CMC · California Mechanical Code

Which construction standards must boilers and pressure vessels meet (ASME, NFPA, etc.)?

Pressure vessels must be built to ASME BPVC Section VIII.1; boilers must meet ASME BPVC Section I or IV or NFPA 85. Oil boilers need UL 726 listing and NFPA 31 installation; electric boilers need UL 834; solid‑fuel boilers need UL 2523 plus manufacturer instructions (CMC **§ 1002.1–§ 1002.4**) .

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Last reviewed: July 6, 2026

What the code requires — plain English

  • Pressure vessels must be constructed and designed to the ASME Boiler & Pressure Vessel Code (BPVC) Section VIII.1 — this is the controlling requirement for vessels under the CMC (§ 1002.1 ).
  • Boilers must be constructed, designed, and installed in accordance with one of: ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85 — also from § 1002.1 .
  • The CMC then adds specific listing/installation standards for oil‑burning, electric, and solid‑fuel‑fired boilers in § 1002.2–§ 1002.4 .

The single most important rule: Pressure vessels follow ASME BPVC Section VIII.1; boilers must follow ASME BPVC Section I or IV or NFPA 85 — check the boiler or vessel’s listing and installation instructions to confirm compliance. § 1002.1

Requirements in detail

Pressure vessels (what to check)

  • Required standard: ASME BPVC Section VIII.1. See § 1002.1 .
  • Practical check: manufacturer documentation, nameplate stamping and construction records should reference ASME BPVC Section VIII.1.

Boilers — general (what to check)

  • Boiler construction/design/install must comply with one of: ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85, per § 1002.1 .
  • Practical check: verify the boiler’s listing label and the installation instructions point to one of those three standards.

Oil‑burning boilers

  • Listing & labeling: Must be listed and labeled to UL 726 (fuel-oil-fired boilers) — § 1002.2.1 .
  • Installation: Tanks, piping, and valves for oil‑burning boilers must be installed per NFPA 31 — § 1002.2.2 .

Electric boilers

  • Listing & labeling: Electric boilers must be listed and labeled to UL 834 — § 1002.3 .

Solid‑fuel‑fired boilers

  • Must comply with UL 2523 and be installed in accordance with the manufacturer’s installation instructions — § 1002.4 .

Decision table — at-a-glance

Equipment / decision dimension Required standard(s) Typical scope (what this covers) Code Reference
Pressure vessel (unfired/fired pressure containers) ASME BPVC Section VIII.1 Materials, construction, welding qualifications, stamping, pressure testing § 1002.1
Boiler — power/steam/hot‑water (general) ASME BPVC Section I or ASME BPVC Section IV or NFPA 85 Boiler construction, design, and installation for the applicable boiler category § 1002.1
Oil‑burning boiler (listing) UL 726 Factory listing & labeling for oil‑fired boilers § 1002.2.1
Oil‑burning boiler (installation) NFPA 31 Tanks, piping, valves, and fuel‑oil system installation § 1002.2.2
Electric boiler UL 834 Product listing & electrical safety labeling for electric boilers § 1002.3
Solid‑fuel‑fired boiler UL 2523 + manufacturer instructions Product listing and installation instructions for solid‑fuel appliances § 1002.4

Exceptions & special cases

  • The CMC chapter on boilers and pressure vessels has broader applicability and separate exemptions elsewhere (for example, certain small potable water heaters and small unfired pressure vessels are excluded in § 1001.1); consult that section when assessing applicability. § 1001.1 .
  • Solid‑fuel‑fired boilers specifically require compliance with UL 2523 and also the manufacturer’s installation instructions — so even if UL compliance is present, follow the manufacturer for clearances and installation details (§ 1002.4 .
  • For oil systems, the code separates product listing (UL) from system installation (NFPA 31) — you must meet both the listing and the NFPA installation standard (§ 1002.2.1, § 1002.2.2 ).

Common mistakes

  • Assuming “ASME = OK for everything.” The CMC requires ASME BPVC Section VIII.1 for pressure vessels but boilers must comply with Section I, Section IV, or NFPA 85 — verify which document the appliance is listed to, per § 1002.1 .
  • Installing oil tanks/piping without checking NFPA 31 installation requirements. Even a UL‑listed oil boiler still requires NFPA 31‑compliant tanks/piping/valves (§ 1002.2.1, § 1002.2.2 ).
  • Relying on generic “manufacturer instructions” for listing: the code explicitly requires specific listings (UL numbers) for electric and oil/solid‑fuel boilers; don’t substitute them. See § 1002.2.1, § 1002.3, § 1002.4 .
  • Skipping nameplate verification — always confirm the appliance plate or documentation references the required standard (ASME/NFPA/UL) listed in the CMC.

Worked example (concrete scenario)

Scenario: A mechanical contractor is installing a 150‑gallon unfired pressure tank that will operate at a maximum working pressure of 120 psi, and an adjacent oil‑fired hydronic boiler rated 200,000 Btu/h.

