CMC · California Mechanical Code

What are the chimney height and termination requirements above roofs?

Your chimney must be tall enough so its top is at least 3 feet above the roof penetration and 2 feet higher than anything within 10 feet horizontally (or meet the larger medium‑heat 10‑ft/25‑ft rule), and it must be at least 5 feet above the appliance draft hood; decorative caps are only allowed if listed for that chimney system (CMC §§ 802.5.4–802.5.4.3).

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

In plain terms, a chimney serving a residential-type or low-heat appliance must rise high enough above the roof penetration and nearby roof surfaces so smoke and products of combustion clear the roof and nearby obstructions. Specifically, the chimney must extend at least 3 feet (914 mm) above the highest point where it passes through the roof and at least 2 feet (610 mm) higher than any portion of the building within a horizontal distance of 10 feet (3048 mm) — § 802.5.4. For medium‑heat appliances the clearance is larger: 10 feet (3048 mm) above any portion of the building within 25 feet (7620 mm) — § 802.5.4.1. A chimney must also extend at least 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar — § 802.5.4.2.

The single most important rule: the chimney must be tall enough so its top is both 3 feet above its roof penetration and 2 feet higher than anything within 10 feet horizontally (or meet the larger medium‑heat / draft‑hood clearances).

Requirements in detail

Primary termination / roof clearances

  • Residential / low‑heat appliances:

    • Extend ≥ 3 ft (914 mm) above the highest point where the chimney passes through the roof. § 802.5.4.
    • Also required to be ≥ 2 ft (610 mm) higher than any portion of the building within 10 ft (3048 mm) horizontally. § 802.5.4.

  • Medium‑heat gas appliances:

    • Chimney must extend ≥ 10 ft (3048 mm) above any portion of any building within 25 ft (7620 mm). § 802.5.4.1.

  • Chimney height relative to appliance connections:

    • Chimney must extend ≥ 5 ft (1524 mm) above the highest connected appliance draft‑hood outlet or flue collar. § 802.5.4.2.

  • Decorative shrouds:

    • Decorative shrouds are not permitted at the termination of factory‑built chimneys unless the shroud is listed and labeled for that specific chimney system and installed per the manufacturer’s instructions. § 802.5.4.3.

See the code figure for typical termination locations: Figure 802.5.4 (illustrative).

Quick reference table (decision‑relevant dimensions)

Situation / threshold Required minimum dimension Code Reference
Above roof penetration (residential / low‑heat) 3 ft (914 mm) above highest point where it passes through roof § 802.5.4
Above any portion of building within 10 ft (residential / low‑heat) 2 ft (610 mm) higher than any portion within 10 ft (3048 mm) horizontal § 802.5.4
Medium‑heat appliance clearance 10 ft (3048 mm) higher than any portion of building within 25 ft (7620 mm) § 802.5.4.1
Minimum above draft hood/flue collar 5 ft (1524 mm) above highest connected appliance draft hood outlet or flue collar § 802.5.4.2
Decorative shrouds at termination Prohibited unless listed & labeled for that system and installed per manufacturer § 802.5.4.3

Exceptions & special cases

  • Decorative shrouds: Allowed only when the shroud is listed and labeled for use with that specific factory‑built chimney system and installed according to the manufacturer’s installation instructions. This is the only exception explicitly stated in § 802.5.4.3.

  • Medium‑heat appliances: Use § 802.5.4.1 whenever the appliance classification is medium‑heat — the larger 10 ft / 25 ft rule supersedes the residential/low‑heat 3 ft / 10 ft rule when applicable.

  • If a chimney serves multiple appliances or a different appliance class (e.g., high‑heat), other code sections (masonry chimney provisions in the California Building Code and sizing provisions in Chapter 803 of the CMC) may apply — see Related Provisions below. (Those other provisions are not the primary termination rules in § 802.5.4–802.5.4.3.)

