CRC · California Residential Code

What flue lining materials are acceptable and how must they be selected for appliances?

Homeowners: masonry chimneys must be lined with a material appropriate to the appliance — usually clay tile (ASTM C315), a UL‑1777 listed liner, or a factory‑built unit — and gas appliances must use the venting called out in the California Mechanical Code. If you reline with a material limited to one fuel or appliance, the chimney must be permanently labeled to prevent unsafe reconnections.

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

Masonry chimneys must be lined and the lining material must be appropriate to the appliance being vented, following the appliance listing and manufacturer’s instructions (§ R1003.11) . For typical residential appliances, the CRC lists specific acceptable options (clay tiles, listed chimney lining systems, factory‑built chimneys/units, or other approved materials that tolerate flue conditions up to 1,800°F (982°C)) (§ R1003.11.1) . Flues serving gas appliances must follow the California Mechanical Code as required by the CRC (§ R1003.11.3) .

The single most important rule: use a liner that is listed/approved for the appliance and fuel type — or, for gas appliances, follow the California Mechanical Code — otherwise the chimney is not code‑compliant. § R1003.11

Requirements in detail

Basic selection rule

  • The masonry chimney shall be lined and the lining material must be selected to match the appliance type and the appliance listing/manufacturer instructions (§ R1003.11) .
  • For residential‑type appliances, choose one of the options listed in § R1003.11.1 or comply with any additional appliance‑specific rules in §§ R1003.11.3–R1003.11.6 where applicable .

Acceptable lining materials (decision table)

Decision dimension Acceptable material / value When to choose it Code reference
Standard clay tile lining Clay flue lining (ASTM C315) Traditional wood/solid‑fuel and many residential uses where clay tile is shown in the appliance/listing § R1003.11.1 (Item 1)
Listed chimney liner system Listed & labeled system (UL 1777) Use when a listed liner system is appropriate for the appliance (relines, retrofit) § R1003.11.1 (Item 2)
Factory‑built chimney unit Factory‑built chimney or unit listed for installation within masonry Where a factory unit is specifically listed to be installed inside masonry — follow the unit listing § R1003.11.1 (Item 3)
High‑temperature/other approved materials Other approved materials that resist corrosion/erosion/softening/cracking to 1,800°F (982°C) Special fuels, high‑heat appliances, or engineered liners approved for service to 1,800°F § R1003.11.1 (Item 4) — 1,800°F (982°C) highlighted
Gas appliance liners Follow California Mechanical Code for gas appliance venting; use the vent type the Mechanical Code/table requires (Type B, listed lining, special gas vent, etc.) All gas‑fired appliances — do not rely on CRC § R1003.11.1 alone for gas appliances § R1003.11.3 and California Mechanical Code (see Table/Sections for gas vent types)

Notes:

  • When using a listed product, install per the product listing and manufacturer’s instructions (installation must follow the listing) (§ R1003.12.1) .
  • The CRC allows “other approved materials” only if they demonstrably resist flue gases and condensate at temperatures up to 1,800°F (982°C) (§ R1003.11.1) .

How appliance type drives the choice

  • Solid‑fuel appliances (wood, coal): clay tile or a listed high‑temperature liner rated for solid fuel. See the clay‑tile standard ASTM references in CRC for manufacture/installation details (§ R1003.11.1) .
  • Gas appliances: selection is governed by the California Mechanical Code — the CRC defers to that code for flue lining systems serving gas appliances (§ R1003.11.3) .
  • Pellet & certain oil appliances: the CRC limits acceptable options (see Exceptions & Special Cases below) — these are handled in adjoining CRC subsections (R1003.11.4, R1003.11.5) .