  1. Pressure tank: because it is a pressure vessel, the contractor must ensure construction and design follow ASME BPVC Section VIII.1. Confirm the tank’s nameplate or manufacturer documentation references ASME BPVC Section VIII.1 and that construction/testing records are available — per § 1002.1 .
  2. Oil‑fired boiler: confirm the boiler is listed and labeled to UL 726 (product listing) — per § 1002.2.1 .
  3. Oil fuel system: install tanks, piping, and valves in accordance with NFPA 31 (fuel‑oil installation standard) — per § 1002.2.2 .
  4. Documentation: keep the UL/ASME certificates and NFPA 31 compliance documentation with the job file and present them at inspection; the Authority Having Jurisdiction will require proof consistent with the CMC (see operation/inspection sections for jurisdictional oversight) — see § 1002.1 and related inspection/operation requirements referenced elsewhere in Chapter 10 .

Related provisions (CMC sections to consult)

  • § 1002.1 — General standards for boilers and pressure vessels (ASME / NFPA references) .
  • § 1002.2 — Oil‑burning boilers: UL 726 listing and NFPA 31 installation requirements .
  • § 1002.3 — Electric boilers: UL 834 listing requirement .
  • § 1002.4 — Solid‑fuel‑fired boilers: UL 2523 and manufacturer instructions .
  • § 1001.1 — Applicability and exemptions for Chapter 10 (useful to determine when Chapter 10 applies) .
  • § 1003.1 — Safety requirements and nationally recognized standards referenced for installation (see Chapter 10 detail) .

If you need the exact UL or ASME edition/year recognized in your jurisdiction (some jurisdictions adopt specific editions), that detail is not shown in the controlling sections retrieved here; you should confirm edition/version via the referenced standards table or the Authority Having Jurisdiction. The sections above state which standard documents are required but do not specify edition years in the excerpt provided § 1002.1–§ 1002.4 .

Code references

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

  • CMC § 1001.3 High relevance — show source text

    1001.3 Air for Combustion and Ventilation. Air for combustion and ventilation shall be provided in accordance with Chapter 7.

    1001.4 Drainage. For heating or hot-water-supply boiler applications, the boiler room shall be equipped with a floor drain or other approved means for disposing of the accumulation of liquid wastes incident to cleaning, recharging, and routine maintenance. No steam pipe shall be directly connected to a part of a plumbing or drainage system, nor shall a water having a temperature above 140°F (60°C) be discharged under pressure directly into a part of a drainage system. Pipes from boilers shall discharge by means of indirect waste piping as determined by the Authority Having Jurisdiction or the boiler manufacturer’s instructions.

    1001.5 Mounting. Equipment shall be set or mounted on a level base capable of supporting and distributing the weight contained thereon. Boilers, tanks, and equipment shall be securely anchored to the structure. Equipment requiring vibration isolation shall be installed as designed by a registered design professional and approved by the Authority Having Jurisdiction.

    1001.5.1 Floors. Boilers shall be mounted on floors of noncombustible construction unless listed for mounting on combustible flooring. 1001.6 Chimneys or Vents. Boilers shall be connected to a chimney or vent, as provided for other fuel-burning equipment in Chapter 8 of this code.

    1002.0 Standards.

    1002.1 General. Pressure vessels shall be constructed and designed in accordance with the ASME Boiler & Pressure Vessel Code (BPVC) Section VIII.1. Boilers shall be constructed, designed, and installed in accordance with one of the following: (1) ASME BPVC Section I (2) ASME BPVC Section IV (3) NFPA 85 1002.2 Oil-Burning Boilers. Oil-burning boilers shall comply with Section 1002.2.1 and Section 1002.2.2. 1002.2.1 Listing & Labeling. Oil-burning boilers shall be listed and labeled in accordance with UL 726.

    1002.2.2 Installation. Tanks, piping, and valves for oil-burning boilers shall be installed in accordance with NFPA 31.

    1002.3 Electric Boilers. Electric boilers shall be listed and

    labeled in accordance with UL 834.

    1002.4 Solid-Fuel-Fired Boilers. Solid-fuel-fired boilers shall comply with UL 2523 and shall be installed in accordance with the manufacturer’s installation instruc tions.

    1002.5 Dual Purpose Water Heaters. Water heaters utilized for combined space- and water-heating applications shall comply with the standards referenced in Table 1203.2, and shall be installed in accordance with the manufacturer’s

    installation instructions.

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    BOILERS AND PRESSURE VESSELS

    1003.0 Detailed Requirements.

    1003.1 Safety Requirements. The construction of boilers and pressure vessels and the installation thereof shall be in accordance with minimum requirements for safety from structural and mechanical failure and excessive pressures as established by the Authority Having Jurisdiction in accordance with nationally recognized standards.

  • CMC § 1102.3 High relevance — show source text

    Chapter 10 Boilers and Pressure Vessels. Chapter 10 regulates the construction, installation, operation, repair, and alteration of boilers and pressure vessels. The safety provisions within this chapter address controls and limit devices for automatic boilers, methods of determining expansion tank capacities, discharge piping, relief valves, shutoff valves, gas-pressure and combustion regulators, and inspections and tests. Potable water heaters are free from the requirements of Chapter 10 as they are within the scope of the Uniform Plumbing Code (UPC).

