CMC · California Mechanical Code

Vented gas fireplaces — application and installation requirements

Q: Where must the vent air intake be located?

For direct‑vent gas fireplaces the vent air intake terminal must be outdoors and installed per the manufacturer’s instructions. § 912.3(4) .

Q: How do I determine combustion‑air openings?

§ 912.4 requires combustion and circulating air per § 701.0 . The specific opening sizes, louvers, or outside‑air requirements are found in § 701.0 (not reproduced here); consult that section and the appliance instructions.

Homeowners: any new gas fireplace in California must be a listed direct‑vent sealed‑combustion unit, installed exactly per the manufacturer’s instructions with the intake outdoors, service panels left removable, and combustion air provided per the code; see **§ 912.1**, **§ 912.3**, and **§ 912.4** for the controlling requirements.

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Last reviewed: July 6, 2026

What the code requires — plain English

Vented gas fireplaces must be a listed appliance meeting ANSI Z21.50/CSA 2.22 and installed as a direct‑vent sealed‑combustion appliance for any new installation. Installations must follow the appliance listing and the manufacturer’s instructions, keep removable service panels unfastened to the building, locate the vent air intake terminal outdoors, and provide combustion and circulating air per the code. See § 912.1, § 912.3, and § 912.4 for the controlling rules.

The single most important rule: any newly installed gas fireplace in California must be a direct‑vent sealed‑combustion unit and be installed exactly per its listing and the manufacturer’s instructions. § 912.3(1) and § 912.3(2).

Requirements in detail

Scope and listing

Appliance must be listed in accordance with ANSI Z21.50/CSA 2.22. Reference: § 912.1.

Installation – summary of mandatory items (from § 912.3)

New installations — must be direct‑vent sealed‑combustion. § 912.3(1).
Install in accordance with the appliance listing and the manufacturer’s installation instructions; where attached to combustible materials the unit must be specifically listed for that condition. § 912.3(2).
Panels, grilles, and access doors that must be removed for normal servicing shall not be attached to the building (they must remain removable without altering building finishes). § 912.3(3).
Direct‑vent units must have the vent air intake terminal located outdoors and installed per the manufacturer’s instructions. § 912.3(4).

Combustion and circulating air

Combustion and circulating air must be provided in accordance with § 701.0 (the CMC combustion‑air/ventilation section). § 912.4.
- Note: § 912.4 delegates the detailed combustion‑air sizing and methods to § 701.0; consult § 701.0 for specific opening sizes, louver requirements, and where outside combustion air is required. The text of § 701.0 was not provided in the retrieved excerpts here, so check § 701.0 in the code or the manufacturer’s instructions to apply combustion‑air sizing.

Quick decision table (decision‑relevant dimensions/values)

Decision item	What to check / value	Code Reference
Appliance listing standard	ANSI Z21.50 / CSA 2.22 required	§ 912.1
New‑install type	Direct‑vent sealed‑combustion mandatory for new installs	§ 912.3(1)
Install instructions	Install per appliance listing & manufacturer's instructions; listed for installation on/attached to combustibles when applicable	§ 912.3(2)
Service access panels	Panels/grilles/access doors required for service must not be attached to the building	§ 912.3(3)
Vent air intake	Vent air intake terminal outdoors for direct‑vent fireplaces	§ 912.3(4)
Combustion & circulating air	Provide per § 701.0 (combustion‑air provisions)	§ 912.4

Exceptions & special cases

The CMC text for § 912.3 includes a clause that any newly installed gas fireplace be direct‑vent sealed‑combustion (no general exception within § 912.3 itself). § 912.3(1).
Decorative appliances for use in vented fireplaces are covered separately (see Chapter 911); those appliances have their own listing/installation limits (e.g., requirements for installation in functional chimneys, prohibition in some occupancies). See § 911.1–§ 911.4 for decorative appliance rules.
Combustion‑air details and allowable methods (inside vs. outside combustion air, minimum free areas, louvers/dampers) are handled under § 701.0; § 912.4 requires compliance with that section. If you need numeric combustion‑air sizing, consult § 701.0 and the appliance manufacturer’s instructions.