If any required clearance would be reduced by rooftop equipment, parapets, or nearby structures, use the larger clearance required by the code language (e.g., medium‑heat rule) — the code’s dimensional triggers determine which clearance governs.

Common mistakes

  • Measuring vertical height only from the roof deck instead of from the highest point where the chimney passes through the roof (the code uses the roof penetration point). See § 802.5.4.
  • Forgetting to check the horizontal distance: nearby roof surfaces within 10 ft (or 25 ft for medium‑heat) can require a taller chimney even if the chimney is already 3 ft above the penetration. See § 802.5.4 and § 802.5.4.1.
  • Installing a decorative shroud at the termination without verifying the shroud is listed and labeled for that specific chimney system and following manufacturer instructions. See § 802.5.4.3.
  • Ignoring the requirement to extend 5 ft above the draft‑hood outlet or flue collar when that condition controls the required chimney height. See § 802.5.4.2.

Worked example

Scenario: A gas water‑heater (residential/low‑heat) vents into a masonry chimney. The chimney passes through the roof at a point that is 0 ft relative to itself (call that the penetration reference). There is a ridge/roof surface located 8 ft horizontally from the chimney penetration that is 1.5 ft (18 in) higher than the penetration. The appliance draft hood outlet is 1 ft below the roof penetration level.

Step 1 — Apply the residential / low‑heat rules (§ 802.5.4):

  • Must be ≥ 3 ft above the highest point where it passes through the roof → 3.0 ft above penetration.
  • Must be ≥ 2 ft higher than any portion of building within 10 ft horizontally. The nearby roof is within 10 ft and is 1.5 ft higher, so chimney must be at least 1.5 ft + 2.0 ft = 3.5 ft above penetration.

Step 2 — Apply draft‑hood requirement (§ 802.5.4.2):

  • Chimney must be ≥ 5 ft above the highest connected appliance draft hood outlet or flue collar. The draft hood is 1 ft below the penetration, so chimney must be 1 ft + 5 ft = 6.0 ft above penetration.

Step 3 — Take the controlling (largest) required height:

  • From the three checks we got 3.0 ft, 3.5 ft, and 6.0 ft. The controlling requirement is 6.0 ft above penetration, per § 802.5.4.2.

Conclusion: In this scenario the installer must extend the chimney to at least 6 ft above the roof penetration to satisfy the draft‑hood rule in § 802.5.4.2, which is higher than the 3 ft / 2 ft roof clearances in § 802.5.4.

Related provisions (CMC) — quick list

  • § 802.5.5 — Size of chimneys (sizing methods and tables).
  • § 802.5.6 — Inspection of chimneys or vents (inspection timing).
  • § 802.5.9 — Support of chimneys (structural support requirements).
  • § 802.5.11 — Space surrounding lining or vent (limitations on using remaining space).
  • § 802.6.1 — Gas vent termination (additional gas‑vent termination rules).

Note: For masonry chimneys serving medium‑ or high‑heat appliances the California Building Code contains additional termination heights (e.g., masonry medium‑heat and high‑heat rules). Those CBC provisions are related but are not replacements for the CMC’s § 802.5.4–.4.3 termination rules when the CMC applies. See the Building Code for masonry‑specific termination heights.

Code references

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

  • CMC § 12.6.2.1 High relevance — show source text

    ** 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 802.5.4) 802.5.4.1 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]

    802.5.4.2 Chimney Height. A chimney shall extend at least 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar.

    [NFPA 54:12.6.2.3]

    802.5.4.3 Decorative Shrouds. Decorative

    shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are

    listed and labeled for use with the specific factorybuilt chimney system and are installed in accordance with the manufacturer’s installation instructions.

    [NFPA 54:12.6.2.4]

    802.5.5 Size of Chimneys. The effective area of a chimney venting system serving listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be in accordance with one of the following methods:

    (1) Those listed in Section 803.0.

    (2) The effective areas of the vent connector and chimney flue of a venting system serving a single appliance with a draft hood shall be not less than the area

    of the appliance flue collar or draft hood outlet or greater than seven times the draft hood outlet area.