    Pressure vessels store large amounts of energy and must comply with ASME Boiler and Pressure Vessel Code (BPVC) Section VIII.1. The stored energy must be contained to prevent disastrous failures. Boilers must comply with ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85. Installing a safety relief valve and expansion tank prevents pressures in the tank from exceeding the design threshold.

    Chapter 11 Refrigeration. Chapter 11 regulates the design, installation, and construction requirements of refrigeration systems and the installation and construction of cooling towers. Refrigeration is a method used for achieving heat transfer to cool spaces. Refrigerants are the most common medium used to transfer the heat energy from the low-temperature level to the high-temperature level. Table

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    FORMAT OF THE UNIFORM MECHANICAL CODE

    1102.3 lists the most commonly used refrigerants and is labeled by a number. The concentration limits provided in Table 1102.3 are useful for the quantity of refrigerant required to cool a volume of space safely.

    A major milestone reached in the industry was the introduction of lower flammability refrigerants such as A2L and B2L. The industry’s concerns to address lower Global Warming Potential (GWP) refrigerants led to the development of these lower flammability refrigerants. Chapter 11 does not only include these lower flammability refrigerants in Table 1102.3, but it also contains specific A2L and B2L provisions to address the precautions necessary for the proper use of these products. In particular, high-probability systems using A2L refrigerants for human comfort applications are covered by provisions which include refrigerant concentration limits, mechanical ventilation, ignition sources, compressors and pressure vessels, and refrigerant sensors.

    In addition, Chapter 11 addresses other minimum requirements for refrigeration systems such as refrigeration machinery rooms (including ventilation), relief valves, and pressure vessels. Apart from refrigerants, the chapter also addresses minimum requirements for systems that use other mediums such as ammonia and brine systems. For ammonia systems, such systems are required to comply with IIAR 2, IIAR 3, IIAR/ANSI 4, IIAR 5, and IIAR 6.

    Chapter 12 Hydronics. Chapter 12 regulates hydronic systems that are part of heating, cooling, ventilation, and conditioning systems. Such piping systems include steam, hot water, radiant heating and cooling, chilled water, steam condensate, condenser water, ground source heat pump systems, snow and ice melt systems, ambient temperature loops, and district ambient temperature loops. Provisions within this chapter addressing ground source heat pumps and ambient temperature loops apply to the hydronic portions of the system. Geothermal energy systems, including ground source heat pumps and ambient temperature loops, are regulated by Chapter 17.

  • CMC § 2025 High relevance — show source text

    Chapter 7 Combustion Air. Chapter 7 regulates combustion air requirements for ventilation and dilution of flue gases for appliances installed in buildings. Fuel-gas appliances not regulated by chapter include direct vent appliances and Type I clothes dryers. Makeup air requirements for Type I clothes dryers are located in Chapter 5. Chapter 7 provides acceptable methods for supplying satisfactory combustion air to ensure proper combustion. Combustion air can be supplied by using indoor combustion air or by introducing the air from the outdoors.

    Combustion is the rapid oxidation of fuel to release energy. The oxygen required to release the energy from the fuel normally comes from the air. Incomplete combustion of fuel occurs when inadequate oxygen is provided to the appliance. Combustion is needed to provide ventilation cooling for the casing and internal controls. When a lack of oxygen occurs, some of the carbon is not oxidized, and carbon monoxide forms.

    Chapter 8 Chimneys and Vents. Chapter 8 regulates the installation, design, and construction of venting systems for fuel-burning appliances. The provisions addressed within this chapter follow procedures an installer would use to design or evaluate a venting system. Many requirements apply to the design and construction of venting systems, chimneys, installation of gas vents, and the sizing of venting system for a Category I appliance. Sizing venting systems require rigorous engineering calculations. However, the venting sizing requirements and sizing tables in this chapter already perform the calculations for the benefit of the end user.

    Combustion appliances produce products of incomplete combustion, including potentially harmful carbon monoxide (CO). It is desirable to vent these products to the outdoors. Although the gas is clean-burning fuel, the products of combustion must not be allowed to collect within a building.

    Chapter 9 Installation of Specific Appliances. Chapter 9 regulates the minimum requirements for the design, construction and installation of specific appliances. The provisions address the minimum requirements for gas-fired appliances, oil-fired appliances, wood-fired appliances, and electric-type appliances. In addition to the requirements of this chapter, appliances are also required to comply with the general requirements of Chapter 3.

    Chapter 10 Boilers and Pressure Vessels. Chapter 10 regulates the construction, installation, operation, repair, and alteration of boilers and pressure vessels. The safety provisions within this chapter address controls and limit devices for automatic boilers, methods of determining expansion tank capacities, discharge piping, relief valves, shutoff valves, gas-pressure and combustion regulators, and inspections and tests. Potable water heaters are free from the requirements of Chapter 10 as they are within the scope of the Uniform Plumbing Code (UPC).

    Pressure vessels store large amounts of energy and must comply with ASME Boiler and Pressure Vessel Code (BPVC) Section VIII.1. The stored energy must be contained to prevent disastrous failures. Boilers must comply with ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85. Installing a safety relief valve and expansion tank prevents pressures in the tank from exceeding the design threshold.