Common mistakes

Installing a newly purchased gas fireplace that is not direct‑vent sealed‑combustion — this violates § 912.3(1).
Ignoring the appliance listing and manufacturer instructions (clearances, venting components, termination); § 912.3(2) makes the listing/manufacturer instructions the primary installation authority.
Permanently fastening service panels, grilles, or doors to the building finishes so they cannot be removed for service without damage — prohibited by § 912.3(3).
Routing the direct‑vent intake to a building cavity or otherwise failing to terminate the vent air intake outdoors — contrary to § 912.3(4).
Omitting required combustion‑air openings or not following § 701.0 for combustion and circulating air — see § 912.4.

Worked example — applying the rules

Scenario: You (or the contractor) plan to replace an old masonry wood fireplace with a new gas fireplace in a California single‑family home.

Verify listing: Require a unit listed to ANSI Z21.50/CSA 2.22 (appliance listing requirement). § 912.1.
Choose appliance: Select a direct‑vent sealed‑combustion gas fireplace (required for any newly installed gas fireplace). § 912.3(1).
Manufacturer instructions: Read the manufacturer’s instructions; follow venting materials, clearances, termination location, and whether the unit is listed for installation against or adjacent to combustible finishes. § 912.3(2).
Vent termination & intake: Install the vent and the outdoor vent air intake terminal exactly where the manufacturer directs; confirm the intake is outdoors (not into a crawlspace or interior chase unless specifically allowed by the manufacturer). § 912.3(4).
Service access: Make sure any service panels/grilles remain removable without cutting into or permanently altering the home (do not attach them to the structure). § 912.3(3).
Combustion air: Determine combustion‑air needs per § 701.0 (sizing/placement) and provide intake/openings as required; consult § 701.0 and the appliance instructions for exact free‑area dimensions and louvers. § 912.4.

If any of the steps above conflict with the manufacturer’s installed instructions, the listing/manufacturer instructions control as required by § 912.3(2).

Related provisions (quick references)

§ 912.1 — Appliance listing requirement (ANSI Z21.50/CSA 2.22).
§ 912.3 — Installation requirements for vented gas fireplaces (detailed items (1)–(4)).
§ 912.4 — Combustion and circulating air must be provided per § 701.0.
§ 911.1–§ 911.4 — Decorative appliances in vented fireplaces (separate rules for decorative inserts).
§ 701.0 — Combustion‑air and ventilation provisions referenced by § 912.4 (consult for sizing and methods). (Text for § 701.0 was not included in the retrieved excerpts.)
See also the venting and chimney rules (Chapter 802 and related) for vent types and terminations when the manufacturer’s instructions reference specific venting systems.

Code references

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

CMC § 911.2 High relevance — show source text
911.2 Prohibited Installations. Decorative appliances for installation in vented fireplaces shall not be installed in bathrooms or bedrooms unless the bedroom or bathroom has the

required volume in accordance with Section 701.4. [NFPA 54:10.6.2] [OSHPD 1, 1R, 2, 4 & 5] A vented decorative appliance shall not be located in any hospital, skilled nursing facility, intermediate care facility, or correctional treatment

center.

911.3 Installation. A decorative appliance for installation in a vented fireplace shall be installed only in a vented fireplace having a working chimney flue and constructed of noncombustible materials. These appliances shall not be thermostatically controlled. [NFPA 54:10.6.3]

911.3.1 Listed Decorative Appliance. A listed decorative appliance for installation in a vented fireplace shall be installed in accordance with its listing and the manufacturer’s installation instructions. {NFPA 54:10.6.3.1}

911.3.2 Reserved

911.4 Fireplace Screens. A fireplace screen shall be installed with a decorative appliance for installation in a vented fireplace. [NFPA 54:10.6.4]

912.0 Gas Fireplaces, Vented.

912.1 Application. Vented gas fireplaces shall be listed in accordance with ANSI Z21.50/CSA 2.22. [NFPA 54:10.7.1]

912.2 Reserved

912.3 Installation. The installation of vented gas fireplaces shall comply with the following requirements:

(1) [HCD 1 & HCD 2] Any newly installed gas fireplace shall be a direct-vent sealed-combustion type.

(2) Vented gas fireplaces shall be installed in accordance with their listing and the manufacturer’s installation instructions and where installed in or attached to com bustible material shall be specifically listed for such installation.

(3) Panels, grilles, and access doors that are required to be removed for normal servicing operations shall not be attached to the building.

(4) Direct vent gas fireplaces shall be installed with the vent air intake terminal in the outdoors and in accor dance with the manufacturer’s installation instructions.

