CRC · California Residential Code
What standards or listings are required for masonry heaters and how must they be installed?
If you install a masonry heater in California it must either be built to ASTM E1602 or be a listed product (UL 1482 or CEN 15250) and installed per the listing/manufacturer; the CRC also prescribes a **4‑inch** noncombustible firebox floor, **36‑inch** default clearances (reducible to **4 inches** when the heater walls/channels meet larger thickness thresholds), and seismic anchorage rules (exceptions when height ≤ **3.5 ×** width) — see **§ R1002.1** and **§ R1002.2** and the related subsections for the numeric thresholds and installation details .
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
A masonry heater is defined by the CRC as a solid‑masonry appliance that stores heat from a solid‑fuel fire and routes exhaust through internal heat‑exchange channels before entering the chimney (see § R1002.1). For installation the CRC requires masonry heaters to either meet ASTM E1602 or be listed and labeled to UL 1482 or CEN 15250 and installed per the manufacturer’s instructions (see § R1002.2) . Additional installation rules in the same section cover footings/foundation, seismic anchorage and clearances to combustibles (see § R1002.3–R1002.5) .
The single most important rule: masonry heaters must be built to the ASTM E1602 prescriptive standard or be a listed product (UL 1482 or CEN 15250) and installed exactly per the listing/manufacturer; anything else must meet the masonry construction requirements in the code (see § R1002.2) .
Requirements in detail
Definition (what counts as a masonry heater)
- Masonry heater — a heating appliance constructed of concrete or solid masonry that absorbs and stores heat from a solid‑fuel fire by routing exhaust through internal heat‑exchange channels (downward or horizontal flow before the chimney). Refer to § R1002.1 for the official definition .
Approved routes to compliance (listing or standard)
- Option A: Construct and install to ASTM E1602 (prescriptive masonry‑heater standard). See § R1002.2.
- Option B: Use a heater listed and labeled to UL 1482 or CEN 15250, and install per the manufacturer’s instructions and the terms of the listing. See § R1002.2.
Structural / installation specifics referenced in the same R1002 section
- Footing / hearth floor minimum thickness: 4 inches (102 mm) of noncombustible material under the firebox floor; supported on a noncombustible footing/foundation per the code (see § R1002.3) .
- Seismic anchorage / reinforcing: In Seismic Design Categories D0, D1 and D2 masonry heaters must be anchored to the masonry foundation per the code. Seismic reinforcing is not required within the heater body when the heater’s height ≤ 3.5 × body width and the masonry chimney is not supported by the heater body. When the chimney shares a wall with the heater facing, the chimney must be reinforced per the chimney section (see § R1002.4) .
- Clearances to combustibles: Default clearance 36 inches (914 mm) from the outside surface of the heater to combustible materials, measured in accordance with NFPA 211 (see § R1002.5) .
- Exception (reduced clearances): If the heater wall thickness is ≥ 8 inches (203 mm) of solid masonry and the heat‑exchange channel wall thickness is ≥ 5 inches (127 mm) of solid masonry, combustible materials may be located as close as 4 inches (102 mm) from the outside surface. Also, provide 8 inches (203 mm) minimum between the gas‑tight capping slab of the heater and a combustible ceiling (see § R1002.5, exceptions) .
Decision‑relevant numbers & code references
| Requirement | Value / threshold | Code Reference |
|---|---|---|
| Heater definition (qualifies as masonry heater) | Solid masonry with internal heat‑exchange channels (horizontal or downward flow) | § R1002.1 |
| Acceptable standards/listings | ASTM E1602 OR UL 1482 OR CEN 15250 (listed & labeled) | § R1002.2 |
| Firebox floor / hearth slab thickness | 4 inches (102 mm) minimum, noncombustible | § R1002.3 |
| Default clearance to combustibles | 36 inches (914 mm) | § R1002.5 |
| Reduced clearance (exception) | 4 inches (102 mm) when heater wall ≥ 8 in (203 mm) and channel wall ≥ 5 in (127 mm) | § R1002.5 (exception) |
| Clearance to combustible ceiling above capping slab | 8 inches (203 mm) | § R1002.5 (exception) |
| Seismic anchorage required | Seismic Design Categories D0, D1, D2 (anchored per code) | § R1002.4 |
| When seismic reinforcing may NOT be required | Heater height ≤ 3.5 × body width and chimney not supported by heater body | § R1002.4 (exception) |
Exceptions & special cases
- Manufacturer/listing route: A heater that is listed and labeled to UL 1482 or CEN 15250 may be installed according to the listing and the manufacturer’s written instructions; when installed this way, the listing/manufacturer instructions control where they differ from prescriptive masonry details (see § R1002.2 and § R1002.5 exception) .