    (3) The effective area of the chimney flue of a venting system serving two appliances with draft hoods shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.

    (4) Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods.

    (5) Other engineering methods. [NFPA 54:12.6.3.1]

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    CHIMNEYS AND VENTS

    FIGURE 802.5.4

    TYPICAL TERMINATION LOCATIONS FOR

    CHIMNEYS AND SINGLE-WALL METAL PIPES SERVING

    RESIDENTIAL-TYPE AND LOW-HEAT APPLIANCE

    [NFPA 54: FIGURE A.12.6.2.1]

    802.5.6 Inspection of Chimneys or Vents. This inspection shall be made after chimneys, vents, or parts thereof, authorized by the permit, have been installed and before such vent or part thereof has been covered or concealed.

  • CMC § 907.0 High relevance — show source text

    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 802.4.3| |Incinerators|In accordance with NFPA 82|In accordance with NFPA 82| |Appliances that can be converted to use of 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 802.5| |Listed combination gas- and oil-burning appliances|Type L vent|Section 802.6| |Listed combination gas- and oil-burning appliances|Chimney|Section 802.5| |Decorative appliances in vented fireplace|Chimney|Section 911.3| |Gas-fired toilets|Single-wall metal pipe|Section 802.7, Section 928.3| |Direct vent appliances|—|Section 802.2.6| |Appliances with integral vents|—|Section 802.2.7|

    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] 802.5.4 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 802.5.4) 802.5.4.1 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]

    802.5.4.2 Chimney Height. A chimney shall extend at least 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar.

    [NFPA 54:12.6.2.3]

    802.5.4.3 Decorative Shrouds. Decorative

    shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are

    listed and labeled for use with the specific factorybuilt chimney system and are installed in accordance with the manufacturer’s installation instructions.

    [NFPA 54:12.6.2.4]

    802.5.5 Size of Chimneys. The effective area of a chimney venting system serving listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be in accordance with one of the following methods:

    (1) Those listed in Section 803.0.

  • CMC § 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.

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    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.

  • CMC § 12.6.1.3 High relevance — show source text

    (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. A chimney shall extend at least 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar.

    [NFPA 54:12.6.2.3]

    509.5.4.3 Decorative Shrouds. Decorative

    shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are listed and labeled for use with the specific factory-built chimney system and are installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.2.4] 509.5.5 Size of Chimneys. The effective area of a chimney venting system serving listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be in accordance with one of the following methods:

    (1) Those listed in Section 510.0.

    (2) The effective areas of the vent connector and chimney flue of a venting system serving a single appliance with a draft hood shall be not less than the area of the appliance flue collar or draft hood outlet or greater than seven times the draft hood outlet area.

    (3) The effective area of the chimney flue of a venting system serving two appliances with draft hoods shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet or greater than seven times the smaller draft hood outlet area.

    (4) Chimney venting systems using mechanical draft shall be sized in accordance with engineering methods.

  • CMC § 11.3.3 High relevance — show source text

    2113 A .11.3.3 Termination height. Concrete and masonry chimneys for high-heat appliances shall extend not less than 20 feet (6096 mm) higher than any portion of any building within 50 feet (15 240 mm).

    2113 A .11.3.4 Clearance. Concrete and masonry chimneys for high-heat appliances shall have approved clearance from buildings and structures to prevent overheating combustible materials, permit inspection and maintenance operations on the chimney and prevent danger of burns to persons.

    2113 A .12 Clay flue lining (installation). Clay flue liners shall be installed in accordance with ASTM C1283 and extend from a point not less than 8 inches (203 mm) below the lowest inlet or, in the case of fireplaces, from the top of the smoke chamber to a point above the enclosing walls. The lining shall be carried up vertically, with a maximum slope not greater than 30 degrees (0.52 rad) from the vertical.