[NFPA 54:10.7.3] 912.4 Combustion and Circulating Air. Combustion and circulating air shall be provided in accordance with Section 701.0. [NFPA 54:10.7.4]

913.0 Factory-Built Fireplaces and Fireplace Stoves. 913.1 Factory-Built Fireplaces. Factory-built fireplaces shall comply with UL 127 and installed in accordance with the manufacturer’s installation instructions. {NFPA 211:11.1.1} 913.1.1 Gasketed Fireplace Doors. A gasketed fireplace door shall not be installed on a factory-built fireplace, except where the fireplace system has been tested in accordance with UL 127.

913.2 Fireplace Stoves. Fireplace stoves shall comply with UL 737 and installed in accordance with the manufac turer’s installation instructions.

913.3 Fireplace Accessories. Heat exchangers, glass doors assemblies, combustion air vents, and termination caps shall comply with UL 907 and installed in accordance with the manufacturer’s installation instructions.
CMC § 10.7.3 High relevance — show source text
(1) [HCD 1 & HCD 2] Any newly installed gas fireplace shall be a direct-vent sealed-combustion type.

(2) Vented gas fireplaces shall be installed in accordance with their listing and the manufacturer’s installation instructions and where installed in or attached to com bustible material shall be specifically listed for such installation.

(3) Panels, grilles, and access doors that are required to be removed for normal servicing operations shall not be attached to the building.

(4) Direct vent gas fireplaces shall be installed with the vent air intake terminal in the outdoors and in accor dance with the manufacturer’s installation instructions.

[NFPA 54:10.7.3] 912.4 Combustion and Circulating Air. Combustion and circulating air shall be provided in accordance with Section 701.0. [NFPA 54:10.7.4]

913.0 Factory-Built Fireplaces and Fireplace Stoves. 913.1 Factory-Built Fireplaces. Factory-built fireplaces shall comply with UL 127 and installed in accordance with the manufacturer’s installation instructions. {NFPA 211:11.1.1} 913.1.1 Gasketed Fireplace Doors. A gasketed fireplace door shall not be installed on a factory-built fireplace, except where the fireplace system has been tested in accordance with UL 127.

913.2 Fireplace Stoves. Fireplace stoves shall comply with UL 737 and installed in accordance with the manufac turer’s installation instructions.

913.3 Fireplace Accessories. Heat exchangers, glass doors assemblies, combustion air vents, and termination caps shall comply with UL 907 and installed in accordance with the manufacturer’s installation instructions.

914.0 Non-Recirculating Direct Gas-Fired Industrial Air Heaters.

914.1 Application. Direct gas-fired heating and forced ventilation appliances for commercial and industrial applications shall be listed in accordance with the following standards as applicable:

(1) ANSI Z83.4/CSA 3.7.

(2) ANSI Z83.18. [NFPA 54:10.8.1] 914.2 Prohibited Installations. Direct gas-fired heating and forced ventilation appliances shall not serve any area containing sleeping quarters. Non-recirculating direct gas-fired heating and forced ventilation appliances shall not recirculate room air.

Recirculating direct gas-fired industrial air heaters shall not recirculate room air in buildings that contain flammable solids, liquids, or gases; explosive materials; or substances that can become toxic when exposed to flame or heat. [NFPA 54:10.8.2.1 – 10.8.2.3]

914.3 Installation. Direct gas-fired heating and forced ventilation appliances shall be installed in accordance with the manufacturer’s instructions. [NFPA 54:10.8.3.1]

914.3.1 Fresh Air Ventilation. Direct gas-fired heating and forced ventilation appliances shall be permitted to provide fresh air ventilation. [NFPA 54:10.8.3.2]

914.3.2 Access Required. Direct gas-fired heating and forced ventilation appliances shall be provided with access for removal of burners; for replacement of motors, controls, filters, and other working parts; and for adjustment and lubrication of parts requiring maintenance.

[NFPA 54:10.8.3.3]

206 2025 CALIFORNIA MECHANICAL CODE
CMC § 907.2.3 High relevance — show source text
907.2.3 Panels, Grilles, and Access Doors. Panels, grilles, and access doors that are required to be removed for normal servicing operations shall not be attached to the building. For additional information on the venting of wall furnaces, see Section 802.0. [NFPA 54:10.25.2.4]

For SI units: 1 inch = 25.4 mm

FIGURE 907.2.1

INSTALLATION OF TYPE B-W GAS VENTS FOR

VENTED WALL FURNACES

[NFPA 54: FIGURE 10.25.2.2]

907.3 Location. Wall furnaces shall be located so as not to cause a hazard to walls, floors, curtains, furniture, or doors. Wall furnaces installed between bathrooms and adjoining rooms shall not circulate air from bathrooms to other parts of the building. [NFPA 54:10.25.3]

2025 CALIFORNIA MECHANICAL CODE 205

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INSTALLATION OF SPECIFIC APPLIANCES

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910.0 Burner Assemblies.