- Reduced clearances are explicitly allowed where the heater has large solid masonry mass (wall ≥ 8 in, channels ≥ 5 in) — this is a prescriptive structural exception in § R1002.5 .
- Seismic exceptions depend on measured proportions and whether the chimney is supported by the heater; check § R1002.4 carefully for the height:width limit (3.5 times) and for requirements when the chimney shares a common wall with the heater facing .
If a particular requirement or detail (for example, footing sizing beyond the 4 in hearth or specific reinforcement bar size) is needed, consult the referenced masonry chimney sections and foundation requirements in Chapter R1003 and the masonry chapters — those details are outside the two controlling subsections but cross‑referenced by § R1002.3 and § R1002.4 .
Common mistakes
- Assuming any heavy masonry heater is automatically code‑compliant — you must meet ASTM E1602 or be a listed product (UL 1482 / CEN 15250) and follow the manufacturer’s listing/installation instructions if listed (see § R1002.2) .
- Forgetting to provide a 4‑inch minimum noncombustible firebox floor or to place it on a noncombustible footing/foundation (required by § R1002.3) .
- Applying reduced clearances without verifying wall and channel thicknesses (must meet 8 in and 5 in thresholds respectively to use the 4‑inch clearance exception) — these numeric thresholds are explicit in § R1002.5 .
- Overlooking seismic anchorage or mis‑calculating the height:width ratio; the 3.5 × body width threshold affects whether reinforcing is required (see § R1002.4) .
- Installing a listed heater but ignoring the listing/manufacturer instructions — listings are only compliant if the unit is installed in accord with its listing and instructions (see § R1002.2) .
Worked example — concrete scenario
Scenario: You are evaluating a field‑built masonry heater to be installed in a home in Seismic Design Category D1. Heater body width = 48 inches; overall heater height = 168 inches; firebox floor is planned as 4 inches thick concrete slab on a noncombustible footing. The heater external wall thickness is 9 inches and heat‑exchange channel walls are 5.5 inches.
Steps and application of code:
Compliance route: This is a field (site‑built) masonry heater — you must build to ASTM E1602 or use a listed unit. The owner chooses to build per ASTM E1602, so verify construction documents/specs reference that standard as required by § R1002.2 .
Footing/hearth: The planned 4 in (102 mm) noncombustible firebox floor meets § R1002.3; ensure the footing is noncombustible and sized per the referenced foundation provisions (see § R1002.3) .
Seismic reinforcing: Heater height (168 in) divided by body width (48 in) = 3.5. Because the height is equal to 3.5 × width, and provided the masonry chimney is not supported by the heater body, seismic reinforcing within the heater body is not required per the exception in § R1002.4; however, because the structure is in D1, the heater must be anchored to the masonry foundation per the anchorage requirements in § R1002.4 . If the chimney were supported by the heater or shared a common wall with the facing, different reinforcing rules would apply (see § R1002.4) .
Clearances: Default clearance is 36 in (914 mm). But the heater walls are 9 in ≥ 8 in, and the channels are 5.5 in ≥ 5 in, so the reduced‑clearance exception applies and combustibles may be placed 4 in (102 mm) from the outside heater surface (also verify 8 in (203 mm) clearance between the gas‑tight capping slab and combustibles above, if a ceiling is nearby) per § R1002.5 (exceptions) .
Document these verifications and show the design/inspection notes referencing § R1002.1, § R1002.2, § R1002.3, § R1002.4, and § R1002.5 as applicable so plan reviewers and inspectors can confirm the ASTM or listing route and the numeric thresholds used for exceptions .
Related provisions
- § R1002.1 — Definition of masonry heater (controls what is regulated as a masonry heater) .
- § R1002.2 — Installation options: ASTM E1602 or listed (UL 1482 / CEN 15250) and manufacturer’s instructions (primary compliance path) .
- § R1002.3 — Firebox floor (hearth) thickness and footing/foundation requirement (4 in minimum) .
- § R1002.4 — Seismic reinforcing and anchorage requirements and the 3.5:1 height:width exception .
