CBC · California Building Code

Masonry heaters: definition, installation standards, footing requirements and seismic reinforcing

For California projects, masonry heaters must meet CBC chapter requirements: defined by their masonry construction and heat-exchange channels (§ 2112.1), installed to ASTM E1602 or as a listed appliance (§ 2112.2), rest on a ≥4 in noncombustible firebox floor supported by proper noncombustible footings (see § 2113.2) (§ 2112.3), be anchored/reinforced for SDC D/E/F per masonry-chimney rules with a limited exception when height ≤3.5×width (§ 2112.4), and maintain required combustibles clearances (36 in or allowed reductions) (§ 2112.5) .

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The California Building Code defines a masonry heater and sets mandatory installation routes: comply with ASTM E1602 or be listed and installed per UL 1482/EN 15250 and the manufacturer’s instructions (§ 2112.2) . The firebox floor must be at least 4 in (102 mm) of noncombustible material and be supported on a noncombustible footing and foundation per the masonry-chimney footing rules in § 2113.2 (§ 2112.3) . In SDC D, E or F masonry heaters must be anchored to the masonry foundation and, where applicable, reinforced per the masonry-chimney reinforcement provisions (§ 2112.4) . Combustible clearance is 36 in (914 mm) from the heater surface (with limited exceptions) and the clearance space must be fully vented (§ 2112.5) .

Requirements in detail

Definition (what a masonry heater is)

  • The CBC defines a masonry heater as a heating appliance constructed of concrete or solid masonry that absorbs and stores heat from a solid-fuel fire by routing exhaust gases through internal heat-exchange channels (the downstream flow includes horizontal or downward flow before entering the chimney) and that delivers heat by radiation from the masonry surface (§ 2112.1) .
  • Note: the CBC § 2112.1 text returned does not state a minimum mass. The California Residential Code contains a mass-based definition (e.g., ≥1,100 lb) in R1002; that is a residential-code provision, not the IBC-style CBC § 2112.1 text retrieved here .

Installation standards (§ 2112.2)

  • Two permitted compliance paths:
    1. Full compliance with ASTM E1602 (design and construction standard for masonry heaters).
    2. Use a listed/labeled unit (UL 1482 or EN 15250) and install per the manufacturer’s instructions (§ 2112.2) .
  • If using a listed heater, relevant listing instructions can modify clearances and some installation details (see § 2112.5 exception) .

Footings and foundations (§ 2112.3 and § 2113.2)

  • Minimum firebox floor: 4 in (102 mm) of noncombustible material (mortar, concrete, etc.) (§ 2112.3) .
  • The firebox floor must be supported on a noncombustible footing/foundation constructed per masonry chimney footing rules: footings of concrete or solid masonry at least 12 in (305 mm) thick and extending not less than 6 in (152 mm) beyond the face of the foundation/support wall on all sides; footings must be founded on natural undisturbed earth or engineered fill below frost depth; in non-freeze areas footings shall be not less than 12 in (305 mm) below finished grade (§ 2113.2) .

Seismic reinforcing and anchorage (§ 2112.4 with masonry-chimney details in § 2113)

  • Required anchorage: In structures assigned to Seismic Design Category (SDC) D, E or F, masonry heaters shall be anchored to the masonry foundation in accordance with the masonry-chimney anchorage/reinforcement provisions (§ 2112.4) .
  • Exception inside the heater body: seismic reinforcing within the body of a masonry heater is not required when the heater height is equal to or less than 3.5 times its body width AND the masonry chimney serving the heater is NOT supported by the heater body (§ 2112.4) .
  • When the masonry chimney shares a common wall with the heater facing, the chimney portion must be reinforced per the chimney rules (§ 2112.4 and § 2113) .

