CRC · California Residential Code
Can a masonry chimney be used for gas appliances — cleanouts & space restrictions
If you convert a masonry chimney that used to vent wood or oil to a gas appliance, the code requires an accessible, tight‑fitting cleanout whose top edge is at least 6 inches below the lowest appliance inlet, and it forbids using the remaining space around any liner or gas vent to vent another appliance or to supply combustion air (except very narrow exceptions). Follow the appliance listing and manufacturer instructions and confirm details with your local inspector.
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
When a masonry chimney that previously served solid or liquid fuel appliances is reused for a fuel‑gas appliance, the chimney must have an accessible cleanout with a tight cover and the cleanout’s upper edge must be located at least 6 inches (152 mm) below the lowest chimney inlet opening (§ 509.5.9). The leftover space (the annulus) around any chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney cannot be used to vent another appliance (§ 509.5.10) nor to supply combustion air (§ 509.5.10.1).
The single most important rule: if you convert a solid- or liquid-fuel masonry flue to gas, provide an accessible tight‑fitting cleanout located ≥ 6 in. (152 mm) below the lowest inlet — and do not use the remaining space around any new liner/vent for another appliance or for combustion air.
Requirements in detail
Cleanouts (when converting to gas)
- Required when a chimney that formerly carried flue products from liquid or solid fuel appliances is used with an appliance using fuel gas. § 509.5.9 is the controlling rule.
- The cleanout must be accessible, have a tight‑fitting cover, and the cleanout’s upper edge must be located at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening (i.e., measured vertically). § 509.5.9.
Annular space (space around liners or vents)
- The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed in a masonry chimney must not be used to vent another appliance. This is the rule in § 509.5.10. Exception: insertion of another liner/vent as allowed by the code and the liner/vent manufacturer’s instructions.
- Likewise, the remaining space surrounding such liners/vents/plastic piping installed within a masonry, metal, or factory‑built chimney flue must not be used to supply combustion air (see § 509.5.10.1). Exception: direct‑vent appliances specifically designed for installation in a solid‑fuel fireplace, if installed per the manufacturer’s instructions.
Short decision table (quick reference)
| Decision item | Required / Limit | Code Reference |
|---|---|---|
| Cleanout required when converting a former solid/liquid‑fuel flue to gas | Yes — accessible cleanout with tight cover | § 509.5.9 |
| Cleanout vertical location relative to lowest inlet | Upper edge ≥ 6 in. (152 mm) below lowest chimney inlet opening | § 509.5.9 |
| Use of annular space to vent another appliance | Prohibited (unless another liner/vent is installed per code/manufacturer) | § 509.5.10 |
| Use of annular space to supply combustion air | Prohibited (exception for specific direct‑vent fireplace appliances) | § 509.5.10.1 |
Exceptions & special cases
- § 509.5.10 contains a specific exception allowing the insertion of another liner or vent inside the chimney when done in accordance with the code and the liner/vent manufacturer’s instructions — in other words, you may add a separate approved liner or vent, but you cannot simply route another appliance’s flue through the leftover annulus. § 509.5.10.
- § 509.5.10.1 allows a limited exception for direct‑vent appliances that are designed for installation in a solid‑fuel burning fireplace — only when installed exactly per the manufacturer’s instructions. Do not assume this exception applies to other direct‑vent or vent‑free appliances. § 509.5.10.1.
Common mistakes
- Installing a gas appliance into a former solid‑fuel chimney without adding an accessible cleanout or placing the cleanout less than 6 inches below the lowest inlet. This violates § 509.5.9.
- Using the leftover annular space between new liner/vent and masonry as a second vent for another appliance (or as the vent path for a second appliance). This is specifically prohibited by § 509.5.10 (unless you install a separate listed liner/vent per manufacturer instructions).
- Using the annular space to route combustion air (for makeup air or an appliance’s combustion air intake). That’s prohibited by § 509.5.10.1 (except the narrow direct‑vent fireplace exception).
- Assuming an unlined masonry flue is suitable for gas appliances — chimneys must be lined with an appropriate lining system for the appliance (see related provisions below). Rely on the appliance listing and the California Mechanical/Residential Code requirements when selecting liner material.
Worked example — concrete scenario
Scenario: You have an existing masonry chimney that used to serve a wood stove; you want to connect a new gas water heater with a single inlet in the chimney.
- Inspect and line the flue as required for gas appliances (follow manufacturer/listing and the Mechanical/Residential Code rules). If you install a liner or gas vent inside the masonry chimney, remember the annular space rules below.