910.1 Oil Burners. Oil burners shall comply with UL 296 and installed in accordance with the manufacturer’s installa tion instructions.

910.2 Gas Burners. Commercial gas burners shall comply with UL 295 and installed in accordance with the manufac turer’s installation instructions.

911.0 Decorative Appliances for Installation in Vented Fireplaces.

911.1 Application. Decorative appliances for installation in vented fireplaces shall be listed in accordance with ANSI Z21.60/CSA 2.26. [NFPA 54:10.6.1]

911.2 Prohibited Installations. Decorative appliances for installation in vented fireplaces shall not be installed in bathrooms or bedrooms unless the bedroom or bathroom has the

required volume in accordance with Section 701.4. [NFPA 54:10.6.2] [OSHPD 1, 1R, 2, 4 & 5] A vented decorative appliance shall not be located in any hospital, skilled nursing facility, intermediate care facility, or correctional treatment

center.

911.3 Installation. A decorative appliance for installation in a vented fireplace shall be installed only in a vented fireplace having a working chimney flue and constructed of noncombustible materials. These appliances shall not be thermostatically controlled. [NFPA 54:10.6.3]

911.3.1 Listed Decorative Appliance. A listed decorative appliance for installation in a vented fireplace shall be installed in accordance with its listing and the manufacturer’s installation instructions. {NFPA 54:10.6.3.1}

911.3.2 Reserved

911.4 Fireplace Screens. A fireplace screen shall be installed with a decorative appliance for installation in a vented fireplace. [NFPA 54:10.6.4]

912.0 Gas Fireplaces, Vented.

912.1 Application. Vented gas fireplaces shall be listed in accordance with ANSI Z21.50/CSA 2.22. [NFPA 54:10.7.1]
CMC § 911.2 High relevance — show source text
911.2 Prohibited Installations . . . . . . . . . 206

911.3 Installation . . . . . . . . . . . . . . . . . . 206

911.4 Fireplace Screens. . . . . . . . . . . . . 206

912.0 Gas Fireplaces, Vented . . . . . . . . 206

912.1 Application . . . . . . . . . . . . . . . . . . 206

912.2 Reserved . . . . . . . . . . . . . . . . . . . 206

912.3 Installation . . . . . . . . . . . . . . . . . . 206

912.4 Combustion and Circulating Air . . . 206

913.0 Factory-Built Fireplaces and Fireplace Stoves. . . . . . . . . . . . . . 206

913.1 Factory-Built Fireplaces . . . . . . . . 206

913.2 Fireplace Stoves. . . . . . . . . . . . . . 206

913.3 Fireplace Accessories . . . . . . . . . 206

914.0 Non-Recirculating Direct Gas-Fired Industrial Air Heaters. . . 206

914.1 Application . . . . . . . . . . . . . . . . . . 206

914.2 Prohibited Installations . . . . . . . . . 206

914.3 Installation . . . . . . . . . . . . . . . . . . 206

914.4 Clearance from Combustible

Materials . . . . . . . . . . . . . . . . . . . . 207

914.5 Air Supply . . . . . . . . . . . . . . . . . . . 207

914.6 Atmospheric Vents, Gas Reliefs, or Bleeds . . . . . . . . . . . . . 207

914.7 Relief Openings . . . . . . . . . . . . . . 207

914.8 Purging . . . . . . . . . . . . . . . . . . . . . 207

915.0 Room Heaters . . . . . . . . . . . . . . . 207

915.1 Application . . . . . . . . . . . . . . . . . . 207

915.2 Electric Room Heaters . . . . . . . . . 207

915.3 Gas-Fired Room Heaters . . . . . . . 207

xxxvi

915.4 Solid-Fuel Type Room Heaters . . 208

916.0 Unit Heaters . . . . . . . . . . . . . . . . . 208

916.1 Application . . . . . . . . . . . . . . . . . . 208

916.2 Support . . . . . . . . . . . . . . . . . . . . 208

916.3 Clearance for Suspended-Type Unit Heaters . . . . . . . . . . . . . . . . . 208

916.4 Combustion and Circulating Air. . . 208

916.5 Ductwork. . . . . . . . . . . . . . . . . . . . 208

916.6 Installation in Commercial

Garages and Aircraft Hangars . . . 208
CMC § 907.0 High relevance — show source text
TABLE OF CONTENTS

