CMC · California Mechanical Code

What clearances and supports are required (including furnace connections)?

Homeowners: duct clearances are set by the California Mechanical Code and the furnace manufacturer. Generally, ducts attached to a listed furnace follow the furnace’s plenum clearance for the first 3 feet; ducts to certain unlisted furnaces with a 250°F limit need 6 inches clearance for the first 6 feet. Appliances must also be properly supported so the building and piping aren’t stressed — always check the furnace listing and installation instructions and confirm with your inspector.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

Duct clearances to combustible construction are governed by § 603.13 and its subsections. In plain English: follow the manufacturer’s listing/instructions for general duct clearance (§ 603.13.1), and when connecting supply ducts to furnaces use the specific minimum run lengths and distances set for listed and unlisted furnaces — 3 feet (914 mm) for listed units and 6 inches (152 mm) for 6 feet (1829 mm) for certain unlisted units with temperature limit controls (§ 603.13.2, § 603.13.3) .

The single most important rule: follow the furnace listing and the manufacturer’s installation instructions for clearances; where the Code gives prescriptive distances, those control the length and size of the required clearance from the furnace supply plenum (see § 603.13 and subsections) .

Requirements in detail

General rule: follow listing & manufacturer

  • Duct clearances are required to be provided in accordance with the appliance listing and the manufacturer’s installation instructions. This is the baseline rule for all duct-to-combustible relationships. See § 603.13.1 .

Supply-air ducts connecting to furnaces — prescriptive distances

Use the table below for the common decision points (rounded values are given in the Code).

Condition / Decision point Minimum clearance to combustible construction How far that clearance must be maintained (run length) Code Reference
Supply duct to a listed central heating furnace Same minimum clearance as required for furnace supply plenum (per the furnace listing) For a distance of not less than 3 feet (914 mm) from the supply plenum; no clearance required beyond that 3 ft distance § 603.13.2
Supply duct to an unlisted central heating furnace equipped with temperature limit controls (max set to 250°F (121°C)) 6 inches (152 mm) minimum clearance to combustibles For a distance of not less than 6 feet (1829 mm) from the supply plenum; no clearance required beyond that 6 ft distance § 603.13.3
Baseline reference for duct clearances Duct clearances are governed by § 603.13 and follow § 603.13.1–.6 for special cases — § 603.13

Notes:

  • “Same minimum clearance as required for the furnace supply plenum” means you must look up the furnace’s listing or the Code table that applies to the furnace plenum clearance (the furnace listing or § 904.* provisions commonly contain the plenum clearances) and apply that clearance to the attached duct for the first 3 feet for listed furnaces .
  • For unlisted furnaces the Code prescribes the 6 in / 6 ft rule only where the unit has a temperature limit control with a maximum setting of 250°F (121°C); if that condition is not met, other clearance rules (or AHJ approval) apply — see § 603.13.3 .

Supports, appliance anchorage and piping connections

  • Appliances and equipment must be provided with load-distributing bases or a sufficient number of supports so the appliance and building are not damaged; the Code explicitly requires appliance support and that piping connections not be subject to undue stress. See § 902.8 (Appliance Support) and § 902.8.1 (Structural Capacity) .
  • Appliances designed to be fixed in position must be securely fastened and supports must be sized/designed to carry vertical and horizontal loads per the building code. See § 303.4 (Anchorage of Appliances) .
  • Gas piping hangers/support spacing and anchoring are covered separately; piping must be supported and anchored so as not to strain connections (see § 1310.3.5 and Table 1310.3.5.1 for spacing) .

Furnace connections — practical connection rules

  • When attaching ducts to the furnace supply plenum, maintain the applicable clearance for the required run length (3 ft or 6 ft) before the duct can be considered free of the special clearance requirement (see § 603.13.2 and § 603.13.3) .
  • If a furnace plenum or supply plenum is supplied as part of the furnace, it must be installed per the manufacturer’s instructions (§ 604.2); if not supplied, follow fabrication/installation instructions the manufacturer provides (§ 604.3) .

Exceptions & special cases

  • Manufacturer’s listing and installation instructions can override or further specify required clearances; if the appliance is listed for reduced clearances, the listing and instructions control (see § 603.13.1) .
  • The prescriptive 3‑ft and 6‑ft run-lengths are maximum extents of the Code-prescribed clearance region — beyond those distances the Code does not require the same clearance to continue (see § 603.13.2 and § 603.13.3) .
  • Duct furnaces and air conditioners installed within enclosures or in special arrangements are subject to related sections (e.g., § 603.13.4, § 905.0, § 604.0) and the manufacturer’s instructions; always check those subsections for special installation rules .

Common mistakes

  • Relying only on a “typical” clearance and ignoring the furnace listing/manufacturer instructions — the Code requires listing/instructions to control where provided (§ 603.13.1) .
  • Applying the 3‑ft / 6‑ft distances to the wrong appliance type (e.g., using the 3‑ft rule for an unlisted furnace that requires the 6‑in/6‑ft rule) — be sure to distinguish listed vs unlisted and whether the unlisted unit has a 250°F (121°C) temperature limit control (§ 603.13.2 and § 603.13.3) .
  • Forgetting to support the appliance and piping so connections aren’t stressed; supports and anchorage are separate code requirements (see § 902.8 and § 303.4) .
  • Assuming clearance is only about fire risk — maintain required front/service clearances for servicing and combustion air access as required by other sections (e.g., furnace servicing requirements in Chapter 9) .

Worked example — concrete scenario

Scenario: You are installing a metal supply duct to a central heating furnace that is NOT listed for closet or reduced-clearance installation, but the furnace has a factory temperature-limit control that cannot be set higher than 250°F (121°C).

Step 1 — determine which subsection applies:

  • Because the furnace is unlisted but has a temperature limit control settable to 250°F (121°C), § 603.13.3 applies .

Step 2 — apply the numbers:

  • The Code requires a minimum clearance of 6 inches (152 mm) from the duct to combustible construction, and that clearance must be maintained for not less than 6 feet (1829 mm) measured from the furnace supply plenum along the duct. After that 6‑ft run length is complete, that specific clearance is not required beyond that point by § 603.13.3 .

Step 3 — practical installation:

  • If your duct runs horizontally from the plenum for 10 feet, maintain 6 in clearance to combustibles for the first 6 ft, then beyond that the duct may be closer per general building rules or manufacturer listing. Also ensure the furnace and ducts are supported so piping and ducts do not place undue stress on connections per § 902.8 and § 1310.3.5 .

Related provisions

  • § 603.13 — Duct clearances (overview); see subsections § 603.13.1–.6
  • § 603.13.1 — General: follow listing/manufacturer’s instructions
  • § 603.13.2 — Supply air ducts to listed furnaces; 3 ft (914 mm) run-length rule
  • § 603.13.3 — Supply air ducts to unlisted furnaces with temp limit controls; 6 in (152 mm) for 6 ft (1829 mm) rule (max temperature 250°F (121°C))
  • § 603.13.4 — Furnace plenums and ducts; air conditioner-in-enclosure requirements
  • § 604.2–604.3 — Installation rules for furnace plenums supplied with / not supplied with the furnace
  • § 902.8 / § 902.8.1 — Appliance support and structural capacity (supports, load-distributing bases, avoid undue stress on piping)
  • § 303.4 — Anchorage of appliances; supports designed for vertical/horizontal loads per building code
  • § 1310.3.5 — Hangers, supports, and anchors for gas piping (spacing and MSS SP‑58)

Code references

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

  • CMC § 307.3 High relevance — show source text

    (1) The name or trademark of the manufacturer.

    (2) The model number or equivalent.

    (3) The serial number.

    (4) The electrical rating in volts, amperes (or watts), and, for other than single phase, the number of phases.

    (5) The output rating in Btu/h (kW).

    (6) The electrical rating in volts, amperes, or watts of each field-replaceable electrical component.

    (7) The symbol of an approved agency certifying compliance of equipment with recognized standards.

    (8) Required clearances from combustible surfaces on which or adjacent to which it is permitted to be mounted.

    An appliance shall be accompanied by clear and complete installation instructions, including required clearances from combustibles other than mounting or adjacent surfaces, and temperature rating of field-installed wiring connections exceeding 140°F (60°C). 307.3 Heat Pump and Electric Cooling Appliances. Heat pumps and electric cooling appliances shall bear a permanent and legible factory-applied nameplate on which shall

    appear:

    (1) The name or trademark of the manufacturer.