    Clay flue liners shall be laid in medium-duty nonwater-soluble refractory mortar conforming to ASTM C199 with tight mortar joints left smooth on the inside and installed to maintain an airspace or insulation not to exceed the thickness of the flue liner separating the flue liners from the interior face of the chimney masonry walls. Flue lining shall be supported on all sides. Only enough mortar shall be placed to make the joint and hold the liners in position.

    2113 A .13 Additional requirements.

    2113 A .13.1 Listed materials. Listed materials used as flue linings shall be installed in accordance with the terms of their listings and the manufacturer’s instructions.

    2113 A .13.2 Space around lining. The space surrounding a chimney lining system or vent installed within a masonry chimney shall not be used to vent any other appliance.

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

    2113 A .14 Multiple flues. Where two or more flues are located in the same chimney, masonry wythes shall be built between adjacent flue linings. The masonry wythes shall be not less than 4 inches (102 mm) thick and bonded into the walls of the chimney.

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

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    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 .
  • CMC § 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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    MASONRY

    FIGURE 2113.16—FLUE SIZES FOR MASONRY CHIMNEYS

  • CMC § 12.6.7 High relevance — show source text

    [NFPA 54:12.6.7] 509.5.10 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.

    Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 509.5.10.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory-built chimney flue shall not be used to supply combustion air.

    Exception: Direct-vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.8.2] 509.6 Gas Vents. The installation of gas vents shall meet the following requirements:

    (1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.

    (2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is

    connected.

    (3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry

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    WATER HEATERS

    chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”

    (4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.

    [NFPA 54:12.7.2]

    509.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:

    (1) A gas vent shall terminate in accordance with one of the following:

    (a) Gas vents that are 12 inches (300 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall

    terminate above the roof in accordance with Figure 509.6.1 and Table 509.6.1.

    (b) Gas vents that are over 12 inches (300 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally.

    (c) Industrial appliances as provided in Section 509.2.5.

    (d) Direct-vent systems as provided in Section 509.2.6.

    (e) Appliances with integral vents as provided in Section 509.2.7.

    (f) Mechanical draft systems as provided in Section 509.3.3 through Section 509.3.3.4.