Exceptions & special cases

  • Gas appliances: The CRC explicitly defers to the California Mechanical Code for flue lining required for gas appliances — follow that code and its tables/sections for the correct vent type and listed systems (§ R1003.11.3) .
  • Pellet fuel appliances: Liners are limited to the list in § R1003.11.1 or pellet vents listed for installation within masonry chimneys (see the CRC’s pellet‑vent marking requirements) — consult § R1003.11.4 for the limitation and marking requirements .
  • Oil appliances approved for Type L vent: Relining options are limited to the general list in § R1003.11.1 and listed liners complying with UL 641 per § R1003.11.5 .
  • Relines that are not the general allowed types: If you reline a flue with a material that does not comply with § R1003.11.1, the chimney must be permanently labeled to identify the specific appliance/fuel for which that flue is approved (§ R1003.11.6) .
  • Installation details (clay tile): clay liners must be installed per ASTM and extend to specified points in the chimney (see CRC § R1003.12 for installation rules) — install per the standard and manufacturer listing when using listed materials .

Common mistakes

  • Assuming “any stainless steel tube” is acceptable — stainless or metal liners must be listed/approved for the appliance and conditions; the CRC requires listed systems or approved materials (§ R1003.11.1) .
  • Using an unlisted liner for a gas appliance without consulting the California Mechanical Code — gas appliance flue lining is governed by that code (§ R1003.11.3) .
  • Relining for one fuel then later connecting a different appliance/fuel type (for example, lining for gas and later connecting a wood stove) — the CRC requires permanent labeling if the liner is limited to a specific appliance/fuel (§ R1003.11.6) .
  • Using the space around a lining to vent another appliance — the CRC prohibits using the surrounding space to vent a different appliance unless a separate lined flue is installed per the manufacturer’s instructions (§ R1003.12.2) .
  • Installing listed liners but ignoring the listing/manufacturer installation instructions — listed materials must be installed per their listing (§ R1003.12.1) .

Worked example — concrete scenario with numbers

Scenario: You have an existing masonry chimney and want to connect a new natural‑gas water heater (Category I, input 40,000 Btu/h). Which lining options meet CRC requirements?

  1. CRC baseline: masonry chimneys must be lined and the lining must be appropriate to the appliance (§ R1003.11) .
  2. CRC residential options include clay tile (ASTM C315), UL 1777 listed liners, factory‑built units, or other approved materials to 1,800°F (§ R1003.11.1) .
  3. BUT: for gas appliances you must follow the California Mechanical Code for the venting type and lining selection (§ R1003.11.3) .
  4. Practical compliance path:
    • Option A: Install a chimney liner system listed to UL 1777 sized per the appliance/Mechanical Code tables and installed per the liner manufacturer’s instructions. This satisfies CRC § R1003.11.1 and is consistent with the Mechanical Code path for listed chimney lining systems .
    • Option B: Install the venting required by the Mechanical Code (for many Category I appliances a Type B gas vent or listed chimney lining for gas venting may be required). Confirm via the Mechanical Code tables which vent is permitted for a 40,000 Btu/h water heater and install accordingly .
  5. Do not reline with an unapproved material. If you choose a liner that is not one of the general accepted types and it’s limited to gas use, permanently label the chimney where the connector enters: “THIS CHIMNEY FLUE IS FOR USE ONLY WITH [TYPE] APPLIANCES THAT BURN [FUEL]…” as required by § R1003.11.6 .

Related provisions

  • § R1003.11 — Flue lining (material) requirement: masonry chimneys shall be lined and the material must be appropriate to the appliance
  • § R1003.11.1 — Residential‑type acceptable lining options (clay tile, UL 1777 systems, factory units, other approved materials to 1,800°F)
  • § R1003.11.3 — Gas appliances: flue lining systems in accordance with the California Mechanical Code
  • § R1003.11.4 — Pellet fuel appliance limitations (pellet vents listed for use in masonry)
  • § R1003.11.5 — Oil‑fired appliances approved for Type L vent (UL 641 liners permitted)
  • § R1003.11.6 — Required permanent label when flue is relined with materials not complying with § R1003.11.1
  • § R1003.12 — Clay flue lining installation and ASTM references; listed materials must be installed per listing (§ R1003.12.1)

If you want, I can extract the exact California Mechanical Code table(s) that govern which vent type (Type B, listed liner, special gas vent) your specific gas appliance needs and show how to size the liner/vent for a given input rating — that requires pulling the relevant Mechanical Code tables.

