CMC · California Mechanical Code
Factory-built fireplaces and fireplace stoves — listings, accessories and installation
Homeowners: California requires factory-built fireplaces and stoves to be listed to specific UL standards (fireplaces UL 127, stoves UL 737, accessories UL 907) and installed exactly per the manufacturer's instructions; gasketed doors are not allowed unless the full fireplace system was tested for them per UL 127.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Factory-built fireplaces, fireplace stoves, and their listed accessories must be listed to the specified UL standard and installed in accordance with the manufacturer's installation instructions. The California Mechanical Code requires factory-built fireplaces to comply with UL 127 (see § 913.1), fireplace stoves to comply with UL 737 (see § 913.2), and heat exchangers, glass-door assemblies, combustion‑air vents and termination caps to comply with UL 907 (see § 913.3). A gasketed fireplace door is expressly prohibited on a factory-built fireplace unless the fireplace system has been tested for that configuration in accordance with UL 127 (see § 913.1.1) .
The single most important rule: use only components that are listed to the UL standard referenced by the code and follow the manufacturer's installation instructions exactly (see § 913.1, § 913.2, § 913.3) .
Requirements in detail
Core listing & installation rules
- Factory-built fireplaces — must be listed to UL 127 and installed per the manufacturer's instructions (§ 913.1).
- Gasketed fireplace doors — prohibited on factory-built fireplaces unless the entire fireplace system was tested for gasketed doors per UL 127 (§ 913.1.1).
- Fireplace stoves — must be listed to UL 737 and installed per the manufacturer's instructions (§ 913.2).
- Fireplace accessories (heat exchangers, glass‑door assemblies, combustion air vents, termination caps) — must be listed to UL 907 and installed per the manufacturer's instructions (§ 913.3) .
Decision table — what to check before purchase/installation
| Decision item | What to look for | Why it matters | Code Reference |
|---|---|---|---|
| Fireplace listing standard | UL 127 on the unit label | Confirms the unit is a factory-built fireplace tested to national standard | § 913.1 |
| Gasketed door allowed? | Explicit statement on the listing/manufacturer docs that the system was tested for gasketed doors | Gasketed doors are not permitted unless system tested | § 913.1.1 |
| Fireplace stove listing | UL 737 on the stove label | Indicates stove meets required safety/performance standard | § 913.2 |
| Accessories (glass doors, heat exchangers, air vents, caps) | UL 907 listing on accessory label | Accessory must be listed to the correct standard for safe use with the appliance | § 913.3 |
| Installation instructions | Manufacturer’s installation instructions present and followed | The code defers to the manufacturer's tested installation for clearances, connections, vents, etc. | § 913.1 / § 913.2 / § 913.3 |
Installation scope left to manufacturer listing
- The sections in § 913.0–§ 913.3 do not themselves give numerical clearances, vent sizes, chimney configurations or combustion‑air openings — they require that the appliance be listed and installed in accordance with the manufacturer's installation instructions and the applicable UL standard. For specific clearances, termination details and combustion‑air requirements, consult the appliance listing and the manufacturer's instructions (per § 913.1, § 913.2, § 913.3) .
Exceptions & special cases
- Gasketed doors: a gasketed fireplace door is an exception only when the fireplace system has been specifically tested and listed for that configuration in accordance with UL 127; otherwise it may not be installed on a factory-built fireplace (§ 913.1.1) .
- The code language in § 913.0–§ 913.3 is limited to listing and installation per manufacturer; it does not create alternate paths (for example, it does not provide its own clearance exceptions or combustion‑air sizing). If you need a permitted alternate, that must come from the listing/label or other adopted code sections.
Common mistakes
- Installing a gasketed glass door on a factory-built fireplace without verifying the system was tested for gasketed doors — violates § 913.1.1.
- Using accessories (heat exchangers, doors, vents, caps) that are not listed to UL 907 — violates § 913.3.
- Assuming the CMC § 913.* provides numeric clearances or combustion‑air sizes — it does not; you must follow the unit’s listing/manufacturer instructions per § 913.1/§ 913.2/§ 913.3.