- Install an accessible cleanout: suppose the lowest chimney inlet opening (the centerline at the inlet) is at 48.0 in. above the cleanout location reference plane. The code requires the cleanout’s upper edge to be at least 6.0 in. (152 mm) below the lower edge of the lowest inlet opening. So the cleanout’s upper edge must be at or below 42.0 in. (48.0 in. − 6.0 in.). This satisfies § 509.5.9.
- Do NOT use the remaining annular space surrounding the liner or gas vent to: (a) connect or vent any other appliance, or (b) route combustion air to the appliance. Those are prohibited by § 509.5.10 and § 509.5.10.1. If you need a second vent, install a separate listed liner/vent per the manufacturer’s instructions (the exception in § 509.5.10).
Related provisions (use these when planning work)
- California Plumbing Code: § 509.5.9, § 509.5.10, § 509.5.10.1 — primary controlling sections for cleanouts and annular‑space restrictions.
- California Residential Code: R1003.12.2 / R1003.11 — space around lining and flue lining requirements for masonry chimneys.
- California Mechanical Code: Section on masonry chimneys, liners and gas vents (see Sections 802.5 and 802.6 for installation, labeling and termination rules). These contain flue sizing, labeling and liner material standards you’ll need to follow when selecting liners or gas vents.
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 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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CRC § 12.6.7 High relevance — show source text
[NFPA 54:12.6.7] 509.5.10 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.
Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 509.5.10.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory-built chimney flue shall not be used to supply combustion air.
Exception: Direct-vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.8.2] 509.6 Gas Vents. The installation of gas vents shall meet the following requirements:
(1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
(2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is
connected.
(3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry
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chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”
(4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.
[NFPA 54:12.7.2]
509.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:
(1) A gas vent shall terminate in accordance with one of the following:
(a) Gas vents that are 12 inches (300 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall
terminate above the roof in accordance with Figure 509.6.1 and Table 509.6.1.
(b) Gas vents that are over 12 inches (300 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally.
(c) Industrial appliances as provided in Section 509.2.5.
(d) Direct-vent systems as provided in Section 509.2.6.
(e) Appliances with integral vents as provided in Section 509.2.7.
(f) Mechanical draft systems as provided in Section 509.3.3 through Section 509.3.3.4.
CRC § 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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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.
CRC § 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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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.
CRC § 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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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:
CRC § 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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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.
CRC § 11.3.3 High relevance — show source text
2113 A .11.3.3 Termination height. Concrete and masonry chimneys for high-heat appliances shall extend not less than 20 feet (6096 mm) higher than any portion of any building within 50 feet (15 240 mm).
2113 A .11.3.4 Clearance. Concrete and masonry chimneys for high-heat appliances shall have approved clearance from buildings and structures to prevent overheating combustible materials, permit inspection and maintenance operations on the chimney and prevent danger of burns to persons.
2113 A .12 Clay flue lining (installation). Clay flue liners shall be installed in accordance with ASTM C1283 and extend from a point not less than 8 inches (203 mm) below the lowest inlet or, in the case of fireplaces, from the top of the smoke chamber to a point above the enclosing walls. The lining shall be carried up vertically, with a maximum slope not greater than 30 degrees (0.52 rad) from the vertical.
Clay flue liners shall be laid in medium-duty nonwater-soluble refractory mortar conforming to ASTM C199 with tight mortar joints left smooth on the inside and installed to maintain an airspace or insulation not to exceed the thickness of the flue liner separating the flue liners from the interior face of the chimney masonry walls. Flue lining shall be supported on all sides. Only enough mortar shall be placed to make the joint and hold the liners in position.
2113 A .13 Additional requirements.
2113 A .13.1 Listed materials. Listed materials used as flue linings shall be installed in accordance with the terms of their listings and the manufacturer’s instructions.
2113 A .13.2 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.
2113 A .14 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 are 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).
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2113 A .15 Flue area (appliance). Chimney flues shall not be smaller in area than the area of the connector from the appliance. Chimney flues connected to more than one appliance shall be not less than the area of the largest connector plus 50 percent of the areas of additional chimney connectors.
Exceptions:
- Chimney flues serving oil-fired appliances sized in accordance with NFPA 31.
- Chimney flues serving gas-fired appliances sized in accordance with the California Mechanical Code .
CRC § 12.4.5.2 High relevance — show source text
(2) The vent system shall be installed such that no fittings or joints between sections are installed in the above-ceiling space.
