CMC · California Mechanical Code
Gas Vents, Terminations & Multi‑story Venting
This page orients you to the CMC rules for gas‑vent systems, where to find venting, termination, sizing and multistory provisions, and which sections require listed products or engineering.
Last reviewed: July 6, 2026
Overview
This hub covers the California Mechanical Code requirements for venting fuel‑burning gas appliances — including gas vents, rooftop and through‑the‑wall terminations, vent connectors, vent sizing, and rules for multistory common vents. The chapter begins with general venting responsibilities and applicability (see §801.0–§802.0) and then moves into specific gas‑vent provisions at §802.0 et seq.
Key operational rules include permitted venting materials and listed‑component requirements (for example Type B, Type B‑W, Type L, special gas vents and plastic venting where listed) under §802.1 and §802.4; sizing and offset limits under §802.6.2 and the related tables in Chapter 803; and the termination/clearance requirements at §802.6.1 and §802.8. These sections emphasize manufacturer instructions, listed products, and engineering methods where required.
Multistory venting (common vents serving appliances on more than one floor) is treated as a special design condition: §802.6.3 requires engineered design, separation from occupiable space and combustion‑air provisions, and sizing rules tied to available height and aggregate input ratings. Expect to consult the multistory provisions and the sizing tables when a single vertical vent serves appliances on multiple levels.
In this section
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 0.79 High relevance — show source text
Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 802.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers’ instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions. [NFPA 54:12.7.4.3] 802.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods. [NFPA 54:12.7.4.4] 802.6.3 Gas Vents Serving Appliances on More than One Floor. Where a common vent is installed in a multistory installation to vent Category I appliances located on more than one floor level, the venting system shall be designed and installed in accordance with engineering methods.
Crawl spaces, basements, and attics shall be considered as floor levels. [NFPA 54:12.7.5.1] 802.6.3.1 Occupiable Space. All appliances connected to the common vent shall be located in rooms separated from occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation, and dilution air that is not supplied from occupiable space. [NFPA 54:12.7.5.2] (See Figure 802.6.3.1) 802.6.3.2 Multistory Venting System. The size of the connectors and common segments of multistory venting systems for appliances listed for use with a Type B double-wall gas vent shall be in accordance with Table 803.2(1), provided all of the following apply: (1) The available total height ( H ) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection tee. (2) The size of the connector for a segment is determined from the appliance’s gas input rate and available connector rise and shall not be smaller
than the draft hood outlet or flue collar size.
(3) The size of the common vertical vent segment, and of the interconnection tee at the base of that segment, is based on the total appliance’s gas input rate entering that segment and its available total height. [NFPA 54:12.7.5.3]
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FIGURE 802.6.3.1
PLAN VIEW OF PRACTICAL SEPARATION METHOD
FOR MULTISTORY GAS VENTING
[NFPA 54: FIGURE A.12.7.5.2]
802.6.4 Support of Gas Vents. Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.7.6]
CMC § 802.6.2 High relevance — show source text
installation instructions.
802.6.2 Size of Gas Vents. Venting systems shall be sized and constructed in accordance with Section 802.6.2.1 through Section 802.6.2.3 and the appliance manufacturer’s instructions. [NFPA 54:12.7.4] 802.6.2.1 Category I Appliances. The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with a Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following: (1) The provisions of Section 803.0. (2) Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion system and draft hood-equipped appliances, shall be sized in accordance with Section 803.0 or other engineering methods. (3) For sizing an individual gas vent for a single, draft hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet or greater than seven times the draft hood outlet area.
(4) For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.
(5) Engineering methods. [NFPA 54:12.7.4.1]
802.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 802.6.2.1(3) or Section 802.6.2.1(4) shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad) except that a vent system having not more than one 60 degree (1 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 802.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers’ instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, III, and IV appliances shall be in accordance with the appliance manufacturers’ instructions. [NFPA 54:12.7.4.3] 802.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods. [NFPA 54:12.7.4.4] 802.6.3 Gas Vents Serving Appliances on More than One Floor. Where a common vent is installed in a multistory installation to vent Category I appliances located on more than one floor level, the venting system shall be designed and installed in accordance with engineering methods.