Key masonry-chimney reinforcement details to apply (see Section 2113):

  • Vertical reinforcement (typical minimum): for chimneys up to 40 in (1016 mm) wide, provide four No. 4 continuous vertical bars anchored in the foundation, placed in the concrete between wythes or in grouted cells; for each additional 40 in or fraction thereof add two No. 4 bars (§ 2113.3.1) .
  • Horizontal reinforcement: vertical bars shall be enclosed by 1/4 in (6.4 mm) ties (or equivalent net area), spaced not to exceed 18 in (457 mm) on center in concrete or placed in masonry bed joints not less frequently than every 18 in vertical height; two ties at each bend in vertical bars (§ 2113.3.2) .
  • Seismic anchorage straps: chimneys and foundations shall be anchored at each floor/ceiling/roof line more than 6 ft (1829 mm) above grade using two 3/16 in × 1 in (4.8 mm × 25 mm) straps embedded not less than 12 in (305 mm) into the chimney; straps hook around outer bars and extend 6 in (152 mm) beyond the bend, and are fastened to not fewer than four floor joists with two 1/2 in (12.7 mm) bolts (§ 2113.4) .

Decision-relevant dimensions and values

Item Required value / limit Code Reference
Firebox floor minimum thickness 4 in (102 mm) noncombustible § 2112.3
Chimney/footing minimum thickness 12 in (305 mm) concrete or solid masonry § 2113.2
Footing projection beyond face ≥ 6 in (152 mm) all sides § 2113.2
Required clearance to combustibles 36 in (914 mm) or allowed reduction per NFPA 211 method § 2112.5
Exception — reduced clearance for thick heater walls 4 in (102 mm) clearance when wall ≥ 8 in and channels ≥ 5 in § 2112.5 Exception 1
Exception — capping slab to combustible ceiling ≥ 8 in (203 mm) between gas-tight capping slab and combustible ceiling § 2112.5 Exception 1
Chimney vertical reinforcement (typical) 4 No.4 bars for ≤ 40 in width; +2 No.4 per additional 40 in § 2113.3.1
Horizontal tie spacing ≤ 18 in (457 mm) vertically § 2113.3.2
Seismic anchorage straps Two 3/16"×1" straps embedded ≥12" and fastened to ≥4 joists with two 1/2" bolts § 2113.4
Seismic categories requiring anchorage SDC D, E, F (heaters anchored to masonry foundation) § 2112.4

Exceptions & special cases

  • Listed units: masonry heaters listed and labeled to UL 1482 or EN 15250 and installed per manufacturer instructions may follow the listing in lieu of some code prescriptive assumptions (exceptions in § 2112.2 and § 2112.5) .
  • Thick-mass heaters: if the heater body is solid masonry ≥ 8 in thick and heat-exchange channel walls ≥ 5 in, the required clearance to combustibles can be reduced to 4 in; and if there is a gas-tight capping slab, provide at least 8 in to a combustible ceiling (§ 2112.5 Exception 1) .
  • Seismic-exception within the heater body: if heater height ≤ 3.5 × body width AND the masonry chimney is not supported by the heater body, seismic reinforcing within the body is not required (§ 2112.4) .
  • Chimney-sharing wall: where the masonry chimney shares a common wall with the heater facing, the chimney portion must be reinforced per § 2113 (no waiver) (§ 2112.4) .

Common mistakes

  • Relying on a residential mass threshold that isn’t in the CBC definition: the CBC § 2112.1 text retrieved here defines the heater by function and construction but does not state a mass minimum — do not assume a mass criterion from other code parts unless you cite them (the CRC R1002 includes mass language for residential heaters) .
  • Skipping the ASTM or listing compliance path: installing a custom masonry heater without either following ASTM E1602 or using a listed appliance plus manufacturer instructions violates § 2112.2 .
  • Under-sizing or omitting the noncombustible firebox floor (less than 4 in) or placing it on combustible supports — the code requires a minimum 4 in noncombustible floor on noncombustible footing (§ 2112.3) .
  • Not providing required footing thickness and projection: some installers treat the heater footing like a small shallow pad when the code requires chimney/footing details in § 2113.2 (12 in thick, extend ≥6 in) .
  • Ignoring seismic anchorage/reinforcement in SDC D/E/F: if the heater or chimney is within these SDCs and the chimney is supported by the heater (or shares its wall), anchorage and reinforcement per the chimney rules are required (§ 2112.4 and § 2113) .
  • Applying clearance reductions without confirming masonry thickness/ channel thickness or the listed-unit allowance — the code exceptions are specific and must be demonstrated (§ 2112.5) .

