CMC · California Mechanical Code
Applicability, Standards, and Boiler Rooms
This hub summarizes CMC Chapter 10 guidance on which boilers and pressure vessels the code governs, the referenced standards that govern construction and listing, and the boiler‑room provisions for ventilation, drainage, mounting, and code coordination.
Last reviewed: July 6, 2026
Overview
This area of the California Mechanical Code covers scope and applicability for boilers and pressure vessels, the nationally recognized construction and listing standards that apply, and site requirements for boiler rooms and enclosures. The chapter opens with applicability and exclusions at §1001.1 and boiler‑room requirements at §1001.2, which make clear when the chapter governs a unit and that boiler rooms must also comply with the California Building Code .
Standards and listed‑equipment requirements are collected at §1002.0–§1002.5: pressure vessels follow ASME BPVC Section VIII.1 and boilers are installed per ASME BPVC Section I or IV or other referenced standards (for example NFPA 85 and various UL listings for oil, electric, and solid‑fuel boilers) . Practical room provisions — combustion/ventilation air, drainage, mounting, chimneys/vents, and detailed safety and control requirements — are addressed in §1001.3–§1003.0 and the remainder of Chapter 10, tying equipment construction and installation to operational safety and to other code chapters such as Chapter 7 (air) and Chapter 8 (vents) .
Because the CMC interfaces with other statewide codes (for example the California Energy Code and the Building Code for mechanical rooms and ductwork), designers and reviewers should use these sections as the primary reference for selection, installation, and room design while checking referenced standards and local Authority Having Jurisdiction requirements for exceptions and OSHPD hospital provisions .
In this section
- Boiler room requirements: clearances, ventilation, drainage and mounting
- Listing and labeling requirements for oil, electric, and solid-fuel boilers
- When does Chapter 10 (Boilers and Pressure Vessels) apply — what is excluded?
- Which construction standards must boilers and pressure vessels meet (ASME, NFPA, etc.)?
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 938.1 High 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
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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 § 2.1 High 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.
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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 § 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 § 932.3 High relevance — show source text
932.3 Access, Inspection, and Repair. . . 213
932.4 Installation . . . . . . . . . . . . . . . . . . 213
933.0 Refrigeration Appliances . . . . . . . 213
933.1 Self-Contained Refrigerators and Freezers . . . . . . . . . . . . . . . . 213
933.2 Unit Coolers . . . . . . . . . . . . . . . . . 214
933.3 Self-Contained Mechanical
Refrigeration Systems . . . . . . . . . 214
934.0 Ductless Mini-Split Systems Installation . . . . . . . . . . . . . . . . . . 214
934.1 General. . . . . . . . . . . . . . . . . . . . . 214
935.0 Air Filter Appliances . . . . . . . . . . . 214
935.1 Electrostatic Air Cleaners . . . . . . . 214
935.2 High-Efficiency Particulate Air Filter Units . . . . . . . . . . . . . . . . 214
936.0 Gaseous Hydrogen Systems . . . . 214
936.1 General. . . . . . . . . . . . . . . . . . . . . 214
937.0 Compressed Natural Gas (CNG) Vehicular Fuel Systems . . . . . . . . 214
937.1 General. . . . . . . . . . . . . . . . . . . . . 214
938.0 Dehumidifiers . . . . . . . . . . . . . . . . 214
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
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TABLE OF CONTENTS
1001.6 Chimneys or Vents . . . . . . . . . . . . 217
1002.0 Standards . . . . . . . . . . . . . . . . . . . 217
1002.1 General. . . . . . . . . . . . . . . . . . . . . 217
CMC § 408.2.1 High relevance — show source text
408.2.1 All air-ventilation systems shall comply with code requirements of this section and shall have filter bank efficiencies as listed in Table 4-B.
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VENTILATION AIR
410.3.2 Special Standards for Use with Strong Oxidants. Fume hoods and their associated equipment in the air stream intended for use with perchloric acid and other strong oxidants shall be constructed of stainless steel or other material consistent with special exposures. Hoods and equipment shall be provided with a water wash and drain system to permit periodic flushing of duct and hood. When perchloric acid or other strong oxidants are only transferred from one container to another, stan- dard laboratory fume hoods and the associated equip- ment may be used in lieu of stainless steel construction.