    Chapter 11 Refrigeration. Chapter 11 regulates the design, installation, and construction requirements of refrigeration systems and the installation and construction of cooling towers. Refrigeration is a method used for achieving heat transfer to cool spaces. Refrigerants are the most common medium used to transfer the heat energy from the low-temperature level to the high-temperature level. Table

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    FORMAT OF THE UNIFORM MECHANICAL CODE

  • CMC § 1002.2.2 High relevance — show source text

    1002.2.2 Installation. Tanks, piping, and valves for oil-burning boilers shall be installed in accordance with NFPA 31.

    1002.3 Electric Boilers. Electric boilers shall be listed and

    labeled in accordance with UL 834.

    1002.4 Solid-Fuel-Fired Boilers. Solid-fuel-fired boilers shall comply with UL 2523 and shall be installed in accordance with the manufacturer’s installation instruc tions.

    1002.5 Dual Purpose Water Heaters. Water heaters utilized for combined space- and water-heating applications shall comply with the standards referenced in Table 1203.2, and shall be installed in accordance with the manufacturer’s

    installation instructions.

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    BOILERS AND PRESSURE VESSELS

    1003.0 Detailed Requirements.

    1003.1 Safety Requirements. The construction of boilers and pressure vessels and the installation thereof shall be in accordance with minimum requirements for safety from structural and mechanical failure and excessive pressures as established by the Authority Having Jurisdiction in accordance with nationally recognized standards.

    1003.2 Controls. Required electrical, mechanical, safety, and operating controls shall carry the approval of an approved testing agency or be accepted by the Authority Having Jurisdiction. Electrical controls shall be of such design and construction as to be suitable for installation in the environment

    in which they are located.

    1003.2.1 Automatic Boilers. Automatic boilers shall

    be equipped with controls and limit devices in accordance with ASME CSD-1 or Table 1003.2.1.

    The Authority Having Jurisdiction shall have the authority to approve solid-fuel-fired boilers that comply with the safety requirements for automatic gas fired boilers or oil fired boilers.

    1003.3 Gauges. Steam boilers shall be provided with a pressure gauge and a water level glass. Water boilers shall be provided with a pressure gauge and a temperature gauge. Automatic boilers shall be equipped with the following gauges, as applicable :

    (1) Oil temperature

    (2) Oil suction pressure

    (3) High and low gas pressure

    (4) Stack temperature

    (5) Windbox pressure

    1003.4 Stack Dampers. Stack dampers on boilers fired with oil or solid fuel shall not close off more than 80 percent of the stack area. Operative dampers shall not be placed within a stack, flue, or vent of a gas-fired boiler.

    Exception: Automatic boilers with prepurge, automatic draft control, and interlock.

    1003.5 Welding. Welding on pressure vessels shall be done by certified welders in accordance with nationally recognized standards.

    1004.0 Expansion Tanks.

    1004.1 General. An expansion tank shall be installed in a hot-water-heating system as a means for controlling increased pressure caused by thermal expansion. Expansion tanks shall be of the closed or open type and securely fastened to or supported by the structure. Tanks shall be rated for the pressure of the system. Supports shall be capable of carrying twice the weight of the tank filled with water without placing a strain on connecting piping.

    Hot-water-heating systems incorporating hot water tanks or fluid relief columns shall be installed to prevent freezing under normal operating conditions.

  • CMC § 1308.9.2 Medium relevance — show source text

    1308.9.2 Construction and Installation. All overpressure protection devices shall meet the following requirements:

    (1) Be constructed of materials so that the operation of the device is not impaired by corrosion of external parts by the atmosphere or of internal parts by the gas.

    (2) Be designed and installed so they can be operated to determine whether the valve is free. The devices shall also be designed and installed so they can be tested to determine the pressure at which they operate and be examined for leakage when in the closed position. [NFPA 54:5.8.4]

    1308.9.3 External Control Piping. External control piping shall be designed and installed so that damage to the control piping of one device does not render both the regulator and the overpressure protective device inoperative. [NFPA 54:5.8.5]

    1308.9.4 Setting. Each pressure limiting or pressure relieving device shall be set so that the gas pressure supplied to the connected appliance(s) does not exceed the limits specified in Section 1308.8 and Section 1308.8.1.

    [NFPA 54:5.8.6]

    1308.9.5 Unauthorized Operation. Where unauthorized operation of any shutoff valve could render a pres

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    FUEL GAS PIPING

    TABLE 1308.12

    MANUAL GAS VALVE STANDARDS

    [NFPA 54: TABLE 5.11]

    SHUTOFF VALVE
    APPLICATION    		 STANDARDS




    Appliance shutoff
    valve up to1_/_2 psi    		 CSA/ANSI Z21.15/CSA 9.1




    Appliance shutoff
    valve up to1_/_2 psi    		 ASME B16.44




    Appliance shutoff
    valve up to1_/_2 psi    		 ASME B16.33 marked 125 G




    Appliance shutoff
    valve up to1_/_2 psi    		 CSA/ANSI LC 4/CSA 6.32



    Valve up to1_/_2 psi    		 ASME B16.44



    Valve up to1_/_2 psi    		 ASME B16.33 marked 125 G



    Valve up to1_/_2 psi    		 CSA/ANSI LC 4/CSA 6.32






    Valve up to 2 psi    		 ASME B16.44 labeled 2G






    Valve up to 2 psi    		 ASME B16.33 marked 125 G






    Valve up to 2 psi    		 CSA/ANSI LC 4/CSA 6.
  • CMC § 3-2020 Medium relevance — show source text