- § R1002.5 — Clearances to combustible materials, and the reduced‑clearance exception for thick masonry walls/channels .
- For masonry chimneys and detailed foundation/reinforcing prescriptions, see Chapter R1003 (masonry chimneys) referenced from the R1002 subsections .
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 2112.1 High relevance — show source text
SECTION 2112—MASONRY HEATERS
2112.1 Definition. A masonry heater is a heating appliance constructed of concrete or solid masonry, hereinafter referred to as “masonry,” which is designed to absorb and store heat from a solid fuel fire built in the firebox by routing the exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox includes flow in either a horizontal or downward direction before entering the chimney and which delivers heat by radiation from the masonry surface of the heater.
2112.2 Installation. Masonry heaters shall be installed in accordance with this section and comply with one of the following:
- Masonry heaters shall comply with the requirements of ASTM E1602.
- Masonry heaters shall be listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.
2112.3 Footings and foundation. The firebox floor of a masonry heater shall be a minimum thickness of 4 inches (102 mm) of noncombustible material and be supported on a noncombustible footing and foundation in accordance with Section 2113.2.
2112.4 Seismic reinforcing. In structures assigned to Seismic Design Category D, E or F, masonry heaters shall be anchored to the masonry foundation in accordance with Section 2113.3. Seismic reinforcing shall not be required within the body of a masonry heater with a height that is equal to or less than 3.5 times its body width and where the masonry chimney serving the heater is not
2025 CALIFORNIA BUILDING CODE 21-13
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
supported by the body of the heater. Where the masonry chimney shares a common wall with the facing of the masonry heater, the chimney portion of the structure shall be reinforced in accordance with Section 2113.
2112.5 Masonry heater clearance. Combustible materials shall not be placed within 36 inches (914 mm) or the distance of the allowed reduction method from the outside surface of a masonry heater in accordance with NFPA 211, Section 12.6, and the required space between the heater and combustible material shall be fully vented to permit the free flow of air around all heater surfaces.
Exceptions:
- Where the masonry heater wall thickness is not less than 8 inches (203 mm) of solid masonry and the wall thickness of the heat exchange channels is not less than 5 inches (127 mm) of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
- Masonry heaters listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.
SECTION 2113—MASONRY CHIMNEYS
2113.1 General. The construction of masonry chimneys consisting of solid masonry units, hollow masonry units grouted solid, stone or concrete shall be in accordance with this section.
CRC § 10-6 High relevance — show source text
internal heat exchange channels in which the flow path downstream of the firebox includes flow in a horizontal or downward direction before entering the chimney and that delivers heat by radiation from the masonry surface of the heater.
R1002.2 Installation. Masonry heaters shall be installed in accordance with this section and comply with one of the following:
- Masonry heaters shall comply with the requirements of ASTM E1602.
- Masonry heaters shall be listed and labeled in accordance with UL 1482 or CEN 15250 and installed in accordance with the manufacturer’s instructions.
R1002.3 Footings and foundation. The firebox floor of a masonry heater shall be a minimum thickness of 4 inches (102 mm) of noncombustible material and be supported on a noncombustible footing and foundation in accordance with Section R1003.2.
10-6 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
CHIMNEYS AND FIREPLACES
R1002.4 Seismic reinforcing. In Seismic Design Categories D 0, D 1 and D 2, masonry heaters shall be anchored to the masonry foundation in accordance with Section R1003.3. Seismic reinforcing shall not be required within the body of a masonry heater whose height is equal to or less than 3.5 times its body width and where the masonry chimney serving the heater is not supported by the body of the heater. Where the masonry chimney shares a common wall with the facing of the masonry heater, the chimney portion of the structure shall be reinforced in accordance with Section R1003.
R1002.5 Masonry heater clearance. Combustible materials shall not be placed within 36 inches (914 mm) of the outside surface of a masonry heater in accordance with NFPA 211 Section 8-7 (clearances for solid-fuel-burning appliances), and the required space between the heater and combustible material shall be fully vented to permit the free flow of air around all heater surfaces.
Exceptions:
- Where the masonry heater wall is not less than 8 inches (203 mm) thick of solid masonry and the wall of the heat exchange channels is not less than 5 inches (127 mm) thick of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
- Masonry heaters listed and labeled in accordance with UL 1482 or CEN 15250 shall be installed in accordance with the listing specifications and the manufacturer’s written instructions.