Crawl spaces, basements, and attics shall be considered as floor levels. [NFPA 54:12.7.5.1] **802.6.3.1 Occupiable Space.
CMC § 3108.12.1 Medium relevance — show source text
3108.12.1 Installation. Heating or cooking equipment, tanks, piping, hoses, fittings, valves, tubing and other related components shall be installed as specified in the International Fuel Gas Code and the California Mechanical Code, and shall be approved by the fire code official.
3108.12.2 Venting. Gas, liquid and solid fuel-burning equipment designed to be vented shall be vented to the outside air as specified in the International Fuel Gas Code and the California Mechanical Code . Such vents shall be equipped with approved spark arresters where required. Where vents or flues are used, all portions of the tent or membrane structure shall be not less than 12 inches (305 mm) from the flue or vent.
3108.12.3 Location. Cooking and heating equipment shall not be located within 10 feet (3048 mm) of exits or combustible materials.
3108.13 Flammable and combustible liquids. The storage of flammable and combustible liquids and the use of flammable-liquidfueled equipment shall be in accordance with Sections 3108.13.1 through 3108.13.3.
3108.13.1 Use. Flammable-liquid-fueled equipment shall not be used in tents or membrane structures.
3108.13.2 Flammable and combustible liquid storage. Flammable and combustible liquids shall be stored outside in an approved manner not less than 50 feet (15 240 mm) from tents or membrane structures. Storage shall be in accordance with Chapter 57.
[California Code of Regulations, Title 19, Division 1, §324.(a) and (b)] Flammable and Combustible Liquids.
(a) Liquids having a flash point below 200°F shall not be stored in any tent nor less than 50 feet from any tent.
(b) Flammable or combustible liquids shall be stored and dispensed in accordance with the provisions of the California Fire Code. The enforcing authority may permit limited quantities of flammable or combustible liquids required for display and normal merchandising.
3108.13.3 Refueling. Refueling shall be performed in an approved location not less than 20 feet (6096 mm) from tents or membrane structures.
3108.14 Display of motor vehicles. Liquid- and gas-fueled vehicles and equipment used for display within tents or membrane structures shall be in accordance with Sections 3108.14.1 through 3108.14.5.3.
3108.14.1 Batteries. Batteries shall be disconnected except where the fire code official requires that the batteries remain connected to maintain safety features.
3108.14.2 Fuel. Vehicles or equipment shall not be fueled or defueled within the tent or membrane structure.
3108.14.2.1 Quantity limit. Fuel in the fuel tank shall not exceed one-quarter of the tank capacity or 5 gallons (19 L), whichever is less.
3108.14.2.2 Inspection. Fuel systems shall be inspected for leaks.
3108.14.2.3 Closure. Fuel tank openings shall be locked and sealed to prevent the escape of vapors.
3108.14.3 Location. The location of vehicles or equipment shall not obstruct means of egress.
CMC § 12.4.5.2 Medium relevance — show source text
(2) The vent system shall be installed such that no fittings or joints between sections are installed in the above-ceiling space.
(3) The venting system shall be installed in a conduit or enclosure with joints between the interior of the enclosure and the ceiling space sealed. [NFPA 54:12.4.5.2] 802.4 Type of Venting System to be Used. The type of venting system to be used shall be in accordance with Table 802.4. [NFPA 54:12.5.1]
802.4.1 Plastic Piping. Where plastic piping is used to vent an appliance, the appliance shall be listed for use with such venting materials and the appliance manufacturer’s installation instructions shall identify the specific plastic piping material. The plastic pipe venting materials shall be labeled in accordance with the product standards specified by the appliance manufacturer or shall be listed and labeled in accordance with UL 1738. [NFPA 54:12.5.2]
802.4.2 Plastic Vent Joints. Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions. Plastic pipe venting materials listed and labeled in accordance with UL 1738 shall be installed in accordance
with the vent manufacturer’s installation instructions. Where primer is required, it shall be of a contrasting color.
[NFPA 54:12.5.3]
802.4.3 Special Gas Vents. Special gas vents shall be listed and labeled in accordance with UL 1738 and installed in accordance with the special gas vent manufacturer’s installation instructions. [NFPA 54:12.5.4]
802.5 Masonry, Metal, and Factory-Built Chimneys. Chimneys shall be installed in accordance with Section 802.5.1 through Section 802.5.3.
