CMC · California Mechanical Code
How must masonry, metal, and factory‑built chimneys be constructed and lined?
For homeowners: the California Mechanical Code requires that factory‑built chimneys be properly listed to specific UL standards, metal chimneys be constructed per NFPA 211, and masonry chimneys be built per NFPA 211 and must have an approved flue lining (clay tile, a UL‑1777 listed liner, or other approved material rated to withstand flue gases up to 1800°F). Always confirm the appliance listing and installer/manufacturer instructions and check the full CMC text or your local building official for any exceptions or labeling requirements .
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
Chimneys must be installed following the California Mechanical Code requirements in § 802.5 and its subsections: factory‑built chimneys must be listed to specific UL standards and, if used with positive‑pressure appliances, listed for that use (§ 802.5.1) . Metal chimneys must be constructed and installed in accordance with NFPA 211 per § 802.5.2 . Masonry chimneys must be built per NFPA 211 and lined with an approved clay flue, a listed chimney‑lining system (UL 1777), or other approved material that resists flue gases at temperatures up to 1800°F (982°C) as stated in § 802.5.3 .
The single most important rule: install chimneys per § 802.5 and the specific subsection for the chimney type — factory‑built chimneys must be listed; metal and masonry chimneys must follow NFPA 211; masonry chimneys must have an approved lining (§ 802.5 through § 802.5.3) .
Requirements in detail
Scope and controlling text
- § 802.5: General statement that chimneys shall be installed in accordance with § 802.5.1 through § 802.5.3 (i.e., follow the specific subsection for the type of chimney) .
- Always cross‑check appliance listings and manufacturer instructions referenced by these sections.
Factory‑built chimneys (what to look for)
- Must be listed in accordance with UL 103, UL 959, or UL 2561. If the appliance produces positive vent pressure, the factory‑built chimney must be listed for positive‑pressure applications — see § 802.5.1 .
- Decorative shrouds at terminations have separate listing requirements (see referenced subsections in the code) — see § 802.5.1.1 .
Metal chimneys
- Must be built and installed in accordance with NFPA 211 (i.e., follow NFPA 211 construction and installation rules) as required by § 802.5.2 .
Masonry chimneys — construction and lining
- Masonry chimneys must be built and installed in accordance with NFPA 211 and must be lined with one of the following per § 802.5.3:
- Approved clay flue lining.
- A chimney lining system listed and labeled in accordance with UL 1777.
- Other approved material that resists corrosion, erosion, softening, or cracking from vent gases at temperatures up to 1800°F (982°C).
- Note: the retrieved CMC snippet showing § 802.5.3 indicates an Exception exists, but the full exception text was not fully available in the provided CMC file excerpts; the exact Exception wording from § 802.5.3 could not be confirmed from the retrieved CMC text. (A similar exception and labeling requirement appears in California Plumbing Code § 509.5.3 in the provided files, but that is a different code document.)
Definitions and temperature classes (for sizing/selection)
- The code defines chimney appliance‑type temperature classes used to select appropriate chimneys:
- Residential‑appliance‑type chimneys — for appliances producing gases not in excess of 1000°F (538°C) at the appliance flue outlet.
- Medium‑heat appliance‑type chimneys — for gases not in excess of 2000°F (1093°C).
- High‑heat appliance‑type chimneys — for gases in excess of 2000°F (1093°C).
These classifications are in the CMC definitions and inform whether a liner or chimney type is acceptable for an appliance (§ 802.5 selections should be made using these categories) .