SECTION R1003—MASONRY CHIMNEYS
R1003.1 Definition. A masonry chimney is a chimney constructed of solid masonry units, hollow masonry units grouted solid, stone or concrete, hereinafter referred to as masonry. Masonry chimneys shall be constructed, anchored, supported and reinforced as required in this chapter.
California Residential Code High relevance — show source text
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|internal heat exchange channels in which the flow path downstream of the firebox includes flow in a horizontal or downward direction before entering the chimney and that delivers heat by radiation from the masonry surface of the heater.
R1002.2 Installation. Masonry heaters shall be installed in accordance with this section and comply with one of the following:
- Masonry heaters shall comply with the requirements of ASTM E1602.
- Masonry heaters shall be listed and labeled in accordance with UL 1482 or CEN 15250 and installed in accordance with the manufacturer’s instructions.
CRC § 2111.14.2 High relevance — show source text
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WOOD MANT|||2111.14.2 Masonry fireplaces. Listed combustion air ducts for masonry fireplaces shall be installed according to the terms of their listing and manufacturer’s instructions.
2111.14.3 Exterior air intake. The exterior air intake shall be capable of providing all combustion air from the exterior of the dwelling. The exterior air intake shall not be located within a garage, attic, basement or crawl space of the dwelling nor shall the air intake be located at an elevation higher than the firebox. The exterior air intake shall be covered with a corrosion-resistant screen of [1] / 4 -inch (6.4 mm) mesh.
2111.14.4 Clearance. Unlisted combustion air ducts shall be installed with a minimum 1-inch (25 mm) clearance to combustibles for all parts of the duct within 5 feet (1524 mm) of the duct outlet. 2111.14.5 Passageway. The combustion air passageway shall be not less than 6 square inches (3870 mm [2] ) and not more than 55 square inches (0.035 m [2] ), except that combustion air systems for listed fireplaces or for fireplaces tested for emissions shall be constructed according to the fireplace manufacturer’s instructions.
2111.14.6 Outlet. The exterior air outlet is permitted to be located in the back or sides of the firebox chamber or within 24 inches (610 mm) of the firebox opening on or near the floor. The outlet shall be closable and designed to prevent burning material from dropping into concealed combustible spaces.
SECTION 2112—MASONRY HEATERS
2112.1 Definition. A masonry heater is a heating appliance constructed of concrete or solid masonry, hereinafter referred to as “masonry,” which is designed to absorb and store heat from a solid fuel fire built in the firebox by routing the exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox includes flow in either a horizontal or downward direction before entering the chimney and which delivers heat by radiation from the masonry surface of the heater.
2112.2 Installation. Masonry heaters shall be installed in accordance with this section and comply with one of the following:
- Masonry heaters shall comply with the requirements of ASTM E1602.
- Masonry heaters shall be listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.
2112.3 Footings and foundation. The firebox floor of a masonry heater shall be a minimum thickness of 4 inches (102 mm) of noncombustible material and be supported on a noncombustible footing and foundation in accordance with Section 2113.2.
2112.4 Seismic reinforcing. In structures assigned to Seismic Design Category D, E or F, masonry heaters shall be anchored to the masonry foundation in accordance with Section 2113.3. Seismic reinforcing shall not be required within the body of a masonry heater with a height that is equal to or less than 3.5 times its body width and where the masonry chimney serving the heater is not
CRC § 3.5 High relevance — show source text
2112 A .2 Installation. Masonry heaters shall be installed in accordance with this section and comply with one of the following:
- Masonry heaters shall comply with the requirements of ASTM E1602.
- Masonry heaters shall be listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.
2112 A .3 Footings and foundation. The firebox floor of a masonry heater shall be a minimum thickness of 4 inches (102 mm) of noncombustible material and be supported on a noncombustible footing and foundation in accordance with Section 2113 A .2.
2112 A .4 Seismic reinforcing. In structures assigned to Seismic Design Category D, E or F, masonry heaters shall be anchored to the masonry foundation in accordance with Section 2113 A .3. Seismic reinforcing shall not be required within the body of a masonry heater with a height that is equal to or less than 3.5 times its body width and where the masonry chimney serving the heater is not supported by the body of the heater. Where the masonry chimney shares a common wall with the facing of the masonry heater, the chimney portion of the structure shall be reinforced in accordance with Section 2113 A .
