CMC · California Mechanical Code
What installation access and maintenance clearances are required for boilers?
For homeowners: the CMC requires at least 18 inches of unobstructed working space around boilers for servicing; taller clearances above the boiler (2 ft, 3 ft, or 7 ft) depend on whether the boiler is a package unit, has a top manhole, or is a large power boiler. Always verify manufacturer instructions and get AHJ approval before reducing clearances.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The California Mechanical Code requires that boilers be installed with sufficient unobstructed access for inspection, maintenance, and repair, including minimum passageway widths and minimum top clearances for certain boiler types. The primary rule for side passageways is an unobstructed width of not less than 18 inches per § 1010.1 . Special, larger top clearances are specified for larger power boilers and for boilers with manholes on top in § 1010.2, § 1010.3, and § 1010.4 .
Keep a continuous, unobstructed working space around boilers so technicians can inspect, service, and remove components — at minimum 18 inches around sides, with larger top clearances for large or man‑hole-equipped boilers (see § 1010.1–1010.4).
Requirements in detail
Key terms (first use)
- 18 inches — minimum unobstructed passageway width around all sides of boilers per § 1010.1.
- Authority Having Jurisdiction — may approve reduced side clearances where they do not inhibit service (exception in § 1010.1).
- 7 feet, 3 feet, 2 feet — minimum top clearances that apply depending on boiler type or features (see table and sections below).
Quick decision table (most common dimensions)
| Decision-relevant dimension / area | Minimum clearance | When it applies | Code Reference |
|---|---|---|---|
| Passageways around all sides of a boiler | 18 inches (457 mm) | All boilers, for inspection/maintenance access | § 1010.1 |
| Top of Power boilers | 7 feet (2134 mm) | Power boilers with steam > 5,000 lb/h, or heating surface > 1000 ft², or input > 5,000,000 Btu/h | § 1010.2 |
| Boilers with manholes on top (steam‑heating, hot‑water, and power boilers not covered by § 1010.2 / § 1010.4) | 3 feet (914 mm) | Boilers that exceed any of the limits listed in § 1010.3 and have top manholes | § 1010.3 |
| Package boilers / boilers without top manhole and within limits | 2 feet (610 mm) | Package boilers, steam‑heating, and hot‑water boilers with no manhole and not exceeding limits in § 1010.3 | § 1010.4 |
| Exception to side clearance | Lesser than 18 inches permitted with approval | Only if the Authority Having Jurisdiction approves and the reduced clearance does not inhibit service | § 1010.1 (Exception) |
How to apply each section (plain language)
§ 1010.1 — General access: Provide unobstructed passageways around all sides of a boiler of at least 18 inches so technicians can perform inspection, maintenance, and repair. The code allows an access opening (door or access panel) to serve as the repair/cleaning clearance if the opening is large enough. Authority Having Jurisdiction (AHJ) may allow a reduced side clearance if it does not inhibit service.
§ 1010.2 — Large power boilers (top clearance): If a power boiler meets any of these thresholds — steam capacity > 5,000 lb/h, heating surface > 1000 ft², or input > 5,000,000 Btu/h — provide at least 7 feet from the top of the boiler to the ceiling to permit safe access to top-mounted manways, fittings, or equipment.
§ 1010.3 — Boilers with manholes (3 ft rule): For steam‑heating and hot‑water boilers (and power boilers that do not meet § 1010.2 limits) that exceed one of the listed limits in § 1010.3 and that have a manhole on top, provide at least 3 feet from the top of the boiler to the ceiling.
§ 1010.4 — Package boilers, no manhole (2 ft rule): Package boilers, steam‑heating boilers, and hot‑water boilers that do not have a top manhole and that are within the limits set in § 1010.3 require a minimum 2 feet of clearance from top of boiler to ceiling.
Manufacturer listing and other clearance rules
- Follow appliance listing and the manufacturer’s installation instructions for required clearances — listed units must be installed per their listing; unlisted units must meet applicable clearance guidance and be approved by the AHJ (see § 303.1 and related provisions).
