CMC · California Mechanical Code
What are inspection, cleanout and support requirements for existing and new chimneys?
Before connecting or concealing any chimney work you must have it inspected, clean and accessible cleanouts are required when converting wood/oil chimneys to gas (cleanout upper edge at least 6" below the lowest inlet), and chimneys must be properly supported — all per the California Mechanical Code §§ 802.5.6, 802.5.7, 802.5.9 and 802.5.10.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The California Mechanical Code requires a pre-cover inspection of chimneys and vents, an examination and cleaning of any existing chimney before connecting an appliance, accessible and tight‑fitting cleanouts when converting formerly solid/liquid‑fuel chimneys to gas, and that all portions of chimneys be supported for their design and weight. The controlling sections are § 802.5.6, § 802.5.7, § 802.5.9, and § 802.5.10.
The single most important rule: inspect chimney passages before they are concealed or before connecting a vent; if an existing chimney is unsafe for the intended appliance it must be repaired, relined, or replaced to meet the applicable standards.
Requirements in detail
Inspection (what, when, and why)
- The code requires an inspection after chimneys, vents, or parts authorized by the permit have been installed and before they are covered or concealed — § 802.5.6. This is a field inspection point; do not conceal work before inspection.
- Before replacing an existing appliance or connecting a vent connector to a chimney, the chimney passageway must be examined to ensure it is clear and free of obstructions and cleaned if previously used for solid‑ or liquid‑fuel appliances — § 802.5.7. If unsafe, the chimney must be repaired, rebuilt, lined/relined, or replaced to conform to NFPA 211 and be suitable for the appliances.
Cleanouts (location, cover, accessibility)
- When a chimney that formerly carried flue products from liquid or solid fuel appliances is repurposed for a fuel‑gas appliance, an accessible cleanout is required — § 802.5.10. The cleanout must have a tight‑fitting cover and must be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening.
- Existing cleanouts must be examined and, where they do not remain tightly closed when not in use, repaired or replaced — § 802.5.7.2.
Support (structural and manufacturer requirements)
- All portions of chimneys must be supported for the design and weight of the materials employed — § 802.5.9. Listed factory‑built chimneys must be supported and spaced in accordance with the manufacturer’s installation instructions. Do not rely on chimney mass or adjacent framing unless the chimney is designed for additional loads.
Quick reference table (decision‑relevant values)
| Item | Requirement / Value | When it applies | Code Reference |
|---|---|---|---|
| Inspection before concealment | Must inspect after installation and before covering | New installations or altered parts under permit | § 802.5.6 |
| Pre‑connection exam & cleaning | Chimney passageway clear; clean if previously used for solid/liquid fuel | Before replacing appliance or connecting vent connector | § 802.5.7 |
| Cleanout required for conversion | Accessible cleanout with tight‑fitting cover | When old solid/liquid fuel chimney used with fuel‑gas appliance | § 802.5.10 |
| Cleanout vertical position | Upper edge at least 6 inches (152 mm) below lowest inlet lower edge | Location of cleanout relative to chimney inlet | § 802.5.10 |
| Cleanout cover condition | Must remain tightly closed when not in use; repair/replace if not | Existing cleanouts | § 802.5.7.2 |
| Chimney support | Supported for design/weight; factory‑built follow manufacturer | All chimneys (masonry, metal, factory) | § 802.5.9 |
| Unsafe existing chimney | Repair, rebuild, line or replace to meet NFPA 211 if unsafe | When inspection reveals chimney not safe for intended application | § 802.5.7.3 |
Exceptions & special cases
- If inspection shows an existing chimney is not safe for the intended appliance, the code requires it to be repaired, rebuilt, lined/relined, or replaced so it conforms to NFPA 211 and is suitable for the appliance — § 802.5.7.3. Do not connect the appliance until the chimney is made suitable.