Worked example — applying the rule with numbers

Scenario: You are designing a masonry heater in an SDC D structure. The heater body width (face-to-back) is 48 in (4 ft) and the proposed heater overall height is 13 ft (156 in). The masonry chimney is independent (it is supported on its own foundation, not by the heater body).

  1. Determine whether seismic reinforcing is required within the heater body:
    • Calculate 3.5 × body width = 3.5 × 48 in = 168 in (14 ft). The heater height is 156 in (13 ft), which is less than 168 in, and the chimney is NOT supported by the heater body. Thus seismic reinforcing within the heater body is NOT required per § 2112.4 .
  2. Anchorage to foundation:
    • Because the structure is SDC D, the heater must be anchored to the masonry foundation in accordance with the masonry-chimney anchorage provisions; coordinate anchorage details with the chimney designer and follow § 2113 provisions as applicable (§ 2112.4) .
  3. Firebox floor and footing:
    • Provide a firebox floor of at least 4 in noncombustible material supported on a noncombustible footing/foundation. Design the heater footing consistent with § 2113.2 — chimney footings are typically 12 in thick and extend ≥6 in beyond the face; use that as the footing template for compatibility and load transfer (§ 2112.3; § 2113.2) .
  4. Clearance:
    • Maintain 36 in clearance from the outside surface of the heater to combustibles unless the heater meets the thick-mass exception (it must have ≥8 in wall thickness and channels ≥5 in to reduce to 4 in clearance). If you are not meeting that mass thickness, provide the 36 in clearance and ensure the clearance cavity is fully vented (§ 2112.5) .
  5. Chimney reinforcement (if chimney is tied or shares a wall):
    • If the chimney shares a wall with the heater or the chimney is supported by the heater, provide the chimney vertical reinforcement (e.g., four No.4 continuous bars for chimney width ≤40 in; increase bars for wider chimneys) and horizontal ties not exceeding 18 in spacing, per § 2113.3.1 and § 2113.3.2. Provide seismic straps at each floor/ceiling/roof line >6 ft above grade per § 2113.4 if required by SDC .

Related provisions (quick references)

  • § 2112.1 — Definition of masonry heater (CBC)
  • § 2112.2 — Installation compliance paths (ASTM E1602 or listed unit)
  • § 2112.3 — Firebox floor minimum thickness and support requirement (§ references § 2113.2)
  • § 2112.4 — Seismic reinforcing requirements and exception (SDC D, E, F)
  • § 2112.5 — Clearance to combustibles and exceptions (NFPA 211 method referenced)
  • § 2113.2 — Footings and foundations for masonry chimneys (12 in thick, extend ≥6 in, founded below frost) — used for heater footing design reference
  • § 2113.3 / § 2113.3.1 / § 2113.3.2 — Seismic reinforcement details for chimneys (vertical/horizontal reinforcement)
  • § 2113.4 — Seismic anchorage straps for chimneys and attachment details
  • CRC R1002 — Residential-code definition and some R-code parallels (mass-based definition appears in the CRC) — consult R1002 for residential specifics if applicable
  • § 1705.4 (Chapter 17) — Special-inspection exception: masonry heaters installed in accordance with § 2112 do not require the same special inspection regimen as other masonry (confirm with enforcing agency)

Code references

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

  • CBC § 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:

    1. Masonry heaters shall comply with the requirements of ASTM E1602.
    2. 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:

    1. 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.
    2. 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.

  • CBC § 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:

    1. Masonry heaters shall comply with the requirements of ASTM E1602.
    2. 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

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    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:

    1. 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.
    2. 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.