    3-2020|Process Piping|Piping|1308.2(9)| |ASME B36.10M-2018|Welded and Seamless Wrought Steel Pipe|Fuel Gas, Piping|1208.5.2.2| |ASME BPVC Section
    VIII.1-2021|Rules for Construction of Pressure Vessels - Division 1|Miscellaneous|505.4, 1309.5(2),
    1310.4(2), 1312.3(2)| |ASME BPVC Section IX-
    2021|Welding, Brazing, and Fusing Qualifications - Qualification
    Standard for Welding, Brazing, and Fusing Procedures;
    Welders; Brazers; and Welding, Brazing, and Fusing Operators|Miscellaneous|1322.1.1, 1322.2.1,
    1323.11| |ASPE|ASPE|ASPE|ASPE| |ASPE/ANSI 45-2018|Siphonic Roof Drainage|Storm Drainage|1106.2| |ARCSA/ASPE/ANSI 63-
    2020|Rainwater Catchment Systems|Miscellaneous|1602.1| |ASSE|ASSE|ASSE|ASSE| |ASSE 1001-2017|Atmospheric Type Vacuum Breakers|Backflow Protection|Table 603.2| |ASSE 1002-2020/ASME
    A112.1002-2020/CSA
    B125.12-2020|Anti-Siphon Fill Valves for Water Closet Tanks|Backflow Protection|413.3, Table 603.2| |ASSE 1003-2020e2|Water Pressure Reducing Valves for Potable Water Distribution
    Systems|Valves|608.2| |ASSE 1004-2017|Commercial Dishwashing Machines|Backflow Protection|414.2| |ASSE 1008-2020|Plumbing Aspects of Residential Food Waste Disposer Units|Appliances|419.1| |ASSE 1010-2004|Water Hammer Arresters|Appliances|609.11| |ASSE 1011-2017|Hose Connection Vacuum Breakers|Backflow Protection|Table 603.2|

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    REFERENCED STANDARDS

    TABLE 1701.1 (continued) REFERENCED STANDARDS

    STANDARD NUMBER STANDARD TITLE APPLICATION REFERENCED
    SECTION
    ASSE 1012-2009 Backflow Preventers with an Intermediate Atmospheric Vent Backflow Protection Table 603.2
    ASSE 1013-2021 Reduced Pressure Principle Backflow Prevention Assemblies Backflow Protection Table 603.2
    ASSE 1014-2020 Backflow Prevention Devices for Hand-Held Showers Backflow Protection 417.3
    ASSE 1015-2021 Double Check Backflow Prevention Backflow Protection Table 603.2
    ASSE 1016-2017/ASME
    A112.1016-2017/CSA
    B125.
  • CMC § 1014.0 Medium relevance — show source text

    Where subject to corrosion and construction permits, they shall be subject to inspection internally biennially.

    Inspection of boilers and pressure vessels covered by insurance shall be permitted to be made by employees of the insuring company holding commissions from the National Board of Boiler and Pressure Vessel Inspectors, subject to approval of the Authority Having Jurisdiction. Approved insuring company inspectors shall make reports on prescribed forms on inspections authorized by the Authority Having Jurisdiction. The reports shall be filed in the Authority Having Jurisdiction office. Company inspectors shall notify the Authority Having Jurisdiction of suspension of insurance because of dangerous conditions, new insurance in effect, and discontinuance of insurance

    coverage.

    1014.0 Operation and Maintenance of Boilers and Pressure Vessels.

    1014.1 General. Boilers and pressure vessels shall be operated and maintained in accordance with requirements for pro

    tection of the public established by the Authority Having Jurisdiction in accordance with nationally recognized standards.

    The Authority Having Jurisdiction shall notify the owner or authorized representative of defects or deficiencies and properly corrected. Where such corrections are not made, or where the operation of the boiler or pressure vessel is deemed unsafe by the Authority Having Jurisdiction, they shall have the authority to revoke the permit to operate the boiler or pressure vessel. Where the operation of a boiler or pressure vessel is deemed by the Authority Having Jurisdiction to constitute an immediate danger, the pressure on such boiler or pressure vessel shall be permitted to be relieved at the owner’s cost and the boiler or pressure vessel shall not thereafter be operated without the approval of the Authority Having Jurisdiction.