907.0 Wall Furnaces. . . . . . . . . . . . . . . . 204

907.1 Application . . . . . . . . . . . . . . . . . . 204

907.2 Installation . . . . . . . . . . . . . . . . . . 204

907.3 Location . . . . . . . . . . . . . . . . . . . . 205

907.4 Combustion and Circulating Air . . 205

907.5 Oil-Fired Wall Furnaces . . . . . . . . 205

908.0 Clothes Dryers . . . . . . . . . . . . . . . 205

908.1 Application . . . . . . . . . . . . . . . . . . 205

908.2 Electric Clothes Dryers . . . . . . . . . 205

908.3 Gas-Fired Clothes Dryers. . . . . . . 205

909.0 Conversion Burners . . . . . . . . . . . 205

909.1 General. . . . . . . . . . . . . . . . . . . . . 205

910.0 Burner Assemblies . . . . . . . . . . . . 206

910.1 Oil Burners . . . . . . . . . . . . . . . . . . 206

910.2 Gas Burners . . . . . . . . . . . . . . . . . 206

911.0 Decorative Appliances for Installation in Vented Fireplaces. . . 206

911.1 Application . . . . . . . . . . . . . . . . . . 206

911.2 Prohibited Installations . . . . . . . . . 206

911.3 Installation . . . . . . . . . . . . . . . . . . 206

911.4 Fireplace Screens. . . . . . . . . . . . . 206

912.0 Gas Fireplaces, Vented . . . . . . . . 206

912.1 Application . . . . . . . . . . . . . . . . . . 206

912.2 Reserved . . . . . . . . . . . . . . . . . . . 206

912.3 Installation . . . . . . . . . . . . . . . . . . 206

912.4 Combustion and Circulating Air . . . 206

913.0 Factory-Built Fireplaces and Fireplace Stoves. . . . . . . . . . . . . . 206

913.1 Factory-Built Fireplaces . . . . . . . . 206

913.2 Fireplace Stoves. . . . . . . . . . . . . . 206

913.3 Fireplace Accessories . . . . . . . . . 206

914.0 Non-Recirculating Direct Gas-Fired Industrial Air Heaters. . . 206

914.1 Application . . . . . . . . . . . . . . . . . . 206

914.2 Prohibited Installations . . . . . . . . . 206

914.3 Installation . . . . . . . . . . . . . . . . . . 206

914.4 Clearance from Combustible

Materials . . . . . . . . . . . . . . . . . . . . 207
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]

156 2025 CALIFORNIA MECHANICAL CODE

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CHIMNEYS AND VENTS

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 § 150.0 Medium relevance — show source text
Closable metal or glass doors covering the entire opening of the firebox; and 2. A combustion air intake to draw air from the outside of the building, which is at least 6 square inches in area and is equipped with a readily accessible, operable and tight-fitting damper or combustion-air control device; and Exception to Section 150.0(e)2: An outside combustion-air intake is not required if the fireplace will be installed over concrete slab flooring and the fireplace will not be located on an exterior wall. 3. A flue damper with a readily accessible control. Exception to Section 150.0(e)3: When a gas log, log lighter or decorative gas appliance is installed in a fireplace, the flue damper shall be blocked open if required by the CMC or the manufacturer’s installation instructions.

(f) Slab edge insulation. Material used for slab edge insulation shall meet the following minimum specifications:
1. Water absorption rate for the insulation material alone without facings no greater than 0.3 percent when tested in accordance with Test Method A – 24-Hour-Immersion of ASTM C272.
2. Water vapor permeance no greater than 2.0 perm/inch when tested in accordance with ASTM E96.
3. Concrete slab perimeter insulation shall be protected from physical damage and ultraviolet light deterioration.
4. Insulation for a heated slab floor shall meet the requirements of Section 110.8(g).
(g) Vapor retarder.
1. In Climate Zones 1–16, the earth floor of unvented crawl space shall be covered with a Class I or Class II vapor retarder. This requirement shall also apply to controlled ventilation crawl space for buildings complying with the Exception to Section 150.0(d).
2. In Climate Zones 14 and 16, a Class I or Class II vapor retarder shall be installed on the conditioned space side of all insulation in all exterior walls, vented attics and unvented attics with air-permeable insulation.
(h) Space-conditioning equipment.
1. Building cooling and heating loads. Building heating and cooling loads shall be determined using a method based on any one of the following: A. The ASHRAE Handbook, Equipment Volume, Applications Volume and Fundamentals Volume; or B. The SMACNA Residential Comfort System Installation Standards Manual; or
C. The ACCA Manual J.