(3) The venting system shall be installed in a conduit or enclosure with joints between the interior of the enclosure and the ceiling space sealed. [NFPA 54:12.4.5.2] 802.4 Type of Venting System to be Used. The type of venting system to be used shall be in accordance with Table 802.4. [NFPA 54:12.5.1]
802.4.1 Plastic Piping. Where plastic piping is used to vent an appliance, the appliance shall be listed for use with such venting materials and the appliance manufacturer’s installation instructions shall identify the specific plastic piping material. The plastic pipe venting materials shall be labeled in accordance with the product standards specified by the appliance manufacturer or shall be listed and labeled in accordance with UL 1738. [NFPA 54:12.5.2]
802.4.2 Plastic Vent Joints. Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions. Plastic pipe venting materials listed and labeled in accordance with UL 1738 shall be installed in accordance
with the vent manufacturer’s installation instructions. Where primer is required, it shall be of a contrasting color.
[NFPA 54:12.5.3]
802.4.3 Special Gas Vents. Special gas vents shall be listed and labeled in accordance with UL 1738 and installed in accordance with the special gas vent manufacturer’s installation instructions. [NFPA 54:12.5.4]
802.5 Masonry, Metal, and Factory-Built Chimneys. Chimneys shall be installed in accordance with Section 802.5.1 through Section 802.5.3.
802.5.1 Factory-Built Chimneys. Factory-built chimneys shall be listed in accordance with UL 103, UL 959, or UL 2561. Factory-built chimneys used to vent appliances that operate at positive vent pressure shall be listed for such application. [NFPA 54:12.6.1.1]
802.5.1.1 Decorative Shrouds. Decorative shrouds addressed in Section 802.5.4.3 shall comply with UL 103 for factory-built residential chimneys, UL 127 for factory-built fireplaces, or UL 1482 for solid-fuel room heaters.
802.5.2 Metal Chimneys. Metal chimneys shall be built and installed in accordance with NFPA 211. [NFPA 54:12.6.1.2]
802.5.3 Masonry Chimneys. Masonry chimneys shall be built and installed in accordance with NFPA 211 and lined with one of the following:
(1) Approved clay flue lining.
(2) A chimney lining system listed and labeled in accordance with UL 1777.
(3) Other approved material that resists corrosion, erosion, softening, or cracking from vent gases at temperatures up to 1800°F (982°C).
Exception: Masonry chimney flues lined with a chimney lining system specifically listed for use with listed appliances with draft hoods, Category I appliances, and
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CRC § 11.5 High relevance — show source text
R1003.11.5 Oil-fired appliances approved for use with Type L vent. Flue lining and vent systems for use in masonry chimneys with oil-fired appliances approved for use with Type L vent shall be limited to the following:
- Flue lining systems complying with Section R1003.11.1.
- Listed chimney liners complying with UL 641 (see Section R1003.11.6 for marking).
R1003.11.6 Notice of usage. Where a flue is relined with a material not complying with Section R1003.11.1, the chimney shall be plainly and permanently identified by a label attached to a wall, ceiling or other conspicuous location adjacent to where the connector enters the chimney. The label shall include the following message or equivalent language:
THIS CHIMNEY FLUE IS FOR USE ONLY WITH [TYPE OR CATEGORY OF APPLIANCE] APPLIANCES THAT BURN [TYPE OF FUEL]. DO NOT CONNECT OTHER TYPES OF APPLIANCES.
R1003.12 Clay flue lining (installation). Clay flue liners shall be installed in accordance with ASTM C1283 and extend from a point not less than 8 inches (203 mm) below the lowest inlet or, in the case of fireplaces, from the top of the smoke chamber to a point above the enclosing walls. The lining shall be carried up vertically, with a slope not greater than 30 degrees (0.52 rad) from the vertical.
Clay flue liners shall be laid in medium-duty water insoluble refractory mortar conforming to ASTM C199 with tight mortar joints left smooth on the inside and installed to maintain an airspace or insulation not to exceed the thickness of the flue liner separating the flue liners from the interior face of the chimney masonry walls. Flue liners shall be supported on all sides. Only enough mortar shall be placed to make the joint and hold the liners in position.
10-8 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
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.
CRC § 9.1 High relevance — show source text
R1003.9 Termination. Chimneys shall extend not less than 2 feet (610 mm) higher than any portion of a building within 10 feet (3048 mm), but shall be not less than 3 feet (914 mm) above the highest point where the chimney passes through the roof.