Code references

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

  • CRC § 10.1 High relevance — show source text

    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:

    1. Clay flue lining complying with the requirements of ASTM C315.
    2. Listed and labeled chimney lining systems complying with UL 1777.
    3. Factory-built chimneys or chimney units listed for installation within masonry chimneys.
    4. 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.

    R1003.11.4 Pellet fuel-burning appliances. Flue lining and vent systems for use in masonry chimneys with pellet fuel-burning appliances shall be limited to the following:

    1. Flue lining systems complying with Section R1003.11.1.
    2. Pellet vents listed for installation within masonry chimneys (see Section R1003.11.6 for marking).

    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:

    1. Flue lining systems complying with Section R1003.11.1.
    2. 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.

  • CRC § 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:

    1. Clay flue lining complying with the requirements of ASTM C315.
    2. Listed chimney lining systems complying with UL 1777.
    3. Factory-built chimneys or chimney units listed for installation within masonry chimneys.
    4. 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.

  • 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:

    1. 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.

    1. The arrestor screen shall have heat and corrosion resistance equivalent to 12 gage wire, 19-gage galvanized steel or 24gage stainless steel.
    2. 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).
    3. 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:

    1. Clay flue lining complying with the requirements of ASTM C315.
    2. Listed and labeled chimney lining systems complying with UL 1777.
    3. Factory-built chimneys or chimney units listed for installation within masonry chimneys.
    4. 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:

    1. 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.

    2113.9.3 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:

    1. Clay flue lining complying with the requirements of ASTM C315.
    2. Listed chimney lining systems complying with UL 1777.
    3. Factory-built chimneys or chimney units listed for installation within masonry chimneys.
    4. 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 § 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:

    1. Flue lining systems complying with Section R1003.11.1.
    2. 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.

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    CHIMNEYS AND FIREPLACES

    R1003.12.1 Listed materials. Listed materials used as flue linings shall be installed in accordance with the terms of their listings and manufacturer’s instructions.

    R1003.12.2 Space around lining. The space surrounding a chimney lining system or vent installed within a masonry chimney shall not be used to vent any other appliance.

    Exception: This shall not prevent the installation of a separate flue lining in accordance with the manufacturer’s instructions.

    R1003.13 Multiple flues. Where two or more flues are located in the same chimney, masonry wythes shall be built between adjacent flue linings. The masonry wythes shall be not less than 4 inches (102 mm) thick and bonded into the walls of the chimney.

    Exception: Where venting only one appliance, two flues shall be permitted to adjoin each other in the same chimney with only the flue lining separation between them. The joints of the adjacent flue linings shall be staggered not less than 4 inches (102 mm).

    R1003.14 Flue area (appliance). Chimney flues shall not be smaller in area than that of the area of the connector from the appliance

    [see Tables R1003.14(1) and R1003.14(2)]. The sizing of a chimney flue to which multiple appliance venting systems are connected shall be in accordance with the California Mechanical Code.

  • CRC § 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:

    1. Clay flue lining complying with the requirements of ASTM C315.
    2. Listed chimney lining systems complying with UL 1777.
    3. Factory-built chimneys or chimney units listed for installation within masonry chimneys.
    4. 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 .

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    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).

  • CRC § 2113.11.3.3 High relevance — show source text

    2113.11.3.3 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).

    2113.11.3.4 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.

    2113.12 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.

    2113.13 Additional requirements.

    2113.13.1 Listed materials. Listed materials used as flue linings shall be installed in accordance with the terms of their listings and the manufacturer’s instructions.

    2113.13.2 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.

    2113.14 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).