Exception 1 to Section 150.0(h)1: Block loads, the total load for all rooms combined that are served by the central equipment, may be used for the purpose of system sizing for additions. 2. Design conditions. Design conditions shall be determined in accordance with the following: A. For the purpose of sizing the space-conditioning (HVAC) system, the indoor design temperatures shall be 68°F for heating and 75°F for cooling. B. Outdoor design conditions shall be selected from one of the following: i. Reference Joint Appendix JA2, which is based on data from the ASHRAE Climatic Data for Region X; or ii. The ASHRAE Handbook, Fundamentals Volume; or

iii. The ACCA Manual J.

C. The outdoor design temperatures for heating shall be no lower than the 99.0 percent Heating Dry Bulb or the Heating Winter Median of Extremes values.

D. The outdoor design temperatures for cooling shall be no greater than the 1.0 percent Cooling Dry Bulb and Mean Coincident Wet Bulb values.
1. Outdoor condensing units. A. **Clearances.
California Mechanical Code Medium relevance — show source text
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H
(feet)|LATERAL
L
(feet)|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR|MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR| |6|0
2
5|39
31
28|70
55
51|116
94
88|170
141
128|232
194
177|312
260
242|500
415
390|750
620
600| |8|0
2
5
10|42
32
29
24|76
61
56
49|126
102
95
86|185
154
141
131|252
210
194
180|340
284
264
250|542
451
430
406|815
680
648
625| |10|0
2
5
10
15|45
35
32
27
NA|84
67
61
54
46|138
111
104
94
84|202
168
153
143
130|279
233
215
200
186|372
311
289
274
258|606
505
480
455
432|912
760
724
700
666| |15|0
2
5
10
15
20|49
39
35
30
NA
NA|91
72
67
58
50
NA|151
122
110
103
93
82|223
186
170
158
144
132|312
260
240
223
207
195|420
350
325
308
291
273|684
570
540
514
488
466|1040
865
825
795
760
726| |20|0
2
5
CMC § 110.5 Medium relevance — show source text
(f) Installation of fireplaces, decorative gas appliances and gas logs. If a masonry or factory-built fireplace is installed, it shall comply with Section 110.5, Section 4.503 of Part 11, and shall have the following:
1. Closable metal or glass doors covering the entire opening of the firebox; and
2. A combustion air intake to draw air from the outside of the building, which is at least 6 square inches in area and is equipped with a readily accessible, operable and tight-fitting damper or combustion-air control device; and Exception to Section 160.1(f)2: An outside combustion-air intake is not required if the fireplace will be installed over concrete slab flooring and the fireplace will not be located on an exterior wall.
3. A flue damper with a readily accessible control. Exception to Section 160.1(f)3: When a gas log, log lighter or decorative gas appliance is installed in a fireplace, the flue damper shall be blocked open if required by the CMC or the manufacturer's installation instructions.
(g) Slab edge insulation. Slab edge insulation shall meet the following minimum specifications:
1. Insulation material alone without the facing shall have a water absorption rate no greater than 0.3 percent when tested in accordance with ASTM C272, Test Method A – 24-Hour-Immersion; and
2. Water vapor permeance no greater than 2.0 perm/inch when tested in accordance with ASTM C272; and
3. Concrete slab perimeter insulation shall be protected from physical damage and ultraviolet light deterioration; and
4. Insulation for a heated slab floor shall meet the requirements of Section 110.8(g).
NOTE: Authority: Sections 25213, 25218, 25218.5, 25402 and 25402.1, Public Resources Code . Reference: Sections 25007, 25008, 25218.5, 25310, 25402, 25402.1, 25402.4, 25402.5, 25402.8 and 25943, Public Resources Code .