    (2) The model number or equivalent.

    (3) The serial number.

    (4) The amount of refrigerant.

    (5) The refrigerant designation.

    (6) The factory test pressures or pressures applied.

    (7) The electrical rating in volts, amperes, and, for other than single phase, the number of phases.

    (8) The output rating in Btu/h (kW).

    (9) The electrical rating in volts, amperes, or watts of each field replaceable electrical component.

    (10)The symbol of an approved agency certifying compliance of the equipment with recognized standards.

    (11)Required clearances from combustible surfaces on which or adjacent to which it is permitted to be mounted.

    An appliance shall be accompanied by clear and complete installation instructions, including required clearances from combustible other than mounting or adjacent surfaces, and temperature rating of field-installed wiring connections exceeding 140°F (60°C). 307.4 Absorption Units. Absorption units shall bear a permanent and legible factory-applied nameplate on which shall

    appear:

    (1) The name or trademark of the manufacturer.

    (2) The model number or equivalent.

    (3) The serial number.

    (4) The amount of refrigerant.

    (5) The refrigerant designation.

    (6) Hourly rating in Btu/h (kW).

    (7) The type of fuel approved for use with the unit.

    (8) Cooling capacity Btu/h (kW).

    (9) Required clearances from combustible surfaces on which or adjacent to which it is permitted to be mounted.

    (10)The symbol of an approved agency certifying compliance of the equipment with recognized standards.

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    GENERAL REGULATIONS

    308.0 Improper Location.

    308.1 General. Piping or equipment shall not be so located as to interfere with the normal use thereof or with the normal operation and use of windows, doors, or other required facilities.

    309.0 Workmanship.

    309.1 Engineering Practices. Design, construction, and workmanship shall comply with accepted engineering practices and shall be of such character as to secure the results sought to be obtained by this code.

  • CMC § 1313.2.1 High relevance — show source text

    1313.2.1, 1313.2.2

    Materials. . . . . . . . . . . . . . . . . . . . . . . . 1308.4, D 109.0

    Obstruction of flow. . . . . . . . . . . . . . . . . . . . . . . 1310.12

    Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313.6 Sizing . . . . . . . . . . . . . 1308.3, 1314.1, 1315.0, D 108.0,

    Table 1315.2(1)–Table 1315.2(36)

    Supports. . . . . . . . . . . . . . . . 1310.3.5, Table 1310.3.5.1

    Underground installations . . . . . . . . . . . . . . 1308.4.2.4,

    1308.4.3.4, 1310.1,

    D 101.2, D 109.3, D 110.3

    Venting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1308.6.4

    FURNACES

    Approximate gas input . . . . . . . . . . . . . . Table 1308.3.1

    Automatic control required . . . . . . . . . . . . . . . . . . 608.6

    Central heating furnaces . . . . . . . . . . . . . . 303.2, 904.0 Clearance for servicing . . . . . . . . . . . . . . . . . . . 304.4.3,

    905.9.2, 906.12

    Clearances . . . . . . . . . . . . . . . 303.10, 303.10.1, 904.3,

    904.4.1.2, 905.2, 906.8,

    Table 303.10.1, Table 904.3.2

    Downflow-type,

    heating, definition . . . . . . . . . . . . . . . . . . . . . . .208.0

    Duct furnace . . . . . . . . . . . . . . . . . . . . . . .206.0, 905.0

    Enclosed furnace, definition . . . . . . . . . . . . . . . . .208.0

    Floor furnace . . . . . . . . . . . . . . . . . . . . . . .208.0, 906.0

    Forced-air heating, definition . . . . . . . . . . . . . . . . .208.0

    Furnace plenums . . . . . . . . . . .802.3.5, 903.2.4, 904.8

    Gravity-type, floor

    furnace, definition . . . . . . . . . . . . . . . . . . . . . . . 209.0

    Horizontal-type furnace . . . . . . . . . . . . . . 208.0, 904.10

  • CMC § 603.13 High relevance — show source text

    603.13 Clearances. Duct clearances shall be in accordance with Section 603.13.1 through Section 603.13.6.

    603.13.1 General. Duct clearances to combustible construction shall be in accordance with the listing and the manufacturer’s installation instructions.

    603.13.2 Supply Air Ducts to Listed Furnaces. Supply air ducts connecting to listed central heating furnaces shall have the same minimum clearance to combustibles as required for the furnace supply plenum for a distance of not less than 3 feet (914 mm) from the supply plenum. Clearance shall not be required beyond the 3 feet (914 mm) distance. [NFPA 54:10.3.3.7] 603.13.3 Supply Air Ducts to Unlisted Furnaces. Supply air ducts connecting to unlisted central heating furnaces equipped with temperature limit controls with a maximum setting of 250°F (121°C) shall have a minimum clearance to combustibles of 6 inches (152 mm) for a distance of not less than 6 feet (1829 mm) from the furnace supply plenum. Clearance shall not be required beyond the 6 feet (1829 mm) distance. [NFPA 54:10.3.3.8]

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    DUCT SYSTEMS

    603.13.4 Furnace Plenums and Air Ducts. Where an air conditioner is installed within an enclosure, the installation shall comply with Section 604.4. [NFPA 54:10.2.6]

    603.13.5 Duct Furnaces. Duct furnaces shall be

    installed in accordance with Section 905.0.

    603.13.6 Fuel-Burning Kilns. A hood and duct serving a fuel-burning kiln shall have a clearance from combustible construction of not less than 18 inches (457 mm). This clearance shall be permitted to be reduced in accordance with Table 303.10.1.

    604.0 Furnace Plenums and Air Ducts Used in Fuel- Gas Appliances. 604.1 Furnace Plenums and Air Ducts. Furnace plenums and air ducts shall be installed in accordance with this Chapter, and NFPA 90A or NFPA 90B. {NFPA 54:10.3.8.1} 604.2 Supplied as a Part of Furnace. A furnace plenum supplied as a part of a furnace shall be installed in accordance with the manufacturer’s instructions. [NFPA 54:10.3.8.2] 604.3 Not Supplied with the Furnace. Where a furnace plenum is not supplied with the furnace, any fabrication and installation instructions provided by the manufacturer shall be followed. The method of connecting supply and return ducts shall facilitate proper circulation of air. [NFPA 54:10.3.8.3]

    604.4 Return Air. Where a furnace is installed so supply ducts carry air circulated by the furnace to areas outside the space containing the furnace, the return air shall also be handled by a duct(s) sealed to the furnace casing and terminating outside the space containing the furnace. Return air shall not be taken from the mechanical room containing the furnace.

    [NFPA 54:10.3.8.4]

  • CMC § 904.12 High relevance — show source text

    instructions.

    904.12 Oil-Fired Central Furnaces. Oil-fired central furnaces shall comply with UL 727 and shall be installed in accordance with the manufacturer’s installation instructions.

    904.13 Commercial or Industrial Gas Heaters. Commercial or industrial gas-fired heaters shall comply with UL 795 and shall be installed in accordance with the manufac turer’s installation instructions.

    904.14 Electric Central Furnaces. Electric central heating furnaces shall comply with UL 1995 or UL 60335-2-40 and shall be installed in accordance with the manufacturer’s

    installation instructions.

    905.0 Duct Furnaces.

    905.1 Application. Duct furnaces with inputs of 10 MBtu/hr (2931 kW) or less shall be listed in accordance with ANSI Z83.8/CSA 2.6. [NFPA 54:10.9.1]

    905.2 Clearances. The installation of duct furnaces shall

    comply with the following clearance requirements:

    (1) Listed duct furnaces shall be installed with clearances of not less than 6 inches (152 mm) between adjacent walls, ceilings, and floors of combustible material and the furnace draft hood. Furnaces listed for installation at lesser

    clearances shall be installed in accordance with their list ings and the manufacturer’s installation instructions. In no case shall the clearance be such as to interfere with

    combustion air and accessibility.

    (2) Unlisted duct furnaces shall be installed with clearances to combustible material in accordance with the clear ances specified for unlisted furnaces and boilers in Table 904.3.2. Combustible floors under unlisted duct furnaces

    shall be protected in an approved manner.