    2113.15 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:

    1. Chimney flues serving oil-fired appliances sized in accordance with NFPA 31.
    2. Chimney flues serving gas-fired appliances sized in accordance with the California Mechanical Code .

    2113.16 Flue area (masonry fireplace). Flue sizing for chimneys serving fireplaces shall be in accordance with Section 2113.16.1 or 2113.16.2.

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    FIGURE 2113.16—FLUE SIZES FOR MASONRY CHIMNEYS

  • 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).

    2025 CALIFORNIA BUILDING CODE 21A-15

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

    MASONRY

    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:

    1. Chimney flues serving oil-fired appliances sized in accordance with NFPA 31.
    2. Chimney flues serving gas-fired appliances sized in accordance with the California Mechanical Code .
  • CRC § 2113.11.2.3 High relevance — show source text

    2113.11.2.3 Multiple passageway. Concrete and masonry chimneys containing more than one passageway shall have the liners separated by a minimum 4-inch-thick (102 mm) concrete or solid masonry wall.

    2113.11.2.4 Termination height. Concrete and masonry chimneys for medium-heat appliances shall extend not less than 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm).

    2113.11.2.5 Clearance. A minimum clearance of 4 inches (102 mm) shall be provided between the exterior surfaces of a concrete or masonry chimney for medium-heat appliances and combustible material.

    2113.11.3 Concrete and masonry chimneys for high-heat appliances. Concrete and masonry chimneys for high-heat appliances shall comply with 2113.11.3.1 through 2113.11.3.4.

    2025 CALIFORNIA BUILDING CODE 21-15

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

    MASONRY

    2113.11.3.1 Construction. Chimneys for high-heat appliances shall be constructed with double walls of solid masonry units or of concrete, each wall to be not less than 8 inches (203 mm) thick with a minimum airspace of 2 inches (51 mm) between the walls.

    2113.11.3.2 Lining. The inside of the interior wall shall be lined with an approved high-duty refractory brick, not less than 4 [1] / 2 inches (114 mm) thick laid on the 4 [1] / 2 -inch bed (114 mm) in an approved high-duty refractory mortar. The lining shall start at the base of the chimney and extend continuously to the top.

    2113.11.3.3 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).

    2113.11.3.4 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.

    2113.12 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.

    2113.13 Additional requirements.

    2113.13.1 Listed materials. Listed materials used as flue linings shall be installed in accordance with the terms of their listings and the manufacturer’s instructions.

  • CRC § 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.

  • CRC § 2.4 High relevance — show source text

    Lab test for percent of clay, silt and sand via hydrometer method.
    2. The Figure 2 Ribbon Test and the Figure 3 Ball Test in the appendix of ASTM E2392/E2392M.
    d. Trace amounts of organic materials are acceptable.|©Douglas Piltingsrud and StrawClay.org. Used by permission.
    a. Interpolation permitted. Extrapolation not permitted.
    b. Water mixed with subsoil equals clay slip.
    c. Subsoil Testing Methods:
    1. Lab test for percent of clay, silt and sand via hydrometer method.
    2. The Figure 2 Ribbon Test and the Figure 3 Ball Test in the appendix of ASTM E2392/E2392M.
    d. Trace amounts of organic materials are acceptable.|©Douglas Piltingsrud and StrawClay.org. Used by permission.
    a. Interpolation permitted. Extrapolation not permitted.
    b. Water mixed with subsoil equals clay slip.
    c. Subsoil Testing Methods:
    1. Lab test for percent of clay, silt and sand via hydrometer method.
    2. The Figure 2 Ribbon Test and the Figure 3 Ball Test in the appendix of ASTM E2392/E2392M.
    d. Trace amounts of organic materials are acceptable.|

    BI103.2.4 Stabilization of light straw-clay. Light straw-clay shall be stabilized as follows, or shall be in accordance with an approved design by a registered design professional:

    1. Vertical stabilization shall be of structural or nonstructural wood framing in accordance with Figure BI103.2.4(1), BI103.2.4(2) or BI103.2.4(3). Framing members that are both load-bearing and stabilization members shall meet the requirements of Section R602 and this section. Nonstructural stabilization members shall be not more than 32 inches (813 mm) on center.
    2. Horizontal stabilization shall be installed at not more than 24 inches (610 mm) on center and in accordance with Figure BI103.2.4(1), BI103.2.4(2) or BI103.2.4(3). Horizontal stabilization shall be of any of the following with the stated minimum dimensions: [3] / 4 -inch (19.1 mm) bamboo, [1] / 2 -inch (12.7 mm) fiberglass rod, 1-inch (25 mm) wood dowel or nominal 1-inch by 2-inch (25 mm by 51 mm) wood.

    FIGURE BI103.2.4(1)—LIGHT STRAW-CLAY WALL WITH LARSEN TRUSSES

    DOUBLE TOP PLATE

    VERTICAL SOLID BLOCKING

    FLAT SOLID BLOCKING

    LADDER (LARSEN) TRUSSES MADE WITH 2x4s AND GUSSETS PER SECTION BI103.2.4, ITEM 1

    GUSSETS: [3] / 8 ″ x 3 ″ PLYWOOD OR 1x4 FASTENERS: 4–4d NAILS OR 4–1¾ ″ STAPLES

    WOOD OR METAL STRAP BRACING (LIB) PER TABLE 602.10.4 WHERE APPLICABLE PER SECTION R602.10

    LIGHT STRAW-CLAY INFILL

    HORIZONTAL STABILIZATION OF LIGHT STRAW-CLAY PER SECTION BI103.4, ITEM 2

    ANCHORAGE PER SECTION R403.1.6

    2X SILL PLATE

  • CRC § 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 vent    		 Type B gas vent Section 802.6
    Listed Category I appliances
    Listed appliances equipped with draft hood
    Appliances listed for use with Type B gas vent    		 Chimney Section 802.5
    Listed Category I appliances
    Listed appliances equipped with draft hood
    Appliances listed for use with Type B gas vent    		 Single-wall metal pipe Section 802.7
    Listed Category I appliances
    Listed appliances equipped with draft hood
    Appliances listed for use with Type B gas vent    		 Listed chimney lining system for gas
    venting    		 Section 802.5.3
    Listed Category I appliances
    Listed appliances equipped with draft hood
    Appliances listed for use with Type B gas vent    		 Special gas vent listed for these
    appliances    		 Section 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 appliances    		 As specified or furnished by
    manufacturers of listed appliances    		 Section 802.4.1, Section 802.4.

Frequently asked questions

Can I use any stainless‑steel liner for a relining job?

Only if the stainless‑steel liner is a listed/approved chimney‑liner product for the appliance and fuel, or otherwise demonstrated to meet the “other approved materials” performance criteria in § R1003.11.1. For gas appliances, follow the California Mechanical Code (§ R1003.11.3) .

What if I reline a flue for gas and later want to connect a wood stove?

You cannot connect a different fuel type to a liner that isn’t listed/approved for that fuel. If the existing liner is limited to a specific appliance/fuel, the chimney must be permanently labeled as required in § R1003.11.6; otherwise a new approved liner or chimney work will be required .

Is clay tile always acceptable?

Clay flue lining manufactured to ASTM C315 is an accepted option for residential appliances per § R1003.11.1, but installation must follow ASTM/installation rules in the CRC (see § R1003.12) and must be appropriate for the appliance/listing .

Do listed liners have to be installed exactly as the manufacturer specifies?

Yes — the CRC requires that listed materials be installed in accordance with their listing and manufacturer’s instructions (§ R1003.12.1) .

Who decides whether an “other approved material” is acceptable?

Approval is through the authority having jurisdiction (AHJ) based on evidence that the material resists flue gases and condensate and temperatures up to 1,800°F (982°C) as required in § R1003.11.1 .

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Masonry Chimneys

California Residential Code