802.5.1 Factory-Built Chimneys. Factory-built chimneys shall be listed in accordance with UL 103, UL 959, or UL 2561. Factory-built chimneys used to vent appliances that operate at positive vent pressure shall be listed for such application. [NFPA 54:12.6.1.1]
802.5.1.1 Decorative Shrouds. Decorative shrouds addressed in Section 802.5.4.3 shall comply with UL 103 for factory-built residential chimneys, UL 127 for factory-built fireplaces, or UL 1482 for solid-fuel room heaters.
802.5.2 Metal Chimneys. Metal chimneys shall be built and installed in accordance with NFPA 211. [NFPA 54:12.6.1.2]
802.5.3 Masonry Chimneys. Masonry chimneys shall be built and installed in accordance with NFPA 211 and lined with one of the following:
(1) Approved clay flue lining.
(2) A chimney lining system listed and labeled in accordance with UL 1777.
(3) Other approved material that resists corrosion, erosion, softening, or cracking from vent gases at temperatures up to 1800°F (982°C).
Exception: Masonry chimney flues lined with a chimney lining system specifically listed for use with listed appliances with draft hoods, Category I appliances, and
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CMC § 802.5.4 Medium relevance — show source text
ROOFTOP TERMINATIONS
Chimneys. . . . . . . . . . . . . . . . . . . . . . . 802.5.4, 802.7.2,
803.1.10, 803.2.20
Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511.1.3.1
Gas vents . . . . . . . . . . . . . . . . . . . . . . 802.6.1, 802.7.2,
803.1.10, 803.2.20
ROOM HEATERS . . . . . . . . . . . . . . . . . . . . . . . 220.0, 915.0
ROOM
Boiler . . . . . . . . . . . . . . . . . 204.0, 303.2, 1001.2, 1001.4
Equipment . . . . . . . . . . . . . . . . . . . . . . . . 303.2, 305.1.3
HPM storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210.0
Machinery . . . . . . . . . . . . 1106.0, 1107.0, 1108.0, 1115.3
Used for ventilation . . . . . . . . . . . . . . . . . . . . . 402.2.1.6
RUPTURE MEMBERS . . . . . . . . . . . . . . . 220.0, 1112.10.1,
1112.13, 1113.3, 1115.4.1
– S –
SAFE TEMPERATURES
Alternate Source of Power . . . . . . . . . . . . . . . . . . 325.0
SCOPE AND ADMINISTRATION . . . . . . . . . . . . . Chapter 1
SEDIMENT TRAPS . . . . . . . . . . . . . . . . . . 1310.9.2, 1312.9
SEEPAGE PAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906.10
SELF-CONTAINED . . . . . . . . . . . . . . . . . . . . . 221.0, 517.1.2
SENSITIVE AREAS OR ROOMS [OSHPD] . . . . . . . . . 322.0
SHAFT
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.0
Fuel gas piping. . . . . . . . . . . . . . . . . . . . . . . . . 1310.3.4
Refrigeration systems . . . . . . . . . . . . . . 305.4, 1109.4.1
CMC § 802.2.3 Medium relevance — show source text
802.2.3 Adjacent Room or Space. Where the calculation includes the volume of an adjacent room or space, the room or space in which the appliances are installed shall be directly connected to the adjacent room or space by a doorway, archway, or other opening of comparable size that cannot be closed. [NFPA 54:12.3.2.2]
802.2.4 Ventilating Hoods. The use of ventilating hoods and exhaust systems to vent appliances shall be limited to industrial appliances and appliances installed in commercial applications. [NFPA 54:12.3.3]
802.2.5 Well-Ventilated Spaces. The flue gases from industrial-type appliances shall not be required to be vented to the outdoors where such gases are discharged into a large and well-ventilated industrial space. [NFPA 54:12.3.4]
802.2.6 Direct Vent Appliances. Listed direct vent appliances shall be installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.3.5.1]
802.2.6.1 Through-the-Wall Vent Terminations. Through-the-wall vent terminations for listed direct vent appliances shall be in accordance with Section 802.8.1. [NFPA 54:12.3.5.2]
802.2.7 Appliances with Integral Vents. Appliances incorporating integral venting means shall be installed in accordance with Section 802.8.1. [NFPA 54:12.3.6]