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    BOILERS AND PRESSURE VESSELS

    CONTROL AND LIMIT DEVICE SYSTEM DESIGN11 Col2 Col3 Required Required Required Required Required Required Required Required Required Per NFPA 85 Per NFPA 85
    APPROVED
    FUEL SHUT-
    OFF10    		 APPROVED
    FUEL SHUT-
    OFF10    		 APPROVED
    FUEL SHUT-
    OFF10    		 Not
    Required    		 Not
    Required    		 Required Required Not
    Required    		 Not
    Required    		 Not
    Required    		 Required Not
    Required    		 Per
    NFPA 85    		 Per
    NFPA 85
    STEAM
    PRESSURE
    AND LOW
    WATER
    LIMIT CON-
    TROLS9    		 STEAM
    PRESSURE
    AND LOW
    WATER
    LIMIT CON-
    TROLS9    		 STEAM
    PRESSURE
    AND LOW
    WATER
    LIMIT CON-
    TROLS9    		 Required Required Required Required Required Required Required Required Required Per
    ASME
    Power
    Boiler
    Code,
  • CMC § 1112.12.4. Medium relevance — show source text

    ( P [2] 0 P 22 ) d - ln ( P0P2 )

    f - C [2] r 6 - f

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    REFRIGERATION

    expected to operate simultaneously, connect to a common discharge pipe, the common pipe shall be sized large enough to prevent the back pressure at each pressure-relief device from exceeding the maximum allowable back pressure in accordance with Section 1112.12.4.

    [ASHRAE 15:9.7.9.3.3]

    1112.13 Rating of Pressure-Relief Device. The rated discharge capacity of a pressure-relief device expressed in pounds of air per minute (kg/s), shall be determined in accordance with ASME BPVC Section VIII.1. Pipe and fittings between the pressure-relief valve and the parts of the system it protects shall have not less than the area of the pressurerelief valve inlet area. [ASHRAE 15:9.7.6]

    1112.14 Rating of Rupture Members and Fusible Plugs. The rated discharge capacity of a rupture member or fusible plug discharging to the atmosphere under critical flow conditions, in pounds of air per minute (kg/s), shall be determined in accordance with the following formulas:

    C = 0.64 P l d [2] [Equation 1112.14(1)]

    d = 1.25 √ C / P l [Equation 1112.14(2)]

    Where:

    C = Rated discharge capacity expressed as mass flow of air, pounds per minute.

    d = Smallest of the internal diameter of the inlet pipe, retaining flanges, fusible plug, and rupture member , inches.

    For rupture members:

    [Equation 1112.14(3)]

    P1 = (rated pressure in psig x 1.1) + 14.7 psia

    For fusible plugs:

    P1 = Absolute saturation pressure corresponding to the stamped temperature melting point of the fusible plug or the critical pressure of the refrigerant used, whichever is smaller, pound-force per square inch atmosphere, psia. [ASHRAE 15:9.7.7]

    For SI units:1 pound per minute = 0.00756 kg/s

    1113.0 Overpressure Protection.

    1113.1 General. Pressure vessels shall be provided with overpressure protection in accordance with ASME BPVC Section VIII.1. Pressure vessels containing liquid refrigerant that are capable of being isolated by stop valves from other parts of a refrigerating system shall be provided with overpressure protection. Pressure relief devices or fusible plugs shall be sized in accordance with Section 1113.5. [ASHRAE 15:9.7.1, 9.7.2]

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    Unless the maximum allowable back pressure ( P0 ) is specified by the relief valve manufacturer, the following maximum allowable back pressure values shall be used for P0, where P is the set pressure and Pa is atmospheric pressure at the nominal elevation of the installation (see Table 1112.12.4):

  • CMC § 3110F.11 Medium relevance — show source text

    3110F.11 References.

    [10.1] American Society of Mechanical Engineers (ASME), 2015, ASME B31.3-2014 (ASME B31.3), “Process Piping,” New York.

    [10.2] Code of Federal Regulations (CFR), Title 33, Section 154.510 – Loading Arms (33 CFR 154.510)

    [10.3] Oil Companies International Marine Forum (OCIMF), 1999, “Design and Construction Specification for Marine Loading Arms,” 3rd ed., Witherby, London.

    [10.4] California Code of Regulations (CCR), Title 2, Division 3, Chapter 1, Article 5 – Marine Terminals Inspection and Monitoring (2 CCR 2300 et seq.)

    [10.5] American Society of Civil Engineers (ASCE), 2014, ASCE/COPRI 61-14 (ASCE/COPRI 61), “Seismic Design of Piers and Wharves”, Reston, VA.

    [10.6] American Society of Mechanical Engineers (ASME), 2013, ASME B40.100-2013 (ASME B40.100), “Pressure Gauges and Gauge Attachments,” New York.

    [10.7] National Fluid Power Association (NFPA), 2009, NFPA T3.6.7 R3-2009 (R2017) (NFPA T3.6.7 R3), “Fluid Power Systems and Products —Square Head Industrial Cylinders - Mounting Dimensions,” Milwaukee, WI.

    [10.8] California Code of Regulations (CCR), Title 24, Part 3, California Electrical Code.

    [10.9] Underwriters Laboratory, Inc., 2013, UL Standard No. 913, “Standard for Intrinsically Safe Apparatus and Associated Appa- ratus for Use in Class I, II, III, Division 1, Hazardous (Classified) Locations,” 8th ed., Northbrook, IL.