  • CBC § 14.3 High relevance — show source text

    2111 A .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 A .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 A .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 A .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 A —MASONRY HEATERS

    2112 A .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 A .2 Installation. Masonry heaters shall be installed in accordance with this section and comply with one of the following:

    1. Masonry heaters shall comply with the requirements of ASTM E1602.
    2. 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 .

  • CBC § 2111.14.2 High relevance — show source text

    The fireblock
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    COMBUSTIBL
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    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:

    1. Masonry heaters shall comply with the requirements of ASTM E1602.
    2. 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

  • CBC § 21-13 High relevance — show source text

    2025 CALIFORNIA BUILDING CODE 21-13

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    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:

    1. 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.
    2. 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.

  • CBC § 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:

    1. Masonry heaters shall comply with the requirements of ASTM E1602.
    2. 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.

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    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:

    1. 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.
    2. 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.

  • CBC § 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:

    1. 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.
    2. 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.

  • CBC § 2113.2 High relevance — show source text

    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. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete, or placed in the bed joints of unit masonry, at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

    2113.4 Seismic anchorage. Masonry chimneys and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.
  • CBC § 3.1 High relevance — show source text

    2111 A .3.1 Ash dump cleanout. Cleanout openings, located within foundation walls below fireboxes, where provided, shall be equipped with ferrous metal or masonry doors and frames constructed to remain tightly closed, except when in use. Cleanouts shall be accessible and located so that ash removal will not create a hazard to combustible materials.

    2111 A .4 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 fireplaces shall be reinforced and anchored in accordance with Sections 2111 A .4.1, 2111 A .4.2 and 2111 A .5. In structures assigned to Seismic Design Category E or F, masonry fireplaces shall be reinforced in accordance with the requirements of Sections 2101 A through 2108 A .

    2111 A .4.1 Vertical reinforcing. For fireplaces with 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. For fireplaces with 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. 2111 A .4.2 Horizontal reinforcing. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete; or placed in the bed joints of unit masonry at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

    2111 A .5 Seismic anchorage. Masonry fireplaces and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not fewer than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.
  • CBC § 1.3 Medium relevance — show source text

    R403.1.3 Footing and stem wall reinforcing in Seismic Design Categories D 0 , D 1 and D 2 . Concrete footings located in Seismic Design Categories D 0, D 1 and D 2, as established in Table R301.2, shall have minimum reinforcement in accordance with this section and Figure R403.1.3. Reinforcement shall be installed with support and cover in accordance with Section R403.1.3.5.

    4-12 2025 CALIFORNIA RESIDENTIAL CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    FOUNDATIONS

    FIGURE R403.1.3—REINFORCED CONCRETE FOOTINGS AND MASONRY AND CONCRETE STEM WALLS IN SDC D 0 , D 1 AND D 2a, b, c, d, e, f

    W = Width of footing, T = Thickness of footing and P = Projection per Section R403.1.1.

    NOTES:

    a. See Section R404.3 for sill requirements. b. See Section R403.1.6 for sill attachment.

    c. See Section R506.3.3 for vapor barrier requirements. d. See Section R403.1 for base.

    e. See Section R408 for under-floor ventilation and access requirements. f. See Section R403.1.3.5 for reinforcement requirements.

    2025 CALIFORNIA RESIDENTIAL CODE 4-13

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    FOUNDATIONS

    R403.1.3.1 Concrete stem walls with concrete footings. In Seismic Design Categories D 0, D 1 and D 2 where a construction joint is created between a concrete footing and a concrete stem wall, not fewer than one No. 4 vertical bar shall be installed at not more than 4 feet (1219 mm) on center. The vertical bar shall have a standard hook and extend to the bottom of the footing and shall have support and cover as specified in Section R403.1.3.5.3 and extend not less than 14 inches (357 mm) into the stem wall. Standard hooks shall comply with Section R608.5.4.5. Not fewer than one No. 4 horizontal bar shall be installed within 12 inches (305 mm) of the top of the stem wall and one No. 4 horizontal bar shall be located 3 to 4 inches (76 mm to 102 mm) from the bottom of the footing.

