CMC · California Mechanical Code

What types of venting systems are permitted for fuel-burning appliances?

Q: Can a Category III appliance use a Type B vent?

No. Category III appliances (positive vent pressure) are not covered by the default Table 802.4 vent types — their vent material and sizing must be provided by the appliance manufacturer and the appliance listing per § 802.4.1 .

Q: Is plastic vent pipe ever allowed?

Yes — but only if the appliance is listed for plastic venting and the manufacturer identifies the specific plastic material ; plastic vent materials must be labeled and installed per § 802.4.1 (UL 1738 where applicable).

Q: Do vents have to be listed?

Yes. Vents and chimneys used must be listed and installed per the manufacturer’s instructions and the chapter; see § 802.1 .

Q: Where do I find the matrix that tells me which vent to use?

See Table 802.4 and § 802.4 — Table 802.4 maps appliance categories/listings to permitted vent types and points you to the detailed sections (e.g., § 802.5, § 802.6, § 802.7).

Homeowner summary: The California Mechanical Code requires you to use the vent type that matches your appliance’s category and listing — check **Table 802.4** and the appliance manufacturer’s instructions. Vents must be listed and installed per the Code; special rules apply if your appliance uses plastic or positive‑pressure venting.

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

In plain terms: the California Mechanical Code requires that the type of venting system used for a fuel‑burning appliance be chosen according to the appliance category and listing. See § 802.4 (which directs you to Table 802.4) for the permitted vent types and the specific code locations for each vent type.

The single most important rule: pick the vent type that matches the appliance listing/category — do not invent a vent type; follow § 802.4 and the appliance manufacturer’s instructions.

Requirements in detail

High-level rule

Per § 802.4, "The type of venting system to be used shall be in accordance with Table 802.4."
Also note the listing requirement: Type B and Type B‑W gas vents must be listed to the applicable UL standard per § 802.1 (e.g., UL 441 for Type B).

Key defined terms (first mention is bolded)

Type B gas vent — a listed double‑wall gas vent for Category I appliances (see § 802.1 and Table).
Chimney — masonry, metal, or factory-built chimneys permitted for listed appliances (see Table 802.4 and § 802.5).
Single‑wall metal pipe — allowed for certain Category I appliances (Table 802.4).
Special gas vent / Plastic piping — permitted only where the appliance is listed for that vent material; plastic venting must be labeled/installed per § 802.4.1 and UL 1738 where applicable.

Decision table — appliance → permitted vent types

Appliance (decision factor)	Permitted venting system(s)	Code reference
Listed Category I appliances or appliances with a draft hood or listed for Type B	Type B gas vent	§ 802.4 / Table 802.4
Same group (above)	Chimney (masonry, metal, factory-built)	§ 802.4, § 802.5 / Table 802.4
Same group (above)	Single‑wall metal pipe (vent connector / certain venting configs)	§ 802.4, § 802.7 / Table 802.4
Same group (above)	Listed chimney lining system for gas venting	§ 802.4, § 802.5.3 / Table 802.4
Same group (above)	Special gas vent listed for the appliances	§ 802.4, § 802.4.3 / Table 802.4
Listed vented wall furnaces	Type B‑W gas vent	Table 802.4; see § 802.6 and § 907.0
Category II, III, IV appliances	As specified or furnished by the appliance manufacturer (follow appliance listing/instructions)	§ 802.4.1 and Table 802.4
Appliances convertible to solid fuel, unlisted combination appliances, or appliances listed for chimneys only	Chimney required	Table 802.4 / § 802.5
Direct‑vent appliances	Use appliance‑integral vent arrangement as allowed by § 802.2.6 (not table‑specified)	§ 802.2.6 (Table 802.4 notes)

(Above table is a distilled mapping of Table 802.4 — see the Code table for the complete matrix.)

Material and listing requirements

All chimneys and vents used must be listed and installed per manufacturer instructions and the chapter: see § 802.1 (listing) and § 802.1.1 (installation).
Plastic vent piping: where plastic is used, the appliance must be listed for plastic venting and the appliance manufacturer must identify the specific plastic material; plastic vent materials should be labeled per UL 1738 where applicable (§ 802.4.1).
Special gas vents must be listed to UL 1738 and installed per the vent manufacturer’s instructions (§ 802.4.3).

Exceptions & special cases

Category II / III / IV appliances: The Code does not prescribe a default vent type — sizing and vent material are governed by the appliance manufacturer’s instructions and listing; see § 802.4.1 and Table 802.4.
Appliances convertible to solid fuel or unlisted appliances: these are restricted to chimney venting only (Table 802.4).
Direct‑vent and integral‑vent appliances: direct‑vent appliances and appliances with integral vents are handled separately (see the connection/installation sections referenced in Table 802.4 and § 802.2).
Above‑ceiling / plenum penetrations: vent systems passing through ceiling plenums or above‑ceiling air spaces must meet special sealing/listing requirements (see related sections for positive‑pressure venting and sealed joints — § 802.3.6 / related NFPA references).

Common mistakes

Assuming any gas appliance can use any vent material. The Code requires that vent material match the appliance listing and Table 802.4 — Category II/III/IV appliances must follow manufacturer instructions (see § 802.4.1).
Installing unlisted vents or skipping manufacturer instructions. § 802.1 requires listed vents and installation per manufacturer instructions.
Using plastic venting without verifying the appliance is listed for plastic or without using materials labeled per UL 1738 (§ 802.4.1).
Connecting natural‑draft Category I vent connectors into a positive‑pressure mechanical draft system — prohibited by the connector rules (see vent connector pressure rules in Chapter 802).

Worked example — concrete scenario

Scenario: You are installing a new, listed Category I storage water heater that has a 4‑inch draft hood outlet. You plan a Type B double‑wall gas vent that is vertical and 10 ft tall (from draft‑hood outlet to vent termination).