R1003.9.1 Chimney caps. Masonry chimneys shall have a concrete, metal or stone cap, a drip edge and a caulked bond break around any flue liners in accordance with ASTM C1283. The concrete, metal or stone cap shall be sloped to shed water.
R1003.9.2 Spark arrestors. All chimneys attached to any appliance or fireplace that burns solid fuel shall be equipped with an approved spark arrester. Where a spark arrestor is installed on a masonry chimney, the spark arrestor shall meet all of the following requirements:
- The net free area of the arrestor shall be not less than four times the net free area of the outlet of the chimney flue it
serves.
- The arrestor screen shall have heat and corrosion resistance equivalent to 12 gage wire, 19-gage galvanized steel or 24gage stainless steel.
- Openings shall not permit the passage of spheres having a diameter greater than [1] / 2 inch (12.7 mm) nor block the passage of spheres having a diameter less than [3] / 8 inch (9.5 mm).
- The spark arrestor shall be located with access for cleaning and the screen or chimney cap shall be removable to allow for cleaning of the chimney flue.
R1003.9.3 Rain caps. Where a masonry or metal rain cap is installed on a masonry chimney, the net free area under the cap shall be not less than four times the net free area of the outlet of the chimney flue it serves.
R1003.10 Wall thickness. Masonry chimney walls shall be constructed of solid masonry units or hollow masonry units grouted solid with not less than a 4-inch (102 mm) nominal thickness.
R1003.10.1 Masonry veneer chimneys. Where masonry is used to veneer a frame chimney, through-flashing and weep holes shall be installed as required by Section R703.
R1003.11 Flue lining (material). Masonry chimneys shall be lined. The lining material shall be appropriate for the type of appliance connected, in accordance with the terms of the appliance listing and manufacturer’s instructions.
R1003.11.1 Residential-type appliances (general). Flue lining systems shall comply with one of the following:
- Clay flue lining complying with the requirements of ASTM C315.
- Listed and labeled chimney lining systems complying with UL 1777.
- Factory-built chimneys or chimney units listed for installation within masonry chimneys.
- Other approved materials that will resist corrosion, erosion, softening or cracking from flue gases and condensate at temperatures up to 1,800°F (982°C).
R1003.11.2 Flue linings for specific appliances. Flue linings other than these covered in Section R1003.11.1, intended for use with specific types of appliances, shall comply with Sections R1003.11.3 through R1003.11.6.
R1003.11.3 Gas appliances. Flue lining systems for gas appliances shall be in accordance with the California Mechanical Code.
CRC § 2113.9.2 High relevance — show source text
2113.9.2 Spark arrestors. [SFM] All chimneys attached to any appliance or fireplace that burns solid fuel shall be equipped with an approved spark arrester. The spark arrestor shall meet all of the following requirements:
- The net free area of the spark arrestor shall not be less than four times the net free area of the outlet of the chimney.
- The spark arrestor screen shall have heat and corrosion resistance equivalent to 12-gage wire, 19-gage galvanized steel or 24-gage stainless steel.
- Openings shall not permit the passage of spheres having a diameter greater than [1] / 2 inch (13 mm) nor block the passage of spheres having a diameter less than [3] / 8 inch (9.5 mm).
- The spark arrestor shall be accessible for cleaning and the screen or chimney cap shall be removable to allow for cleaning of the chimney flue.
2113.9.3 Rain caps. Where a masonry or metal rain cap is installed on a masonry chimney, the net free area under the cap shall be not less than four times the net free area of the outlet of the chimney flue it serves.
2113.10 Wall thickness. Masonry chimney walls shall be constructed of concrete, solid masonry units or hollow masonry units grouted solid with not less than 4 inches (102 mm) nominal thickness.
2113.10.1 Masonry veneer chimneys. Where masonry is used as veneer for a framed chimney, through flashing and weep holes shall be provided as required by Chapter 14.
2113.11 Flue lining (material). Masonry chimneys shall be lined. The lining material shall be appropriate for the type of appliance connected, according to the terms of the appliance listing and the manufacturer’s instructions.
2113.11.1 Residential-type appliances (general). Flue lining systems shall comply with one of the following:
- Clay flue lining complying with the requirements of ASTM C315.
- Listed chimney lining systems complying with UL 1777.
- Factory-built chimneys or chimney units listed for installation within masonry chimneys.
- Other approved materials that will resist corrosion, erosion, softening or cracking from flue gases and condensate at temperatures up to 1,800°F (982°C).
2113.11.1.1 Flue linings for specific appliances. Flue linings other than those covered in Section 2113.11.1 intended for use with specific appliances shall comply with Sections 2113.11.1.2 through 2113.11.1.4, 2113.11.2 and 2113.11.3.