2112 A .5 Masonry heater clearance. Combustible materials shall not be placed within 36 inches (914 mm) or the distance of the allowed reduction method from the outside surface of a masonry heater in accordance with NFPA 211, Section 12.6, and the required space between the heater and combustible material shall be fully vented to permit the free flow of air around all heater surfaces.
Exceptions:
- Where the masonry heater wall thickness is not less than 8 inches (203 mm) of solid masonry and the wall thickness of the heat exchange channels is not less than 5 inches (127 mm) of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
- Masonry heaters listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.
SECTION 2113 A —MASONRY CHIMNEYS
2113 A .1 General. The construction of masonry chimneys consisting of solid masonry units, hollow masonry units grouted solid, stone or concrete shall be in accordance with this section.
2113 A .2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.
CRC § 8-7 High relevance — show source text
R1002.5 Masonry heater clearance. Combustible materials shall not be placed within 36 inches (914 mm) of the outside surface of a masonry heater in accordance with NFPA 211 Section 8-7 (clearances for solid-fuel-burning appliances), and the required space between the heater and combustible material shall be fully vented to permit the free flow of air around all heater surfaces.
Exceptions:
- Where the masonry heater wall is not less than 8 inches (203 mm) thick of solid masonry and the wall of the heat exchange channels is not less than 5 inches (127 mm) thick of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
- Masonry heaters listed and labeled in accordance with UL 1482 or CEN 15250 shall be installed in accordance with the listing specifications and the manufacturer’s written instructions.
SECTION R1003—MASONRY CHIMNEYS
R1003.1 Definition. A masonry chimney is a chimney constructed of solid masonry units, hollow masonry units grouted solid, stone or concrete, hereinafter referred to as masonry. Masonry chimneys shall be constructed, anchored, supported and reinforced as required in this chapter.
R1003.2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.
R1003.3 Seismic reinforcing. Masonry or concrete chimneys shall be constructed, anchored, supported and reinforced as required in this chapter. In all structures regulated by this code assigned to Seismic Design Category C, D 0, D 1 or D 2 masonry and concrete chimneys shall be reinforced and anchored as detailed in Sections R1003.3.1, R1003.3.2 and R1003.4. In Seismic Design Category A or B, reinforcement and seismic anchorage are not required.
R1003.3.1 Vertical reinforcing. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars, anchored in the foundation, shall be placed in the concrete, or between wythes of solid masonry, or within the cells of hollow unit masonry, and grouted in accordance with Section R608.1.1. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys more than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be installed for each additional 40 inches (1016 mm) in width or fraction thereof.
CRC § 902.2. High relevance — show source text
(2) Where approved, one listed wall-mounted unvented room heater equipped with an oxygen depletion safety shutoff system shall be permitted to be installed in a bedroom, provided that the input rating does not exceed 10 000 Btu/h (3 kW) and combustion and ventilation air is provided as specified in Section 902.2. [NFPA 54:10.21.2]
(3) Portable oil fired unvented heating appliances used as supplemental heating in storage occupancies, utility occupancies, and in accordance with the fire code.
[HCD 1 & HCD 2] Unvented fuel-burning room heaters shall not be installed, used, maintained, or permitted to exist in a Group R Occupancy.
915.3.2 Installations in Institutions. Room heaters shall not be installed in the following occupancies:
(1) Residential board and care
(2) Health care [NFPA 54:10.21.3] 915.3.3 Clearance. A room heater shall be placed so as not to cause a hazard to walls, floors, curtains, furniture, doors where open, and to the free movements of persons within the room. Heaters designed and marked, “For use in noncombustible fireplace only,” shall not be installed elsewhere. Listed room heaters shall be installed in accordance with their listings and the manufacturer’s installation instructions. In no case shall the clearances be
2025 CALIFORNIA MECHANICAL CODE 207
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
INSTALLATION OF SPECIFIC APPLIANCES
(1) A listed unit heater shall be installed with clearances from combustible material at the back and one side of not less than 6 inches (152 mm). Where the flue gases are vented horizontally, the 6 inch (152 mm) clearance shall be measured from the draft hood or
vent instead of the rear wall of the unit heater. A unit
heater listed for reduced clearances shall be installed in accordance with its listing and the manufacturer’s installation instructions.
(2) Floor-mounted-type unit heaters installed on combustible floors shall be listed for such installation.