Step-by-step:

Table authority: Table 802.4 allows Type B gas vent for listed Category I appliances — so Type B is an allowed vent type for this appliance per § 802.4 / Table 802.4.
Listing: ensure the chosen Type B vent is listed and installed per the vent manufacturer and § 802.1 (listing/installation).
Sizing: For a single draft‑hood appliance the Code permits sizing methods in § 802.6.2.1 — one acceptable rule is that the effective area of the vent connector and gas vent shall be not less than the area of the appliance draft hood outlet or greater than seven times that area. A 4‑inch collar has an equivalent area (see sizing tables in Chapter 803 / F appendices) and a 10‑ft vertical vent meets the total vent height ≥ 10 ft criterion used in vent‑downsizing rules. Follow the sizing tables in Chapter 803 or the manufacturer instructions to pick the Type B vent diameter that equals or exceeds the draft‑hood area. See § 802.6.2.1 and the sizing chapter § 803.0 for the tables and methods.

Bottom line: If the Type B vent selected is listed, sized per § 803.0 / § 802.6.2.1 so its effective area ≥ appliance draft hood area, and installed per the manufacturer and § 802.1, the installation complies with the CMC.

Related provisions

§ 802.1 — Listing and basic listing/installation requirements for vents.
§ 802.4.1 — Requirements when plastic piping is used; appliance must be listed and plastic must be identified/labeled (UL 1738).
§ 802.4.3 — Special gas vents (UL 1738) and their installation.
§ 802.5 — Masonry, metal, and factory‑built chimney requirements (when chimney is the required vent).
§ 802.6 — Gas vent sizing and installation (Type B, Type L, and related rules).
§ 803.0 — Sizing of Category I venting systems (tables and methods referenced by § 802.6).

Code references

Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:

CMC § 1.11.0. High 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.

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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]
CMC § 803.0. High relevance — show source text
(1) Those listed in Section 803.0.

(2) The effective areas of the vent connector and chimney flue of a venting system serving a single appliance with a draft hood shall be not less than the area

of the appliance flue collar or draft hood outlet or greater than seven times the draft hood outlet area.

(3) The effective area of the chimney flue of a venting system serving two appliances with draft hoods 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.

(4) Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods.

(5) Other engineering methods. [NFPA 54:12.6.3.1]

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CHIMNEYS AND VENTS

FIGURE 802.5.4

TYPICAL TERMINATION LOCATIONS FOR

CHIMNEYS AND SINGLE-WALL METAL PIPES SERVING

RESIDENTIAL-TYPE AND LOW-HEAT APPLIANCE

[NFPA 54: FIGURE A.12.6.2.1]

802.5.6 Inspection of Chimneys or Vents. This inspection shall be made after chimneys, vents, or parts thereof, authorized by the permit, have been installed and before such vent or part thereof has been covered or concealed.

802.5.7 Inspection of Chimneys. Before replacing an existing appliance or connecting a vent connector to a chimney, the chimney passageway shall be examined to ascertain that it is clear and free of obstructions and shall be cleaned if previously used for venting solid- or liquid-fuel-burning appliances or fireplaces. [NFPA 54:12.6.4.1] 802.5.7.1 Standard. Chimneys shall be lined in accordance with NFPA 211. [NFPA 54:12.6.4.2]

802.5.7.2 Cleanouts. Cleanouts shall be examined and where they do not remain tightly closed when not in use, they shall be repaired or replaced. [NFPA 54:12.6.4.3] 802.5.7.3 Existing Chimney. When inspection reveals that an existing chimney is not safe for the intended application, it shall be repaired, rebuilt, lined, relined, or replaced with a vent or chimney to conform to NFPA 211 and shall be suitable for the appliances to be attached. [NFPA 54:12.6.4.4] 802.5.8 Chimney Serving Appliances Burning Other Fuels. An appliance shall not be connected to a chimney flue serving a separate appliance designed to burn solid fuel. [NFPA 54:12.6.5.1] 802.5.8.1 Gas and Liquid Fuel-Burning Appliances. Where one chimney serves gas appliances and liquid fuel-burning appliances, the appliances shall be connected through separate openings or connected through a single opening where joined by a suitable fitting located as close as practical to the chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels.
CMC § 2025 High relevance — show source text
Systems that carry nonabrasive exhaust, such as smoke, moderate abrasives such as sawdust, and high abrasives such as manganese or acid vapors use product-conveying ducts. Part II provides the minimum fire safety requirements related to the design, installation, inspection, and maintenance of grease-type operations, such as cooking, for both fuel-gas and solid fuel. Cooking produces a significant amount of smoke, fumes, vapors, heat, and other pollutants. Therefore, acceptable kitchen ventilation is necessary to prevent fires from the build-up of grease and to provide the occupants protection from smoke, unpleasant odors, pollutants, and dangerous gases. There are two types of exhaust hoods (Type I and Type II) used in commercial kitchen applications.

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FORMAT OF THE UNIFORM MECHANICAL CODE

Type I hoods are intended to be installed above equipment or appliances that generate grease or smoke. Type II hoods are intended to be installed above equipment or appliances that generate steam, vapor, heat, or odors and do not generate grease or smoke.

Chapter 6 Duct Systems. Chapter 6 regulates requirements for ducts and plenums that are portions of a heating, cooling, ventilation, or exhaust system. This chapter contains material and installation requirements for metal, gypsum, factory-made, flexible, and plastic ducts. It also contains provisions for duct insulation, dampers, fire protection, and automatic shutoff for the building’s air distribution system. It is worth noting that exhaust ducts are regulated by Chapter 5, and combustion air ducts are regulated by Chapter 7.

Chapter 7 Combustion Air. Chapter 7 regulates combustion air requirements for ventilation and dilution of flue gases for appliances installed in buildings. Fuel-gas appliances not regulated by chapter include direct vent appliances and Type I clothes dryers. Makeup air requirements for Type I clothes dryers are located in Chapter 5. Chapter 7 provides acceptable methods for supplying satisfactory combustion air to ensure proper combustion. Combustion air can be supplied by using indoor combustion air or by introducing the air from the outdoors.

Combustion is the rapid oxidation of fuel to release energy. The oxygen required to release the energy from the fuel normally comes from the air. Incomplete combustion of fuel occurs when inadequate oxygen is provided to the appliance. Combustion is needed to provide ventilation cooling for the casing and internal controls. When a lack of oxygen occurs, some of the carbon is not oxidized, and carbon monoxide forms.