    905.3 Installation of Duct Furnaces. Duct furnaces shall

    be installed in accordance with the manufacturer’s instruc tions. [NFPA 54:10.9.3]

    905.4 Access Panels. The ducts connected to duct fur naces shall have removable access panels on both the upstream and downstream sides of the furnace. [NFPA 54:10.9.4]

    905.5 Location of Draft Hoods and Controls. The con trols, combustion air inlet, and draft hoods for duct furnaces shall be located outside the ducts. The draft hood shall be

    located in the same enclosure from which combustion air is

    taken. [NFPA 54:10.9.5]

    905.6 Circulating Air. Where a duct furnace is installed so that supply ducts carry air circulated by the furnace to areas outside the space containing the furnace, the return air shall

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    INSTALLATION OF SPECIFIC APPLIANCES

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    906.2 Installation. The installation of floor furnaces shall comply with the following requirements:

    (1) Listed floor furnaces shall be installed in accordance with their listing and the manufacturer’s installation instructions.

    (2) Unlisted floor furnaces shall not be installed on combustible floors.

  • CMC § 9.1.18 High relevance — show source text

    (4) In the case of bleed lines entering the combustion chamber, the bleed line shall be located so the bleed gas is readily ignited by the pilot and the heat liberated thereby does not adversely affect the normal operation of the safety shutoff system. The terminus of the bleed line shall be securely held in a fixed position relative to the pilot. For manufactured gas, the need for a flame arrester in the bleed line piping shall be determined.

    (5) A bleed line(s) from a diaphragm-type valve and a vent line(s) from an appliance pressure regulator shall not be connected to a common manifold terminating in a combustion chamber. Bleed lines shall not terminate in positive-pressure-type combustion chambers. [NFPA 54:9.1.18]

    903.0 Air-Conditioning Appliances.

    903.1 Electric Air Conditioners. Electric air conditioning systems designed for permanent installation shall comply with UL 1995 or UL 60335-2-40.

    903.2 Gas-Fired Air Conditioners and Heat Pumps. Gas-fired air conditioners shall comply with Section 903.2.1 through Section 903.2.7.

    903.2.1 Application. Gas-fired air conditioners and heat pumps shall be listed in accordance with ANSI Z21.40.1/CGA 2.91 or ANSI Z21.40.2/CGA 2.92.

    [NFPA 54:10.2.1]

    903.2.2 Independent Gas Piping. Gas piping serving heating appliances shall be permitted to also serve cooling appliances where heating and cooling appliances cannot be operated simultaneously. [NFPA 54:10.2.2]

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    INSTALLATION OF SPECIFIC APPLIANCES

    904.3.3 Listed and Unlisted Units. Central heating furnaces and low-pressure boilers shall be permitted to be installed with reduced clearances to combustible material, provided that the combustible material or appliance is protected as described in Table 303.10.1 and Figure 303.10.1(1) through Figure 303.10.1(3), and such reduction is allowed by the manufacturer’s installation instructions. [NFPA 54:10.3.3.3]

    904.3.4 Front Clearance. Front clearance shall be sufficient for servicing the burner and the furnace or boiler.

    [NFPA 54:10.3.3.4]

    904.3.5 Adjacent to Plaster or Noncombustible Materials. Where the furnace plenum is adjacent to plaster on metal lath or noncombustible material attached to combustible material, the clearance shall be measured to the surface of the plaster or other noncombustible finish where the clearance specified is 2 inches (51 mm) or less. [NFPA 54:10.3.3.5]

    904.3.6 Interference. The clearances to these appliances shall not interfere with combustion air, draft hood clearance and relief, and accessibility for servicing.

  • CMC § 9.1.8.1 High relevance — show source text

    ** Appliances and equipment shall be furnished either with load-distributing bases or with a sufficient number of supports to prevent damage to either the building structure or the appliance and the equipment.

    [NFPA 54:9.1.8.1] 902.8.1 Structural Capacity. At the locations selected for installation of appliances and equipment, the dynamic and static load-carrying capacities of the building structure shall be checked to determine whether they are adequate to carry the additional loads. The appliances and equipment shall be supported and shall be connected to the piping so as not to exert undue stress on the connections. [NFPA 54:9.1.8.2] 902.9 Flammable Vapors. Appliances shall not be installed in areas where the open use, handling, or dispensing of flammable liquids occurs, unless the design, operation, or installation reduces the potential of ignition of the flammable vapors. Appliances installed in compliance with Section 305.1 through Section 305.1.2, Section 303.11, or Section 303.12 shall be considered to comply with the intent of this provision. [NFPA 54:9.1.9] 902.10 Solid-Fuel-Burning Appliances. Unless otherwise specified, solid-fuel-burning appliances shall be installed in accordance with NFPA 211 and the manufacturer’s instal lation instructions.

    902.11 Combination of Appliances and Equipment. Any combination of appliances, equipment, attachments, or devices used together in any manner shall comply with the standards that apply to the individual appliance and equipment. [NFPA 54:9.1.19] 902.12 Protection of Gas Appliances from Fumes or Gases Other than Products of Combustion. Nondirect-vent appliances installed in beauty shops, barber shops, or other facilities where chemicals that generate corrosive or flammable products such as aerosol sprays are routinely used shall be located in a mechanical room separate or partitioned off from other areas with provisions for combustion and dilution air from outdoors. Direct vent appliances in such facilities shall be in accordance with the appliance manufacturer’s installation instructions. [NFPA 54:9.1.6.2]

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    INSTALLATION OF SPECIFIC APPLIANCES

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    903.2.3 Connection of Gas Engine-Powered Air Conditioners. Gas engines shall not be rigidly connected to the gas supply piping. [NFPA 54:10.2.3]

    903.2.4 Clearances for Indoor Installation. The installation of air-conditioning appliances shall comply with the following requirements:

    (1) Air-conditioning appliances shall be installed with clearances in accordance with the terms of their listing and the manufacturer’s instructions. {NFPA 54:10.2.4(1)}

    (2) Air-conditioning appliances shall be permitted to be installed with reduced clearances to combustible material, provided that the combustible material or appliance is protected as described in Table 303.10.1 and such reduction is allowed by the manufacturer’s installation instructions. [NFPA 54:10.2.4(2)]

    (3) Where the furnace plenum is adjacent to plaster on metal lath or noncombustible material attached to

  • CMC § 10.3.3.6 High relevance — show source text

    [NFPA 54:10.3.3.6] 904.3.7 Central Heating Furnaces. Central heating furnaces other than those listed in Section 603.13.2 or Section 603.13.3 shall have clearances from the supply ducts of not less than 18 inches (457 mm) from the furnace plenum for the first 3 feet (914 mm), then 6 inches (152 mm) for the next 3 feet (914 mm) and 1 inch (25.4 mm) beyond 6 feet (1829 mm). [NFPA 54:10.3.3.9] 904.4 Assembly and Installation. A central heating boiler or furnace shall be installed in accordance with the manufacturer’s instructions in one of the following manners:

    (1) On a floor of noncombustible construction with noncombustible flooring and surface finish and with no combustible material against the underside thereof.

    (2) On fire-resistive slabs or arches having no combustible material against the underside thereof.

    Exceptions:

    (1) Appliances listed for installation on a combustible floor.

    (2) Installation on a floor protected in an approved manner.

    [NFPA 54:10.3.4]

    904.4.1 Under-Floor Installation. Furnaces installed in an under-floor area of the building shall be in accordance with the Section 904.4.1.1 through Section 904.4.1.3.

    904.4.1.1 Supported by Ground. Where a furnace is supported by the ground, it shall be installed on a concrete slab not less than 3 inches (76 mm) above the adjoining ground level.

    904.4.1.2 Supported from Above. Where a furnace is supported from above, a clearance of not less than 6 inches (152 mm) shall be provided from finished grade.

    904.4.1.3 Excavation. Where excavation is necessary to install a furnace, it shall be installed in accordance with Section 303.11.

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    (b) Low-pressure boilers listed in accordance with ANSI Z21.13/CSA 4.9. [NFPA 54:10.3.1.1]

    (2) Furnaces and boilers having input ratings greater than 400 000 Btu/hr (117 kW) shall be listed or in accordance with Section 904.1(2)(a) and Section 904.1(2)(b). [NFPA 54:10.3.1.2]

    (a) Acceptance of unlisted appliances, equipment, and accessories shall be on the basis of engineering methods. [NFPA 54:9.1.1.2]

    (b) The unlisted appliance, equipment, or accessory shall be safe and suitable for the proposed service and shall be recommended for the service by the manufacturer. [NFPA 54:9.1.1.3]

    904.2 Location. Central heating furnace and low-pressure boiler installations in bedrooms or bathrooms shall comply with one of the following:

  • CMC § 1.0 High relevance — show source text

    D. The outdoor design temperatures for cooling shall be no greater than the 1.0 percent Cooling Dry Bulb and Mean Coincident Wet Bulb values.