(3) Combustible floors under unlisted floor-mounted unit heaters shall be protected in an approved man ner.
(4) Clearances for servicing shall be in accordance with the manufacturer’s instructions.
916.4 Combustion and Circulating Air. Combustion and circulating air shall be provided in accordance with Section 701.0. [NFPA 54:10.24.4]
916.5 Ductwork. A unit heater shall not be attached to a warm air duct system unless listed and marked for such installation. [NFPA 54:10.24.5] 916.6 Installation in Commercial Garages and Air- craft Hangars. Unit heaters installed in garages for more than three motor vehicles or in aircraft hangars shall be installed in accordance with Section 303.11 and Section 303.12. [NFPA 54:10.24.6]
916.7 Oil-Fired Unit Heaters. Oil-fired unit heaters shall comply with UL 731 and installed in accordance with the manufacturer’s installation instructions.
917.0 Food Service Appliance, Floor-Mounted. 917.1 Application. Floor-mounted food service appliances shall be listed in accordance with ANSI Z83.11/CSA 1.8.
CRC § 2.32 High relevance — show source text
shall be listed in accordance with ANSI Z21.86/CSA 2.32 or CSA/ANSI Z21.88/CSA 2.33. [NFPA 54:10.21.1.1]
915.1.2 Unvented Room Heaters. Unvented room
heaters shall be listed in accordance with CSA/ANSI
Z21.11.2. [NFPA 54:10.21.1.2]
915.2 Electric Room Heaters. Electric room heaters shall comply with UL 2021.
915.3 Gas-Fired Room Heaters. Gas-fired room heaters shall comply with Section 915.3.1 through Section 915.3.4. 915.3.1 Prohibited Installations. Unless specifically permitted by the Authority Having Jurisdiction, unvented room heaters shall not be installed as primary heat sources. Unvented room heaters shall not be permitted in spaces that do not have the required volume of indoor air as defined in Section 701.4.
[HCD 1 & HCD 2] Unvented fuel-burning room heaters shall not be installed, used, maintained, or permitted to exist in a Group R Occupancy.
915.3.1.1 Unvented Room Heaters. Unvented
room heaters shall not be installed in bathrooms or
bedrooms.
Exceptions:
(1) Where approved, one listed wall-mounted unvented room heater equipped with an oxygen depletion safety shutoff system shall be permitted to be installed in a bathroom, provided that the input rating does not exceed 6000 Btu/h (1.76 kW) and combustion and ventilation air is provided as specified in Section 902.2.
(2) Where approved, one listed wall-mounted unvented room heater equipped with an oxygen depletion safety shutoff system shall be permitted to be installed in a bedroom, provided that the input rating does not exceed 10 000 Btu/h (3 kW) and combustion and ventilation air is provided as specified in Section 902.2. [NFPA 54:10.21.2]
(3) Portable oil fired unvented heating appliances used as supplemental heating in storage occupancies, utility occupancies, and in accordance with the fire code.
[HCD 1 & HCD 2] Unvented fuel-burning room heaters shall not be installed, used, maintained, or permitted to exist in a Group R Occupancy.
915.3.2 Installations in Institutions. Room heaters shall not be installed in the following occupancies:
(1) Residential board and care
(2) Health care [NFPA 54:10.21.3] 915.3.3 Clearance. A room heater shall be placed so as not to cause a hazard to walls, floors, curtains, furniture, doors where open, and to the free movements of persons within the room. Heaters designed and marked, “For use in noncombustible fireplace only,” shall not be installed elsewhere. Listed room heaters shall be installed in accordance with their listings and the manufacturer’s installation instructions. In no case shall the clearances be
2025 CALIFORNIA MECHANICAL CODE 207
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
INSTALLATION OF SPECIFIC APPLIANCES
CRC § 21-13 High relevance — show source text
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supported by the body of the heater. Where the masonry chimney shares a common wall with the facing of the masonry heater, the chimney portion of the structure shall be reinforced in accordance with Section 2113.
2112.5 Masonry heater clearance. Combustible materials shall not be placed within 36 inches (914 mm) or the distance of the allowed reduction method from the outside surface of a masonry heater in accordance with NFPA 211, Section 12.6, and the required space between the heater and combustible material shall be fully vented to permit the free flow of air around all heater surfaces.