Chapter 8 Chimneys and Vents. Chapter 8 regulates the installation, design, and construction of venting systems for fuel-burning appliances. The provisions addressed within this chapter follow procedures an installer would use to design or evaluate a venting system. Many requirements apply to the design and construction of venting systems, chimneys, installation of gas vents, and the sizing of venting system for a Category I appliance. Sizing venting systems require rigorous engineering calculations. However, the venting sizing requirements and sizing tables in this chapter already perform the calculations for the benefit of the end user.

Combustion appliances produce products of incomplete combustion, including potentially harmful carbon monoxide (CO). It is desirable to vent these products to the outdoors. Although the gas is clean-burning fuel, the products of combustion must not be allowed to collect within a building.
CMC § 9.2.2 High relevance — show source text
** Appliances and their vent connectors shall be installed with clearances from combustible material so their operation does not create a hazard to persons or property. Minimum clearances between combustible walls and the back and sides of various conventional types of appliances and their vent connectors are specified in Chapter 8 and Chapter 9, or NFPA 211.

[NFPA 54:9.2.2] Where not provided in this code, listed and unlisted equipment or appliances shall be installed to maintain the required clearances for servicing and to combustible construction in accordance with the listing and the manufacturer’s installation instructions.

303.10.1 Clearance Reduction. Reduced clearances to combustible construction for listed equipment and appliances shall comply with the listing and Table 303.10.1. Where permitted by the manufacturer, and not provided in this code, reduced clearances to combustible construction for unlisted equipment and appliances shall comply with Table 303.10.1. 303.10.1.1 Type I Hood Exhaust System. Reduced clearances for Type I exhaust systems shall be in accordance with Section 507.4.2 through Section 507.4.2.3. Clearances from the duct or the

exhaust fan to the interior surface of enclosures of

combustible construction shall be in accordance with

Section 510.7.3 and clearances shall not be reduced.

303.10.1.2 Product Conveying Ducts. Reduced clearances to combustibles construction for product conveying ducts shall be in accordance with Section 506.10.3 through Section 506.11.6.3.

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GENERAL REGULATIONS

»

303.10.1.3 Solid-Fuel-Burning Appliances. For solid-fuel-burning appliances, the clearance shall not be less than 12 inches (305 mm) to combustible walls and not less than 18 inches (457 mm) to combustible ceilings. The clearance, after reduction, shall be permitted to be less than 12 inches (305 mm) to combustible walls and less than 18 inches (457 mm) to combustible ceilings. Solid-fuel-burning appliances listed for lesser clearances shall be permitted to be installed in accordance with the manufacturer’s instructions and their listing. 303.11 Installation in Commercial Garages. Appliances installed in commercial garages shall be in accordance with Section 303.11.1 through Section 303.11.2. 303.11.1 Parking Structures. Appliances installed in enclosed, basement, and underground parking structures shall be installed in accordance with NFPA 88A. [NFPA 54:9.1.11.1] 303.11.2 Repair Garages. Appliances installed in repair garages shall be installed in accordance with NFPA 30A. [NFPA 54:9.1.11.2]

303.12 Installation in Aircraft Hangars. Heaters in aircraft hangars shall be installed in accordance with NFPA 409.

[NFPA 54:9.1.12]
CMC § 8-901.5 High relevance — show source text
8-901.5 Energy conservation. Qualified historical buildings or properties covered by this part are exempted from compliance with energy conservation standards. When new nonhistorical lighting and space conditioning system components, devices, appliances and equipment are installed, they shall comply with the requirements of Title 24, Part 6, The California Energy Code, except where the historical significance or character-defining features are threatened.

SECTION 8-902 — MECHANICAL

8-902.1 General. Mechanical systems shall comply with the regular code unless otherwise modified by this chapter.

8-902.1.1 The provisions of the CHBC shall apply to the acceptance, location, installation, alteration, repair, relocation, replacement or addition of any heating, ventilating, air conditioning, domestic incinerators, kilns or miscellaneous heat-producing appliances or equipment within or attached to a historical building.

8-902.1.2 Existing systems which do not, in the opinion of the enforcing agency, constitute a safety hazard may remain in use.

8-902.1.3 The enforcing agency may approve any alternative to the CHBC which would achieve equivalent life safety.

8-902.2 Heating facilities. All dwelling-type occupancies covered under this chapter shall be provided with heating facilities. Woodburning or pellet stoves or fireplaces may be acceptable as heating facilities.

8-902.3 Fuel oil piping and tanks. Fuel oil piping and tanks shall comply with regular code requirements except that the enforcing agency may waive such requirements where the lack of compliance does not create a safety or environmental hazard.

8-902.4 Heat-producing and cooling equipment. Heat-producing and cooling equipment shall comply with the regular code requirements governing equipment safety, except that the enforcing agency may accept alternatives which do not create a safety hazard.

8-902.5 Combustion air.

8-902.5.1 All fuel-burning appliances and equipment shall be provided a sufficient supply of air for proper fuel combustion, ventilation and draft hood dilution.

8-902.5.2 The enforcing agency may require operational tests for combustion air systems which do not comply with applicable requirements of the regular code.

8-902.6 Venting of appliances.

8-902.6.1 Every appliance required to be vented shall be connected to an approved venting system. Venting systems shall develop a positive flow adequate to convey all combustion products to the outside atmosphere.

8-902.6.2 Masonry chimneys in structurally sound condition may remain in use for all fuel-burning appliances, provided the flue is evaluated and documentation provided that the masonry and grout are in good condition. Terra cotta chimneys and Type C metallic vents installed in concealed spaces shall not remain in use unless otherwise mitigated and approved on a case-by-case basis.

8-902.6.3 The enforcing agency may require operational tests for venting systems which do not comply with applicable requirements of the regular code.

8-902.7 Ducts.

8-902.7.1 New ducts shall be constructed and installed in accordance with applicable requirements of the regular code.

8-902.7.2 Existing duct systems which do not comply with applicable requirements of the regular code and do not, in the opinion of the enforcing agency, constitute a safety or health hazard may remain in use.

