANANA
NANANANANANA
827667NANANA
NANANANANANA
NANANANANANA
13712811510791NA
NANANANANANA
NANANANANANA
216198184171159NA
4775NANANANA
581561NANANANA
303281263243227188
50 2510152030
NANANANANANA
NANANANANANA
NANANANANANA
NANANANANANA
NANANANANANA
92NANANANANA
NANANANANANA
NANANANANANA
161131138127NANA
NANANANANANA
NANANANANANA
251230215199185NA
NANANANANANA
NANANANANANA
351323304282264NA
Minimuminternalarea of
chimney(in.2)
12 19 28 38 50
Maximuminternalarea of
chimney(in.2)
Seven times the listed appliance categorized vent area, flue collar area, or draft hood outlet area.
For SI units, 1 in. = 25.4 mm, 1 ft. = 0.305 m, 1 in.2 = 645 mm2, 1,000 Btu/hr = 0.293 kW
CHIMNEYS AND VENTS Table 8-14 continued
131
Number of Appliances: Two or MoreAppliance Type: Draft Hood-Equipment
Appliance Vent Connection: Direct to Pipe or VentVent Connector Capacity
Total Vent HeightH(ft)
ConnectorRise
R(ft)
Vent Connector Diameter – D (in.)3 4 5 6 7 8
Maximum Appliance Input Rating in Thousands of Btu per Hour6-8 1
23
212834
405361
688698
102124147
146178204
205235275
15 123
233035
445664
7792102
117134155
179194216
240265298
30and up
123
253136
495868
8497107
129145164
190211232
270295321
Common Vent Capacity
Total Vent HeightH(ft)
Common Vent Diameter – D (in.)4 5 6 7 8 10 12
Combined Appliance Input Rating in Thousands ofBtu per Hour
681015203050
4855597180NANA
788995115129147NA
111128136168186215NA
155175190228260300360
205234250305340400490
320365395480550650810
NA5055606907909401190
Table 8-14Single-Wall Metal Pipe or Type B Asbestos Cement Vent [NFPA 54: Table 13.2(e)]
For SI units, 1 in. = 25.4 mm, 1 ft. = 0.305 m, 1 in.2 = 645 mm2, 1,000 Btu/hr = 0.293 kW
UNIFORM MECHANICAL CODETable 8-15
132
Number of Appliances: SingleAppliance Type: NAT
Appliance Vent Connection: Type B Double-Wall ConnectorINTENDED USE: Minimum allowable Input Rating of Space-Heating Appliance in Thousands of Btu per Hour
Vent HeightH (ft)
Internal Area of chimney (in.2)12 19 28 38 50 63 78 113
Local 99% winter design temperature: 37ºF or lower681015203050
000
NANANANA
0000
NANANA
0000
123NANA
0000
190NANA
0000
249NANA
0000
184393NA
00000
334NA
000000
579Local 99% winter design temperature: 27ºF to 36ºF
681015203050
000
NANANANA
0051NANANANA
688297NANANANA
116127141NANANANA
156167183233NANANA
180187201253307419NA
212214225274330445NA
266263265305362485763
Local 99% winter design temperature: 17ºF to 26ºF681015203050
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANANANANANANA
NA197214NANANANA
215226245296352NANA
259264278331387507NA
349352358398457581NA
Local 99% winter design temperature: 5ºF to 16ºF681015203050
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANA289NANANANA
NA312331393450NANA
416423430485547682972
Local 99% winter design temperature: -10ºF to 4ºF681015203050
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANANANANANANA
NANANANANANANA
4844945135866508051003
Local 99% winter design temperature -11ºF or lowerNot recommended for any vent configurations
For SI units, 1 in. = 25.4 mm, 1 in.2 = 645 mm2, 1 ft. = 0.305 m, 1,000 Btu/hr = 0.293 kW, ºC = (ºF - 32)/1.8Note: See Figure G.2.4 for a map showing local 99 percent winter design temperatures in the United States.