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

    MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS

    1. Outdoor condensing units . A. Clearances. Installed air conditioner and heat pump outdoor condensing units shall have a clearance of at least 5 feet (1.5 meters) from the outlet of any dryer vent. B. Liquid line drier. Installed air conditioner and heat pump systems shall be equipped with liquid line filter driers if required, as specified by manufacturer’s instructions.
    2. Central forced-air heating furnaces . A. Temperature rise . Central forced-air heating furnace installations shall be configured to operate in conformance with the furnace manufacturer's maximum inlet-to-outlet temperature rise specifications.
    3. Air-distribution and ventilation system ducts, plenums and fans. A. CMC compliance.

    i. All air-distribution system ducts and plenums, including, but not limited to, mechanical closets and air-handler boxes, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0 and 605.0 and ANSI/SMACNA006-2006 HVAC Duct Construction Standards Metal and Flexible 3rd Edition, incorporated herein by reference. ii. Portions of supply-air and return-air ducts and plenums of a space heating or cooling system shall be insulated in accordance with either Subsection a or b below:

    a. Ducts shall have a minimum installed level of R-6.0, or

    Exception to Section 160.3(b)5Aiia : Portions of the duct system located in conditioned space below the ceiling separating the occupiable space from the attic are not required to be insulated if all of the following conditions are met: i. The noninsulated portion of the duct system is located entirely inside the building’s thermal envelope as confirmed by visual inspection. ii. At all locations where noninsulated portions of the duct system penetrate into unconditioned space, the penetration shall be draft stopped compliant with CFC Sections 703.1 and 704.1 and air-sealed to the construction materials that are penetrated, using materials compliant with CMC Section E502.4.2 to prevent air infiltration into the cavity. All connections in unconditioned space are insulated to a minimum of R-6.0 as confirmed by visual inspection. b. Ducts do not require insulation when the duct system is located entirely in conditioned space. For buildings with three or fewer habitable stories, duct systems located entirely in conditioned space shall be confirmed through field verification and diagnostic testing in accordance with the requirements of Reference Residential Appendix RA3.1.4.3.8. iii. Connections of metal ducts and the inner core of flexible ducts shall be mechanically fastened. iv. Openings shall be sealed with mastic, tape or other duct-closure system that meets the applicable requirements of UL 181, UL 181A or UL 181B or aerosol sealant that meets the requirements of UL 723. If mastic or tape is used to seal openings greater than [1] / 4 inch, the combination of mastic and either mesh or tape shall be used. v. Building cavities, support platforms for air handlers, and plenums designed or constructed with materials other than sealed sheet metal, duct board or flexible duct shall not be used for conveying conditioned air.

  • CMC § 10.10.7 High relevance — show source text

    [NFPA 54:10.10.7] 906.8 Clearance. The lowest portion of the floor furnace shall have at least a 6 inch (152 mm) clearance from the general ground level. A reduced clearance to a minimum of 2 inches (51 mm) shall be permitted, provided the lower 6 inches (152 mm) portion of the floor furnace is sealed by the manufacturer to prevent entrance of water. Where these clearances are not present, the ground below and to the sides shall be excavated to form a “basin-like” pit under the furnace so that the required clearance is provided beneath the lowest portion of the furnace. A 12 inch (305 mm) clearance shall be provided on all sides except the control side, which shall have an 18 inch (457 mm) clearance. [NFPA 54:10.10.8]

    906.9 Access. The space in which any floor furnace is installed shall be accessible by an opening in the foundation not less than 24 inches by 18 inches (610 mm by 457 mm) or

    by a trapdoor not less than 24 inches by 24 inches (610 mm by 610 mm) in any cross-section thereof, and a passageway not less than 24 inches by 18 inches (610 mm by 457 mm) in any cross-section thereof. [NFPA 54:10.10.9] 906.10 Seepage Pan. Where the excavation exceeds 12 inches (305 mm) in depth or water seepage is likely to collect, a watertight copper pan, concrete pit, or other suitable material shall be used, unless adequate drainage is provided or the appliance is sealed by the manufacturer to meet this condition. A copper pan shall be made of not less than 16 ounces per square foot (oz/ft [2] ) (4.9 kg/m [2] ) sheet copper. The pan shall be anchored in place so as to prevent floating, and the walls shall extend at least 4 inches (102 mm) above the ground level with at least a 6 inches (152 mm) clearance on all sides, except on the control side, which shall have at least an 18 inch (457 mm) clearance. [NFPA 54:10.10.10] 906.11 Wind Protection. Floor furnaces shall be protected, where necessary, against severe wind conditions. [NFPA 54:10.10.11]

    906.12 Upper Floor Installations. Floor furnaces shall be permitted to be installed in an upper floor, provided the furnace assembly projects below into a utility room, closet, garage, or similar nonhabitable space. In such installations, the floor furnace shall be enclosed completely (entirely separated from the nonhabitable space) with means for air intake to meet the provisions of Section 701.0, with access for servicing, minimum furnace clearances of 6 inches (152 mm) to all sides and bottom, and with the enclosure constructed of Portland cement plaster or metal lath or other noncombustible material. [NFPA 54:10.10.12]

    906.13 First Floor Installation. Floor furnaces installed in the first or ground floors of buildings shall not be required to be enclosed unless the basements of these buildings have been converted to apartments or sleeping quarters, in which case the floor furnace shall be enclosed as specified for upper floor installations and shall project into a nonhabitable space.

    [NFPA 54:10.10.13]

  • CMC § 313.6 Medium relevance — show source text

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

    Hydronics. . . . . . . . . . . . . . . . . . . . . . . . . . Table 1210.1

    Joining

    and connections . . . . . . (see Joints and connections)

    CIRCULATORS . . . . . . . . . . . . . . . . . 205.0, 1208.0, 1214.5

    CLASSIFICATION OF

    Air . . . . . . . . . . . . . . . . . . . . . 203.0, Table 402.1, 403.9

    Chimney, definition . . . . . . . . . . . . . . . . . . . . . . . . 205.0

    Occupancy, definition. . . . . . . . . . . . . . . . . . . . . . . 217.0

    Product-conveying ducts. . . . . . . . . . . . . . . . . . . . 505.8

    Refrigerants. . . . . . . . . . . . . . . . . . . . . 1103.1, 1103.1.1,

    Table 1102.3

    Refrigeration systems . . . . . . . . . . . . . . . . . . . . . 1103.2

    CLEAN AIR DELIVERY . . . . . . . . . . . . . . . . . . .Appendix J

    Carbon dioxide detection . . . . . . . . .J 301.1.3, J 301.1.4

    Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .J 301.1.2

    Demand Control Ventilation (DCV) . . . . . . . . . . .J 301.0

    Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .J 201.1.1

    CLEARANCES FOR

    Air-conditioning appliances,

    gas type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.2.4

    Air heaters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914.4

    Appliances . . . . . . . . . . . . . . . . . 303.3, 303.8, 303.8.4,

    303.8.4.1, 303.10, 304.1,

    303.10.1, 304.3.1.1, 516.2.1,

    701.6.2, Table 303.10.1

    Boilers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.2, 904.3,

    1010.0, Table 904.3.2

    Broilers units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 921.2

  • CMC § 906.4 Medium relevance — show source text

    906.4 Combustion and Circulating Air. Combustion and circulating air shall be provided in accordance with Section 701.0. [NFPA 54:10.10.4]

    906.5 Placement. The following provisions apply to furnaces that serve one story:

    (1) Floors. Floor furnaces shall not be installed in the floor of any doorway, stairway landing, aisle, or passageway of any enclosure, public or private, or in an exitway from any such room or space.

    (2) Walls and Corners. The register of a floor furnace with a horizontal warm air outlet shall not be placed closer than 6 inches (152 mm) from the nearest wall. A distance of at least 18 inches (457 mm) from two adjoining sides of the floor furnace register to walls shall be provided to eliminate the necessity of occupants walking over the warm air discharge. The remaining sides shall be a minimum of 6 inches (152 mm) from a wall. Wall register models shall not be placed closer than 6 inches (152 mm) to a corner.

    (3) Draperies. The furnace shall be placed so that a door, drapery, or similar object cannot be nearer than 12 inches (305 mm) to any portion of the register of the furnace.