8-902.8 Ventilating systems.

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CMC § 8-902.5 High relevance — show source text
8-902.5 Combustion air.

8-902.5.1 All fuel-burning appliances and equipment shall be provided a sufficient supply of air for proper fuel combustion, ventilation and draft hood dilution.

8-902.5.2 The enforcing agency may require operational tests for combustion air systems which do not comply with applicable requirements of the regular code.

8-902.6 Venting of appliances.

8-902.6.1 Every appliance required to be vented shall be connected to an approved venting system. Venting systems shall develop a positive flow adequate to convey all combustion products to the outside atmosphere.

8-902.6.2 Masonry chimneys in structurally sound condition may remain in use for all fuel-burning appliances, provided the flue is evaluated and documentation provided that the masonry and grout are in good condition. Terra cotta chimneys and Type C metallic vents installed in concealed spaces shall not remain in use unless otherwise mitigated and approved on a case-by-case basis.

8-902.6.3 The enforcing agency may require operational tests for venting systems which do not comply with applicable requirements of the regular code.

8-902.7 Ducts.

8-902.7.1 New ducts shall be constructed and installed in accordance with applicable requirements of the regular code.

8-902.7.2 Existing duct systems which do not comply with applicable requirements of the regular code and do not, in the opinion of the enforcing agency, constitute a safety or health hazard may remain in use.

8-902.8 Ventilating systems.

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MECHANICAL, PLUMBING AND ELECTRICAL REQUIREMENTS

8-902.8.1 Ventilating systems shall be installed so that no safety hazard is created.

8-902.8.2 Grease hoods and grease hood exhaust systems shall be furnished and installed in accordance with applicable requirements of the regular code. Existing systems which are altered shall comply with the regular code.

8-902.9 Miscellaneous equipment requirements.

8-902.9.1 The following appliances and equipment shall be installed so that no safety hazard is created: warm air furnaces, space heating equipment, vented decorative appliances, floor furnaces, vented wall furnaces, unit heaters, room heaters, absorption units, refrigeration equipment, duct furnaces, infrared radiant heaters, domestic incinerators, miscellaneous heat-producing appliances and water heaters.

8-902.9.2 Storage-type water heaters shall be equipped with a temperature- and pressure-relief valve in accordance with applicable requirements of the regular code.

SECTION 8-903 — PLUMBING

8-903.1 General. Plumbing systems shall comply with the regular code unless otherwise noted.

8-903.1.1 The provisions of the CHBC shall apply to the acceptance, location, installation, alteration, repair, relocation, replacement or addition of any plumbing system or equipment within or attached to a historical building.

8-903.1.2 Existing systems which do not, in the opinion of the enforcing agency, constitute a safety hazard may remain in use.

8-903.1.3 The enforcing agency may approve any alternative to these regulations which achieves reasonably equivalent life safety.

8-903.2 Residential occupancies.
CMC § 503.4.6.4 High relevance — show source text
Stair and shaft vents . . . . . . . . . . . . . . . . . . E 503.4.6.4

SHAFT ENCLOSURE

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.0

SHUTOFF

Automatic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609.0

Fuel. . . . . . . . . . . . . . . . . . . . . . . 513.4, 513.8, C 102.0,

Table 1003.2.1

SMOKE DAMPERS . . . . . . . . . . . . . . . . 206.0, 606.0 , 606.8

SMOKE DETECTORS . . . . . . . . . . . . . . 221.0, 609.0 , 609.2

SNOWMELT SYSTEMS . . . . . . . . . . . . . . 1220.4, 1220.4.1,

1217.8.2, Table 1220.4.2

SOLAR ENERGY SYSTEMS . . . . . . . . . . . . . . . . . . . . 1502.0

SOLID-FUEL

Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002.4

Burning appliances . . . . . . . . . . . . . . . . . . . . . . . 902.10 Chimney, combination

gas- and solid-fuel. . . . . . . . . . . . . . . . . . . . 802.5.8.2 Cooking operations . . . . . . . . . . . . . . . . . . . . . . . . 517.0

Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.11

Room heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.4

Venting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801.3

SPARK ARRESTERS

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.0

Solid-fuel cooking operations . . . . . . . . . . . . . . . 517.1.6

SPECIFIC APPLIANCES,

INSTALLATION OF . . . . . . . . . . . . . . . . . . . . . . Chapter 9

STANDARDS

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.0
CMC § 902.10 High relevance — show source text
Burning appliances . . . . . . . . . . . . . . . . . . . . . . . 902.10 Chimney, combination

gas- and solid-fuel. . . . . . . . . . . . . . . . . . . . 802.5.8.2 Cooking operations . . . . . . . . . . . . . . . . . . . . . . . . 517.0

Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.11

Room heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.4

Venting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801.3

SPARK ARRESTERS

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.0

Solid-fuel cooking operations . . . . . . . . . . . . . . . 517.1.6

SPECIFIC APPLIANCES,

INSTALLATION OF . . . . . . . . . . . . . . . . . . . . . . Chapter 9

STANDARDS

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.0

General . . . . . . . . . . . . . . . . . . . . . . . . . . 301.2, 302.1.2

Fire-extinguishing systems. . . . . . . . . . . . . . . . . 513.2.2

Fuel gas piping. . . . . . . . . . . . . . . . . . . . . . . . . . D 115.1

Hydronics . . . . . . . . . . . . . 1203.2, 1207.3, Table 1210.1

Oil-or liquid-fuel

burning equipment. . . . . . . . . . . . . . . . . . . . . C 103.0 Referenced. . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 18

Steam and hot water boilers . . . . . . . . . . . . . . . . 1002.0

STATIONARY

Engine generators. . . . . . . . . . . . . . . . . . . . . . . . 1602.0

Fuel Cell Power Plant . . . . . . . . . . . . . . . . 221.0, 1601.0

Gas Engines . . . . . . . . . . . . . . . . . . . . . . . . . . . .1602.0

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INDEX

STEAM AND HOT-WATER SYSTEMS (Hospitals) . . . .319.0

CMC § 802.4 High relevance — show source text

154 2025 CALIFORNIA MECHANICAL CODE

CHIMNEYS AND VENTS

TABLE 802.4

TYPE OF VENTING SYSTEM TO BE USED

[NFPA 54: TABLE 12.5.1]