CHIMNEYS AND VENTS Table 8-16
133
Number of Appliances: Two or MoreAppliance Type: NAT + NAT
Appliance Vent Connection: Type B Double-Wall ConnectorINTENDED USE: Combined Appliance Maximum Input Rating in Thousands of Btu per Hour
For SI units, 1 in. = 25.4 mm, 1 ft. = 0.305 m, 1 in.2 = 645 mm2, 1,000 Btu/hr = 0.293 kW
UNIFORM MECHANICAL CODETable 8-17
134
Number of Appliances: Two or MoreAppliance Type: NAT + NAT
Appliance Vent Connection: Type B Double-Wall ConnectorINTENDED USE: Minimum Allowable Input Rating of Space-Heating Appliance in Thousands of Btu per Hour
Vent HeightH(ft)
Internal Area of Chimney (in.2)
12 19 28 38 50 63 78 113
Local 99% winter design temperature: 37ºF or greater681015203050100
000NANANANANA
0000NANANANA
0000NANANANA
0000NANANANA
0000NANANANA
0000184393NANA
00000334NANA
NA00000579NA
Local 99% winter design temperature: 27ºF to 36ºF681015203050100
000NANANANANA
0051NANANANANA
6882NANANANANANA
NANANANANANANANA
NANANANANANANANA
180187201253307NANANA
212214225274330445NANA
NA263265305362485763NA
Local 99% winter design temperature: 17ºF to 26ºF681015203050100
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NA264278331387NANANA
NA352358398457581862NA
Local 99% winter design temperature: 5ºF to 16ºF681015203050100
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANANANANANANANA
NANA430485547682NANA
Local 99% winter design temperature: 4ºF or lowerNot recommended for any vent configurations
For SI units, 1 in. = 25.4 mm, 1 in.2 = 645 mm2, 1 ft. = 0.305 m, 1,000 Btu/hr = 0.293 kW, ºC = (ºF - 32)/1.8Note: See Figure G.2.4 for a map showing local 99 percent winter design temperatures in the United States.
CHIMNEYS AND VENTS Table 8-18
135
Number of Appliances: Two or MoreAppliance Type: FAN + NAT
Appliance Vent Connection: Type B Double-Wall ConnectorINTENDED USE: Combined Appliance Maximum Input Rating in Thousands of Btu per Hour
For SI units, 1 in. = 25.4 mm, 1 ft. = 0.305 m, 1 in.2 = 645 mm2, 1,000 Btu/hr = 0.293 kW
UNIFORM MECHANICAL CODETable 8-19
136
Number of Appliances: Two or MoreAppliance Type: FAN + NAT
Appliance Vent Connection: Type B Double-Wall ConnectorINTENDED USE: Minimum Allowable Input Rating of Space-Heating Appliance in Thousands of Btu per Hour
Vent HeightH(ft)
Internal Area of Chimney (in.2)
12 19 28 38 50 63 78 113
Local 99% winter design temperature: 37ºF or greater681015203050100
000NANANANANA
0000NANANANA
0000123NANANA
0000190334NANA
0000249398NANA
0000184393714NA
00000334707NA
0000005791600
Local 99% winter design temperature: 27ºF to 36ºF681015203050100
000NANANANANA
0051111NANANANA
688297142187NANANA
116127141183230330NANA
156167183233284319NANA
180187210253307419672NA
212214225274330445705NA
2662632653053624857631554
Local 99% winter design temperature: 17ºF to 26ºF681015203050100
052NANANANANANA
557490NANANANANA
99111125167212NANANA
141154169212258362NANA
182197214263316429NANA
215226245296352470723NA
259264278331387507766NA
3493523583984575818621669
Local 99% winter design temperature: 5ºF to 16ºF681015203050100
NANANANANANANANA
7894111NANANANANA
121135149193NANANANA
166182198247293377NANA
214230250305360450NANA
252269289346408531797NA
301312331393450580853NA
4164234304855476829721833
Local 99% winter design temperature: -10ºF to 4ºF681015203050100
NANANANANANANANA
NANANANANANANANA
145159175NANANANANA
196213231283333NANANA
249269292351408NANANA
296320339404468603NANA
349371397457528667955NA
4844945135866508051003NA
Local 99% winter design temperature: -11ºF or lowerNot recommended for any vent configurations
For SI units, 1 in. = 25.4 mm, 1 in.2 = 645 mm2, 1 ft. = 0.305 m, 1,000 Btu/hr = 0.293 kW .Note: See Figure G.2.4 for a map showing local 99 percent winter design temperatures in the United States.