Exceptions:
- Where the masonry heater wall thickness is not less than 8 inches (203 mm) of solid masonry and the wall thickness of the heat exchange channels is not less than 5 inches (127 mm) of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
- Masonry heaters listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.
SECTION 2113—MASONRY CHIMNEYS
2113.1 General. The construction of masonry chimneys consisting of solid masonry units, hollow masonry units grouted solid, stone or concrete shall be in accordance with this section.
2113.2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.
2113.3 Seismic reinforcement. In structures assigned to Seismic Design Category A or B, seismic reinforcement is not required. In structures assigned to Seismic Design Category C or D, masonry chimneys shall be reinforced and anchored in accordance with Sections 2113.3.1, 2113.3.2 and 2113.4. In structures assigned to Seismic Design Category E or F, masonry chimneys shall be reinforced in accordance with the requirements of Sections 2101 through 2108 and anchored in accordance with Section 2113.4.
2113.3.1 Vertical reinforcement. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars anchored in the foundation shall be placed in the concrete between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103.3. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof. **2113.3.2 Horizontal reinforcement.
CRC § 10-8 High relevance — show source text
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CHIMNEYS AND FIREPLACES
R1003.12.1 Listed materials. Listed materials used as flue linings shall be installed in accordance with the terms of their listings and manufacturer’s instructions.
R1003.12.2 Space around lining. The space surrounding a chimney lining system or vent installed within a masonry chimney shall not be used to vent any other appliance.
Exception: This shall not prevent the installation of a separate flue lining in accordance with the manufacturer’s instructions.
R1003.13 Multiple flues. Where two or more flues are located in the same chimney, masonry wythes shall be built between adjacent flue linings. The masonry wythes shall be not less than 4 inches (102 mm) thick and bonded into the walls of the chimney.
Exception: Where venting only one appliance, two flues shall be permitted to adjoin each other in the same chimney with only the flue lining separation between them. The joints of the adjacent flue linings shall be staggered not less than 4 inches (102 mm).
R1003.14 Flue area (appliance). Chimney flues shall not be smaller in area than that of the area of the connector from the appliance
[see Tables R1003.14(1) and R1003.14(2)]. The sizing of a chimney flue to which multiple appliance venting systems are connected shall be in accordance with the California Mechanical Code.
TABLE R1003.14(1)—NET CROSS-SECTIONAL AREA OF ROUND FLUE SIZESa Col2 ** FLUE SIZE, INSIDE DIAMETER (inches)** ** CROSS-SECTIONAL AREA (square inches)** 6 28 7 38 8 50 10 78 103/4 90 12 113 15 176 18 254 For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2.
a. Flue sizes are based on ASTM C315.For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2.
a. Flue sizes are based on ASTM C315.CRC § 12.7 Medium relevance — show source text
Bolts shall be solidly embedded in grout._ 5. Bent bar anchor bolts shall not be allowed. The maximum size anchor shall be [1] / 2 -inch (12.7 mm) diameter for 6-inch (152 mm) nominal masonry, [3] / 4 -inch (19.1 mm) diameter for 8-inch (203 mm) nominal masonry, [7] / 8 -inch (22.2 mm) diameter for 10-inch (254 mm) nominal masonry, and 1-inch (25.4 mm) diameter for 12-inch (305 mm) nominal masonry. 6. Bolts shall be accurately set with templates or by approved equivalent means and held in place to prevent dislocation during grouting.
2104.2.4 TMS 602, Article 3.5 F.1 Grout key. Replace TMS 602, Article 3.5 F.1 as follows: 1. Between grout pours or where grouting has been stopped more than an hour, a horizontal construction joint shall be formed by terminating grout a minimum of 1 [1] / 2 inches (38.1 mm) and a maximum of one-half the masonry unit height below a mortar joint, except at the top of the wall. Where bond beams occur, the grout pour shall be terminated a minimum of [1] / 2
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inch (12.7 mm) below the mortar joint. Horizontal reinforcement shall be placed in bond beam units with a minimum grout cover of 1 inch (25.4 mm) above reinforcing steel for each grout pour.
2104.3 Aluminum equipment. [OSHPD 1R, 2 & 5] Grout shall not be handled nor pumped utilizing aluminum equipment unless it can be demonstrated with the materials and equipment to be used that there will be no deleterious effect on the strength of the grout.
SECTION 2105—QUALITY ASSURANCE
2105.1 General. A quality assurance program shall be used to ensure that the constructed masonry is in compliance with the approved construction documents.