APPLIANCES	TYPE OF VENTING SYSTEM	LOCATION OF REQUIREMENTS
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Type B gas vent	Section 802.6
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Chimney	Section 802.5
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Single-wall metal pipe	Section 802.7
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Listed chimney lining system for gas venting	Section 802.5.3
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Special gas vent listed for these appliances	Section 802.4.3
Listed vented wall furnaces	Type B-W gas vent	Section 802.6, Section 907.0
Category II, Category III, and Category IV appliances	As specified or furnished by manufacturers of listed appliances	Section 802.4.1, Section 802.4.3
Incinerators	In accordance with NFPA 82	In accordance with NFPA 82
Appliances that can be converted to use of solid fuel Unlisted combination gas- and oil-burning appliances Combination gas- and solid-fuel-burning appliances Appliances listed for use with chimneys only Unlisted appliances	Chimney	Section 802.5
Listed combination gas- and oil-burning appliances	Type L vent	Section 802.6
Listed combination gas- and oil-burning appliances	Chimney	Section 802.5
Decorative appliances in vented fireplace	Chimney	Section 911.3
Gas-fired toilets	Single-wall metal pipe	Section 802.7, Section 928.3
Direct vent appliances	—	Section 802.2.6
Appliances with integral vents	—	Section 802.2.7

other appliances listed for use with Type B vents shall be permitted. The liner shall be installed in accordance with the liner manufacturer’s installation instructions. A permanent identifying label shall be attached at the point where the connection is to be made to the liner. The label shall read: “This chimney liner is for appliances that burn gas only. Do not connect to solid-or liquid-fuel-burning appliances or incinerators.” [NFPA 54:12.6.1.3] **802.5.4 Termination.

CMC § 510.1 High relevance — show source text
(1) Draft regulators and safety controls specifically listed for installation in venting systems and installed in accordance with the manufacturer’s installation instructions.

(2) Approved draft regulators and safety controls designed and installed in accordance with engineering methods.

(3) Listed heat reclaimers and automatically operated vent dampers installed in accordance with the manufacturers’ installation instructions.

(4) Vent dampers serving listed appliances installed in accordance with Section 510.1 or Section 510.2 or engineering methods.

(5) Approved economizers, heat reclaimers, and recuperators installed in venting systems of appliances not required to be equipped with draft hoods, provided the appliance manufacturer’s instructions cover the installation of such a device in the venting system and performance in accordance with Section 509.3 and Section 509.3.1 is obtained. [NFPA 54:12.16]

510.0 Sizing of Category I Venting Systems. 510.1 Additional Requirements to Single Appliance Vent. Venting Table 510.1.2(1) through Table 510.1.2(6) shall not be used where obstructions are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer’s instructions or in accordance with the following:

»

B gas vents that pass through walls or partitions constructed of combustible material shall be installed

with not less than the listed clearance to combustible

material.

(2) Vent connectors shall be permitted to pass through ceilings, floors, or walls in accordance with Section 509.7.3.1 and Section 509.7.3.5.

509.10.13.1 Medium-Heat Appliances. Vent connectors for medium-heat appliances shall not pass through walls or partitions constructed of combustible material. [NFPA 54:12.11.14.2] 509.11 Vent Connectors for Category II, Category III, and Category IV Appliances. The vent connectors for Category II, Category III, and Category IV appliances shall be in accordance with Section 509.4 through Section 509.4.3.

[NFPA 54:12.12]

509.12 Appliances Requiring Draft Hoods. Vented appliances shall be installed with draft hoods.

Exception: Dual oven-type combination ranges; direct vent appliances; fan-assisted combustion system appliances; appliances requiring chimney draft for operation; single-firebox boilers equipped with conversion burners with inputs greater than 400 000 Btu/h (117 kW); appliances equipped with blast, power, or pressure burners that are not listed for use with draft hoods; and appliances designed for forced venting. [NFPA 54:12.13.1]

509.12.1 Installation. A draft hood supplied with or forming a part of a listed vented appliance shall be installed without alteration, exactly as furnished and specified by the appliance manufacturer. [NFPA 54:12.13.2]

If a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, be of a listed or approved type, and, in the absence of other instructions, be of the same size as the appliance flue collar. Where a draft hood is required with a conversion burner, it shall be of a listed or approved type. [NFPA 54:12.13.2.1]
CMC § 2025 High relevance — show source text
Chapter 7 Combustion Air. Chapter 7 regulates combustion air requirements for ventilation and dilution of flue gases for appliances installed in buildings. Fuel-gas appliances not regulated by chapter include direct vent appliances and Type I clothes dryers. Makeup air requirements for Type I clothes dryers are located in Chapter 5. Chapter 7 provides acceptable methods for supplying satisfactory combustion air to ensure proper combustion. Combustion air can be supplied by using indoor combustion air or by introducing the air from the outdoors.

Combustion is the rapid oxidation of fuel to release energy. The oxygen required to release the energy from the fuel normally comes from the air. Incomplete combustion of fuel occurs when inadequate oxygen is provided to the appliance. Combustion is needed to provide ventilation cooling for the casing and internal controls. When a lack of oxygen occurs, some of the carbon is not oxidized, and carbon monoxide forms.

Chapter 8 Chimneys and Vents. Chapter 8 regulates the installation, design, and construction of venting systems for fuel-burning appliances. The provisions addressed within this chapter follow procedures an installer would use to design or evaluate a venting system. Many requirements apply to the design and construction of venting systems, chimneys, installation of gas vents, and the sizing of venting system for a Category I appliance. Sizing venting systems require rigorous engineering calculations. However, the venting sizing requirements and sizing tables in this chapter already perform the calculations for the benefit of the end user.

Combustion appliances produce products of incomplete combustion, including potentially harmful carbon monoxide (CO). It is desirable to vent these products to the outdoors. Although the gas is clean-burning fuel, the products of combustion must not be allowed to collect within a building.