    [NFPA 54:10.10.5]

    906.6 Bracing. The space provided for the furnace shall be framed with doubled joists and with headers not lighter than the joists. [NFPA 54:10.10.6] 906.7 Support. Means shall be provided to support the furnace when the floor register is removed. [NFPA 54:10.10.7] 906.8 Clearance. The lowest portion of the floor furnace shall have at least a 6 inch (152 mm) clearance from the general ground level. A reduced clearance to a minimum of 2 inches (51 mm) shall be permitted, provided the lower 6 inches (152 mm) portion of the floor furnace is sealed by the manufacturer to prevent entrance of water. Where these clearances are not present, the ground below and to the sides shall be excavated to form a “basin-like” pit under the furnace so that the required clearance is provided beneath the lowest portion of the furnace. A 12 inch (305 mm) clearance shall be provided on all sides except the control side, which shall have an 18 inch (457 mm) clearance. [NFPA 54:10.10.8]

    906.9 Access. The space in which any floor furnace is installed shall be accessible by an opening in the foundation not less than 24 inches by 18 inches (610 mm by 457 mm) or

    by a trapdoor not less than 24 inches by 24 inches (610 mm by 610 mm) in any cross-section thereof, and a passageway not less than 24 inches by 18 inches (610 mm by 457 mm) in any cross-section thereof. [NFPA 54:10.10.9] 906.10 Seepage Pan. Where the excavation exceeds 12 inches (305 mm) in depth or water seepage is likely to collect, a watertight copper pan, concrete pit, or other suitable material shall be used, unless adequate drainage is provided or the appliance is sealed by the manufacturer to meet this condition.

  • CMC § 903.2.2 Medium relevance — show source text

    903.2.2 Independent Gas Piping. Gas piping serving heating appliances shall be permitted to also serve cooling appliances where heating and cooling appliances cannot be operated simultaneously. [NFPA 54:10.2.2]

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    INSTALLATION OF SPECIFIC APPLIANCES

    904.3.3 Listed and Unlisted Units. Central heating furnaces and low-pressure boilers shall be permitted to be installed with reduced clearances to combustible material, provided that the combustible material or appliance is protected as described in Table 303.10.1 and Figure 303.10.1(1) through Figure 303.10.1(3), and such reduction is allowed by the manufacturer’s installation instructions. [NFPA 54:10.3.3.3]

    904.3.4 Front Clearance. Front clearance shall be sufficient for servicing the burner and the furnace or boiler.

    [NFPA 54:10.3.3.4]

    904.3.5 Adjacent to Plaster or Noncombustible Materials. Where the furnace plenum is adjacent to plaster on metal lath or noncombustible material attached to combustible material, the clearance shall be measured to the surface of the plaster or other noncombustible finish where the clearance specified is 2 inches (51 mm) or less. [NFPA 54:10.3.3.5]

    904.3.6 Interference. The clearances to these appliances shall not interfere with combustion air, draft hood clearance and relief, and accessibility for servicing.

    [NFPA 54:10.3.3.6] 904.3.7 Central Heating Furnaces. Central heating furnaces other than those listed in Section 603.13.2 or Section 603.13.3 shall have clearances from the supply ducts of not less than 18 inches (457 mm) from the furnace plenum for the first 3 feet (914 mm), then 6 inches (152 mm) for the next 3 feet (914 mm) and 1 inch (25.4 mm) beyond 6 feet (1829 mm). [NFPA 54:10.3.3.9] 904.4 Assembly and Installation. A central heating boiler or furnace shall be installed in accordance with the manufacturer’s instructions in one of the following manners:

    (1) On a floor of noncombustible construction with noncombustible flooring and surface finish and with no combustible material against the underside thereof.

    (2) On fire-resistive slabs or arches having no combustible material against the underside thereof.

    Exceptions:

    (1) Appliances listed for installation on a combustible floor.

    (2) Installation on a floor protected in an approved manner.

    [NFPA 54:10.3.4]

    904.4.1 Under-Floor Installation. Furnaces installed in an under-floor area of the building shall be in accordance with the Section 904.4.1.1 through Section 904.4.1.3.

    904.4.1.1 Supported by Ground. Where a furnace is supported by the ground, it shall be installed on a concrete slab not less than 3 inches (76 mm) above the adjoining ground level.

  • CMC § 303.2 Medium relevance — show source text

    303.2 Closet or Alcove Installations. [Not adopted for OSHPD 1, 1R, 2, 3, 4 & 5] Central heating furnaces and boilers installed in closets or alcoves shall be listed for such

    installation. Central heating furnaces not listed for closet or alcove installation shall be installed in a room or space having a volume not less than 12 times the total volume of the furnace. Central heating boilers not listed for closet or alcove installation shall be installed in a room or space having a volume 16 times the volume of the boiler. Where the ceiling height of the room or space exceeds 8 feet (2438 mm), the volume shall be calculated on the basis of an 8 foot (2438 mm) height.

    The installation clearances shall be in accordance with

    the appliance listing, shall not be reduced, and shall be installed in accordance with Section 904.3.

    303.3 Unlisted Appliances. Except as otherwise permitted in this code, unlisted equipment and appliances shall be approved by the Authority Having Jurisdiction prior to being installed. Unlisted equipment and appliances shall be installed in accordance with the manufacturer’s installation instruc tions and with clearances from combustible materials in

    accordance with Section 303.10 or Section 303.10.1.

    303.4 Anchorage of Appliances. Appliances designed to be fixed in position shall be securely fastened in place in

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    GENERAL REGULATIONS

    accordance with the manufacturer’s installation instructions.

    Supports for appliances shall be designed and constructed to sustain vertical and horizontal loads within the stress limita tions specified in the building code.

    303.5 Restraining Device. Movement of appliances with casters shall be limited by a restraining device installed in accordance with the connector and appliance manufacturer’s installation instructions. [NFPA 54:9.6.1.4]

    303.6 Identification of Equipment. Where more than one heating, cooling, ventilating, or refrigerating system is installed on the roof of a building or within a building, it shall be permanently identified as to the area or space served by the equipment.

    303.7 Liquefied Petroleum Gas (LP-Gas) Facilities. Containers, container valves regulating equipment, and appurtenances for the storage and supply of liquefied petroleum gas (LP-Gas) shall be installed in accordance with NFPA 58 and the California Fire Code .

    303.7.1 Liquefied Petroleum Gas (LP-Gas) Appli- ances. [HCD 1 & HCD 2] Liquefied petroleum gas- burning appliances shall not be installed in a pit, basement, or similar location where heavier-than-air gas might collect. Appliances so fueled shall not be installed in an above-grade under-floor space or basement unless such location is provided with an approved means for removal of unburned gas.

  • CMC § 902.0 Medium relevance — show source text

    902.0 General.

    902.1 Nonindustrial Appliances. This chapter is applicable primarily to nonindustrial-type appliances and installations and, unless specifically indicated, does not apply to industrial-type appliances and installations. Listed appliances shall be installed in accordance with their listing and the manufacturer’s installation instructions or, as elsewhere specified in this chapter, as applicable to the appliance. Unlisted appliances shall be installed as specified in this part as applicable to the appliances.

    902.2 Combustion Air from Bedroom or Bathroom. Appliances shall not be installed so their combustion, ventilation, and dilution air are obtained only from a bedroom or bathroom unless the bedroom or bathroom has the required volume in accordance with Section 701.4. [NFPA 54:10.1.2]

    [OSHPD 1, 1R, 2, 4 & 5] Warm air furnaces shall not be installed under openable windows on exterior walls. 902.3 Added or Converted Appliances. When additional or replacement appliances or equipment is installed or an appliance is converted to gas from another fuel, the location in which the appliances or equipment is to be operated shall be checked to verify the following:

    (1) Air for combustion and ventilation is provided where required, in accordance with the provisions of Section 701.0. Where existing facilities are not adequate, they shall be upgraded to meet Section 701.0 specifications.

    (2) The installation components and appliances meet the clearances to combustible material provisions of Section 303.10. It shall be determined that the installation and operation of the additional or replacement appliances do not render the remaining appliances unsafe for continued operation.