802.2.8 Incinerators, Commercial–Industrial. Incinerators shall be vented in accordance with NFPA 82.
[NFPA 54:12.3.7]
802.3 Minimum Safe Performance. Venting systems shall be designed and constructed to convey all flue and vent gases to the outdoors. [NFPA 54:12.1]
802.3.1 Appliance Draft Requirements. A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer’s instructions. [NFPA 54:12.4.1]
802.3.2 Appliance Venting Requirements. Appliances required to be vented shall be connected to a vent
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CHIMNEYS AND VENTS
ing system designed and installed in accordance with the provisions of Section 802.4 through Section 802.15.
[NFPA 54:12.4.2]
802.3.3 Mechanical Draft Systems. Mechanical draft systems shall be listed in accordance with UL 378 and installed in accordance with both the appliance and the mechanical draft system manufacturer’s installation instructions. [NFPA 54:12.4.3.1]
802.3.3.1 Venting. Appliances requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design. [NFPA 54:12.4.3.2]
802.3.3.2 Leakage. Forced draft systems and all portions of induced draft systems under positive pressure during operation shall be designed and installed so as to prevent leakage of flue or vent gases into a building. [NFPA 54:12.4.3.3]
CMC § 1.11.0. Medium relevance — show source text
Adopting Agency BSC BSC-
CGSFM HCD Col6 Col7 DSA Col9 Col10 OSHPD Col12 Col13 Col14 Col15 Col16 Col17 BSCC DPH AGR DWR CEC CA SL SLC Adopting Agency BSC BSC-
CGSFM 1 2 1-AC AC ** SS** ** SS/CC** 1 1R 2 3 4 5 6 6 6 6 6 6 6 6 6 Adopt Entire Chapter X X X X X X X X X X X X Adopt Entire Chapter as
amended (amended sections
listed below)Adopt only those sections
that are listed belowChapter/Section This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
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CHAPTER 8
CHIMNEYS AND VENTS
801.0 General.
801.1 Applicability. The requirements of this chapter shall govern the venting of fuel-burning appliances.
801.2 Venting of Gas Appliances. Low-heat and medium-heat gas appliances shall be vented in accordance with this chapter. Other gas appliances shall be vented in accordance with NFPA 211 or other applicable standards.
801.3 Appliances Fueled by Other Fuels. Appliances 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 Listing. Type B and Type B-W gas vents shall comply with UL 441, Type L gas vents shall comply with UL 641.
802.1.1 Installation. Listed chimneys and vents shall be installed in accordance with this chapter and the manufacturer’s installation instructions. [NFPA 54:12.2.1]
CMC § 701.4 Medium relevance — show source text
701.4 Indoor Combustion Air . . . . . . . . . 147
701.5 Indoor Opening Size and Location . . . . . . . . . . . . . . . . . . . . 147
701.6 Outdoor Combustion Air . . . . . . . . 147
701.7 Combination Indoor and Outdoor
Combustion Air . . . . . . . . . . . . . . . 148
701.8 Engineered Installations . . . . . . . . 149
701.9 Mechanical Combustion Air
Supply. . . . . . . . . . . . . . . . . . . . . . 149
701.10 Louvers, Grilles, and Screens . . . 149
701.11 Combustion Air Ducts. . . . . . . . . . 150
701.12 Dampers Prohibited . . . . . . . . . . . 150
702.0 Extra Device or Attachment . . . . . 150
702.1 General. . . . . . . . . . . . . . . . . . . . . 150
CHAPTER 8 CHIMNEYS AND VENTS. . . . . . . 151
801.0 General. . . . . . . . . . . . . . . . . . . . . 153
801.1 Applicability. . . . . . . . . . . . . . . . . . 153
801.2 Venting of Gas Appliances . . . . . . 153
801.3 Appliances Fueled by Other Fuels. 153
802.0 Venting of Appliances. . . . . . . . . . 153
xxxiv
802.1 Listing . . . . . . . . . . . . . . . . . . . . . . 153
802.2 Connection to Venting Systems . . 153
802.3 Minimum Safe Performance . . . . . 153
802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 154
802.5 Masonry, Metal, and Factory-Built Chimneys . . . . . . . . . . . . . . . . . . . 154
Table 802.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . . . . 155
802.6 Gas Vents. . . . . . . . . . . . . . . . . . . 157
Table 802.6.1 Roof Slope Heights. . . . . . . . . . . . 158
802.7 Single-Wall Metal Pipe . . . . . . . . . 159
Table 802.7.3.3 Clearance for Connectors. . . . . . . 160
802.8 Through-the-Wall Vent Termination . . . . . . . . . . . . . . . . . . 160
802.9 Condensation Drain . . . . . . . . . . . 160
802.10 Vent Connectors for Category I Appliances . . . . . . . . . . . . . . . . . . 160
Table 802.10.1.3 Minimum Thickness for Galvanized
Steel Vent Connectors for Low Heat Appliances . . . . . . . . . . . . . . 161
CMC § 12.6.5.3 Medium relevance — show source text
The chimney flue shall be sized to properly vent the appliance.