    R403.1.3.2 Masonry stem walls with concrete footings. In Seismic Design Categories D 0, D 1 and D 2 where a masonry stem wall is supported on a concrete footing, not fewer than one No. 4 vertical bar shall be installed at not more than 4 feet (1219 mm) on center. The vertical bar shall have a standard hook and extend to the bottom of the footing and shall have support and cover as specified in Section R403.1.3.5.3 and extend not less than 14 inches (357 mm) into the stem wall. Standard hooks shall comply with Section R608.5.4.5. Not fewer than one No. 4 horizontal bar shall be installed within 12 inches (305 mm) of the top of the wall and one No.

  • California Building Code Medium 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:

    1. Masonry heaters shall comply with the requirements of ASTM E1602.
    2. Masonry heaters shall be listed and labeled in accordance with UL 1482 or CEN 15250 and installed in accordance with the manufacturer’s instructions.
  • CBC § 21-5 Medium relevance — show source text

    2104 Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-5

    2105 Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6

    2106 Seismic Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-7

    2107 Allowable Stress Design. . . . . . . . . . . . . . . . . . . . . . . . 21-8

    2025 CALIFORNIA BUILDING CODE xxvii

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    CONTENTS

    2108 Strength Design of Masonry . . . . . . . . . . . . . . . . . . . . 21-8

    2109 Empirical Design of Adobe Masonry . . . . . . . . . . . . . 21-9

    2110 Glass Unit Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-11

    2111 Masonry Fireplaces . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-11

    2112 Masonry Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-13

    2113 Masonry Chimneys . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-14

    2114 Dry-Stack Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-19

    2115 Additional Requirements for Community Colleges

    [DSA-SS/CC]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-19

    CHAPTER 21A MASONRY . . . . . . . . . . . . . . . . . . . . . . . . . . .21A-1

    2101A General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21A-3

    2102A Notations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21A-4

    2103A Masonry Construction Materials. . . . . . . . . . . . . . . . . . 21A-4

    2104A Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21A-5

    2105A Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21A-7

Frequently asked questions

Do masonry heaters always require seismic reinforcement?

Not always. In SDC D, E or F they must be anchored to the masonry foundation, but seismic reinforcing inside the heater body is not required when the heater height is ≤ 3.5 × its body width and the masonry chimney is not supported by the heater (§ 2112.4) .

Can I reduce combustible clearances by using a listed heater?

Yes. Listed and labeled heaters (UL 1482 or EN 15250) installed per the manufacturer's instructions may be installed in accordance with their listing; the CBC permits listed-unit installation as an alternate to the prescriptive clearance in § 2112.5 (§ 2112.2, § 2112.5) .

What minimum thickness is required for the firebox floor and the footing?

The firebox floor must be at least 4 in (102 mm) of noncombustible material supported on a noncombustible footing/foundation; masonry-chimney footings are described as a minimum 12 in (305 mm) thick and extending ≥6 in beyond the face (§ 2112.3; § 2113.2) .

If my heater is 8 ft tall and 2 ft deep, do I need seismic reinforcing in the heater body?

Compute 3.5 × body width: 3.5 × 24 in = 84 in (7 ft). Your heater is 8 ft tall (> 7 ft), so the exception (height ≤ 3.5×width) does not apply; if the structure is in SDC D, E or F and the chimney is supported by the heater or shares its wall, reinforcing/anchorage will be required (§ 2112.4) .

Where can I find the vertical/horizontal reinforcement details for chimneys that apply to heaters?

See § 2113.3.1 for vertical reinforcement quantities (e.g., four No.4 bars for chimneys ≤40 in) and § 2113.3.2 for horizontal-tie spacing (≤18 in) and tie details; these apply when the chimney portion is required to be reinforced (§ 2113.3.1, § 2113.3.2) .

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Related in the CBC

Masonry chimneys: footing dimensions, vertical/horizontal reinforcement and seismic anchorage

Masonry fireplaces: construction requirements, clearances and seismic anchorage exceptions

Chimneys, fireplaces and masonry heaters

California Building Code