- Altering listed components (for example, modifying flues, termination caps, or vent connectors) without confirming the change is permitted by the listing or manufacturer — this can invalidate the listing and violate the installation requirement in § 913.1–§ 913.3.
Worked example — concrete scenario applying the rule
Scenario: You are replacing a masonry fireplace with a factory-built unit and want a glass door.
- You buy a factory-built fireplace with label showing it is listed to UL 127. That meets the requirement of § 913.1. Confirm the unit comes with the manufacturer's installation instructions and that you will install per those instructions (§ 913.1).
- You plan to add a gasketed glass door. Check the fireplace system's listing or manufacturer's documents for an explicit test/listing statement that the system (fireplace + door) has been tested for gasketed doors per UL 127. If the listing does not show that, you must not install the gasketed door — this is prohibited by § 913.1.1.
- You also plan to add a heat‑exchange accessory. Verify the accessory is listed to UL 907 (look for the UL 907 marking) and follow the accessory manufacturer’s installation instructions. If it is not UL 907‑listed, do not install it with the factory-built fireplace — doing so would violate § 913.3.
In short: unit must be UL 127; gasketed door allowed only if the full system was tested/listed for it; accessories must be UL 907 listed and installed per instructions.
Related provisions
- § 912.1 — Vented gas fireplaces must be listed in accordance with ANSI Z21.50/CSA 2.22 (related to gas fireplaces and to decisions whether a unit is a vented gas fireplace).
- § 912.3 — Installation rules for vented gas fireplaces; emphasizes direct‑vent sealed‑combustion and installing per listing/manufacturer instructions.
- § 911.3 — Installation of decorative appliances in vented fireplaces (useful when a decorative gas appliance is inserted into a fireplace).
- § 914.3 — Installation requirements for direct gas‑fired industrial air heaters (example of the code following manufacturer’s instructions for appliances).
(These related sections are in nearby CMC chapters and reinforce the pattern: listing to the referenced standard and installation per manufacturer’s instructions.)
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
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 § 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 § 25.4 High relevance — show source text
FIGURE R1003.20—CHIMNEY CRICKET
AIRSPACE
ROOF LINE
For SI: 1 inch = 25.4 mm.
FLUE LINER Col2 Col3 Col4 Col5 1 IN.
AIRS1 IN.
AIRS1 IN.
AIRS1 IN.
AIRS1 IN.
AIRSW W W W W 2025 CALIFORNIA RESIDENTIAL CODE 10-11
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
�
CHIMNEYS AND FIREPLACES
SECTION R1004—FACTORY-BUILT FIREPLACES
R1004.1 General. Factory-built fireplaces shall be listed and labeled and shall be installed in accordance with the conditions of the listing. Factory-built fireplaces shall be tested in accordance with UL 127.
R1004.1.1 Factory-built wood burning fireplaces. Factory-built wood burning fireplaces shall be qualified at the U.S. EPA’s Volun- tary Fireplace Program Phase 2 emissions level and be in accordance with the California Green Building Standards Code, Chapter 4, Division 4.5.
R1004.2 Hearth extensions. Hearth extensions of approved factory-built fireplaces shall be installed in accordance with the listing of the fireplace. The hearth extension shall be readily distinguishable from the surrounding floor area. Listed and labeled hearth extensions shall comply with UL 1618.
R1004.3 Decorative shrouds. Decorative shrouds shall not be installed at the termination of chimneys for factory-built fireplaces except where the shrouds are listed and labeled for use with the specific factory-built fireplace system and installed in accordance with the manufacturer’s instructions.
R1004.5 Gasketed fireplace doors. A gasketed fireplace door shall not be installed on a factory-built fireplace except where the fireplace system has been specifically tested, listed and labeled for such use in accordance with UL 127.
SECTION R1005—FACTORY-BUILT CHIMNEYS
R1005.1 Listing. Factory-built chimneys shall be listed and labeled and shall be installed and terminated in accordance with the manufacturer’s installation instructions.