[NFPA 54:12.6.5.3] 802.5.8.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4]
802.5.9 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6]
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802.5.10 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7] 802.5.11 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.
Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 802.5.11.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal or factory-built chimney flue shall not be used to supply combustion air.
Exception: Direct vent appliances designed for installation in a solid-fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.8.2] 802.6 Gas Vents. The installation of gas vents shall meet the following requirements:
(1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
(2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is
connected.
(3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”
(4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.
[NFPA 54:12.7.2] 802.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:
(1) A gas vent shall terminate in accordance with one of the following:
CMC § 1.0 Medium relevance — show source text
ROOF SLOPE H (minimum) (feet)
Flat to6⁄121.0
Over6⁄12 to7⁄121.25
Over7⁄12 to8⁄121.5
Over8⁄12 to9⁄122.0
Over9⁄12 to10⁄122.5
Over10⁄12 to11⁄123.25 Over11⁄12 to12⁄12 4.0
Over12⁄12 to14⁄125.0
Over14⁄12 to16⁄126.0
Over16⁄12 to18⁄127.0
Over18⁄12 to20⁄127.5
Over20⁄12 to21⁄128.0 For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm
802.6.1.1 Insulation Protection Shield. Where a vent passes through an insulated assembly, an approved metal shield constructed of steel having a thickness of not less than 0.0179 inch (0.45 mm) (26 gauge) shall be installed between the vent and insulation. The shield shall extend not less than 2 inches (51 mm) above the insulation and be secured to the structure in accordance with the manufacturer’s
installation instructions.
802.6.2 Size of Gas Vents. Venting systems shall be sized and constructed in accordance with Section 802.6.2.1 through Section 802.6.2.3 and the appliance manufacturer’s instructions. [NFPA 54:12.7.4] 802.6.2.1 Category I Appliances. The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with a Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following: (1) The provisions of Section 803.0. (2) Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion system and draft hood-equipped appliances, shall be sized in accordance with Section 803.0 or other engineering methods. (3) For sizing an individual gas vent for a single, draft hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet or greater than seven times the draft hood outlet area.
(4) For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.
(5) Engineering methods. [NFPA 54:12.7.4.1]
**802.6.2.2 Vent Offsets.
CMC § 509.2.1 Medium relevance — show source text
** Where any or all of the appliances in Section 509.2.1(1) and Section 509.2.1(2) are installed so the aggregate input rating exceeds 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 conveying the vent gases to the outdoors so that the aggregate input rating of the remaining unvented appliances does not exceed 20 (Btu/h)/ft [3] (207 W/m [3] ). [NFPA 54:12.3.2.1] 509.2.3 Adjacent Room or Space. Where the calculation includes the volume of an adjacent room or space, the room or space in which the appliances are installed shall be directly connected to the adjacent room or space by a doorway, archway, or other opening of comparable size that cannot be closed. [NFPA 54:12.3.2.2]
509.2.4 Ventilating Hoods. The use of ventilating hoods and exhaust systems to vent appliances shall be limited to industrial appliances and appliances installed in commercial applications. [NFPA 54:12.3.3] 509.2.5 Well-Ventilated Spaces. The flue gases from industrial-type appliances shall not be required to be vented to the outdoors where such gases are discharged into a large and well-ventilated industrial space. [NFPA 54:12.3.4]
509.2.6 Direct-Vent Appliances. Listed direct vent appliances shall be installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.3.5.1]
509.2.6.1 Through-the-Wall Vent Termination. Through-the-wall vent terminations for listed directvent appliances shall be in accordance with Section 509.8.1. [NFPA 54:12.3.5.2]
509.2.7 Appliances with Integral Vents. Appliances incorporating integral venting means shall be installed in accordance with Section 509.8. [NFPA 54:12.3.6] 509.3 Minimum Safe Performance. Venting systems shall be designed and constructed to convey all flue and vent gases to the outdoors. [NFPA 54:12.1] 509.3.1 Appliance Draft Requirements. A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer’s instructions.