Quick reference table (decision‑relevant values)
| Element | Required value / standard | Code Reference |
|---|---|---|
| Chimney general requirement | Install per § 802.5 (follow the relevant subtype sections) | § 802.5 |
| Factory‑built chimneys — listing | Listed to UL 103, UL 959, or UL 2561; listed for positive vent pressure if used with positive‑pressure appliances | § 802.5.1 |
| Factory‑built decorative shrouds | Must comply with the applicable UL standard indicated in the code for shrouds | § 802.5.1.1 |
| Metal chimneys — construction | Build and install per NFPA 211 | § 802.5.2 |
| Masonry chimneys — lining options | (1) Approved clay flue liner; (2) Lining system listed to UL 1777; (3) Other approved material resistant to flue gases up to 1800°F (982°C) | § 802.5.3 |
| Appliance‑type temperature thresholds | Residential ≤ 1000°F; Medium‑heat ≤ 2000°F; High‑heat > 2000°F (use to select chimney type) | Code definitions (Chimney classes) |
Exceptions & special cases
- The retrieved CMC text for § 802.5.3 indicates there is an Exception permitting certain chimney flues lined with particular chimney lining systems, but the full Exception wording was not fully present in the supplied CMC excerpts. Do not rely on an unverified paraphrase — consult the full text of § 802.5.3 in the California Mechanical Code at plan review or on the code book to confirm the Exception wording and any labeling/installation requirements .
- Decorative shrouds and special terminations are handled in related subsections; if a shroud is used it must be specifically listed for the chimney system (see § 802.5.1.1) .
- For chimneys serving gas appliances, the CMC definitions and the appliance listing determine acceptable liner types and materials — cross‑reference appliance listings and manufacturer instructions before selecting a liner .
Common mistakes
- Assuming any factory‑built chimney may be used with any appliance. The code requires specific UL listings (UL 103/959/2561) and a listing for positive‑pressure if the appliance produces positive vent pressure (§ 802.5.1) .
- Failing to line a masonry chimney. Masonry chimneys must be lined per § 802.5.3 — unlined masonry chimneys are not compliant for typical appliance connections .
- Choosing a liner material without confirming the temperature resistance. The code permits other approved materials only if they resist flue gases at temperatures up to 1800°F (982°C) — verify the material's rating and listing (§ 802.5.3) .
- Ignoring NFPA 211 for metal and masonry construction details. § 802.5.2 and § 802.5.3 require compliance with NFPA 211 for construction and installation details; NFPA contains critical clearances, support, and construction rules not repeated verbatim in the CMC .
Worked example — concrete scenario with numbers
Scenario: You are connecting a residential gas furnace that produces flue gases at about 700°F at the appliance outlet to an existing masonry chimney.
Steps and application of the code:
- Determine appliance type: 700°F is below 1000°F, so this is a residential‑appliance‑type (residential) application per the CMC definitions. Use an appropriate residential chimney/liner selection .
- Masonry chimney requirement: § 802.5.3 requires the chimney be lined. Acceptable options include:
- Install an approved clay flue lining (e.g., ASTM‑compliant clay) — permitted by § 802.5.3 ; or
- Install a chimney lining system listed to UL 1777 (commonly used stainless steel relining systems) — also permitted by § 802.5.3 .
- Verify the liner selection with appliance listing/manufacturer instructions: because this is a gas appliance, the CMC emphasizes lining consistent with appliance listings and instructions (definitions and cross‑references) — consult appliance listing and the liner manufacturer’s installation instructions before proceeding .
- Exception check: The retrieved CMC snippet shows an Exception exists but the full text was not available in the provided excerpts; therefore, do not assume any alternate allowance without checking the full § 802.5.3 text or the AHJ (Authority Having Jurisdiction) .
Practical outcome: For a 700°F gas furnace you would typically select a UL‑1777 stainless steel chimney liner or approved clay flue tiles and install per the liner manufacturer and NFPA 211 construction guidance to meet § 802.5.3 requirements .
Related provisions (to check during design or review)
- § 802.4 — Type of venting system to be used (table of vent types vs. appliances) .
- § 802.5.1 — Factory‑built chimney listing requirements (UL 103/959/2561; positive pressure) .
- § 802.5.1.1 — Decorative shrouds requirements for factory‑built chimneys .
- § 802.5.2 — Metal chimneys — built/installed per NFPA 211 .
- CMC definitions for Chimney and Chimney classes (residential/medium/high) — useful for selecting liner/chimney type .
- Consult NFPA 211 for construction details that § 802.5.2/§ 802.5.3 reference (clearances, offsets, supports) — referenced by the CMC § 802.5 subsections .