R1005.2 Decorative shrouds. Decorative shrouds shall not be installed at the termination of factory-built chimneys except where the shrouds are listed and labeled for use with the specific factory-built chimney system and installed in accordance with the manufacturer’s installation instructions.
R1005.3 Solid-fuel appliances. Factory-built chimneys installed in dwelling units with solid-fuel-burning appliances shall comply with the Type HT requirements of UL 103 and shall be marked “Type HT” and “Residential Type and Building Heating Appliance Chimney.”
Exception: Chimneys for use with open combustion chamber fireplaces shall comply with the requirements of UL 103 and shall be marked “Residential Type and Building Heating Appliance Chimney.”
Chimneys for use with open combustion chamber appliances installed in buildings other than dwelling units shall comply with the requirements of UL 103 and shall be marked “Building Heating Appliance Chimney” or “Residential Type and Building Heating Appliance Chimney.”
R1005.4 Factory-built fireplaces. Chimneys for use with factory-built fireplaces shall comply with the requirements of UL 127.
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 § 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 § 25.4 High relevance — show source text
br>G||||||||||||||| |FLUE
LINING
FLUE
LINING
G|||||||||||||||R1003.19 Chimney fireblocking. Spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between chimneys and wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible
material and the chimney.
R1003.20 Chimney crickets. Chimneys shall be provided with crickets where the dimension parallel to the ridgeline is greater than
30 inches (762 mm) and does not intersect the ridgeline. The intersection of the cricket and the chimney shall be flashed and counter-
flashed in the same manner as normal roof-chimney intersections. Crickets shall be constructed in compliance with Figure R1003.20
and Table R1003.20.Col2 TABLE R1003.20—CRICKET DIMENSIONS TABLE R1003.20—CRICKET DIMENSIONS ** ROOF SLOPE** ** H** 12:12 1/2 of W 8:12 1/3 of W 6:12 1/4 of W 4:12 1/6 of W 3:12 1/8 of W FIGURE R1003.20—CHIMNEY CRICKET
AIRSPACE
ROOF LINE
For SI: 1 inch = 25.4 mm.
FLUE LINER Col2 Col3 Col4 Col5 1 IN.
AIRS1 IN.
AIRS1 IN.
AIRS1 IN.
AIRS1 IN.
AIRSW W W W W 2025 CALIFORNIA RESIDENTIAL CODE 10-11
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
�
CHIMNEYS AND FIREPLACES
SECTION R1004—FACTORY-BUILT FIREPLACES
R1004.1 General. Factory-built fireplaces shall be listed and labeled and shall be installed in accordance with the conditions of the listing. Factory-built fireplaces shall be tested in accordance with UL 127.
R1004.1.1 Factory-built wood burning fireplaces. Factory-built wood burning fireplaces shall be qualified at the U.S. EPA’s Volun- tary Fireplace Program Phase 2 emissions level and be in accordance with the California Green Building Standards Code, Chapter 4, Division 4.5.
R1004.2 Hearth extensions. Hearth extensions of approved factory-built fireplaces shall be installed in accordance with the listing of the fireplace. The hearth extension shall be readily distinguishable from the surrounding floor area. Listed and labeled hearth extensions shall comply with UL 1618.
CMC § 0.52 High relevance — show source text
R1004.5 Gasketed fireplace doors. A gasketed fireplace door shall not be installed on a factory-built fireplace except where the fireplace system has been specifically tested, listed and labeled for such use in accordance with UL 127.
SECTION R1005—FACTORY-BUILT CHIMNEYS
R1005.1 Listing. Factory-built chimneys shall be listed and labeled and shall be installed and terminated in accordance with the manufacturer’s installation instructions.
R1005.2 Decorative shrouds. Decorative shrouds shall not be installed at the termination of factory-built chimneys except where the shrouds are listed and labeled for use with the specific factory-built chimney system and installed in accordance with the manufacturer’s installation instructions.
R1005.3 Solid-fuel appliances. Factory-built chimneys installed in dwelling units with solid-fuel-burning appliances shall comply with the Type HT requirements of UL 103 and shall be marked “Type HT” and “Residential Type and Building Heating Appliance Chimney.”