[NFPA 54:12.4.1]
509.3.2 Appliance Venting Requirements. Appliances required to be vented shall be connected to a venting system designed and installed in accordance with the provisions of Section 509.4 through Section 509.15.
[NFPA 54:12.4.2] 509.3.3 Mechanical Draft Systems. Mechanical draft systems shall be listed in accordance with UL 378 and installed in accordance with both the appliance and the mechanical draft system manufacturer’s installation instructions. [NFPA 54:12.4.3.1]
2025 CALIFORNIA PLUMBING CODE 91
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WATER HEATERS
CMC § 1.11.0. Medium relevance — show source text
This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
2025 CALIFORNIA MECHANICAL CODE 151
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CHAPTER 8
CHIMNEYS AND VENTS
801.0 General.
801.1 Applicability. The requirements of this chapter shall govern the venting of fuel-burning appliances.
801.2 Venting of Gas Appliances. Low-heat and medium-heat gas appliances shall be vented in accordance with this chapter. Other gas appliances shall be vented in accordance with NFPA 211 or other applicable standards.
801.3 Appliances Fueled by Other Fuels. Appliances 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 Listing. Type B and Type B-W gas vents shall comply with UL 441, Type L gas vents shall comply with UL 641.
802.1.1 Installation. Listed chimneys and vents shall be installed in accordance with this chapter and the manufacturer’s installation instructions. [NFPA 54:12.2.1]
802.1.2 Prohibited Discharge. Appliance vents shall not discharge into a space enclosed by screens having openings less than [1] ⁄ 4 of an inch (6.4 mm) mesh.
802.2 Connection to Venting Systems. Except as permitted in Section 802.2.1 through Section 802.2.7, all appliances shall be connected to venting systems. [NFPA 54:12.3.1]
802.2.1 Appliances Not Required to be Vented. The following appliances shall not be required to be vented:
(1) Listed ranges.
(2) Built-in domestic cooking units listed and marked for optional venting.
(3) Listed hot plates.
(4) Listed Type 1 clothes dryers exhausted in accordance with Section 504.4.
(5) A single listed booster-type (automatic instantaneous) water heater, when designed and used solely for the sanitizing rinse requirements of a dishwashing machine, provided that the appliance is installed with the draft hood in place and unaltered, if a draft hood is required, in a commercial kitchen having a mechanical exhaust system. [Where installed in this manner, the draft hood outlet shall not be less than 36 inches (914 mm) vertically and 6 inches (152 mm) horizontally from any surface other than the appliance.]
(6) Listed refrigerators.
(7) Counter appliances.
(8) Room heaters listed for unvented use.
(9) Direct gas-fired makeup-air heaters.
(10)Other appliances listed for unvented use and not provided with flue collars.
(11)Specialized appliances of limited input such as laboratory burners or gas lights. [NFPA 54:12.3.2]
Frequently asked questions
When must a multistory common vent be engineered?
Any common vent serving Category I appliances on more than one floor must be designed and installed using engineering methods; §802.6.3 requires engineered design, separation from occupiable space, and combustion‑air provisions for each connected room.
Where are vent termination and rooftop clearance rules found?
Gas vent termination and rooftop clearance requirements are in §802.6.1 (vent termination details, insulation shields, etc.), and related rooftop termination guidance appears throughout Chapter 8 and the referenced termination tables. Consult §802.6.1 and the roof‑slope/height tables when locating terminations.
Can I use plastic piping for gas vents?
Plastic venting is permitted only where the appliance is listed for use with the specific plastic material and installed per the appliance and vent listing (see §802.4.1–§802.4.2 and UL 1738 requirements). Always follow the appliance manufacturer’s instructions.
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