- Factory‑built (listed) chimneys are governed both by the CMC support requirement and the manufacturer’s installation instructions; follow the manufacturer where those instructions provide the required spacing and supports — § 802.5.9.
- The code requires a cleanout when a flue previously used for solid/liquid fuel will be used for gas; it does not itself prescribe additional sizing or covering details beyond the 6‑inch vertical placement and a tight‑fitting cover — other detailed cleanout dimensions may be found in the Building Code for masonry fireplaces, but are outside the specific text of these CMC sections.
If you need decisions about lining materials, liner sizing, or structural design to carry additional loads, those are governed elsewhere (NFPA 211, manufacturer instructions, or the California Building Code) and are not fully specified by the four CMC sections cited above. The retrieved CMC text does not contain manufacturer‑specific support spacing or detailed liner material specifications; consult those documents where required.
Common mistakes
- Covering or concealing chimney/vent components before the required inspection has been made (violates § 802.5.6).
- Failing to clean a chimney that previously vented solid/liquid fuel before connecting a gas appliance (violates § 802.5.7).
- Installing a cleanout whose upper edge is closer than 6 inches to the lowest inlet or using a loose/non‑tight cover (violates § 802.5.10 and § 802.5.7.2).
- Assuming a chimney can support extra loads (e.g., framing, equipment) without design—the code requires chimneys be supported for the design and weight of materials; factory units must follow manufacturers’ instructions (§ 802.5.9).
Worked example — converting a masonry chimney previously used for wood to serve a gas furnace
Scenario: You have an existing masonry chimney. The lowest chimney inlet opening (where a connector will enter) has a lower edge at 48 inches above the cleanout base.
Steps required by the CMC:
- Do not connect the gas furnace until the chimney is inspected. An inspector must examine the installed/uncovered chimney components before any concealment — § 802.5.6.
- Before connecting the furnace vent connector, the chimney passageway must be examined and cleaned (because it formerly served solid fuel) to ensure it is clear and free of obstructions — § 802.5.7.
- Provide an accessible cleanout with a tight‑fitting cover whose upper edge is at least 6 inches (152 mm) below the lower edge of the lowest inlet. With the inlet lower edge at 48 in, the cleanout upper edge must be at 42 in or lower (48 in − 6 in = 42 in) — § 802.5.10.
- Verify the chimney structure is properly supported for its materials and any loads; if it’s a factory‑built chimney, follow the manufacturer’s installation instructions for supports and spacing — § 802.5.9. If inspection reveals the chimney is not safe for the gas furnace, repair/reline or replace to conform to NFPA 211 before connecting — § 802.5.7.3.
Related provisions
- § 802.5.8 — Chimney serving appliances burning other fuels (restrictions on mixing fuel types).
- § 802.5.11 — Space surrounding lining or vent; prohibits using remaining space for venting another appliance.
- § 802.6 — Gas vent installation requirements (manufacturer instructions, labeling, fastener restrictions).
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 802.5.7.2 High relevance — show source text
802.5.7.2 Cleanouts. Cleanouts shall be examined and where they do not remain tightly closed when not in use, they shall be repaired or replaced. [NFPA 54:12.6.4.3] 802.5.7.3 Existing Chimney. When inspection reveals that an existing chimney is not safe for the intended application, it shall be repaired, rebuilt, lined, relined, or replaced with a vent or chimney to conform to NFPA 211 and shall be suitable for the appliances to be attached. [NFPA 54:12.6.4.4] 802.5.8 Chimney Serving Appliances Burning Other Fuels. An appliance shall not be connected to a chimney flue serving a separate appliance designed to burn solid fuel. [NFPA 54:12.6.5.1] 802.5.8.1 Gas and Liquid Fuel-Burning Appliances. Where one chimney serves gas appliances and liquid fuel-burning appliances, the appliances shall be connected through separate openings or connected through a single opening where joined by a suitable fitting located as close as practical to the chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels. Where the gas appliance is automatically controlled, it shall be equipped with a safety shutoff device. [NFPA 54:12.6.5.2] 802.5.8.2 Gas and Solid Fuel-Burning Appli- ances. A listed combination gas- and solid fuelburning appliance connected to a single chimney flue shall be equipped with a manual reset device to shut off gas to the main burner in the event of sustained backdraft or flue gas spillage. The chimney flue shall be sized to properly vent the appliance.