- Distinguish between maintenance access clearances (Chapter 10, § 1010.x) and clearance to combustible materials (Chapter 9, e.g., § 904.3). Both may apply and are separate requirements: you must satisfy both where relevant.
Exceptions & special cases
- The explicit exception in § 1010.1 allows reduced side clearance (< 18 inches) if the Authority Having Jurisdiction approves AND the reduction “does not inhibit inspection, maintenance, or repair.” Do not assume automatic approval — get AHJ acceptance.
- Access through another room or an access panel is allowed for repair/cleaning clearances provided the opening is large enough to perform the required maintenance — this can be acceptable instead of full unobstructed perimeter clearance per § 1010.1.
- Where boilers are listed for closet or alcove installations or have manufacturer-stated clearances, the listing/instructions take precedence and must be followed (see § 303.1 and § 1001.2.1 for listed‑unit constraints).
Common mistakes
- Confusing clearance to combustible materials with service/maintenance clearances. Chapter 9 (e.g., § 904.3) addresses combustible clearances; Chapter 10 (§ 1010.1–.4) addresses access and working clearances — you must comply with both where applicable.
- Measuring from the wrong datum: top clearances are measured from the top of the boiler to the ceiling — don’t measure to flues, casings, or nearby obstructions unless the manufacturer or AHJ specifies otherwise. See § 1010.2–.4.
- Relying solely on tight closet or alcove installations without confirming the unit is listed for closet/alcove use or that the room volume and clearance meet code/manufacturer instructions (§ 303.2, § 1001.2.1).
- Assuming AHJ approval for reduced clearances is automatic; the AHJ must explicitly approve reductions and verify serviceability per the exception in § 1010.1.
Worked example — concrete scenario
Scenario: You are installing a steam‑heating boiler that has a heating surface of 1,200 ft², does not exceed 5,000 lb/h steam capacity, and has a manhole on top. The ceiling above the boiler room is finished (no drop ceiling).
- Does the boiler exceed any of the § 1010.3 limits? Yes — heating surface > 1000 ft², so § 1010.3 applies. § 1010.2 (7‑ft rule) does not apply because the boiler’s steam capacity is ≤ 5,000 lb/h and input is not > 5,000,000 Btu/h.
- Top clearance required: Because the boiler has a manhole on top and exceeds the § 1010.3 limit, provide at least 3 feet (914 mm) from the top of the boiler to the ceiling per § 1010.3.
- Side clearances: Maintain at least 18 inches of unobstructed passageway around all sides for inspection and maintenance per § 1010.1 (unless you obtain AHJ approval for reduced side clearance that does not inhibit service).
- Confirm combustible clearances and manufacturer instructions as additional requirements (see § 904.3 and § 303.1).
Related provisions
- § 1001.2 — Boiler rooms and enclosures: boiler rooms must comply with the California Building Code; listed boiler clearances cannot be reduced below listing.
- § 303.1 — Listed appliances: install per listing and manufacturer’s instructions; manufacturer instructions must be retained on the appliance.
- § 904.3 — Clearance for central heating boilers and furnaces (clearance to combustible materials) — separate from access clearances in Chapter 10.
- § 304.1 — Accessibility for service (general working‑space guidance, 30 in. where not otherwise specified). This is broader service-access guidance that may apply to rooftop/attic installations.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 1010.0 High relevance — show source text
1010.0 Clearance for Access.
1010.1 General. Where boilers are installed or replaced, clearance shall be provided to allow access for inspection, maintenance, and repair. Passageways around all sides of boilers shall have an unobstructed width of not less than 18 inches (457 mm). Clearance for repair and cleaning shall be permitted to be provided through a door or access panel into another area, provided the opening is of sufficient size.
Exception: Subject to the approval of the Authority Having Jurisdiction, boilers shall be permitted to be installed with a side clearance of less than 18 inches (457 mm), provided that the lesser clearance does not inhibit inspection, maintenance, or repair.