Exception: Chimneys for use with open combustion chamber fireplaces shall comply with the requirements of UL 103 and shall be marked “Residential Type and Building Heating Appliance Chimney.”
Chimneys for use with open combustion chamber appliances installed in buildings other than dwelling units shall comply with the requirements of UL 103 and shall be marked “Building Heating Appliance Chimney” or “Residential Type and Building Heating Appliance Chimney.”
R1005.4 Factory-built fireplaces. Chimneys for use with factory-built fireplaces shall comply with the requirements of UL 127.
R1005.5 Support. Where factory-built chimneys are supported by structural members, such as joists and rafters, those members shall be designed to support the additional load.
R1005.6 Medium-heat appliances. Factory-built chimneys for medium-heat appliances producing flue gases having a temperature above 1,000°F (538°C), measured at the entrance to the chimney, shall comply with UL 959.
R1005.7 Factory-built chimney offsets. Where a factory-built chimney assembly incorporates offsets, no part of the chimney shall be at an angle of more than 30 degrees (0.52 rad) from vertical at any point in the assembly and the chimney assembly shall not include more than four elbows.
R1005.8 Insulation shield. Where factory-built chimneys pass through insulated assemblies, an insulation shield constructed of steel having a thickness of not less than 0.0187 inch (0.4712 mm) (No. 26 gage) shall be installed to provide clearance between the chimney and the insulation material. The clearance shall be not less than the clearance to combustibles specified by the chimney manufacturer’s installation instructions. Where chimneys pass through attic space, the shield shall terminate not less than 2 inches (51 mm) above the insulation materials and shall be secured in place to prevent displacement. Insulation shields provided as part of a listed chimney system shall be installed in accordance with the manufacturer’s installation instructions.
R1005.9 Factory-built chimney offsets. Where a fireplace manufacturer’s instructions do not address factory-built chimney offsets, no part of the chimney shall be at an angle of more than 30 degrees (0.52 rad) from vertical at any point in the assembly and the chimney assembly shall not include more than four elbows.
SECTION R1006—EXTERIOR AIR SUPPLY
CMC § 3.2 High relevance — show source text
Exceptions:
Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL 127 and installed in accordance with the manufacturer’s instructions are permitted to have combustible material in contact with their exterior surfaces.
Where masonry fireplaces are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.
Exposed combustible trim and the edges of sheathing materials, such as wood siding, flooring and drywall, are permitted to abut the masonry fireplace sidewalls and hearth extension, in accordance with Figure 2111 A .12, provided that such combustible trim or sheathing is not less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.
Exposed combustible mantels or trim is permitted to be placed directly on the masonry fireplace front surrounding the fireplace opening, provided that such combustible materials shall not be placed within 6 inches (153 mm) of a fireplace opening. Combustible material directly above and within 12 inches (305 mm) of the fireplace opening shall not project more than [1] / 8 inch (3.2 mm) for each 1-inch (25 mm) distance from such opening. Combustible materials located along the sides of the fireplace opening that project more than 1 [1] / 2 inches (38 mm) from the face of the fireplace shall have an additional clearance equal to the projection.
FIGURE 2111 A .12—ILLUSTRATION OF EXCEPTION TO FIREPLACE CLEARANCE PROVISION
EDGE ABUTTING MASONRY
2 ″ CLEARANCE (AIRSPACE) TO COMBUSTIBLE FRAMING
WOOD MANTEL
MASONRY
COMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMB
FRAME WCOMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMBCol3 COMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
MASONRY
2″ CLEAR
TO COMB
FRAME WFor SI: 1 inch = 25.4 mm
2111 A .13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.
2111 A .14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.
2111 A .14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.
21A-12 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
CMC § 21-12 High relevance — show source text
- Where masonry fireplaces are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.
21-12 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
- Exposed combustible trim and the edges of sheathing materials, such as wood siding, flooring and drywall, are permitted to abut the masonry fireplace sidewalls and hearth extension, in accordance with Figure 2111.12, provided that such combustible trim or sheathing is not less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.