Chapter 9 Installation of Specific Appliances. Chapter 9 regulates the minimum requirements for the design, construction and installation of specific appliances. The provisions address the minimum requirements for gas-fired appliances, oil-fired appliances, wood-fired appliances, and electric-type appliances. In addition to the requirements of this chapter, appliances are also required to comply with the general requirements of Chapter 3.

Chapter 10 Boilers and Pressure Vessels. Chapter 10 regulates the construction, installation, operation, repair, and alteration of boilers and pressure vessels. The safety provisions within this chapter address controls and limit devices for automatic boilers, methods of determining expansion tank capacities, discharge piping, relief valves, shutoff valves, gas-pressure and combustion regulators, and inspections and tests. Potable water heaters are free from the requirements of Chapter 10 as they are within the scope of the Uniform Plumbing Code (UPC).

Pressure vessels store large amounts of energy and must comply with ASME Boiler and Pressure Vessel Code (BPVC) Section VIII.1. The stored energy must be contained to prevent disastrous failures. Boilers must comply with ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85. Installing a safety relief valve and expansion tank prevents pressures in the tank from exceeding the design threshold.

Chapter 11 Refrigeration. Chapter 11 regulates the design, installation, and construction requirements of refrigeration systems and the installation and construction of cooling towers. Refrigeration is a method used for achieving heat transfer to cool spaces. Refrigerants are the most common medium used to transfer the heat energy from the low-temperature level to the high-temperature level. Table

2025 CALIFORNIA MECHANICAL CODE xv

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FORMAT OF THE UNIFORM MECHANICAL CODE
CMC § 907.0 High relevance — show source text
6, Section 907.0| |Category II, Category III, and
Category IV appliances|As specified or furnished by
manufacturers of listed appliances|Section 802.4.1, Section 802.4.3| |Incinerators|In accordance with NFPA 82|In accordance with NFPA 82| |Appliances that can be converted to use of solid fuel

Unlisted combination gas- and oil-burning appliances

Combination gas- and solid-fuel-burning appliances

Appliances listed for use with chimneys only

Unlisted appliances|Chimney|Section 802.5| |Listed combination gas- and oil-burning appliances|Type L vent|Section 802.6| |Listed combination gas- and oil-burning appliances|Chimney|Section 802.5| |Decorative appliances in vented fireplace|Chimney|Section 911.3| |Gas-fired toilets|Single-wall metal pipe|Section 802.7, Section 928.3| |Direct vent appliances|—|Section 802.2.6| |Appliances with integral vents|—|Section 802.2.7|

other appliances listed for use with Type B vents shall be permitted. The liner shall be installed in accordance with the liner manufacturer’s installation instructions. A permanent identifying label shall be attached at the point where the connection is to be made to the liner. The label shall read: “This chimney liner is for appliances that burn gas only. Do not connect to solid-or liquid-fuel-burning appliances or incinerators.” [NFPA 54:12.6.1.3] 802.5.4 Termination. A chimney for residential-type or low-heat appliances shall extend at least 3 feet (914 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). [NFPA 54:12.6.2.1] (See Figure 802.5.4) 802.5.4.1 Medium-Heat Gas Appliances. A chimney for medium-heat appliances shall extend at least 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm). [NFPA 54:12.6.2.2]

802.5.4.2 Chimney Height. A chimney shall extend at least 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar.

[NFPA 54:12.6.2.3]

802.5.4.3 Decorative Shrouds. Decorative

shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are

listed and labeled for use with the specific factorybuilt chimney system and are installed in accordance with the manufacturer’s installation instructions.

[NFPA 54:12.6.2.4]

802.5.5 Size of Chimneys. The effective area of a chimney venting system serving listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be in accordance with one of the following methods:

(1) Those listed in Section 803.0.

CMC § 12.4.5.2 High relevance — show source text

(1) The venting system shall be a listed special gas vent, other system serving a Category III or Category IV appliance, or other positive pressure vent, with joints sealed in accordance with the appliance or vent manufacturer’s instructions.

(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]

509.4 Type of Venting System to be Used. The type of venting system to be used shall be in accordance with Table 509.4. [NFPA 54:12.5.1]

509.4.1 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 manufac

turer’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]

TABLE 509.4

TYPE OF VENTING SYSTEM TO BE USED {NFPA 54: TABLE 12.5.1}

APPLIANCES	TYPE OF VENTING SYSTEM	LOCATION OF REQUIREMENTS
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Type B gas vent	Section 509.6
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Chimney	Section 509.5
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Single-wall metal pipe	Section 509.7
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Listed chimney lin- ing system for gas venting	Section 509.5.3
Listed Category I appliances Listed appliances equipped with draft hood Appliances listed for use with Type B gas vent	Special gas vent listed for these appliances	Section 509.4.3
Listed vented wall fur- naces	Type B-W gas vent	Section 509.

CMC § 701.4 High 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 § 223.0 High relevance — show source text
223.0 – U –

UMC. [HCD 1, HCD 2, OSHPD 1, 1R, 2, 3, 4, 5 & 6] The most recent edition of Uniform Mechanical Code published by the International Association of Plumbing and Mechanical Officials.

Unconditioned Space. An area, room, or space not being heated or cooled by any equipment.

Unit Heater. A heating appliance designed for nonresidential space heating and equipped with an integral means for circulation of air.

46 2025 CALIFORNIA MECHANICAL CODE

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DEFINITIONS

Vented Appliance Categories. Category I. An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.

[NFPA 54:3.3.4.10.1] Category II. An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that can cause excessive condensate production in the vent. [NFPA 54:3.3.4.10.2] Category III. An appliance that operates with a positive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.

[NFPA 54:3.3.4.10.3] Category IV. An appliance that operates with a positive vent static pressure and with a vent gas temperature that can cause excessive condensate production in the vent.

[NFPA 54:3.3.4.10.4] Vented Decorative Appliance. A vented appliance whose only function is providing an aesthetic effect of flames. Vented Wall Furnace. A self-contained, vented, fuel gasburning appliance complete with grilles or equivalent, designed for incorporation in or permanent attachment to the structure of a building and furnishing heated air, circulated by gravity or by a fan, directly into the space to be heated through openings in the casing. [NFPA 54:3.3.45.7] Ventilating Ceiling. A suspended ceiling containing many small apertures through which air, at low pressure, is forced downward from an overhead plenum dimensioned by the concealed space between the suspended ceiling and the floor or roof above.