[NFPA 54:12.6.5.3] 802.5.8.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4]
802.5.9 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6]
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CHIMNEYS AND VENTS
802.5.10 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7] 802.5.11 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.
CMC § 803.0. High relevance — show source text
(1) Those listed in Section 803.0.
(2) The effective areas of the vent connector and chimney flue of a venting system serving a single appliance with a draft hood shall be not less than the area
of the appliance flue collar or draft hood outlet or greater than seven times the draft hood outlet area.
(3) The effective area of the chimney flue of a venting system serving two appliances with draft hoods shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.
(4) Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods.
(5) Other engineering methods. [NFPA 54:12.6.3.1]
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CHIMNEYS AND VENTS
FIGURE 802.5.4
TYPICAL TERMINATION LOCATIONS FOR
CHIMNEYS AND SINGLE-WALL METAL PIPES SERVING
RESIDENTIAL-TYPE AND LOW-HEAT APPLIANCE
[NFPA 54: FIGURE A.12.6.2.1]
802.5.6 Inspection of Chimneys or Vents. This inspection shall be made after chimneys, vents, or parts thereof, authorized by the permit, have been installed and before such vent or part thereof has been covered or concealed.
802.5.7 Inspection of Chimneys. Before replacing an existing appliance or connecting a vent connector to a chimney, the chimney passageway shall be examined to ascertain that it is clear and free of obstructions and shall be cleaned if previously used for venting solid- or liquid-fuel-burning appliances or fireplaces. [NFPA 54:12.6.4.1] 802.5.7.1 Standard. Chimneys shall be lined in accordance with NFPA 211. [NFPA 54:12.6.4.2]
802.5.7.2 Cleanouts. Cleanouts shall be examined and where they do not remain tightly closed when not in use, they shall be repaired or replaced. [NFPA 54:12.6.4.3] 802.5.7.3 Existing Chimney. When inspection reveals that an existing chimney is not safe for the intended application, it shall be repaired, rebuilt, lined, relined, or replaced with a vent or chimney to conform to NFPA 211 and shall be suitable for the appliances to be attached. [NFPA 54:12.6.4.4] 802.5.8 Chimney Serving Appliances Burning Other Fuels. An appliance shall not be connected to a chimney flue serving a separate appliance designed to burn solid fuel. [NFPA 54:12.6.5.1] 802.5.8.1 Gas and Liquid Fuel-Burning Appliances. Where one chimney serves gas appliances and liquid fuel-burning appliances, the appliances shall be connected through separate openings or connected through a single opening where joined by a suitable fitting located as close as practical to the chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels.
CMC § 12.6.5.3 High relevance — show source text
The chimney flue shall be sized to properly vent the appliance.
[NFPA 54:12.6.5.3] 802.5.8.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4]
802.5.9 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6]
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CHIMNEYS AND VENTS
802.5.10 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7] 802.5.11 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.
Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 802.5.11.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal or factory-built chimney flue shall not be used to supply combustion air.
Exception: Direct vent appliances designed for installation in a solid-fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.8.2] 802.6 Gas Vents. The installation of gas vents shall meet the following requirements:
(1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
(2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is
connected.
(3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”
(4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.
[NFPA 54:12.7.2] 802.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:
(1) A gas vent shall terminate in accordance with one of the following:
CMC § 12.6.5.2 High relevance — show source text
chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels. Where the gas appliance is automatically controlled, it shall be equipped with a safety shutoff device. [NFPA 54:12.6.5.2] 509.5.7.2 Gas and Solid Fuel-Burning Appli- ances. A listed combination gas- and solid-fuelburning appliance connected to a single chimney flue shall be equipped with a manual reset device to shut off gas to the main burner in the event of sustained backdraft or flue gas spillage. The chimney flue shall be sized to properly vent the appliance.