- Exposed combustible mantels or trim is permitted to be placed directly on the masonry fireplace front surrounding the fireplace opening, provided that such combustible materials shall not be placed within 6 inches (153 mm) of a fireplace opening. Combustible material directly above and within 12 inches (305 mm) of the fireplace opening shall not project more than [1] / 8 inch (3.2 mm) for each 1-inch (25 mm) distance from such opening. Combustible materials located along the sides of the fireplace opening that project more than 1 [1] / 2 inches (38 mm) from the face of the fireplace shall have an additional clearance equal to the projection.
FIGURE 2111.12—ILLUSTRATION OF EXCEPTION TO FIREPLACE CLEARANCE PROVISION
EDGE ABUTTING MASONRY
2 ″ CLEARANCE (AIRSPACE) TO COMBUSTIBLE FRAMING
For SI: 1 inch = 25.4 mm
2111.13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.
2111.14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.
2111.14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.
MASONRY
COMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMB
FRAME W
WOOD MANT
spaces between fireplaces and floors and
al securely fastened in place. The fireblock
nd shall only be placed on strips of metal
r masonry fireplaces covered in this sect
s the room is mechanically ventilated an
es. Exterior combustion air ducts for fact
o the fireplace manufacturer’s instructionCOMBUSTIBL
EDGE ABUTTI
12″ MIN FROM
2″ CLEAR
TO COMBCol3 spaces between fireplaces and floors and
al securely fastened in place.CMC § 1001.11 Medium relevance — show source text
3||||X|||||||||||||||||||| |R1001.4||||X|||||||||||||||||||| |Table R1001.1, Footnote (b)||||X|||||||||||||||||||| |R1001.11|||X||||||||||||||||||||| |Figure 1001.11|||X||||||||||||||||||||| |R1001.12|||X||||||||||||||||||||| |R1003.3||||X|||||||||||||||||||| |R1003.4||||X|||||||||||||||||||| |R1003.9.1|||X||||||||||||||||||||| |R1003.9.2|||X||||||||||||||||||||| |R1003.11.3||||X|||||||||||||||||||| |R1003.14||||X|||||||||||||||||||| |R1003.18|||X||||||||||||||||||||| |Figure R1003.18|||X||||||||||||||||||||| |R1003.19|||X||||||||||||||||||||| |R1004.1.1||||X|||||||||||||||||||| |R1004.4||||†||||||||||||||||||||
The state agency does not adopt sections identified with the following symbol: †
2025 CALIFORNIA RESIDENTIAL CODE 10-1
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
10-2 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
10 CHIMNEYS AND FIREPLACES
User notes:
About this chapter: Chapter 10 contains requirements for the construction, seismic reinforcing and anchorage of masonry chimneys and fireplaces; and establishes standards for the use and installation of factory-built chimneys, fireplaces and masonry heaters. Chimneys and fireplaces constructed of masonry rely on prescriptive requirements for the details of their construction; factory-built versions rely on the listing and labeling method of approval.
SECTION R1001—MASONRY FIREPLACES
R1001.1 General. Masonry fireplaces shall be constructed in accordance with this section and the applicable provisions of Chapters 3 and 4.
TABLE R1001.1—SUMMARY OF REQUIREMENTS FOR MASONRY FIREPLACES AND CHIMNEYS Col2 Col3 ** ITEM** ** LETTERa** ** REQUIREMENTS** Hearth slab thickness A 4 inches Hearth extension (each side of opening) B 8-inch fireplace opening < 6 square feet.
12-inch fireplace opening ≥ 6 square feet.Hearth extension (front of opening) C 16-inch fireplace opening < 6 square feet.
20-inch fireplace opening ≥ 6 square feet.Hearth slab reinforcing D Reinforced to carry its own weight and all imposed loads. Thickness of wall of firebox E 10-inch solid brick or 8 inches where a firebrick lining is used.
Joints in firebrick1/4-inch maximum.Distance from top of opening to throat F 8 inches Smoke chamber wall thickness
Unlined wallsG 6 inches
8 inchesChimney
Vertical reinforcingbH Four No. 4 full-length bars for chimney up to 40 inches wide.