Ventilation System. All of that equipment intended or installed for the purpose of supplying air to or removing air from, any room or space by mechanical means, other than equipment that is a portion of an environmental heating, cooling, absorption, or evaporative cooling system. Venting Collar. The outlet opening of an appliance provided for connection of the vent system. Venting System. The vent or chimney and its connectors, assembled to form a continuous open passageway from an appliance to the outdoors for the purpose of removing products of combustion. This definition also shall include a venting assembly that is an integral part of an appliance. Venting System, Gravity-Type. A system that depends entirely on the heat from the fuel being used to provide the energy required to vent an appliance. Venting System, Power-Type. A system that depends on a mechanical device to provide a positive draft within the venting system. **Volume, Internal Gross.
CMC § 802.10.13.1 High relevance — show source text
802.10.13.1 Medium-Heat Appliances. Vent connectors for medium-heat appliances shall not pass through walls or partitions constructed of combustible material. [NFPA 54:12.11.14.2]

802.11 Vent Connectors for Category II, Category III, and Category IV Appliances. The vent connectors for Category II, Category III, and Category IV appliances shall be in accordance with Section 802.4 through Section 802.4.3.

[NFPA 54:12.12]

802.12 Appliances Requiring Draft Hoods. Vented appliances shall be installed with draft hoods.

Exception: Dual oven-type combination ranges; direct vent appliances; fan-assisted combustion system appliances; appli

»

»

»

»

802.10.3.1 Height of Connector. Where two or more vent connectors enter a common vent, chimney flue, or single-wall metal pipe, the smaller connector shall enter at the highest level consistent with the available headroom or clearance to combustible material. [NFPA 54:12.11.4.2]

802.10.3.2 Pressure. Vent connectors serving Category I appliances shall not be connected to any portion of a mechanical draft system operating under positive static pressure, such as those serving Category III or Category IV appliances. [NFPA 54:12.11.4.3]

802.10.4 Clearance. Minimum clearances from vent

connectors to combustible material shall be in accor dance with Table 802.7.3.3.

Exception: The clearance between a vent connector and combustible material shall be permitted to be reduced where the combustible material is protected as specified for vent connectors in Table 303.10.1. [NFPA 54:12.11.5]

802.10.5 Joints. Joints between sections of connector piping and connections to flue collars or draft hood outlets shall be fastened in accordance with one of the following methods:

(1) Mechanically fastened by means of not less than three sheet-metal screws equally spaced around the joint.

(2) Vent connectors of listed vent material assembled and connected to flue collars or draft hood outlets in

accordance with the manufacturer’s instructions.

(3) Other approved means. {NFPA 54:12.11.6}

802.10.6 Connector Junctions. Where vent connectors are joined together, the connection shall be made with a manufactured tee or wye fitting. [NFPA 54:12.11.7]

802.10.7 Slope. A vent connector shall be installed without any dips or sags and shall slope upward toward the vent or chimney at least [1] ⁄ 4 inch per foot (20.8 mm/m).

Exception: Vent connectors attached to a mechanical draft system installed in accordance with appliance and the draft system manufacturers’ instructions. [NFPA 54:12.11.8]

802.10.8 Length of Vent Connector. The length of vent connectors shall comply with Section 802.10.8.1 or Section 802.10.8.2.

802.10.8.1 Single Wall Connector. The maximum horizontal length of a single-wall connector shall be 75 percent of the height of the chimney or vent, except for engineered systems. [NFPA 54:12.11.9.1]
CMC § 802.1 High relevance — show source text
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

Table 802.10.1.4 Minimum Thickness for Steel

Vent Connectors for Medium Heat Appliances . . . . . . . . . . . . . . 161

Table 802.8.1 Through-the-Wall Direct Vent Termination Clearances . . . . . . . . 162

802.11 Vent Connectors for Category II, Category III, and Category IV Appliances . . . . . . . . . . . . . . . . . . 164

802.12 Appliances Requiring Draft Hoods . . . . . . . . . . . . . . . . . . 164

802.13 Manually Operated Dampers . . . . 165

802.14 Automatically Operated Vent Dampers . . . . . . . . . . . . . . . . . . . . 165

802.15 Obstruction of Flow. . . . . . . . . . . . 165

803.0 Sizing of Category I Venting Systems . . . . . . . . . . . . . . . . . . . . 165

803.1 Additional Requirements to Single Appliance Vent . . . . . . . . . 165

803.2 Additional Requirements to Multiple-Appliance Vent.. . . . . . . . 167

Table 803.2.1 Vent Connector Maximum

Length. . . . . . . . . . . . . . . . . . . . . . 167

Table 803.1.2(1) Type B Double-Wall Gas Vent . . . 172

Table 803.1.2(2) Type B Double-Wall Gas Vent . . . 175
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]

158 2025 CALIFORNIA MECHANICAL CODE

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CHIMNEYS AND VENTS

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 § 509.3.3.1 High relevance — show source text
WATER HEATERS

509.3.3.1 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]

509.3.3.2 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]

509.3.3.3 Vent Connectors. Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure. [NFPA 54:12.4.3.4]

509.3.3.4 Operation. Where a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance. [NFPA 54:12.4.3.5]

509.3.4 Ventilating Hoods and Exhaust Systems. Where automatically operated appliances, other than food service appliances, are vented through a ventilating hood or exhaust system equipped with a damper or with a power means of exhaust, provisions shall be made to allow the flow of gas to the main burners only when the damper is open to a position to properly vent the appliance and when the power means of exhaust is in operation. [NFPA 54:12.4.4.1]

509.3.5 Circulating Air Ducts, Above-Ceiling Air- Handling Spaces, and Furnace Plenums. Venting systems shall not extend into or pass through any fabricated air duct or furnace plenum. [NFPA 54:12.4.5.1] 509.3.6 Above-Ceiling or Nonducted Air Han- dling System. Where a venting system passes through an above-ceiling air space or other nonducted portion of an air-handling system, it shall conform to one of the following requirements:

(1) The venting system shall be a listed special gas vent, other system serving a Category III or Category IV appliance, or other positive pressure vent, with joints sealed in accordance with the appliance or vent manufacturer’s instructions.