410.3.3 Special Standards for Use with Infectious or Radioactive Materials. Each hood shall have a minimum face velocity of 90 to 110 feet per minute (0.45 to 0.56 meters per second) with suitable pressure-inde- pendent air-modulating devices and alarms to alert staff of fan shutdown or loss of airflow. Each hood shall have filters with a 99.97 percent efficiency (based on the DOP test method) in the exhaust stream and be designed and equipped to permit the safe removal, disposal, and replacement of contaminated filters. Filters shall be as close to the hood as practical to minimize duct contam- ination. Fume hoods intended for use with radioactive isotopes shall be constructed of stainless steel or other material suitable for the particular exposure.
411.0 Kitchen and Dining Areas. [OSHPD 1, 2, 3, 4 & 5]
411.1 The air from dining areas may be used to ventilate the food preparation areas only after it has passed through a fil- ter with at least an 80 percent average efficiency based on ASHRAE 52.2 or a minimum efficiency reporting value (MERV) of 13, based on ASHRAE 52.2.
Exception: For skilled nursing facilities, intermediate care facilities and correctional treatment centers, the air from dining area may be used to ventilate food preparation areas only after it has passed through a filter with a 50 percent average effi- ciency based on ASHRAE 52.2 or a minimum efficiency report- ing value (MERV) of 10, based on ASHRAE 52.2.
412.0 Boiler, Mechanical, and Electrical Rooms.
[OSHPD 1, 2, 3, 4 & 5]
412.1 Boiler, heater and electrical equipment rooms shall be provided with outdoor air so as to maintain combustion rates of equipment and temperatures in the rooms and in adjoining areas as rated in this chapter.
412.2 Floor surfaces in occupied spaces above such rooms should not exceed a temperature of 85°F (29.4°C), and suit- able insulation may be required.
413.0 Odorous Rooms. [OSHPD 1, 2, 3, 4 & 5]
CMC § 0.14 Medium relevance — show source text
(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.
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.
CMC § 90.1 Medium relevance — show source text
(2) Systems serving zones where specific humidity levels are required, such as museums and hospitals, and approved by the Authority Having Jurisdiction or required by accreditation standards, and where humidistatic controls are capable of and configured to maintain a dead band of at least 10 percent relative humidity where no active humidification or dehumidification takes place.
(3) Systems serving zones where humidity levels are required to be maintained with precision of not more than ±5 percent relative humidity to comply with applicable codes or accreditation standards or as approved by the Authority Having Jurisdiction.
[ASHRAE 90.1:6.4.3.6.1]
E 503.4.6.7.2 Humidification. Humidistatic controls shall not use fossil fuel or electricity to produce relative humidity above 30 percent in the warmest zone served by the system.
Exceptions:
(1) Systems serving zones where specific humidity levels are required, such as museums and hospitals, and approved by the Authority Having Jurisdiction or required by accreditation standards, and where humidistatic controls are capable of and configured to maintain a dead band of at least 10 percent relative humidity where no active humidification or dehumidification takes place.
TABLE E 503.4.6.4.2 MAXIMUM DAMPER LEAKAGE [1, 2]
(cubic foot per minute per square foot) at 1.0 inch water gauge
[ASHRAE 90.1: TABLE 6.4.3.4.3]
Col1 OUTDOOR AIR INTAKE (CFM/ft2) Col3 EXHAUST/RELIEF (CFM/ft2) Col5 CLIMATE ZONE NONMOTORIZED1 MOTORIZED NONMOTORIZED3 MOTORIZED 0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2 Any height 20 4 20 4 3 3 3 3 3 Any height 20 10 20 10 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C Fewer than three stories 204 10 20 10 Three or more stories 204 10 204 10 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 Fewer than three stories 204 4 20 4 Three or more stories 204 4 204 4 CMC § 317.3 Medium relevance — show source text
317.3 Open Trenches. Excavations required to be made for the installation of a mechanical system or part thereof, within the walls of a building, shall be open trench work and shall be kept open until it has been inspected, tested, and accepted.
317.4 Excavations. Excavations shall be completely backfilled as soon after inspection as practicable. Precaution shall be taken to ensure compactness of backfill around piping without damage to such piping. Trenches shall be backfilled in thin layers to 12 inches (305 mm) above the top of the piping with clean earth, which shall not contain stones, boulders, cinderfill, frozen earth, construction debris, or other materials that will damage or break the piping or cause corrosive action. Mechanical devices such as bulldozers, graders, etc., shall be permitted to then be used to complete backfill to grade. Fill shall be properly compacted. Precautions shall be taken to ensure permanent stability for pipe laid in filled or made ground.