[NFPA 54:12.6.5.3] 509.5.7.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4] 509.5.8 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6] 509.5.9 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7] 509.5.10 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.
Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 509.5.10.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory-built chimney flue shall not be used to supply combustion air.
Exception: Direct-vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.8.2] 509.6 Gas Vents. The installation of gas vents shall meet the following requirements:
(1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
(2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is
connected.
(3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry
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WATER HEATERS
CMC § 509.5.6.2 High relevance — show source text
509.5.6.2 Cleanouts. Cleanouts shall be examined and where they do not remain tightly closed when not in use, they shall be repaired or replaced.
[NFPA 54:12.6.4.3] 509.5.6.3 Existing Chimney. When inspection reveals that an existing chimney is not safe for the intended application, it shall be repaired, rebuilt, lined, relined, or replaced with a vent or chimney to conform to NFPA 211 and shall be suitable for the appliances to be attached. [NFPA 54:12.6.4.4] 509.5.7 Chimney Serving Appliances Burning Other Fuels. An appliance shall not be connected to a chimney flue serving a separate appliance designed to burn solid fuel. [NFPA 54:12.6.5.1] 509.5.7.1 Gas and Liquid Fuel-Burning Appli- ances. Where one chimney serves gas appliances and liquid fuel-burning appliances, the appliances shall be connected through separate openings or connected through a single opening where joined by a suitable fitting located as close as practical to the
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WATER HEATERS
FIGURE 509.5.4
TYPICAL TERMINATION LOCATIONS FOR CHIMNEYS AND
SINGLE-WALL METAL PIPES SERVING RESIDENTIAL-TYPE
AND LOW-HEAT APPLIANCE
[NFPA: 54: FIGURE A.12.6.2.1]
chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels. Where the gas appliance is automatically controlled, it shall be equipped with a safety shutoff device. [NFPA 54:12.6.5.2] 509.5.7.2 Gas and Solid Fuel-Burning Appli- ances. A listed combination gas- and solid-fuelburning appliance connected to a single chimney flue shall be equipped with a manual reset device to shut off gas to the main burner in the event of sustained backdraft or flue gas spillage. The chimney flue shall be sized to properly vent the appliance.
[NFPA 54:12.6.5.3] 509.5.7.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4] 509.5.8 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6] 509.5.9 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening.
CMC § 2113.17 High relevance — show source text
2113.17 Inlet. Inlets to masonry chimneys shall enter from the side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of the inlet or from extending beyond the wall of the liner.
2113.18 Masonry chimney cleanout openings. Cleanout openings shall be provided within 6 inches (152 mm) of the base of each flue within every masonry chimney. The upper edge of the cleanout shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The height of the opening shall be not less than 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.
Exception: Chimney flues serving masonry fireplaces, where cleaning is possible through the fireplace opening.
2113.19 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be filled, except to provide fireblocking in accordance with Section 2113.20.
Exceptions:
Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777, and installed in accordance with the manufacturer’s instructions, are permitted to have combustible material in contact with their exterior surfaces.
Where masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 12 inches (305 mm) from the inside surface of the nearest flue lining.
Exposed combustible trim and the edges of sheathing materials, such as wood siding, are permitted to abut the masonry chimney sidewalls, in accordance with Figure 2113.19, provided that such combustible trim or sheathing is not less than 12 inches (305 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm).
FIGURE 2113.19—ILLUSTRATION OF EXCEPTION THREE CHIMNEY CLEARANCE PROVISION
MASONRY ABUTTING
COMBUSTIBLE SHEATHING
12" FROM FLUE LINING
Col1 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 M
C
121" CLEARANCE (AIRSPACE) TO COMBUSTIBLE SHEATHING
2113.20 Chimney fireblocking. All 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 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.