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 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
154 2025 CALIFORNIA MECHANICAL CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
CHIMNEYS AND VENTS
CMC § 802.5.1 High relevance — show source text
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
154 2025 CALIFORNIA MECHANICAL CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
CHIMNEYS AND VENTS
TABLE 802.4
TYPE OF VENTING SYSTEM TO BE USED
[NFPA 54: TABLE 12.5.1]
APPLIANCES TYPE OF VENTING SYSTEM LOCATION OF REQUIREMENTS Listed Category I appliances
Listed appliances equipped with draft hood
Appliances listed for use with Type B gas ventType B gas vent Section 802.6 Listed Category I appliances
Listed appliances equipped with draft hood
Appliances listed for use with Type B gas ventChimney Section 802.5 Listed Category I appliances
Listed appliances equipped with draft hood
Appliances listed for use with Type B gas ventSingle-wall metal pipe Section 802.7 Listed Category I appliances
Listed appliances equipped with draft hood
Appliances listed for use with Type B gas ventListed chimney lining system for gas
ventingSection 802.5.3 Listed Category I appliances
Listed appliances equipped with draft hood
Appliances listed for use with Type B gas ventSpecial gas vent listed for these
appliancesSection 802.4.3 Listed vented wall furnaces Type B-W gas vent Section 802.6, Section 907.0 Category II, Category III, and
Category IV appliancesAs specified or furnished by
manufacturers of listed appliancesSection 802.4.1, Section 802.4. CMC § 9.5 High relevance — show source text
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. 2. The spark arrestor screen shall have heat and corrosion resistance equivalent to 12-gage wire, 19-gage galvanized steel or 24-gage stainless steel. 3. 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). 4. 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 A .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 A .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 A .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 A .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 A .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 A .11.1.1 Flue linings for specific appliances. Flue linings other than those covered in Section 2113 A .11.1 intended for use with specific appliances shall comply with Sections 2113 A .11.1.2 through 2113 A .11.1.4, 2113 A .11.2 and 2113 A .11.3.
2113 A .11.1.2 Gas appliances. Flue lining systems for gas appliances shall be in accordance with the California Mechanical Code .
21A-14 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
2113 A .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 A .11.1 and pellet vents listed for installation within masonry chimneys (see Section 2113 A .11.1.5 for marking).
CMC § 205.0 High relevance — show source text
205.0 – C –
CAS Number. The Chemical Abstract System registry number.
Central Heating Plant or Heating Plant. Environmental heating equipment installed in a manner to supply heat by means of ducts or pipes to areas other than the room or space in which the equipment is located.
Certified. A formally stated recognition and approval of an acceptable level of competency, acceptable to the Authority Having Jurisdiction. [NFPA 96:3.3.10]
Certified Person. A person trained and certified by the equipment manufacturer, or by a recognized organization through a formal certification program for the system to be serviced or cleaned; that is acceptable to the Authority Having Jurisdiction.
Chilled Water. Water or fluid that is cooled below the surrounding air temperature via mechanical or other means for the purpose of removing excess heat from conditioned spaces or equipment via hydronic piping distribution.
Chimney. One or more passageways, vertical or nearly so, for conveying flue or vent gases to the outdoors. [NFPA 54:3.3.17]
Chimney, Factory-Built. A chimney composed of listed factory-built components assembled in accordance with the manufacturer’s installation instructions to form the completed chimney. [NFPA 54:3.3.17.2] Chimney, Masonry. A field-constructed chimney of solid masonry units, bricks, stones, listed masonry chimney units, or reinforced Portland cement concrete, lined with suitable chimney flue liners. [NFPA 54:3.3.17.3] Chimney, Metal. A field-constructed chimney of metal.
[NFPA 54:3.3.17.4]
Chimney Classifications:
Chimney, High-Heat Appliance-Type. A factorybuilt, masonry, or metal chimney suitable for removing the products of combustion from fuel-burning high-heat appliances producing combustion gases in excess of 2000°F (1093°C), measured at the appliance flue outlet.