  • CMC § 802.5.4.2 High relevance — show source text

    Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .802.5.4.2

    Inspection . . . . . . . . . . . . . . . . . . . . . .802.5.6, 802.5.7

    Installation . . . . . . . . . . . . . . . . . . . . . . . . . . .Chapter 8

    Location . . . . . . . . . . . . . . . . . . . . . . . . . .Table 402.4.1

    Masonry . . . . . . . . . . . . . . . . .802.5.3, 802.5.11, 802.6,

    Table 803.1.2(3), Table 803.1.2(4),

    Table 803.1.2(6), 803.1.6,

    803.1.9, 803.1.10, Table 803.2(3),

    Table 803.2(4), Table 803.2(6)-Table 803.2(9),

    803.2.19, 803.2.20, Appendix F

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    INDEX

    Metal . . . . . . . . . . . . . . . . . . . . . . . . .802.5.2, 802.10.11

    Serving appliances . . . . . . . . . . . . . . . . . . . . . .802.5.8

    Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .802.5.5

    Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .802.5.9

    Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . .802.5.4

    Venting systems . . . . . . . . . . . . . . . .802.5.5, 802.6.2.4

    CHIMNEY CLASSIFICATIONS

    High-heat appliances-type . . . . . . . . . . . . . . . . . . 205.0

    Low-heat appliances-type. . . . . . . . . . . . . . . . . . . 205.0

    Medium-heat

    appliances-type. . . . . . . . . . . . . . . . . . . . . . . . . 205.0

    Residential appliances-type . . . . . . . . . . . . . . . . . . 205.0

    CHLORINATED POLYVINYL

    CHLORIDE (CPVC) PIPE OR TUBING

    Condensate waste piping . . . . . . . . . . . . . . . . . . . 310.3

    Ground source loop . . . . . . . . . . . . . . . . . . Table 1703.2

    Hangers and supports. . . . . . . . . . . . . . . . . Table 313.6

  • CMC § 1.5. Medium relevance — show source text

    For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.|For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 ksi = 1,000 psi = 6.895 MPa.
    a. Deflection limit:L/240.
    b. Head and sill track spans are based on components and cladding wind pressures and 48-inch tributary span.
    c. For openings less than 4 feet in height that have both a head track and sill track, the spans are permitted to be multiplied by 1.75. For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.|For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 ksi = 1,000 psi = 6.895 MPa.
    a. Deflection limit:L/240.
    b. Head and sill track spans are based on components and cladding wind pressures and 48-inch tributary span.
    c. For openings less than 4 feet in height that have both a head track and sill track, the spans are permitted to be multiplied by 1.75. For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.|For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 ksi = 1,000 psi = 6.895 MPa.
    a. Deflection limit:L/240.
    b. Head and sill track spans are based on components and cladding wind pressures and 48-inch tributary span.
    c. For openings less than 4 feet in height that have both a head track and sill track, the spans are permitted to be multiplied by 1.75. For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses.

  • CMC § 802.10.1.4 Medium relevance — show source text

    Table 802.10.1.4 Minimum Thickness for Steel

    Vent Connectors for Medium Heat Appliances . . . . . . . . . . . . . . 161

    Table 802.8.1 Through-the-Wall Direct Vent Termination Clearances . . . . . . . . 162

    802.11 Vent Connectors for Category II, Category III, and Category IV Appliances . . . . . . . . . . . . . . . . . . 164

    802.12 Appliances Requiring Draft Hoods . . . . . . . . . . . . . . . . . . 164

    802.13 Manually Operated Dampers . . . . 165

    802.14 Automatically Operated Vent Dampers . . . . . . . . . . . . . . . . . . . . 165

    802.15 Obstruction of Flow. . . . . . . . . . . . 165

    803.0 Sizing of Category I Venting Systems . . . . . . . . . . . . . . . . . . . . 165

    803.1 Additional Requirements to Single Appliance Vent . . . . . . . . . 165

    803.2 Additional Requirements to Multiple-Appliance Vent.. . . . . . . . 167

    Table 803.2.1 Vent Connector Maximum

    Length. . . . . . . . . . . . . . . . . . . . . . 167

    Table 803.1.2(1) Type B Double-Wall Gas Vent . . . 172

    Table 803.1.2(2) Type B Double-Wall Gas Vent . . . 175

    Table 803.1.2(3) Masonry Chimney. . . . . . . . . . . . . 177

    Table 803.1.2(4) Masonry Chimney. . . . . . . . . . . . . 179

    Table 803.1.2(5) Single-Wall Metal Pipe or Type B Asbestos-Cement Vent. . . . . . . . . 181

    Table 803.1.2(6) Exterior Masonry Chimney . . . . . . 182

    2025 CALIFORNIA MECHANICAL CODE

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    TABLE OF CONTENTS

    Table 803.2(1) Type B Double-Wall Vent . . . . . . 183

    Table 803.2(2) Type B Double-Wall Vent . . . . . . . 187

    Table 803.2(3) Masonry Chimney. . . . . . . . . . . . . 189

    Table 803.2(4) Masonry Chimney. . . . . . . . . . . . . 191

    Table 803.2(5) Single-Wall Metal Pipe or Type B Asbestos-Cement Vent . . . 193

    Table 803.2(6) Exterior Masonry Chimney . . . . . . 193

    Table 803.2(7) Exterior Masonry Chimney . . . . . . 194

    Table 803.2(8) Exterior Masonry Chimney . . . . . . 195

    Table 803.2(9) Exterior Masonry Chimney . . . . . . 196

    CHAPTER 9 INSTALLATION OF

    SPECIFIC APPLIANCES. . . . . . . 197

  • CMC § 90.1 Medium relevance — show source text

    [ASHRAE 90.1: TABLE 6.4.3.4.3]