2113.11.1.2 Gas appliances. Flue lining systems for gas appliances shall be in accordance with the California Mechanical Code .
2113.11.1.3 Pellet fuel-burning appliances. Flue lining and vent systems for use in masonry chimneys with pellet fuel-burning appliances shall be limited to flue lining systems complying with Section 2113.11.1 and pellet vents listed for installation within masonry chimneys (see Section 2113.11.1.5 for marking).
CRC § 0.000472 High relevance — show source text
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USEFUL TABLES
UNIT CONVERSIONS (continued)
MULTIPLY BY TO OBTAIN
Cubic feet/minute (ft [3] /min ).0.000472 .Cubic meters/second (m [3] /s) Cubic feet/minute (ft [3] /min ).0.1247 .Gallons/second Cubic feet/minute (ft [3] /min ).0.47194 .Liters/second (L/s) Cubic feet/second (ft [3] /s) .646 316.89 .Gallons/day Cubic feet/second (ft [3] /s) .448.831 .Gallons/minute (gpm) Cubic inches (in [3] ).1.64 x 10 [-5] .Cubic meters (m [3] ) Cubic inches (in [3] ) .0.01639 .Liters (L) Cubic meters (m [3] ).264.17 .Gallons (U.S. liquid) Cubic yards (yd [3] ).............................................................27 ............................Cubic feet (ft [3] ) Cubic yards (yd [3] )....................................................0.76455 ............................Cubic meters (m [3] ) Cubic yards (yd [3] )......................................................201.97 ............................Gallons (U.S. liquid)
Degrees (deg)............................................................0.0174 ............................Radians (rad)
Fahrenheit (°F)...................................................(°F-32)/1.8 ............................Celsius (°C)
Feet (ft) .....................................................................0.3048 ............................Meters (m)
Feet (ft) .......................................................................304.8 ............................Millimeters (mm)
Feet of water (4°C)...................................................0.0295 ............................Atmosphere (standard) (atm)
Feet of water (4°C)...................................................0.8827 ............................Inches of mercury (0°C)
Feet of water (4°C).....................................................62.43 ............................Pounds-force/square feet
Feet of water (4°C)...................................................0.4335 ............................Pounds-force/square inch
Feet/minute (ft/min)................................................0.01667 ............................Feet/second (ft/s)
Feet/minute (ft/min)................................................0.01136 ............................Miles/hour (mi/h)
Feet/second (ft/s) ......................................................0.3048 ............................Meters/second (m/s)
Feet/second (ft/s) ......................................................0.6818 ............................Miles/hour (mi/h)
Feet/second (ft/s) ....................................................0.01136 ............................Miles/minute (mi/min) Foot lambert (fL) ..................................................3.426259 ............................Candela per square meter (cd/m [2] )
Frequently asked questions
Do I always need a cleanout if I install any gas appliance into an old masonry flue?
Yes — when a chimney that previously carried flue products from liquid or solid fuel appliances is reused for a fuel‑gas appliance, an accessible cleanout with a tight cover is required; its upper edge must be ≥ 6 in. (152 mm) below the lowest inlet opening (§ 509.5.9).
Can I run combustion air for the new gas appliance through the space between a new liner and the chimney wall?
No. The remaining space around a liner/vent/plastic piping installed in a masonry, metal, or factory‑built chimney flue shall not be used to supply combustion air (Exception only for specific direct‑vent fireplace appliances installed per the manufacturer). See § 509.5.10.1.
If I install a listed liner inside the chimney, can I also put a second liner for another appliance in the same chimney?
Not by using the leftover annular space. You may install another separate liner or vent only if it is done in accordance with this code and the liner/vent manufacturer’s instructions (the exception in § 509.5.10). Otherwise, the annulus cannot be used to vent another appliance.
What is an “accessible” cleanout?
The code requires the cleanout to be accessible (able to be reached for inspection/cleaning) and to have a tight‑fitting cover; the requirement is stated in § 509.5.9. Local enforcement may interpret “accessible” with regard to how the cleanout is located (e.g., at grade, in a utility room), so confirm with your local building official if in doubt.
Who should install the liner / cleanout — contractor or DIY?
Because lining, vent selection, and cleanout location have safety and performance implications (and are code‑regulated), these tasks are normally performed by licensed contractors familiar with appliance listings and the California Mechanical/Plumbing/Residential Code. Confirm compliance with the appliance manufacturer’s instructions and the applicable code sections cited here.
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