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CMC § 304.8 Medium relevance — show source text
)
140
110
76
70
53
32|269
214
168
124
82
58
37
91|||||||||||||| |224
187
MIN. CROSS-SECTIONAL AREA (SQ. IN.)
140
110
76
70
53
32|269
214
168
124
82
58
37
91|||||||||||||| |224
187
MIN. CROSS-SECTIONAL AREA (SQ. IN.)
140
110
76
70
53
32|269
214
168
124
82
58
37
91|||||||||||||| |224
187
MIN. CROSS-SECTIONAL AREA (SQ. IN.)
140
110
76
70
53
32|269
214
168
124
82
58
37
91|||||||||||||| |224
187
MIN. CROSS-SECTIONAL AREA (SQ. IN.)
140
110
76
70
53
32|269
214
168
124
82
58
37
91||||||||||||||13 14 15 16 17 18 19 20 21 22 23 24 25
HEIGHT, MEASURED FROM FLOOR OF COMBUSTION CHAMBER TO TOP OF FLUE (FT)
For SI: 1 foot = 304.8 mm, 1 square inch = 645.16 mm [2] .
R1003.16 Inlet. Inlets to masonry chimneys shall enter from the side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of the inlet or from extending beyond the wall of the liner.
R1003.17 Masonry chimney cleanout openings. Cleanout openings shall be provided within 6 inches (152 mm) of the base of each flue within every masonry chimney. The upper edge of the cleanout shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The height of the opening shall be not less than 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.
Exception: Chimney flues serving masonry fireplaces where cleaning is possible through the fireplace opening.
R1003.18 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be filled, except to provide fire blocking in accordance with Section R1003.19.
Exceptions:
- Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777 and installed in accordance with the manufacturer’s instructions are permitted to have combustible material in contact with their exterior surfaces.
CMC § 605.1.5.2 Medium relevance — show source text
605.1.5.2 Operating instructions. After completing the installation, the installer shall instruct the owner or operator in the proper operation of the equipment. The installer shall furnish the owner or operator with the manufacturer’s operating instructions.
605.1.6 Clearances. Working clearances between fuel-fired appliances and electrical panelboards and equipment shall be in accordance with the California Electrical Code . Clearances between oil-fired equipment and oil supply tanks shall be in accordance with the California Electrical Code .
605.2 Abatement of unsafe conditions. The fire code official is authorized to order that measures be taken to prevent the operation of any existing stove, oven, furnace, incinerator, boiler or any other heat-producing device or appliance found to be defective or in violation of code requirements for existing appliances after giving notice to this effect to any person, owner, firm or agent or operator in charge of the same. The fire code official is authorized to take measures to prevent the operation of any device or appliance without notice when inspection shows the existence of an immediate fire hazard or when imperiling human life. The defective device shall remain withdrawn from service until all necessary repairs or alterations have been made or replaced in accordance with Section 605.1.
605.2.1 Chimneys and appliances. Chimneys, vents, incinerators, smokestacks or similar devices for conveying smoke or hot gases to the outer air and the appliances such as stoves, furnaces, fireboxes or boilers to which such devices are connected, shall be maintained so as not to create a fire hazard.
605.2.1.1 Masonry chimneys. Masonry chimneys that, upon inspection, are found to be without a flue liner and that have open mortar joints which will permit smoke or gases to be discharged into the building, or which are cracked as to be dangerous, shall be repaired or relined with a listed chimney liner system installed in accordance with the manufacturer’s instructions and the California Mechanical Code or a flue lining system installed in accordance with the requirements of the California Build- ing Code and appropriate for the intended class of chimney service.
605.2.1.2 Metal chimneys. Metal chimneys that are corroded or improperly supported shall be repaired or replaced in accordance with the California Mechanical Code .