Add two No. 4 bars for each additional 40 inches or fraction of
width or each additional flue.CMC § 160.1 Medium relevance — show source text
(d) Vapor retarder.
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 160.1(c).
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.
(e) Fenestration products. Fenestration separating conditioned space from unconditioned space or outdoors shall meet the requirements of either Item 1 or 2 below:
- Fenestration, including skylight products, must have a maximum U- factor of 0.58. Exception 1 to Section 160.1(e)1: Up to 0.5 percent of the conditioned floor area is not required to comply with the maximum U- factor requirement. Exception 2 to Section 160.1(e)1: For dual-glazed greenhouse or garden windows, up to 30 square feet of fenestration area per dwelling unit is not required to comply with the maximum U- factor requirement.
- The area-weighted average U- factor of all fenestration, including skylight products, shall not exceed 0.58.
Exception to Section 160.1(e): Fenestration installed in buildings meeting Part 7 of the California Building Code, California Wild- land-Urban Interface Code, where the building is located in Fire Hazard Severity Zones or Wildland-Urban Interface (WUI) Fire Areas as designated by the local enforcement agency.
(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:
- Closable metal or glass doors covering the entire opening of the firebox; and
- 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.
- 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:
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
Water vapor permeance no greater than 2.0 perm/inch when tested in accordance with ASTM C272; and
Concrete slab perimeter insulation shall be protected from physical damage and ultraviolet light deterioration; and
Insulation for a heated slab floor shall meet the requirements of Section 110.8(g).
CMC § 9-4 Medium relevance — show source text
R904 Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4
R905 Requirements for Roof Coverings . . . . . . . . . . . . . . . . 9-4
R906 Roof Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19
R907 Rooftop-Mounted Photovoltaic Panel Systems . . . 9-19
R908 Reroofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19
R909 Roof Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20
CHAPTER 10 CHIMNEYS AND FIREPLACES . . . . . . . . . . . .10-3
R1001 Masonry Fireplaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3
R1002 Masonry Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-6
R1003 Masonry Chimneys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-7
R1004 Factory-Built Fireplaces. . . . . . . . . . . . . . . . . . . . . . . . 10-12
R1005 Factory-Built Chimneys . . . . . . . . . . . . . . . . . . . . . . . . 10-12
R1006 Exterior Air Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12
Part IV—Energy Conservation. . . . . . . . . . . . . . . . . . . . . . . .11-1
Part V—Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12-1
Part VI—Fuel Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-1
Part VII—Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25-1
Part VIII—Electrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-1
Part IX— Referenced Standards . . . . . . . . . . . . . . . . . . . . . .44-3
CHAPTER 44 REFERENCED STANDARDS . . . . . . . . . . . . . .44-3
Frequently asked questions
Can I install any glass door on a factory-built fireplace?
No. A gasketed fireplace door cannot be installed unless the fireplace system has been specifically tested and listed for gasketed doors per UL 127; see § 913.1.1. Always check the listing/manufacturer documents first.
What UL standard must a replacement fireplace stove meet?
A fireplace stove must be listed to UL 737 and installed according to the manufacturer's installation instructions (see § 913.2).
Are heat exchangers and termination caps regulated?
Yes — heat exchangers, glass‑door assemblies, combustion‑air vents and termination caps used with factory‑built fireplaces must be listed to UL 907 and installed per manufacturer instructions (see § 913.3).
If the manufacturer’s instructions call for a specific clearance, which controls: the code or the instructions?
Both matter, but § 913.1–§ 913.3 explicitly require installation in accordance with the manufacturer’s installation instructions; therefore you must follow the tested/listed installation (manufacturer's instructions) for the unit as labeled. The code defers numeric clearances to the listing/instructions.
Where do I find combustion‑air or flue termination sizes?
Those specifics are normally provided in the appliance's listing and manufacturer’s installation instructions; § 913.1–§ 913.3 require you to follow those instructions rather than providing the sizes directly.
More in California Mechanical Code
Ask about the CMC
Get cited, plain-English answers on the California Mechanical Code for your project — any code section, any scenario.
Start Free Trial