(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]

509.4 Type of Venting System to be Used. The type of venting system to be used shall be in accordance with Table 509.4. [NFPA 54:12.5.1]

509.4.1 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 manufac

turer’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]

TABLE 509.4
CMC § 12.7.4.1 High relevance — show source text
(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] 509.6.2.2 Vent Offsets. Type B and Type L vents sized in accordance with Section 509.6.2.1(3) or Section 509.6.2.1(4) shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60 degree (1.05 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.4.2] 509.6.2.3 Category II, Category III, and Cate- gory IV Appliances. The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance 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] 509.6.2.4 Sizing. Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods. [NFPA 54:12.7.4.4] 509.6.3 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]

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

FIGURE 509.6.3.1

PLAN VIEW OF PRACTICAL SEPARATION

METHOD FOR MULTISTORY GAS VENTING

[NFPA 54: FIGURE A.12.7.5.2]

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

(1) The available total height ( H ) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection

tee.
CMC § 509.1 High relevance — show source text
509.1 Listing . . . . . . . . . . . . . . . . . . . . . . .91

509.2 Connection to Venting Systems . . .91

509.3 Minimum Safe Performance . . . . . .91

509.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . . . .92

Table 509.4 Type of Venting System to be Used . . . . . . . . . . . . . . . . . . .92

509.5 Masonry, Metal, and Factory-Built Chimneys . . . . . . . . .93

509.6 Gas Vents . . . . . . . . . . . . . . . . . . . .94

Table 509.6.1 Roof Slope Heights . . . . . . . . . . . .95

509.7 Single-Wall Metal Pipe . . . . . . . . . .97

Table 509.7.3.4(1) Clearances for Connectors . . . . . . .97

Table 509.7.3.4(2) Reduction of Clearances with Specified Forms of Protection . . . .99

509.8 Through-the-Wall Vent Termination . . . . . . . . . . . . . . . . . .100

509.9 Condensation Drain . . . . . . . . . . .100

509.10 Vent Connectors for

Category I Appliances . . . . . . . . .100

Table 509.8.1 Through-the-Wall Direct-Vent Termination Clearances . . . . . . . .101

Table 509.10.1.3 Minimum Thickness for

Galvanized Steel Vent

Connectors for Low-Heat

Appliances . . . . . . . . . . . . . . . . . .102

Table 509.10.1.4 Minimum Thickness for Steel

Vent Connectors for

Medium-Heat Appliances . . . . . . .102

509.11 Vent Connectors for

Category II, Category III, and Category IV Appliances . . . . . . . .104

509.12 Appliances Requiring Draft Hoods . . . . . . . . . . . . . . . . . . . . . .104

509.13 Manually Operated Dampers . . . .104

509.14 Automatically Operated Vent Dampers . . . . . . . . . . . . . . . .104

509.15 Obstructions . . . . . . . . . . . . . . . . .104

510.0 Sizing of Category I Venting Systems . . . . . . . . . . . . . . . . . . . .104

510.1 Additional Requirements to Single Appliance Vent . . . . . . . . .104

510.2 Additional Requirements to Multiple-Appliance Vent . . . . . . . . .106

Table 510.2.1 Vent Connector Maximum

Length . . . . . . . . . . . . . . . . . . . . . .106

Table 510.1.2(1) Type B Double-Wall Gas Vent . . .110

Table 510.1.2(2) Type B Double-Wall Gas Vent . . .113

Table 510.1.2(3) Masonry Chimney . . . . . . . . . . . . .115
CMC § 802.3.3.3 High relevance — show source text
802.3.3.3 Vent Connectors. Vent connectors

serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure. [NFPA 54:12.4.3.4]

802.3.3.4 Operation. Where a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance. [NFPA 54:12.4.3.5]

802.3.4 Ventilating Hoods and Exhaust Systems. Where automatically operated appliances, other than food service appliances, are vented through a ventilating hood or exhaust system equipped with a damper or with a power means of exhaust, provisions shall be made to allow the flow of gas to the main burners only when the damper is open to a position to properly vent the appliance and when the power means of exhaust is in operation. [NFPA 54:12.4.4.1]

802.3.5 Circulating Air Ducts, Above-Ceiling Air- Handling Spaces, and Furnace Plenums. Venting systems shall not extend into or pass through any fabricated air duct or furnace plenum. [NFPA 54:12.4.5.1]

802.3.6 Above-Ceiling or Nonducted Air Han- dling System. Where a venting system passes through an above-ceiling air space or other nonducted portion of an air-handling system, it shall conform to one of the following requirements:

(1) The venting system shall be a listed special gas vent, other system serving a Category III or Category IV appliance, or other positive pressure vent, with joints sealed in accordance with the appliance or vent manufacturer’s instructions.

(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]

Frequently asked questions

Can a Category III appliance use a Type B vent?

No. Category III appliances (positive vent pressure) are not covered by the default Table 802.4 vent types — their vent material and sizing must be provided by the appliance manufacturer and the appliance listing per § 802.4.1.

Is plastic vent pipe ever allowed?

Yes — but only if the appliance is listed for plastic venting and the manufacturer identifies the specific plastic material; plastic vent materials must be labeled and installed per § 802.4.1 (UL 1738 where applicable).

Do vents have to be listed?

Yes. Vents and chimneys used must be listed and installed per the manufacturer’s instructions and the chapter; see § 802.1.

Where do I find the matrix that tells me which vent to use?

See Table 802.4 and § 802.4 — Table 802.4 maps appliance categories/listings to permitted vent types and points you to the detailed sections (e.g., § 802.5, § 802.6, § 802.7).

If an appliance is listed for multiple vent types which do I choose?

Choose any vent type allowed by Table 802.4 and ensure the specific vent product is listed, sized, and installed per the relevant sections (§ 802.1, § 802.6, Chapter 803) and the vent/appliance manufacturer’s instructions.

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