Chimney, Low-Heat Appliance-Type. A factorybuilt, masonry, or metal chimney suitable for removing the products of combustion from fuel-burning low-heat appliances producing combustion gases not in excess of 1000°F (538°C) under normal operating conditions, but capable of producing combustion gases of 1400°F (760°C) during intermittent forced firing for periods up to one hour. All temperatures are measured at the appliance flue outlet.
Chimney, Medium-Heat Appliance-Type. A factory-built, masonry, or metal chimney suitable for removing the products of combustion from fuel-burning medium-heat appliances producing combustion gases, not in excess of 2000°F (1093°C), measured at the appliance flue outlet.
Chimney, Residential Appliance-Type. A factorybuilt or masonry chimney suitable for removing products of combustion from residential-type appliances producing combustion gases not in excess of 1000°F (538°C), measured at the appliance flue outlet. Factory-built Type HT chimneys have high-temperature thermal shock resistance.
Chimney Connector. The pipe that connects a fuel-burning appliance to a chimney. [NFPA 211:3.3.48.1] Circulators (Circulating Pump). A device that circulates liquids within a closed circuit for an intended purpose.
CMC § 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).
CMC § 12.5.3 High relevance — show source text
92 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
WATER HEATERS
tions. Where primer is required, it shall be of a contrasting color. [NFPA 54:12.5.3] 509.4.3 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] 509.5 Masonry, Metal, and Factory-Built Chimneys. Chimneys shall be installed in accordance with Section 509.5.1 through Section 509.5.3. 509.5.1 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]
509.5.1.1 Decorative Shrouds. Decorative
shrouds addressed in Section 509.5.4.3 shall comply with UL 103 for factory -built residential chim neys. 509.5.2 Metal Chimneys. Metal chimneys shall be built and installed in accordance with NFPA 211. [NFPA 54:12.6.1.2] 509.5.3 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 other appliances listed for use with Type B vents shall be permitted. The liner shall be installed in accordance with the liner manufacturer’s installation instructions. A permanent identifying label shall be attached at the point where the connection is to be made to the liner. The label shall read “This chimney liner is for appliances that burn gas only. Do not connect to solid or liquid fuel-burning appliances or incinerators.” [NFPA 54:12.6.1.3] 509.5.4 Termination. A chimney for residential-type or low-heat appliances shall extend at least 3 feet (914 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). [NFPA 54:12.6.2.1] (See Figure 509.5.4) 509.5.4.1 Medium-Heat Gas Appliances. A chimney for medium-heat appliances shall extend at least 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm). [NFPA 54:12.6.2.2] **509.5.4.2 Chimney Height.
CMC § 3.3.20 High relevance — show source text
** A Category 3 vacuum distribution system that can be either a wet system designed to remove liquids, air-gas, or solids from the treated area; or a dry system designed to trap liquid and solids before the service inlet and to accommodate air-gas only through the service inlet. [NFPA 99:3.3.20] Category 4. Activities, systems, or equipment whose failure would have no impact on patient care. [NFPA 99:3.3.162.4] Certified Backflow Assembly Tester. A person who has shown competence to test and maintain backflow assemblies to the satisfaction of the Authority Having Jurisdiction. Cesspool. A lined excavation in the ground that receives the discharge of a drainage system or part thereof, so designed as to retain the organic matter and solids discharging therein but permitting the liquids to seep through the bottom and sides.
Chemical Waste. See Special Wastes. Chimney. One or more passageways, vertical or nearly so, for conveying flue or vent gases to the outdoors. [NFPA 54:3.3.17] Chimney, Factory-Built. A chimney composed of listed factory-built components assembled in accordance with the manufacturer’s installation instructions to form the completed chimney. [NFPA 54:3.3.17.2] Chimney, Masonry. A field-constructed chimney of solid masonry units, bricks, stones, listed masonry chimney units, or reinforced Portland cement concrete, lined with suitable chimney flue liners. [NFPA 54:3.3.17.3] Chimney, Metal. A field-constructed chimney of metal.