    [10.10] Code of Federal Regulations (CFR), Title 47, Part 15 – Radio Frequency Devices (47 CFR 15)

    [10.11] Code of Federal Regulations (CFR), Title 33, Section 154.500 – Hose Assemblies (33 CFR 154.500)

    [10.12] American Society of Mechanical Engineers (ASME), 2013, ASME B16.5-2013 (ASME B16.5), “Pipe Flanges and Flanged Fittings,” 13th ed., New York.

    [10.13] American Society for Testing and Materials (ASTM), 2010, ASTM F1122-04(2010) (ASTM F1122), “Standard Specification for Quick Disconnect Couplings (6 in. NPS and Smaller),” 4th ed., West Conshohocken, PA.

    [10.14] American Society of Mechanical Engineers (ASME), 2010, ASME B30.4-2010 (ASME B30.4), “Portal Tower and Pedestal Cranes,” 10th ed., New York.

    [10.15] American Society of Mechanical Engineers (ASME), 2011, ASME B30.7-2011 (ASME B30.7), “Winches,” 11th ed., New York.

  • CMC § 2.1 Medium relevance — show source text

    2.1_||||||||||X|X|X|X|X|X||||||||||

    This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.

    2025 CALIFORNIA MECHANICAL CODE 215

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

    216 2025 CALIFORNIA MECHANICAL CODE

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

    CHAPTER 10

    BOILERS AND PRESSURE VESSELS

    1001.0 General.

    1001.1 Applicability. The requirements of this chapter shall apply to the construction, installation, operation, repair, and alteration of boilers and pressure vessels. Low-pressure boilers shall comply with this chapter and Section 904.0.

    Exceptions:

    (1) Listed and approved potable water heaters with a nominal capacity not exceeding 120 gallons (454 L) and having a heat input not exceeding 200 000 British thermal units per hour (Btu/h) (58.6 kW) used for hot water supply at a pressure not exceeding 160 pounds-force per square inch (psi) (1103 kPa) and at temperatures not exceeding 210°F (99°C), in accordance with the plumbing code.

    (2) Pressure vessels used for unheated water supply, including those containing air that serves as a cushion and is compressed by the introduction of water and tanks connected to sprinkler systems.

    (3) Portable unfired pressure vessels and Interstate Commerce Commission (I.C.C.) containers.

    (4) Containers for liquefied petroleum gases, bulk oxygen, and medical gas that are regulated by the fire code.

    (5) Unfired pressure vessels in business, factory, hazardous, mercantile, residential, storage, and utility occupancies having a volume not exceeding 5 cubic feet (0.14 m [3] ) and operating at pressures not exceeding 250 psi (1724 kPa).

    (6) Pressure vessels used in refrigeration systems shall comply with Chapter 11.

    (7) Pressure tanks used in conjunction with coaxial cables, telephone cables, power cables, and other similar humidity control systems.

    (8) A boiler or pressure vessel subject to regular inspection by federal inspectors or licensed by federal authorities.

    (9) Pressure vessels used in specific appliances shall comply with Chapter 9.

    1001.2 Boiler Rooms and Enclosures. Boiler rooms and enclosures shall comply with the California Building Code .

    1001.2.1 [OSHPD 1, 1R, 2, 3, 4 & 5] In no case shall boiler room volume or clearances be reduced below those required by the conditions of the boiler listing. The boiler and the boiler room ventilation system, including fans, con- trols, and damper motors shall be on essential power when required by Section 321.0. The ventilation system shall either operate continuously, or, if interlocked with the boiler(s) it shall not interfere with the proper boiler oper- ation. Listed boilers shall be installed with clearances in accordance with the manufacturer’s instructions.