1010.2 Power Boilers. Power boilers having a steam-generating capacity in excess of 5000 pounds per hour (lb/h) (0.6299 kg/s) or having a heating surface in excess of 1000 square feet (92.9 m [2] ) or input in excess of 5 000 000 Btu/h (1464 kW) shall have a clearance of not less than 7 feet (2134 mm) from the top of the boiler to the ceiling.
1010.3 Steam-Heating Boilers, Hot Water Boilers, and Power Boilers. Steam-heating boilers and hot-water-heating boilers that exceed one of the following limits:
(1) 5 000 000 Btu/h input (1464 kW)
(2) 5000 pounds steam per hour (0.6299 kg/s) capacity
(3) 1000 square foot (92.9 m [2] ) heating surface
Power boilers that do not exceed one of the following limits:
(1) 5 000 000 Btu/h input (1464 kW)
(2) 5000 pounds steam per hour (0.6299 kg/s) capacity (3) 1000 square foot (92.9 m [2] ) heating surface
Boilers with manholes on top of the boiler, except those described in Section 1010.2 and Section 1010.4, shall have a clearance of not less than 3 feet (914 mm) from the top of the boiler to the ceiling. 1010.4 Package Boilers, Steam-Heating Boilers, and Hot-Water-Heating Boilers. Package boilers, steam-heating boilers, and hot-water-heating boilers with no manhole on top of the shell and not exceeding one of the above limits shall have a clearance of not less than 2 feet (610 mm) from the ceiling.
1011.0 Boilers, Stokers, and Steam Generators.
1011.1 General. The design, installation, and operation of single burner boilers, multiple burner boilers, stokers, and atmospheric fluidized-bed boilers with not less than a fuel input rating of 12.5 E+06 Btu/h (3.663 MW) to pulverized fuel systems, fired or unfired steam generators used to recover heat from combustion turbines and to other combustion turbine exhaust systems shall be in accordance with NFPA 85. That portion of the oil-burning system supplied on boilers and covered within the scope of NFPA 85 shall be installed in accordance with NFPA 85.
CMC § 1007.0 High relevance — show source text
1007.0 Gas-Pressure Regulators.
1007.1 General. An approved gas-pressure regulator shall be installed on gas-fired boilers where the gas supply pressure is exceeding that at which the main burner is designed to operate. A separate approved gas-pressure regulator shall be installed to regulate the gas pressure to the pilot or pilots.
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BOILERS AND PRESSURE VESSELS
1008.0 Low-Water Cutoff.
1008.1 General. Hot water boilers and steam boilers shall be installed with a low-water cutoff. A coil-type boiler or a water-tube boiler that requires forced circulation to prevent overheating of the coils or tubes shall be installed with a flowsensing device in the outlet piping in lieu of the low-water cutoff. The low-water cutoff or the flow sensing device shall be installed so as to prevent damage to the boiler and to permit testing of the fuel-supply cutoff without draining the heating system. The low-water cutoff shall shut off the energy source at a water level setpoint that is in accordance with the boiler manufacturer’s instructions.
1009.0 Combustion Regulators – Safety Valves.
1009.1 General. The following requirements shall be retroactive:
(1) Hot-water-heating boilers, other than manually fired, shall be equipped with two temperature combustion regulators in series. Steam-heating boilers, other than manually fired, shall be equipped with a pressure combustion regulator and a low-water cutoff. (See Section 1008.0)
(2) Boilers and pressure vessels shall be provided with the required number, size, and capacity of safety or relief valves to ensure positive relief of overpressure in accordance with nationally recognized standards, as applicable. Valves so employed shall be constructed, sealed, and installed in accordance with nationally recognized standards, as applicable.
1010.0 Clearance for Access.
1010.1 General. Where boilers are installed or replaced, clearance shall be provided to allow access for inspection, maintenance, and repair. Passageways around all sides of boilers shall have an unobstructed width of not less than 18 inches (457 mm). Clearance for repair and cleaning shall be permitted to be provided through a door or access panel into another area, provided the opening is of sufficient size.
Exception: Subject to the approval of the Authority Having Jurisdiction, boilers shall be permitted to be installed with a side clearance of less than 18 inches (457 mm), provided that the lesser clearance does not inhibit inspection, maintenance, or repair.