    (3) The venting system is constructed and sized in accordance with the provisions of Section 802.0. Where the existing venting system is not adequate, it shall be upgraded to comply with Section 802.0. [NFPA 54:9.1.2] 902.4 Type of Gas(es). The appliance shall be connected to the fuel gas for which it was designed. No attempt shall be made to convert the appliance from the gas specified on the rating plate for use with a different gas without consulting the installation instructions, the serving gas supplier, or the appliance manufacturer for complete instructions. Listed appliances shall not be converted unless permitted by and in accordance with the manufacturer’s installation instructions. [NFPA 54:9.1.3] 902.5 Safety Shutoff Devices for Unlisted LP-Gas Appliances Used Indoors. Unlisted appliances for use

    with undiluted LP-Gases and installed indoors, except attended laboratory equipment, shall be equipped with safety shutoff devices of the complete shutoff type. [NFPA 54:9.1.4] 902.6 Fuel Input Rate. The fuel input rate to the appliance shall not be increased or decreased in violation of the approved rating at the altitude where it is being used. 902.7 Use of Air or Oxygen Under Pressure. Where air or oxygen under pressure is used in connection with the gas supply, effective means such as a back pressure regulator and relief valve shall be provided to prevent air or oxygen from passing back into the gas piping. Where oxygen is used, installation shall be in accordance with NFPA 51. [NFPA 54:9.1.5] 902.8 Appliance Support. Appliances and equipment shall be furnished either with load-distributing bases or with a sufficient number of supports to prevent damage to either the building structure or the appliance and the equipment.

  • CMC § 802.0. Medium relevance — show source text

    Where the existing venting system is not adequate, it shall be upgraded to comply with Section 802.0. [NFPA 54:9.1.2] 902.4 Type of Gas(es). The appliance shall be connected to the fuel gas for which it was designed. No attempt shall be made to convert the appliance from the gas specified on the rating plate for use with a different gas without consulting the installation instructions, the serving gas supplier, or the appliance manufacturer for complete instructions. Listed appliances shall not be converted unless permitted by and in accordance with the manufacturer’s installation instructions. [NFPA 54:9.1.3] 902.5 Safety Shutoff Devices for Unlisted LP-Gas Appliances Used Indoors. Unlisted appliances for use

    with undiluted LP-Gases and installed indoors, except attended laboratory equipment, shall be equipped with safety shutoff devices of the complete shutoff type. [NFPA 54:9.1.4] 902.6 Fuel Input Rate. The fuel input rate to the appliance shall not be increased or decreased in violation of the approved rating at the altitude where it is being used. 902.7 Use of Air or Oxygen Under Pressure. Where air or oxygen under pressure is used in connection with the gas supply, effective means such as a back pressure regulator and relief valve shall be provided to prevent air or oxygen from passing back into the gas piping. Where oxygen is used, installation shall be in accordance with NFPA 51. [NFPA 54:9.1.5] 902.8 Appliance Support. Appliances and equipment shall be furnished either with load-distributing bases or with a sufficient number of supports to prevent damage to either the building structure or the appliance and the equipment.

    [NFPA 54:9.1.8.1] 902.8.1 Structural Capacity. At the locations selected for installation of appliances and equipment, the dynamic and static load-carrying capacities of the building structure shall be checked to determine whether they are adequate to carry the additional loads. The appliances and equipment shall be supported and shall be connected to the piping so as not to exert undue stress on the connections. [NFPA 54:9.1.8.2] 902.9 Flammable Vapors. Appliances shall not be installed in areas where the open use, handling, or dispensing of flammable liquids occurs, unless the design, operation, or installation reduces the potential of ignition of the flammable vapors. Appliances installed in compliance with Section 305.1 through Section 305.1.2, Section 303.11, or Section 303.12 shall be considered to comply with the intent of this provision. [NFPA 54:9.1.9] 902.10 Solid-Fuel-Burning Appliances. Unless otherwise specified, solid-fuel-burning appliances shall be installed in accordance with NFPA 211 and the manufacturer’s instal lation instructions.

    902.11 Combination of Appliances and Equipment. Any combination of appliances, equipment, attachments, or devices used together in any manner shall comply with the standards that apply to the individual appliance and equipment. [NFPA 54:9.1.19] 902.12 Protection of Gas Appliances from Fumes or **Gases Other than Products of Combustion.

  • CMC § 17958.5. Medium relevance — show source text

    Note: [HCD 1 & HCD 2] Reference Health and Safety Code Section 19211(a) which addresses new, replacement, and existing water heaters. Note: The applicable subsection of Health and Safety Code Sec- tion 19211(a) which addresses new, replacement, and existing water heaters is repeated here for clarity and reads as follows: Section 19211(a) Notwithstanding Section 19100, all new and replacement water heaters, and all existing residential water heaters shall be braced, anchored, or strapped to resist falling or horizontal displacement due to earthquake motion. At a minimum, any water heater shall be secured in accor- dance with the California Plumbing Code, or modifications made thereto by a city, county, or city and county pursuant to Section 17958.5.

    507.3 Appliance Support. Appliances and equipment shall be furnished either with load distributing bases or with a suf

    ficient number of supports to prevent damage to either the building structure or the appliance and the equipment. [NFPA 54:9.1.8.1] 507.3.1 Structural Capacity. At the locations selected for installation of appliances and equipment, the dynamic and static load carrying capacities of the building structure shall be checked to determine whether they are adequate to carry the additional loads. The appliances and equipment shall be supported and shall be connected to the piping so as not to exert undue stress on the connections. [NFPA 54:9.1.8.2] 507.4 Ground Support. A water heater supported from the earth shall rest on level concrete or other approved base extending not less than 3 inches (76 mm) above the adjoining ground level. 507.5 Drainage Pan. Where a water heater is located in an attic, in or on an attic ceiling assembly, floor-ceiling assembly, floor-subfloor assembly or where damage results from a leaking water heater, a watertight pan of corrosion-resistant materials shall be installed beneath the water heater in accordance with the following: (1) The drainage pan shall be provided with not less than [3] ⁄ 4 of an inch (20 mm) diameter drain to an approved location. The terminating end of the drainpipe shall be readily visible. (2) The drainage pan shall be not less than 1 [1] ⁄ 2 inches (38 mm) in depth. (3) Where a drainage pan pipe is installed, the material of the piping shall be rated for the temperature rating of the water heater and shall be approved for use with the liquid being discharged. (4) Discharge from a relief valve into a drainage pan shall be prohibited. 507.6 Added or Converted Equipment or Appliances. When additional or replacement appliances or equipment is installed or an appliance is converted to gas from another fuel, the location in which the appliances or equipment is to be operated shall be checked to verify the following: (1) Air for combustion and ventilation is provided where required, in accordance with the provisions of Section 506.0. Where existing facilities are not adequate, they shall be upgraded to meet Section 506.0 specifications. (2) The installation components and appliances meet the clearances to combustible material provisions of Section 507.26. It shall be determined that the installation and operation of the additional or replacement appliances do not render the remaining appliances unsafe for continued operation. (3) The venting system is constructed and sized in accordance with the provisions of Section 509.0.

  • CMC § 9.3.8.8 Medium relevance — show source text

    (6) Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level.

    [NFPA 54:9.3.8.8]

    (7) Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]

    (8) The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory built chimney 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 54:9.3.8.7]

    507.0 Appliance and Equipment Installation Require- ments.

    507.1 Dielectric Insulator. The Authority Having Jurisdiction shall have the authority to require the use of an approved dielectric insulator on the water piping connections of water heaters and related water heating appliances.

    507.2 Seismic Provisions. Water heaters shall be anchored or strapped to resist horizontal displacement due to earthquake motion. Strapping shall be at points within the upper one-third ( [1] ∕ 3 ) and lower one-third ( [1] ∕ 3 ) of its vertical dimensions. At the lower point, minimum a distance of not less than four ( 4 ) inches (102 mm) shall be maintained above the controls with the strapping. Note: [HCD 1 & HCD 2] Reference Health and Safety Code Section 19211(a) which addresses new, replacement, and existing water heaters. Note: The applicable subsection of Health and Safety Code Sec- tion 19211(a) which addresses new, replacement, and existing water heaters is repeated here for clarity and reads as follows: Section 19211(a) Notwithstanding Section 19100, all new and replacement water heaters, and all existing residential water heaters shall be braced, anchored, or strapped to resist falling or horizontal displacement due to earthquake motion. At a minimum, any water heater shall be secured in accor- dance with the California Plumbing Code, or modifications made thereto by a city, county, or city and county pursuant to Section 17958.5.