605.2.1.3 Decorative shrouds. Decorative shrouds installed at the termination of factory-built chimneys or vents shall be removed except where such shrouds are listed and labeled for use with the specific factory-built chimney system and are installed in accordance with the chimney or vent manufacturer’s instructions and the California Mechanical Code or Interna- tional Fuel Gas Code .
605.2.1.4 Factory-built chimney and vent systems. Existing factory-built chimneys and vent systems that are damaged, corroded or improperly supported shall be repaired or replaced in accordance with the California Mechanical Code .
605.2.1.5 Connectors. Existing chimney and vent connectors that are damaged, corroded or improperly supported shall be repaired or replaced in accordance with the California Mechanical Code .
605.3 Chimneys and vents. Masonry chimneys shall be constructed in accordance with the California Building Code . Factory-built chimneys and vent systems serving solid-fuel-fired appliances or oil-fired appliances shall be installed in accordance with the Califor- nia Mechanical Code . Metal chimneys shall be constructed and installed in accordance with the California Mechanical Code . Factorybuilt chimneys and vent systems serving gas-fired appliances shall be installed in accordance with the International Fuel Gas Code .
CMC § 16.2 Medium relevance — show source text
2113 A .16.2 Determination of minimum area. The minimum net cross-sectional area of the flue shall be determined in accordance with Figure 2113 A .16. A flue size providing not less than the equivalent net cross-sectional area shall be used. Crosssectional areas of clay flue linings are as provided in Tables 2113 A .16(1) and 2113 A .16(2) or as provided by the manufacturer or as measured in the field. The height of the chimney shall be measured from the firebox floor to the top of the chimney flue.
2113 A .17 Inlet. Inlets to masonry chimneys shall enter from the side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of the inlet or from extending beyond the wall of the liner.
2113 A .18 Masonry chimney cleanout openings. Cleanout openings shall be provided within 6 inches (152 mm) of the base of each flue within every masonry chimney. The upper edge of the cleanout shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The height of the opening shall be not less than 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.
Exception: Chimney flues serving masonry fireplaces, where cleaning is possible through the fireplace opening.
2113 A .19 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be filled, except to provide fireblocking in accordance with Section 2113 A .20.
Exceptions:
Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777, and installed in accordance with the manufacturer’s instructions, are permitted to have combustible material in contact with their exterior surfaces.
Where masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 12 inches (305 mm) from the inside surface of the nearest flue lining.
Exposed combustible trim and the edges of sheathing materials, such as wood siding, are permitted to abut the masonry chimney sidewalls, in accordance with Figure 2113 A .19, provided that such combustible trim or sheathing is not less than 12 inches (305 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm).
2025 CALIFORNIA BUILDING CODE 21A-17
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
FIGURE 2113 A .19—ILLUSTRATION OF EXCEPTION THREE CHIMNEY CLEARANCE PROVISION
MASONRY ABUTTING
COMBUSTIBLE SHEATHING
12" FROM FLUE LINING
CMC § 21-17 Medium relevance — show source text
2025 CALIFORNIA BUILDING CODE 21-17
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
TABLE 2113.16(2)—NET CROSS-SECTIONAL AREA OF SQUARE AND RECTANGULAR FLUE SIZES—continued Col2 FLUE SIZE, OUTSIDE NOMINAL DIMENSIONS (inches) CROSS-SECTIONAL AREA (square inches) 13 × 18 173 16 × 16 181 16 × 20 222 18 × 18 233 20 × 20 298 20 × 24 335 24 × 24 431 For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2. For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2. 2113.16.1 Minimum area. Round chimney flues shall have a minimum net cross-sectional area of not less than [1] / 12 of the fireplace opening. Square chimney flues shall have a minimum net cross-sectional area of not less than [1] / 10 of the fireplace opening. Rectangular chimney flues with an aspect ratio less than 2 to 1 shall have a minimum net cross-sectional area of not less than [1] / 10 of the fireplace opening. Rectangular chimney flues with an aspect ratio of 2 to 1 or more shall have a minimum net cross-sectional area of not less than [1] / 8 of the fireplace opening.