1010.2 Power Boilers. Power boilers having a steam-generating capacity in excess of 5000 pounds per hour (lb/h) (0.6299 kg/s) or having a heating surface in excess of 1000 square feet (92.9 m [2] ) or input in excess of 5 000 000 Btu/h (1464 kW) shall have a clearance of not less than 7 feet (2134 mm) from the top of the boiler to the ceiling.
1010.3 Steam-Heating Boilers, Hot Water Boilers, and Power Boilers. Steam-heating boilers and hot-water-heating boilers that exceed one of the following limits:
(1) 5 000 000 Btu/h input (1464 kW)
CMC § 302.3.2 High relevance — show source text
302.3.2 Technical Data. The registered design professional shall submit sufficient technical data to substantiate the proposed alternative engineered design and to prove that the performance meets the intent of this code.
302.3.3 Design Documents. The registered design professional shall provide two complete sets of signed and sealed design documents for the alternative engineered design for submittal to the Authority Having Jurisdiction. The design documents shall include floor plans of the work. Where appropriate, the design documents shall indicate location, sizing, and loading of appurtenances, equipment, appliances, and devices.
302.3.4 Design Approval. An approval of an alternative engineered design shall be at the discretion of the Authority Having Jurisdiction. The exercise of this discretionary approval by the Authority Having Jurisdiction shall have no effect beyond the jurisdictional boundaries of said Authority Having Jurisdiction. An alternative engineered design so approved shall not be considered as in accordance with the requirements, intent, or both of this code for a purpose other than that granted by the Authority Having Jurisdiction.
302.3.5 Design Review. The Authority Having Jurisdiction shall have the authority to require testing of the alternative engineered design in accordance with Section 302.2.1, including the authority to require an independent review of the design documents by a registered design professional selected by the Authority Having Jurisdiction and at the expense of the applicant.
302.3.6 Inspection and Testing. The alternative engineered design shall be tested and inspected in accordance with the submitted testing and inspection plan and the requirements of this code.
303.0 Installation.
303.1 Listed Appliances. The installation of equipment and appliances regulated by this code shall be in accordance with the conditions of the listing, the manufacturer’s installation instructions and this code. The manufacturer’s instal lation and operating instructions shall be attached to the appliance. Clearances of listed equipment and appliances from combustible materials shall be as specified in the listing or on the rating plate.
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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CMC § 904.2.1 High relevance — show source text
obtained from the outdoors. The closet shall be for the exclusive use of the central heating furnace or low-pressure boiler.
(2) Central heating furnaces and low-pressure boilers shall be of the direct vent type.
904.2.1 Self-Closing Doors. Self-closing doors shall swing easily and freely, and shall be equipped with a self-closing device to cause the door to close and latch each time it is opened. The closing mechanism shall not have a hold-open feature.
904.2.2 Gasketing. Gasketing on gasketed doors or frames shall be furnished in accordance with the published listings of the door, frame, or gasketing material manufacturer.
Exception: Where acceptable to the Authority Having Jurisdiction, gasketing of noncombustible or limitedcombustible material shall be permitted to be applied to the frame, provided closing and latching of the door are not inhibited.
904.3 Clearance. Central heating furnaces and low-pressure boilers shall be provided with clearances in accordance with Section 904.3.1 through Section 904.3.7.