    507.3 Appliance Support. Appliances and equipment shall be furnished either with load distributing bases or with a suf

    ficient number of supports to prevent damage to either the building structure or the appliance and the equipment. [NFPA 54:9.1.8.1] 507.3.1 Structural Capacity. At the locations selected for installation of appliances and equipment, the dynamic and static load carrying capacities of the building structure shall be checked to determine whether they are adequate to carry the additional loads. The appliances and equipment shall be supported and shall be connected to the piping so as not to exert undue stress on the connections. [NFPA 54:9.1.8.2] 507.4 Ground Support. A water heater supported from the earth shall rest on level concrete or other approved base extending not less than 3 inches (76 mm) above the adjoining ground level. **507.5 Drainage Pan.

  • CMC § 303.5 Medium relevance — show source text

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    GENERAL REGULATIONS

    accordance with the manufacturer’s installation instructions.

    Supports for appliances shall be designed and constructed to sustain vertical and horizontal loads within the stress limita tions specified in the building code.

    303.5 Restraining Device. Movement of appliances with casters shall be limited by a restraining device installed in accordance with the connector and appliance manufacturer’s installation instructions. [NFPA 54:9.6.1.4]

    303.6 Identification of Equipment. Where more than one heating, cooling, ventilating, or refrigerating system is installed on the roof of a building or within a building, it shall be permanently identified as to the area or space served by the equipment.

    303.7 Liquefied Petroleum Gas (LP-Gas) Facilities. Containers, container valves regulating equipment, and appurtenances for the storage and supply of liquefied petroleum gas (LP-Gas) shall be installed in accordance with NFPA 58 and the California Fire Code .

    303.7.1 Liquefied Petroleum Gas (LP-Gas) Appli- ances. [HCD 1 & HCD 2] Liquefied petroleum gas- burning appliances shall not be installed in a pit, basement, or similar location where heavier-than-air gas might collect. Appliances so fueled shall not be installed in an above-grade under-floor space or basement unless such location is provided with an approved means for removal of unburned gas.

    303.8 Appliances on Roofs. Appliances on roofs shall be designed or enclosed so as to withstand climatic conditions in the area in which they are installed. Where enclosures are provided, each enclosure shall permit easy entry and movement, shall be of reasonable height, and shall have at least a 30 inch (762 mm) clearance between the entire service access panel(s) of the appliance and the wall of the enclosure. [NFPA 54:9.4.1.1]

    303.8.1 Load Capacity. Roofs on which appliances are to be installed shall be capable of supporting the additional load or shall be reinforced to support the additional load. [NFPA 54:9.4.1.2]

    303.8.2 Fasteners. All access locks, screws, and bolts shall be of corrosion-resistant material. [NFPA 54:9.4.1.3]

    303.8.3 Installation of Appliances on Roofs. Appliances shall be installed in accordance with the manufacturer’s installation instructions. [NFPA 54:9.4.2.1]

    303.8.4 Edge of Roof Clearance. Appliances shall be installed on a well-drained surface of the roof. At least 6 feet (1829 mm) of clearance shall be available between any part of the appliance and the edge of a roof or similar hazard, or rigidly fixed rails, guards, parapets, or other building structures at least 42 inches (1067 mm) in height shall be provided on the exposed side. [NFPA 54:9.4.2.2]

    303.8.4.1 Guards and Rails. Guards or rails shall be required where the following exist:

  • CMC § 6.4 Medium relevance — show source text

    (1) The underside of the combustible material or metal cabinet above the cooking top is protected with not less than [1] ⁄ 4 of an inch (6.4 mm) insulating millboard covered with sheet metal not less than 0.0122 of an inch (0.3099 mm) thick.

    (2) A metal ventilating hood of sheet metal not less than 0.0122 of an inch (0.3099 mm) thick is installed above the cooking top with a clearance of not less than [1] ⁄ 4 of an inch (6.4 mm) between the hood and the underside of the combustible material or metal

    cabinet, and the hood is not less than the width of the appliance and is centered over the appliance.

    (3) A listed cooking appliance or microwave oven installed over a listed cooking appliance shall be in accordance with the terms of the upper appliance’s listing and the manufacturer’s installation instructions. {NFPA 54:10.13.3.1} Microwave ovens shall comply with UL 923.

    919.5 Built-In Units. Built-in units shall be installed in accor dance with Section 919.5.1 and Section 919.5.2.

    919.5.1 Installation. Listed built-in household cooking appliances shall be installed in accordance with their listing and the manufacturer’s installation instructions. The installation shall not interfere with combustion air, accessibility for operation, and servicing. Unlisted builtin household cooking appliances shall not be installed in or adjacent to combustible material.

    919.5.2 Vertical Clearance Above Cooking Top. Built-in top (or surface) cooking appliances shall have a vertical clearance above the cooking top of not less than 30 inches (762 mm) to combustible material or metal cabinets. A clearance of not less than 24 inches (610 mm) is permitted where one of the following is installed:

    (1) The underside of the combustible material or metal cabinet above the cooking top is protected with not less than [1] ⁄ 4 of an inch (6.4 mm) insulating millboard covered with sheet metal not less than 0.0122 of an inch (0.3099 mm) thick.

    (2) A metal ventilating hood of sheet metal not less than 0.0122 of an inch (0.3099 mm) thick is installed above the cooking top with a clearance of not less

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    than [1] ⁄ 4 of an inch (6.4 mm) between the hood and the underside of the combustible material or metal

    cabinet, and the hood not less than the width of the appliance and is centered over the appliance.

    (3) A listed cooking appliance or microwave oven installed over a listed cooking appliance shall be in accordance with the terms of the upper appliance’s listing and the manufacturer’s installation instructions. Microwave ovens shall comply with UL 923.

    919.6 Level Installation. Cooking appliances shall be installed so that the cooking top, broiler pan, or oven racks are level. [NFPA 54-2018:10.14.3]

    920.0 Cooking Appliance Listings.

    920.1 Commercial Electric Ranges. Commercial electric ranges shall comply with UL 197 and installed in accordance with the manufacturer’s installation instructions.

  • CMC § 1310.3.1 Medium relevance — show source text

    1310.3.1 Protective Coating. Where piping is in contact with a material or an atmosphere corrosive to the piping system, the piping and fittings shall be coated with a corrosion-resistant material. Any such coating used on piping or components shall not be considered as adding strength to the system. [NFPA 54:7.2.2]

    1310.3.2 Building Structure. The installation of gas piping shall not cause structural stresses within building components to exceed allowable design limits. Approval shall be obtained before any beams or joists are cut or notched. [NFPA 54:7.2.3.1 – 7.2.3.2]

    1310.3.3 Gas Piping to be Sloped. Piping for other than dry gas conditions shall be sloped not less than [1] ⁄ 4 inch in 15 feet (1.4 mm/m) to prevent traps. [NFPA 54:7.2.4]

    1310.3.3.1 Ceiling Locations. Gas piping shall be permitted to be installed in accessible spaces between a fixed ceiling and a dropped ceiling, whether or not such spaces are used as a plenum. Valves shall not be located in such spaces.

    Exception: Appliance or equipment shutoff valves required by this code shall be permitted to be installed in accessible spaces containing vented appliances.

    1310.3.4 Prohibited Locations. Gas piping inside any building shall not be installed in or through a clothes chute, chimney or gas vent, dumbwaiter, elevator shaft, or air duct, other than combustion air ducts. [NFPA 54:7.2.5]

    Exception: Ducts used to provide ventilation air in accordance with Section 701.0 or to above-ceiling spaces in accordance with Section 1310.3.3.1.

    1310.3.5 Hangers, Supports, and Anchors. Piping shall be supported with metal pipe hooks, metal pipe straps, metal bands, metal brackets, metal hangers, or building structural components, suitable for the size of piping, of adequate strength and quality, and located at intervals so as to prevent or damp out excessive vibration. Piping shall be anchored to prevent undue strains on connected appliances and equipment and shall not be supported by other piping. Pipe hangers and supports shall conform to the requirements of MSS SP-58. [NFPA 54:7.2.6.1]

    1310.3.5.1 Spacing. Spacing of supports in gas piping installations shall not be greater than shown in Table 1310.3.5.1. Spacing of supports of CSST shall be in accordance with the CSST manufac turer’s instructions. [NFPA 54:7.2.6.2]

    TABLE 1310.3.5.1

    SUPPORT OF PIPING

    [NFPA 54: TABLE 7.2.6.2]

  • CMC § 519.1 Medium relevance — show source text

    519.1 Where Required. Type II hoods shall be installed above equipment and dishwashers that generate steam, heat, or products of combustion, and where grease or smoke is not present.