[NFPA 54:3.3.18.4] Chimney Classifications: Chimney, High-Heat Appliance-Type. A factorybuilt, masonry, or metal chimney suitable for removing the products of combustion from fuel-burning high-heat appliances producing combustion gases in excess of 2000°F (1093°C), measured at the appliance flue outlet.
Chimney, Low-Heat Appliance-Type. A factorybuilt, masonry, or metal chimney suitable for removing the products of combustion from fuel-burning low-heat appliances producing combustion gases not in excess of 1000°F (538°C) under normal operating conditions, but capable of producing combustion gases of 1400°F (760°C) during intermittent forced firing for periods up to one hour. Temperatures are measured at the appliance flue outlet. Chimney, Medium-Heat Appliance-Type. A factory-built, masonry, or metal chimney suitable for removing the products of combustion from fuel-burning medium-heat appliances producing combustion gases, not in excess of 2000°F (1093°C), measured at the appliance flue outlet.
Chimney, Residential Appliance-Type. A factorybuilt or masonry chimney suitable for removing products of combustion from residential-type appliances producing combustion gases, not in excess of 1000°F (538°C), measured at the appliance flue outlet. Factory-built Type HT chimneys have high-temperature thermal shock resistance.
Circuit Vent. The vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps connected into a battery of fixtures. Clarifier. See Interceptor (Clarifier). Clear Water Waste. Cooling water and condensate drainage from refrigeration and air-conditioning equipment; cooled condensate from steam heating systems, and cooled boiler blowdown water.
CMC § 9.1 High relevance — show source text
2113 A .7 Offsets. Where a masonry chimney is constructed with a fireclay flue liner surrounded by one wythe of masonry, the maximum offset shall be such that the centerline of the flue above the offset does not extend beyond the center of the chimney wall below the offset. Where the chimney offset is supported by masonry below the offset in an approved manner, the maximum offset limitations shall not apply. Each individual corbeled masonry course of the offset shall not exceed the projection limitations specified in Section 2113 A .5.
2113 A .8 Additional load. Chimneys shall not support loads other than their own weight unless they are designed and constructed to support the additional load. Masonry chimneys are permitted to be constructed as part of the masonry walls or concrete walls of the building.
2113 A .9 Termination. Chimneys shall extend not less than 2 feet (610 mm) higher than any portion of the 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.
2113 A .9.1 Chimney caps. Masonry chimneys shall have a concrete, metal or stone cap, sloped to shed water, a drip edge and a caulked bond break around any flue liners in accordance with ASTM C1283.
2113 A .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 A .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 A .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 A .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 A .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.
CMC § 605.1.5.2 High 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 § 605.2.1.2 High relevance — show source text
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 .
605.4 Fuel oil storage systems. Fuel oil storage systems for combustion engines and gas turbines shall be installed and maintained in accordance with this code. Tanks and fuel oil piping systems for building heating systems shall be installed in accordance with this section and NFPA 31. Tanks and fuel oil piping systems for generators and fire pumps shall be installed in accordance with Section 605.4.2 or Chapter 57.
605.4.1 Fuel oil storage in outside, above-ground tanks. Where connected to a fuel oil piping system, the maximum amount of fuel oil storage allowed outside above ground without additional protection shall be 660 gallons (2498 L). The storage of fuel oil above ground for building heating systems in quantities exceeding 660 gallons (2498 L) shall comply with NFPA 31. The storage of fuel oil above ground for combustion engines and gas turbines in portable tanks exceeding a capacity of 660 gallons (2498 L) shall comply with Chapter 57.
605.4.1.1 Approval. Outdoor fuel oil storage tanks shall be in accordance with UL 80, UL 142 or UL 2085.
605.4.2 Fuel oil storage inside buildings. Fuel oil storage inside buildings shall comply with Sections 605.4.2.2 through 605.4.2.8 or Chapter 57.