904.3.1 Listed Units. Listed central heating furnaces and low-pressure boilers shall be installed with clearances in accordance with the terms of their listings and the manufacturer’s installation instructions. {NFPA 54:10.3.3.1}
904.3.2 Unlisted Units. Unlisted central heating furnaces and low-pressure boilers shall be installed with clearances from combustible material not less than those specified in Table 904.3.2. [NFPA 54:10.3.3.2]
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INSTALLATION OF SPECIFIC APPLIANCES
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904.5 Temperature or Pressure Limiting Devices. Steam and hot water boilers, respectively, shall be provided with approved automatic limiting devices for shutting down the burner(s) to prevent boiler steam pressure or boiler water temperature from exceeding the maximum allowable working pressure or temperature. Safety limit controls shall not be used as operating controls. [NFPA 54:10.3.5]
904.6 Low-Water Cutoff. All water boilers and steam boilers shall be provided with an automatic means to shut off the fuel supply to the burner(s) if the boiler water level drops below the lowest safe water line. In lieu of the low-water cutoff, water tube or coil-type boilers that require forced circulation to prevent overheating and failure shall have an approved flow sensing device arranged to shut down the boiler when the flow rate is inadequate to protect the boiler against overheating. [NFPA 54:10.3.6]
904.7 Steam Safety and Pressure Relief Valves. Steam and hot water boilers shall be equipped, respectively, with listed or approved steam safety or pressure relief valves of appropriate discharge capacity and conforming with ASME requirements. A shutoff valve shall not be placed between the relief valve and the boiler or on discharge pipes between such valves and the atmosphere. [NFPA 54:10.3.7]
904.7.1 Discharge. Relief valves shall be piped to discharge near the floor. [NFPA 54:10.3.7.1]
CMC § 903.2.2 High 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 § 902.15 High relevance — show source text
902.15 Bleed Lines for Diaphragm-Type Valves. . . . . . . . . . . . . . . . . . . . . . 200
903.0 Air-Conditioning Appliances . . . . . 200
903.1 Electric Air Conditioners . . . . . . . . 200
903.2 Gas-Fired Air Conditioners
and Heat Pumps. . . . . . . . . . . . . . 200
903.3 Packaged Terminal Air Conditioners . . . . . . . . . . . . . . . . . 200
904.0 Central Heating Boilers and Furnaces. . . . . . . . . . . . . . . . . . . . 200
904.1 Application . . . . . . . . . . . . . . . . . . 200
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904.2 Location . . . . . . . . . . . . . . . . . . . . 201
904.3 Clearance . . . . . . . . . . . . . . . . . . . 201
904.4 Assembly and Installation. . . . . . . 201
904.5 Temperature or Pressure Limiting Devices . . . . . . . . . . . . . . 202
904.6 Low-Water Cutoff . . . . . . . . . . . . . 202
904.7 Steam Safety and Pressure Relief Valves. . . . . . . . . . . . . . . . . 202
904.8 Refrigeration Coils . . . . . . . . . . . . 202
904.9 Cooling Units Used with Heating Boilers. . . . . . . . . . . . . . . . . . . . . . 202
904.10 Furnace (Upright and Horizontal) . . 202
Table 904.3.2 Clearances to Combustible
Material for Unlisted Furnaces
and Boilers . . . . . . . . . . . . . . . . . . 202
904.11 Solid-Fuel-Fired Furnaces . . . . . . 203
904.12 Oil-Fired Central Furnaces . . . . . . 203
904.13 Commercial or Industrial
Gas Heaters . . . . . . . . . . . . . . . . . 203
904.14 Electric Central Furnaces . . . . . . . 203
905.0 Duct Furnaces . . . . . . . . . . . . . . . 203
905.1 Application . . . . . . . . . . . . . . . . . . 203
905.2 Clearances . . . . . . . . . . . . . . . . . . 203
905.3 Installation of Duct Furnaces. . . . . 203
905.4 Access Panels . . . . . . . . . . . . . . . 203
905.5 Location of Draft Hoods
and Controls . . . . . . . . . . . . . . . . . 203
905.6 Circulating Air . . . . . . . . . . . . . . . . 203
905.7 Duct Furnaces Used with
Refrigeration Systems . . . . . . . . . 203
905.8 Installation in Commercial
Garages and Aircraft Hangars . . . 203
CMC § 303.2 High 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 § 904.9 High relevance — show source text