  • CMC § 938.1 Medium relevance — show source text

    938.1 General. . . . . . . . . . . . . . . . . . . . . 214

    939.0 Sauna Heaters . . . . . . . . . . . . . . . 214

    939.1 Electric Sauna Heaters. . . . . . . . . 214

    CHAPTER 10 BOILERS AND

    PRESSURE VESSELS . . . . . . . . 215

    1001.0 General. . . . . . . . . . . . . . . . . . . . . 217

    1001.1 Applicability. . . . . . . . . . . . . . . . . . 217

    1001.2 Boiler Rooms and Enclosures . . . 217

    1001.3 Air for Combustion

    and Ventilation . . . . . . . . . . . . . . . 217

    1001.4 Drainage . . . . . . . . . . . . . . . . . . . . 217

    1001.5 Mounting. . . . . . . . . . . . . . . . . . . . 217

    xxxvii

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

    TABLE OF CONTENTS

    1001.6 Chimneys or Vents . . . . . . . . . . . . 217

    1002.0 Standards . . . . . . . . . . . . . . . . . . . 217

    1002.1 General. . . . . . . . . . . . . . . . . . . . . 217

    1002.2 Oil-Burning Boilers . . . . . . . . . . . . 217

    1002.3 Electric Boilers . . . . . . . . . . . . . . . 217

    1002.4 Solid-Fuel-Fired Boilers . . . . . . . . 217

    1002.5 Dual Purpose Water Heaters . . . . 217

    1003.0 Detailed Requirements . . . . . . . . . 218

    1003.1 Safety Requirements . . . . . . . . . . 218

    1003.2 Controls . . . . . . . . . . . . . . . . . . . . 218

    1003.3 Gauges . . . . . . . . . . . . . . . . . . . . . 218

    1003.4 Stack Dampers . . . . . . . . . . . . . . . 218

    1003.5 Welding. . . . . . . . . . . . . . . . . . . . . 218

    1004.0 Expansion Tanks . . . . . . . . . . . . . 218

    1004.1 General. . . . . . . . . . . . . . . . . . . . . 218

    1004.2 Open-Type Expansion Tanks . . . . 218

    1004.3 Closed-Type Systems . . . . . . . . . 218

    1004.4 Minimum Capacity of ClosedType Tank. . . . . . . . . . . . . . . . . . . 218

    Table 1004.4(1) Expansion Tank Capacities for Gravity Hot Water Systems . . . . . 219

    Table 1004.4(2) Expansion Tank Capacities for Forced Hot Water Systems . . . . . 219

  • CMC § 26-2018 Medium relevance — show source text

    26-2018|Cast Copper Alloy Fittings for Flared Copper Tubes|Fittings|Table 604.1| |ASME B16.29-2017|Wrought Copper and Wrought Copper Alloy Solder-Joint
    Drainage Fittings – DWV|Fittings|Table 701.2| |ASME B16.33-2012
    (R2017)|Manually Operated Metallic Gas Valves for Use in Gas Piping
    Systems Up to 175 psi (Sizes NPS1⁄2 through NPS 2)|Valves|Table 1208.13| |ASME B16.34-2020|Valves-Flanged, Threaded, and Welding End|Valves|606.1| |ASME B16.42-2016|Ductile Iron Pipe Flanges and Flanged Fittings: Classes 150
    and 300|Fuel Gas Piping|1208.5.11.4| |ASME B16.44-2012
    (R2017)|Manually Operated Metallic Gas Valves for Use in Above
    Ground Piping Systems up to 5 psi|Valves|Table 1208.13| |ASME B16.47-2020|Large Diameter Steel Flanges: NPS 26 through NPS 60 Met-
    ric/Inch|Fittings|1208.5.11.2(2)| |ASME B16.50-2018|Wrought Copper and Copper Alloy Braze-Joint Pressure Fit-
    tings|Fittings|Table 604.1, 1321.1,
    1321.11| |ASME B16.51-2018|Copper and Copper Alloy Press-Connect Pressure Fittings|Fittings|Table 604.1| |ASME B31.3-2020|Process Piping|Piping|1308.2(9)| |ASME B36.10M-2018|Welded and Seamless Wrought Steel Pipe|Fuel Gas, Piping|1208.5.2.2| |ASME BPVC Section
    VIII.1-2021|Rules for Construction of Pressure Vessels - Division 1|Miscellaneous|505.4, 1309.5(2),
    1310.4(2), 1312.3(2)| |ASME BPVC Section IX-
    2021|Welding, Brazing, and Fusing Qualifications - Qualification
    Standard for Welding, Brazing, and Fusing Procedures;
    Welders; Brazers; and Welding, Brazing, and Fusing Operators|Miscellaneous|1322.1.1, 1322.2.1,
    1323.11| |ASPE|ASPE|ASPE|ASPE| |ASPE/ANSI 45-2018|Siphonic Roof Drainage|Storm Drainage|1106.2| |ARCSA/ASPE/ANSI 63-
    2020|Rainwater Catchment Systems|Miscellaneous|1602.1| |ASSE|ASSE|ASSE|ASSE| |ASSE 1001-2017|Atmospheric Type Vacuum Breakers|Backflow Protection|Table 603.2| |ASSE 1002-2020/ASME
    A112.1002-2020/CSA
    B125.12-2020|Anti-Siphon Fill Valves for Water Closet Tanks|Backflow Protection|413.3, Table 603.

Frequently asked questions

Do pressure relief valves need to follow ASME too?

Yes — overpressure protection and related sizing/requirements are generally tied to the ASME BPVC or other nationally recognized standards; pressure vessels themselves are required to conform to ASME BPVC Section VIII.1 per § 1002.1 .

If a boiler is UL‑listed, can I ignore NFPA/National standards?

No — listing (UL) and installation standards are separate. For example, oil‑burning boilers must be listed to UL 726 and their tanks/piping/valves must be installed per NFPA 31; you must meet both (§ 1002.2.1, § 1002.2.2) .

Which standard applies to an electric steam boiler?

An electric boiler must be listed and labeled in accordance with UL 834 per § 1002.3 .

Do I have to follow manufacturer instructions for solid‑fuel boilers?

Yes — § 1002.4 requires compliance with UL 2523 and installation in accordance with the manufacturer’s installation instructions .

Where do I find installation details (clearances, venting, etc.)?

The controlling sections here identify required standards and listings. Installation details such as clearances and venting are found in the appliance listing/manufacturer instructions and in other CMC chapters (e.g., ventilation and chimneys); consult the manufacturer's instructions and the applicable CMC installation chapters in addition to § 1002.1–§ 1002.4 .

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When does Chapter 10 (Boilers and Pressure Vessels) apply — what is excluded?

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California Mechanical Code