The quality assurance program shall comply with the inspection and testing requirements of Chapter 17 and TMS 602. 2105.2 Compressive strength , f ′ m . [OSHPD 1R, 2 & 5] Testing of masonry shall be provided in accordance with TMS 602, Article 1.4 B.
Exception: Where values of f ′ m greater than 2,000 psi (13.79 MPa) are used in the design of reinforced grouted multi-wythe masonry and reinforced hollow unit masonry, they shall be based on prism test results in accordance with TMS 602, Article 1.4 B.3 submitted by the architect or engineer to the enforcement agency which demonstrate the ability of the proposed construction to meet prescribed performance criteria for strength exceed 3,000 psi (20.7 MPa).
CRC § 2.3 Medium relevance — show source text
SIP R610.8
Steel R603.6
Wood R602.7
Hearth R1001.9
Extension R1001.10, R1001.9
Heaters
Masonry R1002 Heating Required R325.8 Height Ceiling R313 Mezzanines R314.2 Sleeping lofts R315.3 Hollow-Unit Masonry (see Masonry)
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INDEX
Roof shingles R905.4 Methods Water distribution pipe sizing Appendix CF Mezzanines (see also Sleeping Lofts) R314, R321 Modifications R104.2.3 Moisture Content, Building Materials R109.1.4.1
Moisture Control R702.7
Mortar
Joints R606.3.1 Multiple Flues R1003.13
Natural Light (see Light) Natural Ventilation (see Ventilation) Notching Steel joists R505.2.5, R505.3.5, R804.2.5, R804.3.3 Steel studs R603.2.6, R603.3.4 Wood joists R502.8, R802.7.1 Wood studs R602.6 Wood top plates R602.6.1
Opening Protection R302.5
Parapets R302.2.2, R606.4.4 Particleboard
Floor R503.3
Walls R605 Patio Covers Appendix BF Penetrations R302.4, R302.5 Permits 1.8.4, R105, R105.5.1 Permit fees Appendix AB Photovoltaic Panel Systems R907 Ground-mounted definition R202
Photovoltaic Support Structure, Elevated R202, R324.8, R324.8.1, R324.8.2 Piers R606.7
Masonry R404.1.9 Planning Building Chapter 3 Plans R106
Plaster
Exterior R703.7
Interior R702.2
Platform Lifts R323.2, R323.3 Plumbing Fixture clearances R327
Fixtures R326, R327 Inspection 109.1.2 Requirements and definitions R202 System, definition R202 Plywood Application R703.5 Materials, walls R604
Precast Concrete
Footings R403.4 Foundation material R402.3.1
Foundation walls R404.5
Protection Against decay and termites R304, R305 Against radon Appendix BE Public Way R318.1, R319.1 Purlins R802.4.5
Hot Tubs (see Swimming Pools) R324.3.1, R328 Hurricane (see Storm Shelter)
Impact Protective System Energy storage system R330.8 Flood R306.1.4.2, R306.3.3 Human impact R324.3 Storm shelter R307.2.1
Frequently asked questions
What listings/standards are acceptable to comply with the CRC for masonry heaters?
Either design/build to ASTM E1602, or use a unit listed and labeled to UL 1482 or CEN 15250 and install per the listing/manufacturer; this requirement is in § R1002.2 .
Can I reduce required clearance to combustibles around a masonry heater?
Yes — the code allows 4 inches (102 mm) clearance if the heater wall is ≥ 8 inches (203 mm) of solid masonry and channel walls are ≥ 5 inches (127 mm); otherwise the default clearance is 36 inches (914 mm). See § R1002.5 .
Are listed heaters allowed to use manufacturer instructions instead of the prescriptive masonry rules?
Yes. A heater listed to UL 1482 or CEN 15250 may be installed according to its listing and the manufacturer’s written instructions (see § R1002.2 and the related exception in § R1002.5) .
Do masonry heaters require seismic anchorage in California?
Yes — in seismic categories D0, D1 and D2 masonry heaters must be anchored to the masonry foundation; internal reinforcing may or may not be required depending on the height ≤ 3.5 × width exception and whether the chimney is supported by the heater (see § R1002.4) .
What is the minimum firebox floor thickness?
The firebox floor must be at least 4 inches (102 mm) of noncombustible material and supported on a noncombustible footing/foundation (see § R1002.3) .
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