904.9 Cooling Units Used with Heating Boilers. . . . . . . . . . . . . . . . . . . . . . 202
904.10 Furnace (Upright and Horizontal) . . 202
Table 904.3.2 Clearances to Combustible
Material for Unlisted Furnaces
and Boilers . . . . . . . . . . . . . . . . . . 202
904.11 Solid-Fuel-Fired Furnaces . . . . . . 203
904.12 Oil-Fired Central Furnaces . . . . . . 203
904.13 Commercial or Industrial
Gas Heaters . . . . . . . . . . . . . . . . . 203
904.14 Electric Central Furnaces . . . . . . . 203
905.0 Duct Furnaces . . . . . . . . . . . . . . . 203
905.1 Application . . . . . . . . . . . . . . . . . . 203
905.2 Clearances . . . . . . . . . . . . . . . . . . 203
905.3 Installation of Duct Furnaces. . . . . 203
905.4 Access Panels . . . . . . . . . . . . . . . 203
905.5 Location of Draft Hoods
and Controls . . . . . . . . . . . . . . . . . 203
905.6 Circulating Air . . . . . . . . . . . . . . . . 203
905.7 Duct Furnaces Used with
Refrigeration Systems . . . . . . . . . 203
905.8 Installation in Commercial
Garages and Aircraft Hangars . . . 203
905.9 Electric Duct Heaters . . . . . . . . . . 203
906.0 Floor Furnaces . . . . . . . . . . . . . . . 203
906.1 Application . . . . . . . . . . . . . . . . . . 203
906.2 Installation . . . . . . . . . . . . . . . . . . 204
906.3 Temperature Limit Controls . . . . . 204
906.4 Combustion and Circulating Air. . . 204
906.5 Placement. . . . . . . . . . . . . . . . . . . 204
906.6 Bracing . . . . . . . . . . . . . . . . . . . . . 204
906.7 Support . . . . . . . . . . . . . . . . . . . . . 204
906.8 Clearance . . . . . . . . . . . . . . . . . . . 204
906.9 Access . . . . . . . . . . . . . . . . . . . . . 204
906.10 Seepage Pan . . . . . . . . . . . . . . . . 204
906.11 Wind Protection . . . . . . . . . . . . . . 204
906.12 Upper Floor Installations. . . . . . . . 204
906.13 First Floor Installation . . . . . . . . . . 204
906.14 Oil-Fired Floor Furnaces. . . . . . . . 204
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CMC § 303.10.1.3 High relevance — show source text
2025 CALIFORNIA MECHANICAL CODE 53
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
GENERAL REGULATIONS
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303.10.1.3 Solid-Fuel-Burning Appliances. For solid-fuel-burning appliances, the clearance shall not be less than 12 inches (305 mm) to combustible walls and not less than 18 inches (457 mm) to combustible ceilings. The clearance, after reduction, shall be permitted to be less than 12 inches (305 mm) to combustible walls and less than 18 inches (457 mm) to combustible ceilings. Solid-fuel-burning appliances listed for lesser clearances shall be permitted to be installed in accordance with the manufacturer’s instructions and their listing. 303.11 Installation in Commercial Garages. Appliances installed in commercial garages shall be in accordance with Section 303.11.1 through Section 303.11.2. 303.11.1 Parking Structures. Appliances installed in enclosed, basement, and underground parking structures shall be installed in accordance with NFPA 88A. [NFPA 54:9.1.11.1] 303.11.2 Repair Garages. Appliances installed in repair garages shall be installed in accordance with NFPA 30A. [NFPA 54:9.1.11.2]
303.12 Installation in Aircraft Hangars. Heaters in aircraft hangars shall be installed in accordance with NFPA 409.
[NFPA 54:9.1.12]
304.0 Accessibility for Service. 304.1 General. All appliances shall be located with respect to building construction and other equipment so as to permit access for repair or replacement of the appliance. Clearance shall be maintained to permit removal of the appliance; cleaning of heating surfaces; the replacement of filters, blowers, motors, burners, controls, and vent connections; the lubrication of moving parts where necessary; the adjustment and cleaning of burners and pilots; and the proper functioning of explosion vents, if provided. For attic installation, the passageway and servicing area adjacent to the appliance shall be in accordance with Section 304.4. {NFPA 54:9.2.1}
Unless otherwise specified, clearances of not less than 30 inches (762 mm) in depth, width, and height of working space shall be maintained.