    Col1 OUTDOOR AIR INTAKE (CFM/ft2) Col3 EXHAUST/RELIEF (CFM/ft2) Col5
    CLIMATE ZONE NONMOTORIZED1 MOTORIZED NONMOTORIZED3 MOTORIZED
    0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2
    Any height 20 4 20 4
    3 3 3 3 3
    Any height 20 10 20 10
    4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C
    Fewer than three stories 204 10 20 10
    Three or more stories 204 10 204 10
    5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8
    Fewer than three stories 204 4 20 4
    Three or more stories 204 4 204 4

    For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.00047 m [3] /s, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ], 1 inch water gauge = 0.249 kPa

    Notes:

    1 When tested in accordance with AMCA 500D.

    2 Dampers smaller than 12 inches (305 mm) in height, width, or diameter need not be tested but shall be of the same design and construction as the smallest tested damper meeting the listed leakage rate requirement.

    3 Nonmotorized dampers smaller than 24 inches (610 mm) in height, width, or diameter shall be permitted to have a leakage rate of 40 CFM/ft 2 [0.203 (m 3 /s)/m 2 ].

    4 Where permitted by Section E 503.4.6.4.1, exception 2.

    2025 CALIFORNIA MECHANICAL CODE 425

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    APPENDIX E

    (2) Systems serving zones where humidity levels are required to be maintained with precision of not more than ±5 percent relative humidity to comply with applicable codes or accreditation standards or as approved by the Authority Having Jurisdiction.

    [ASHRAE 90.1:6.4.3.6.2]

  • CMC § 12.6.5.3 Medium relevance — show source text

    The chimney flue shall be sized to properly vent the appliance.

    [NFPA 54:12.6.5.3] 802.5.8.3 Combination Gas- and Oil-Burning Appliances. A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized in accordance with the appliance manufacturer’s instructions. [NFPA 54:12.6.5.4]

    802.5.9 Support of Chimneys. All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.6]

    156 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

    802.5.10 Cleanouts. Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7] 802.5.11 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appli ance.

    Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1] 802.5.11.1 Combustion Air. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal or factory-built chimney flue shall not be used to supply combustion air.

    Exception: Direct vent appliances designed for installation in a solid-fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.6.8.2] 802.6 Gas Vents. The installation of gas vents shall meet the following requirements:

    (1) Gas vents shall be installed in accordance with the manufacturer’s installation instructions.

    (2) A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is

    connected.

    (3) Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel–burning appliances or incinerators.”

    (4) Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent.

    [NFPA 54:12.7.2] 802.6.1 Gas Vent Termination. The termination of gas vents shall comply with the following requirements:

    (1) A gas vent shall terminate in accordance with one of the following:

Frequently asked questions

Can a decorative cap or shroud be added to any chimney termination?

Only if the decorative shroud is listed and labeled for use with that specific factory‑built chimney system and installed exactly per the manufacturer’s instructions. Otherwise decorative shrouds are prohibited at factory‑built chimney terminations (see § 802.5.4.3).

Which rule controls if the 3‑ft and the 2‑ft clearances conflict?

You must satisfy both: the chimney must be at least 3 ft above the penetration and also at least 2 ft above any portion of the building within 10 ft; the final required top is the greater height resulting from those two checks (see § 802.5.4).

Do the rules change for a medium‑heat appliance?

Yes. For medium‑heat appliances the chimney must extend at least 10 ft above any portion of any building within 25 ft; that larger clearance governs when the appliance is medium‑heat (§ 802.5.4.1).

How far above the draft hood must the chimney extend?

A chimney must extend at least 5 ft (1524 mm) above the highest connected appliance draft hood outlet or flue collar (see § 802.5.4.2).

Where can I see an illustration of typical termination locations?

The code provides Figure 802.5.4 illustrating typical termination locations for residential‑type and low‑heat appliances; refer to § 802.5.4 and the figure in the CMC.

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