2113.16.2 Determination of minimum area. The minimum net cross-sectional area of the flue shall be determined in accordance with Figure 2113.16. A flue size providing not less than the equivalent net cross-sectional area shall be used. Cross-sectional areas of clay flue linings are as provided in Tables 2113.16(1) and 2113.16(2) or as provided by the manufacturer or as measured in the field. The height of the chimney shall be measured from the firebox floor to the top of the chimney flue.
2113.17 Inlet. Inlets to masonry chimneys shall enter from the side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of the inlet or from extending beyond the wall of the liner.
2113.18 Masonry chimney cleanout openings. Cleanout openings shall be provided within 6 inches (152 mm) of the base of each flue within every masonry chimney. The upper edge of the cleanout shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The height of the opening shall be not less than 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.
Exception: Chimney flues serving masonry fireplaces, where cleaning is possible through the fireplace opening.
2113.19 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be filled, except to provide fireblocking in accordance with Section 2113.20.
CMC § 304.8 Medium relevance — show source text
For SI: 1 foot = 304.8 mm, 1 square inch = 645.16 mm [2] .
R1003.16 Inlet. Inlets to masonry chimneys shall enter from the side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of the inlet or from extending beyond the wall of the liner.
R1003.17 Masonry chimney cleanout openings. Cleanout openings shall be provided within 6 inches (152 mm) of the base of each flue within every masonry chimney. The upper edge of the cleanout shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The height of the opening shall be not less than 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.
Exception: Chimney flues serving masonry fireplaces where cleaning is possible through the fireplace opening.
R1003.18 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be filled, except to provide fire blocking in accordance with Section R1003.19.
Exceptions:
Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777 and installed in accordance with the manufacturer’s instructions are permitted to have combustible material in contact with their exterior surfaces.
Where masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 8 inches (203 mm) from the inside surface of the nearest flue lining.
10-10 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
CHIMNEYS AND FIREPLACES
- Combustible materials shall be permitted to abut the masonry chimney side walls, in accordance with Figure R1003.18, provided such combustible material is not less than 8 inches (203 mm) from the inside surface of the nearest flue lining.
FIGURE R1003.18—CLEARANCE FROM COMBUSTIBLES
COMBUSTIBLE SHEATHING 8 IN. FROM FLUE LINING
1 IN. CLEARANCE (AIRSPACE) TO COMBUSTIBLE SHEATHING
For SI: 1 inch = 25.4 mm.
FFLLUUEE
LLIINNIINNGG
GCol2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13 Col14 Col15 CMC § 3.1 Medium 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:
- In structures assigned to Seismic Design Category A or B.
- Where the masonry fireplace is constructed completely within the exterior walls.
Frequently asked questions
Who must perform the required inspection?
The code requires that the chimney/vent be inspected after installation and before concealment; inspections are performed by the authority having jurisdiction (building/mechanical inspector) as part of the permit inspection process — see § 802.5.6.
Is a cleanout always required for masonry chimneys?
Not always — but if a chimney formerly used for solid or liquid fuel will be used with a fuel‑gas appliance, an accessible cleanout with a tight cover is required and must be positioned per § 802.5.10.
How far below the inlet must the cleanout be?
The upper edge of the cleanout must be at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening, per § 802.5.10.
What if the chimney is found unsafe during inspection?
If inspection reveals the chimney is not safe for the intended application, it must be repaired, rebuilt, lined/relined, or replaced to conform to NFPA 211 and be suitable for the appliance before connection — § 802.5.7.3.
Do factory‑built chimneys follow the same support rules?
Yes—all portions of chimneys must be supported for their design and weight; for listed factory‑built chimneys, support and spacing must follow the manufacturer’s installation instructions, per § 802.5.9.
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