    Exceptions:

    (1) Dishwashing machines connected to a Type II duct system and exhausted directly to the outdoors.

    (2) Dishwashing machines with a self-contained condensing system listed in accordance with UL 921 and installed in a space where the HVAC system has been engineered to accommodate the latent and sensible heat load emitted from such appliances as approved by the Authority Having Jurisdiction. Such equipment shall be provided with an interlocking device to prevent opening of the appliance prior to completion of its cycle. 519.2 Construction of Type II Hoods. Type II hoods constructed of steel shall be not less than 0.024 of an inch (0.61 mm) (No. 24 gauge). Hoods constructed of copper shall be of copper sheets weighing not less than 0.17 ounces per square inch (oz/in [2] ) (7.47 kg/m [2] ). Joints and seams shall be substantially tight. Solder shall not be used except for sealing a joint or seam. 519.3 Type II Hood Exhaust System Net Airflow. The net airflow for Type II hoods shall be in accordance with Section 508.5.1.5 for light-duty cooking appliances. The net airflow for Type II hoods serving dishwashing appliances shall comply with Section 519.3.1.

    519.3.1 Dishwashing Appliances. The net airflow for Type II hoods used for dishwashing equipment shall be not less than 200 cubic feet per minute (0.094 m [3] /s) per linear foot (m) of hood length.

    519.4 Type II Exhaust Duct Systems. Ducts and plenums serving Type II hoods shall be constructed of rigid metallic materials in accordance with Chapter 6. Duct bracing and supports shall comply with Chapter 6. Ducts subject to positive pressure shall be adequately sealed.

    519.5 Termination of Type II Hood Exhaust System. The exhaust system shall terminate in accordance with Section 502.2.2. Rooftop terminations shall be directed away

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    132 2025 CALIFORNIA MECHANICAL CODE

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    EXHAUST SYSTEMS

    from roof surfaces within 40 inches (1016 mm). The discharge outlet of moisture conveying exhaust ducts, such as dishwasher exhaust ducts, shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.

    519.6 Makeup Air. Makeup air shall be provided in accordance with Section 511.3.

    519.7 Independent Exhaust Duct System. Single or combined Type II exhaust systems shall be independent of all other exhaust systems.

    2025 CALIFORNIA MECHANICAL CODE 133

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

    134 2025 CALIFORNIA MECHANICAL CODE

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    CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

    CHAPTER 6 – DUCT SYSTEMS

  • CMC § 1220.4.2 Medium relevance — show source text

    8|1220.4.2 – 1220.4.6| |1221.7|1221.6| |1308.2 – 1308.4.1|1308.3 – 1308.5.1| |Table 1308.3.1|Table 1308.4.1| |1308.4.2|1308.5.2| |1308.4.2.2 – 1308.6.4|1308.5.2.1 – 1308.7.3| |Table 1308.4.6.2|Table 1308.5.6.2| |1308.6.5 – 1308.13.1|1308.7.7 – 1308.14.1| |1312.1.2 – 1312.1.3|1312.1.1 – 1312.1.2| |Chapter 17|Appendix F| |Chapter 18|Chapter 17| |D 103.2|D 103.1| |E 503.5.6.7|E 503.5.6.6| |E 503.5.7.2 – E 503.5.7.6|E 503.5.7.1 – E 503.5.7.5| |Table E 503.5.7.2|Table E 503.5.7.1| |Table E 503.5.7.6|Table E 503.5.7.5| |Table E 503.5.10.1.2(1)|Table E 503.5.10(1)| |Table E 503.5.10.1.2(2)|Table E 503.5.10(2)| |E 503.5.10.1.2|E 503.5.10| |E 503.5.10.2 – E 503.5.10.2.2|E 503.5.10.1 – E 503.5.10.1.2| |E 503.5.12.1|E 503.5.12| |E 503.5.12.2|E 503.5.12.1| |E 503.6.5.4|E 503.6.5.4.1|

    xxii 2025 CALIFORNIA MECHANICAL CODE

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    Uniform Mechanical Code – 2024 Edition:

    The Uniform Mechanical Code contains complete requirements for the installation and maintenance of heating, ventilating, cooking and refrigeration systems.

    Uniform Mechanical Code Illustrated Training Manual:

  • CMC § 100.0 Medium relevance — show source text

    Exception 1 to Section 100.0(f): If one occupancy constitutes at least 80 percent of the conditioned floor area of the building, the entire building envelope, HVAC and water heating may be designed to comply with the provisions of Part 6 applicable to that occupancy, provided that the applicable lighting requirements in Sections 140.6 through 140.8, 150.0(k), or 160.5 and 170.2(e) are met for each occupancy and space, and mandatory measures in Sections 110.0 through 130.5, 150.0, and 160.0 through 160.9 are met for each occupancy and space.

    Exception 2 to Section 100.0(f): If one occupancy constitutes at least 90 percent of the combined conditioned plus unconditioned floor area of the building, the entire building indoor lighting may be designed to comply with only the lighting provisions of Part 6 applicable to that occupancy.

    (g) Administrative requirements. Administrative requirements relating to permit requirements, enforcement by the Commission, locally adopted energy standards, interpretations, claims of exemption, approved calculation methods, rights of appeal, and certification and labeling requirements of fenestration products and roofing products are specified in California Code of Regulations, Title 24, Part 1, Sections 10-101 to 10-114.

    (h) Certification requirements for manufactured equipment, products and devices. Part 6 limits the installation of manufactured equipment, products and devices to those that have been certified as specified by Sections 110.0 and 110.1. Requirements for manufactured equipment, products, and devices, when not specified in Title 24 Part 6, are specified in California Code of Regulations, Title 20, Sections 1601–1609.

    Note: Authority: Sections 25213, 25218, 25218.5, 25402 and 25402.1, Public Resources Code . Reference: Sections 25007, 25008, 25218.5, 25310, 25402, 25402.1, 25402.4, 25402.5, 25402.8, and 25943, Public Resources Code .

    SECTION 100.1 — DEFINITIONS AND RULES OF CONSTRUCTION

    (a) Rules of Construction.

    1. Where the context requires, the singular includes the plural and the plural includes the singular.
    2. The use of “and” in a conjunctive provision means that all elements in the provision must be complied with or must exist to make the provision applicable. Where compliance with one or more elements suffices, or where existence of one or more elements makes the provision applicable, “or” (rather than “and/or”) is used.
    3. “Shall” is mandatory and “may” is permissive.

    (b) Definitions. Terms, phrases, words and their derivatives in Part 6 shall be defined as specified in Section 100.1. Terms, phrases, words and their derivatives not found in Section 100.1 shall be defined as specified in the “Definitions” chapters of Title 24, Parts 1 through 5 of the California Code of Regulations. Where terms, phrases, words and their derivatives are not defined in any of the references above, they shall be defined as specified in Webster’s Third New International Dictionary of the English Language, Unabridged (1961 edition, through the 2002 addenda), unless the context requires otherwise.

Frequently asked questions

Do these clearance rules apply to both metal and flexible ducts?

Yes. The clearance requirements in § 603.13 apply to the duct regardless of material; however, specific manufacturer listings or product listings may provide alternative clearances — follow those where present (§ 603.13.1) .

If a furnace is listed for reduced clearance, which governs — the listing or § 603.13?

The furnace listing and the manufacturer’s installation instructions govern; § 603.13.1 requires compliance with listing/manufacturer for duct clearances .

For an unlisted furnace without a 250°F limit control, what clearance applies?

The § 603.13.3 6‑in/6‑ft rule specifically applies only when the unlisted furnace is equipped with a temperature limit control with a maximum setting of 250°F (121°C). If the unlisted furnace lacks that control, consult the appliance installation chapter (e.g., § 904.3.* and Table provisions) or the AHJ for applicable clearances; the Code requires approval/installation per those provisions .

How long must I keep the duct supported near the furnace?

Support needs are not limited to the clearance zone; appliances must be furnished with load-distributing bases or adequate supports and piping must not be stressed. See § 902.8 and § 303.4 for support/anchorage requirements and § 1310.3.5 for piping hanger spacing .

Can I reduce the 6‑inch or 3‑foot clearances by protecting the combustible material?

If the furnace or finish is listed for reduced clearances (or combustible material is protected per the Code and the manufacturer allows it), reduced clearances permitted by the listing/manufacturer may be used — otherwise the prescriptive distances in § 603.13.2/§ 603.13.3 apply. Always document the applicable listing/instruction and confirm with the AHJ where unclear .

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