Exception: A platform shall not be required for unit heaters or room heaters.
304.2 Sloped Roof. Where equipment or appliances that require service are installed on a roof having a slope of 4 units vertical in 12 units horizontal (33 percent slope) or more, a level platform of not less than 30 inches by 30 inches (762 mm by 762 mm) shall be provided at the service side of the equipment or appliance. 304.3 Access to Appliances on Roofs. Appliances located on roofs or other elevated locations shall be accessible. [NFPA 54:9.4.3.1]
304.3.1 Access from the Inside. Buildings of more than 15 feet (4572 mm) in height shall have an inside means of access to the roof unless other means acceptable to the Authority Having Jurisdiction are used. [NFPA 54:9.4.3.2]
CMC § 505.8 High relevance — show source text
Product conveying ducts . . . . . . . . . . . . . . . . . . . . 505.8
ENCLOSURES
For equipment on roof. . . . . . . . . . . . . . . . . . . . . . 303.8
For boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1001.2
ENERGY STAR, DEFINITION . . . . . . . . . . . . . . . . . . E 201.1
ENFORCEMENT (SFM) . . . . . . . . . . . . . . . . . . . . . . . 1.11.2.1
ENFORCING AGENCY
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.0
SFM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.11.2
ENGINE, GAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1602.0
EQUIPMENT
Clearances. . . . . . . . . 303.10, 303.10.1, Table 303.10.1
Converted equipment . . . . . . . . . . . . . . . . . . . . . . 902.3
578 2025 CALIFORNIA MECHANICAL CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
INDEX
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.0
Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.3
Identification of . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.6
Improper location . . . . . . . . . . . . . . . . . . . . . . . . . 308.0
Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.2
On roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.8, 304.0
Protection against flood damage. . . . . . . . . . . . . . 305.3
Service and access. . . . . . . . . . . . . . . . . . . . . . . . 304.0
Types of Fire Extinguishing Equipment. . . . . . . . . 513.2
ESSENTIAL MECHANICAL PROVISIONS . . . . . . . . . . 321.0
ETO STERILIZATION AREAS . . . . . . . . . . . . . . . . . . . . 418.0
CMC § 1005.0 High relevance — show source text
1005.0 Safety or Relief Valve Discharge . . 219
1005.1 General. . . . . . . . . . . . . . . . . . . . . 219
1005.2 Discharge Piping . . . . . . . . . . . . . 219
1005.3 Splash Shield . . . . . . . . . . . . . . . . 219
1005.4 Hazardous Discharge . . . . . . . . . . 219
1005.5 Vacuum Relief Valve . . . . . . . . . . 219
1006.0 Shutoff Valves . . . . . . . . . . . . . . . 219
1006.1 General. . . . . . . . . . . . . . . . . . . . . 219
1007.0 Gas-Pressure Regulators . . . . . . . 219
1007.1 General. . . . . . . . . . . . . . . . . . . . . 219
1008.0 Low-Water Cutoff . . . . . . . . . . . . . 220
1008.1 General. . . . . . . . . . . . . . . . . . . . . 220
1009.0 Combustion Regulators Safety Valves . . . . . . . . . . . . . . . . 220
1009.1 General. . . . . . . . . . . . . . . . . . . . . 220
1010.0 Clearance for Access . . . . . . . . . . 220
1010.1 General. . . . . . . . . . . . . . . . . . . . . 220
1010.2 Power Boilers . . . . . . . . . . . . . . . . 220
1010.3 Steam-Heating Boilers, Hot Water Boilers, and Power Boilers. . 220
1010.4 Package Boilers, Steam-Heating Boilers, and Hot-Water-Heating Boilers. . . . . . . . . . . . . . . . . . . . . . 220
1011.0 Boilers, Stokers, and Steam
Generators . . . . . . . . . . . . . . . . . . 220
xxxviii
1011.1 General. . . . . . . . . . . . . . . . . . . . . 220
1012.0 Operating Adjustments and Instructions . . . . . . . . . . . . . . . . . . 220
1012.1 General. . . . . . . . . . . . . . . . . . . . . 220
1013.0 Inspections and Tests. . . . . . . . . . 220
1013.1 General. . . . . . . . . . . . . . . . . . . . . 220
1013.2 Operating Permit . . . . . . . . . . . . . 221
1013.3 Maintenance Inspection . . . . . . . . 221
1013.4 Power and Miniature Boilers. . . . . 221
1013.5 Steam-Heating and WaterHeating Boilers . . . . . . . . . . . . . . . 221
CMC § 1609.3.1. High relevance — show source text
Provisions shall be made for drainage by a riser of not less than1/8 inch at each nail or by 4-foot-
long battens with not less than a1/2-inch separation between battens. Horizontal battens are required for slopes over 7:12.