SECTION 160.2—MANDATORY REQUIREMENTS FOR VENTILATION AND INDOOR AIR QUALITY

(a) General requirements.
1. Attached dwelling units in multifamily buildings shall comply with the applicable requirements of Subsection 160.2(b) below. Occupiable spaces in multifamily buildings other than attached dwelling units shall comply with the applicable requirements of Section 160.2(c). When field verification and diagnostic testing of attached dwelling units is required by Section 160.2, buildings with three habitable stories or fewer shall use the applicable procedures in the Residential Appendices, and buildings with four or more habitable stories shall use the applicable procedures in Nonresidential Appendices NA1 and NA2.
NOTE: Section 160.2 is not applicable to townhouses or dwellings that contain two dwelling units.

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MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS
1. The required outdoor air-ventilation rate and the air-distribution system design shall be clearly identified on the building design plans submitted to the enforcement agency in accordance with Section 10-103 of Title 24, Part 1.
(b) Attached dwelling units. Attached dwelling units shall comply with the requirements of Subsections 1 and 2 below.
1. Air filtration.
CMC § 223.0 Medium 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.

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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 § 12.6.7 Medium relevance — show source text
[NFPA 54:12.6.7] 509.5.10 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] 509.5.10.1 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] 509.6 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

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WATER HEATERS

chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”

(4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.

[NFPA 54:12.7.2]

509.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:

(1) A gas vent shall terminate in accordance with one of the following:

(a) Gas vents that are 12 inches (300 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall

terminate above the roof in accordance with Figure 509.6.1 and Table 509.6.1.

(b) Gas vents that are over 12 inches (300 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally.

(c) Industrial appliances as provided in Section 509.2.5.

(d) Direct-vent systems as provided in Section 509.2.6.

(e) Appliances with integral vents as provided in Section 509.2.7.

(f) Mechanical draft systems as provided in Section 509.3.3 through Section 509.3.3.4.
CMC § 4.1 Medium relevance — show source text
4.1
and Section
509.4.3| |

Appliances that can be
converted to use 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 509.5| |

Listed combination
gas- and oil-burning
appliances|Type L vent|Section 509.6| |

Listed combination
gas- and oil-burning
appliances|Chimney|Section 509.5| |

Decorative appliance in
vented fireplace|Chimney|UMC Section
911.2| |
Gas-fired toilets|Single-wall metal
pipe|Section 509.7| |
Direct-vent appliances|—|Section 509.2.6| |
Appliances with
integral vents|—|Section 509.2.7|

509.4.2 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 accor dance with the vent manufacturer’s installation instruc

TABLE 509.4

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

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WATER HEATERS

tions. Where primer is required, it shall be of a contrasting color. [NFPA 54:12.5.3] 509.4.3 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] 509.5 Masonry, Metal, and Factory-Built Chimneys. Chimneys shall be installed in accordance with Section 509.5.1 through Section 509.5.3. 509.5.1 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]

509.5.1.1 Decorative Shrouds. Decorative

shrouds addressed in Section 509.5.4.3 shall comply with UL 103 for factory -built residential chim neys. 509.5.2 Metal Chimneys. Metal chimneys shall be built and installed in accordance with NFPA 211. [NFPA 54:12.6.1.2] 509.5.3 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

Frequently asked questions

Can I replace my old wood fireplace with any gas fireplace?

No. For a new gas installation in California the unit must be a direct‑vent sealed‑combustion type and listed to ANSI Z21.50/CSA 2.22; installation must follow the appliance listing and manufacturer’s instructions. § 912.3(1), § 912.1.

Do service panels have to be removable?

Yes. Panels, grilles, and access doors that are required to be removed for normal servicing shall not be attached to the building (they must be removable without damaging building finishes). § 912.3(3).

Where must the vent air intake be located?

For direct‑vent gas fireplaces the vent air intake terminal must be outdoors and installed per the manufacturer’s instructions. § 912.3(4).

Who controls when manufacturer instructions conflict with local practice?

The code requires installation to comply with the appliance listing and the manufacturer’s installation instructions; those control the installation details unless the local enforcement authority has an approved modification. § 912.3(2).

How do I determine combustion‑air openings?

§ 912.4 requires combustion and circulating air per § 701.0. The specific opening sizes, louvers, or outside‑air requirements are found in § 701.0 (not reproduced here); consult that section and the appliance instructions.

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Related in the CMC

Decorative appliances for installation in vented fireplaces — prohibitions and installation

Wall furnaces — application, installation, location, air requirements

Factory-built fireplaces and fireplace stoves — listings, accessories and installation

Space Heating & Fireplaces

California Mechanical Code