605.4.2.1 Approval. Indoor fuel oil storage tanks shall be in accordance with UL 80, UL 142 or UL 2085.
CMC § 4.1 High relevance — show source text
4.1
and Section
509.4.3| |
Appliances that can be
converted to use solid
fuel
Unlisted combination
gas- and oil-burning
appliances
Combination gas- and
solid fuel-burning
appliances
Appliances listed for
use with chimneys only
Unlisted appliances|Chimney|Section 509.5| |
Listed combination
gas- and oil-burning
appliances|Type L vent|Section 509.6| |
Listed combination
gas- and oil-burning
appliances|Chimney|Section 509.5| |
Decorative appliance in
vented fireplace|Chimney|UMC Section
911.2| |
Gas-fired toilets|Single-wall metal
pipe|Section 509.7| |
Direct-vent appliances|—|Section 509.2.6| |
Appliances with
integral vents|—|Section 509.2.7|509.4.2 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 accor dance with the vent manufacturer’s installation instruc
TABLE 509.4
TYPE OF VENTING SYSTEM TO BE USED {NFPA 54: TABLE 12.5.1}
92 2025 CALIFORNIA PLUMBING CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
WATER HEATERS
tions. Where primer is required, it shall be of a contrasting color. [NFPA 54:12.5.3] 509.4.3 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] 509.5 Masonry, Metal, and Factory-Built Chimneys. Chimneys shall be installed in accordance with Section 509.5.1 through Section 509.5.3. 509.5.1 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]
509.5.1.1 Decorative Shrouds. Decorative
shrouds addressed in Section 509.5.4.3 shall comply with UL 103 for factory -built residential chim neys. 509.5.2 Metal Chimneys. Metal chimneys shall be built and installed in accordance with NFPA 211. [NFPA 54:12.6.1.2] 509.5.3 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
CMC § 2113.11 High relevance — show source text
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).
2113.11.1.4 Oil-fired appliances approved for use with 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 flue lining systems complying with Section 2113.11.1 and listed chimney liners complying with UL 641 (see Section 2113.11.1.5 for marking).
2113.11.1.5 Notice of usage. When a flue is relined with a material not complying with Section 2113.11.1, 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 is for use only with (type or category of appliance) that burns (type of fuel). Do not connect other types of appliances.”
2113.11.2 Concrete and masonry chimneys for medium-heat appliances. Concrete and masonry chimneys for medium-heat appliances shall comply with Sections 2113.11.2.1 through 2113.11.2.5.
2113.11.2.1 Construction. Chimneys for medium-heat appliances shall be constructed of solid masonry units or of concrete with walls not less than 8 inches (203 mm) thick, or with stone masonry not less than 12 inches (305 mm) thick.
Frequently asked questions
What does “listed” mean for factory‑built chimneys?
“Listed” means the chimney assembly is tested and certified by a nationally recognized testing lab to the referenced UL standard (e.g., UL 103, UL 959, UL 2561) and marked/listed accordingly, as required by § 802.5.1 .
Can I reline an old masonry chimney with stainless steel for a gas furnace?
Yes — the code permits chimneys lined with a chimney lining system listed to UL 1777 or other approved materials that resist flue gases up to 1800°F under § 802.5.3; ensure the liner is listed for the appliance and installed per the manufacturer and AHJ .
Are metal chimneys allowed for solid‑fuel appliances?
Metal chimneys are permitted but must be built and installed per NFPA 211, per § 802.5.2. NFPA 211 contains specific requirements for solid‑fuel (wood/coal) service; consult NFPA 211 and the AHJ for the correct metal chimney type and clearances .
The CMC mentions an Exception in § 802.5.3 — can I rely on it?
The provided CMC excerpts show an Exception exists for § 802.5.3 but the full text wasn’t available in the retrieved files. Do not rely on an incomplete excerpt — consult the complete CMC text or your AHJ for the Exception wording and conditions .
Where do I find the construction details (clearances, wall thickness, caps)?
§ 802.5 subsections reference NFPA 211 for construction and installation details. Masonry‑specific construction details (wall thickness, caps, rain caps, spark arrestors) are also covered in the California Building Code; check both NFPA 211 and the applicable building‑code sections when designing or inspecting chimneys
More in California Mechanical Code
Ask about the CMC
Get cited, plain-English answers on the California Mechanical Code for your project — any code section, any scenario.
Start Free Trial