e. Perimeter fastening areas include three tile courses but not less than 36 inches from either side of hips or ridges and edges of eaves and_gable_ rakes.
f._ Vasd_ shall be determined in accordance with Section 1609.3.1.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 pound per square foot = 4.882 kg/m2.
a. Minimum fastener size. Corrosion-resistant nails not less than No. 11 gage with5/16-inch head. Fasteners shall be long enough to penetrate into the sheathing3/4 inch or
through the thickness of the sheathing, whichever is less. Attaching wire for clay and concrete tile shall not be smaller than 0.083 inch.
b. Snow areas. Not fewer than two fasteners per tile are required or battens and one fastener.
c. Roof slopes greater than 24:12. The nose of all tiles shall be securely fastened.
d. Horizontal battens. Battens shall be not less than 1 inch by 2 inches nominal. Provisions shall be made for drainage by a riser of not less than1/8 inch at each nail or by 4-foot-
long battens with not less than a1/2-inch separation between battens. Horizontal battens are required for slopes over 7:12.
e. Perimeter fastening areas include three tile courses but not less than 36 inches from either side of hips or ridges and edges of eaves and_gable_ rakes.
f._ Vasd_ shall be determined in accordance with Section 1609.3.1.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 pound per square foot = 4.882 kg/m2.
a. Minimum fastener size. Corrosion-resistant nails not less than No. 11 gage with5/16-inch head. Fasteners shall be long enough to penetrate into the sheathing3/4 inch or
through the thickness of the sheathing, whichever is less. Attaching wire for clay and concrete tile shall not be smaller than 0.083 inch.
b. Snow areas. Not fewer than two fasteners per tile are required or battens and one fastener.
c. Roof slopes greater than 24:12. The nose of all tiles shall be securely fastened.
d. Horizontal battens. Battens shall be not less than 1 inch by 2 inches nominal. Provisions shall be made for drainage by a riser of not less than1/8 inch at each nail or by 4-foot-
long battens with not less than a1/2-inch separation between battens. Horizontal battens are required for slopes over 7:12.
e.
Frequently asked questions
Can the 18‑inch side clearance be reduced if space is tight?
Yes — the code’s exception in § 1010.1 allows a side clearance of less than 18 inches if the Authority Having Jurisdiction approves the reduction and determines it “does not inhibit inspection, maintenance, or repair.”
Which clearance governs if the manufacturer’s instructions say something different?
Listed units must be installed with the clearances required by their listing and the manufacturer’s instructions (see § 303.1). If the listing requires greater clearances than Chapter 10, follow the listing/manufacturer.
How do I measure the top clearance for a boiler with a manhole?
Measure from the top of the boiler to the ceiling. If the boiler meets the § 1010.3 thresholds and has a manhole, provide 3 feet; if it is a large power boiler meeting § 1010.2 thresholds, provide 7 feet.
Do roof or attic installations have different access rules?
Roof and attic installations must still be accessible for service; broader access rules (e.g., platforms, service space) are in § 304.1 and related sections and may require 30‑inch working space where not otherwise specified.
If my boiler is within the § 1010.3 limits and has no manhole, what top clearance is required?
Package boilers and boilers without a top manhole that do not exceed the § 1010.3 limits require 2 feet (610 mm) from the top of the boiler to the ceiling under § 1010.4.
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