318.0 Scope. 318.1 Applicability. This part is applicable to health facil- ities regulated by OSHPD.
Note: This section has no corresponding provisions in the UMC. For the scope and authority of each state agency, refer to Chapter 1. 318.2 Services/Systems and Utilities. Refer to Section 1224.4.1, 1225.2.1 and 1228.4.1.1 of the California Building Code.
319.0 Steam and Hot-Water Systems. 319.1 Requirements for Hospitals and Optional Serv- ices Provided in Correctional Treatment Centers.
[OSHPD 1, 1R, 4 & 5]
319.1.1 Boilers shall have the capacity, based upon the rest ratings published by the Hydronics Institute or another acceptable national standard to supply the nor- mal operating requirements of all connected systems and equipment.
319.1.2 A minimum of two boilers shall be provided. The arrangement of boilers shall be based on the capacity and capability of a boiler or boilers to operate all sys- tems during-periods of breakdown or maintenance of any one boiler.
319.1.3 Boiler systems providing space heating shall be designed to maintain a minimum temperature of 60 ° F (15.6 ° C) in general patient areas and the temperatures specified in Table 4-A for sensitive areas during periods of breakdown or maintenance of any one boiler.
319.1.4 Boiler feed pumps, condensate return pumps, fuel oil pumps, and heating circulating pumps shall be connected and installed to provide standby service in the
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GENERAL REGULATIONS
CMC § 120.4 Medium relevance — show source text
Nonresidential and hotel/motel buildings shall comply with the applicable requirements of Sections 120.4(a) through 120.4(g).
Exception to Section 120.4: Systems serving healthcare facilities shall comply with the applicable requirements of the California Mechanical Code.
(a) CMC compliance. All air distribution system ducts and plenums, including but not limited to building cavities, mechanical closets, air-handler boxes and support platforms used as ducts or plenums, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0, and 605.0, and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible, 3rd Edition incorporated herein by reference. Connections of metal ducts and the inner core of flexible ducts shall be mechanically fastened. Openings shall be sealed with mastic, tape, aerosol sealant or other duct-closure system that meets the applicable requirements of UL 181, UL 181A, or UL 181B. 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.
Portions of supply-air and return-air ducts conveying heated or cooled air located in one or more of the following spaces shall be insulated to a minimum installed level of R-8:
Outdoors; or
In a space between the roof and an insulated ceiling; or
In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces; or
In an unconditioned crawlspace; or
In other unconditioned spaces.
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NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS
Portions of supply-air ducts that are not in one of these spaces, including ducts buried in concrete slab, shall be insulated to a minimum installed level of R-4.2 or be enclosed in directly conditioned space.
(b) Duct and plenum materials.
- Factory-fabricated duct systems. A. All factory-fabricated duct systems shall comply with UL 181 for ducts and closure systems, including collars, connections and splices, and be labeled as complying with UL 181. UL 181 testing may be performed by UL laboratories or a laboratory approved by the Executive Director. B. All pressure-sensitive tapes, heat-activated tapes, and mastics used in the manufacture of rigid fiberglass ducts shall comply with UL 181 and UL 181A. C. All pressure-sensitive tapes and mastics used with flexible ducts shall comply with UL 181 and UL 181B. D. All ductwork and plenums with pressure class ratings shall be constructed to Seal Class A. Joints and seams of duct systems and their components shall not be sealed with cloth-back rubber adhesive duct tapes unless such tape is used in combination with mastic and drawbands.
Exception to Section 120.4(b)1D: Ductwork located in occupied space and exposed to view is not required to meet Seal Class A.
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]
»
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 § 304.8 Medium relevance — show source text
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
1112.12.5 Simultaneous Operation. When outlets of two or more relief devices or fusible plugs, which are
TABLE 1112.12.4
ATMOSPHERIC PRESSURE AT NOMINAL INSTALLATION ELEVATION ( Pa )
[ASHRAE 15: TABLE 9-2]
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
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REFRIGERATION
1113.2 Type of Protection. Pressure vessels with an internal gross volume of 3 cubic feet (0.1 m [3] ) or less shall use one or more pressure relief devices or a fusible plug. Pressure vessels of more than 3 cubic feet (0.1 m [3] ) but less than 10 cubic feet (0.28 m [3] ) internal gross volume shall use one or more pressure relief devices. Fusible plugs shall not be used.
[ASHRAE 15:9.7.2.1, 9.7.2.2]
1113.3 Discharging into Lowside of System. For pressure-relief valves discharging into the lowside of the system, a single relief valve (not rupture member) of the required relieving capacity shall not be used on vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume except under the conditions permitted in Section 1112.11.3. [ASHRAE 15:9.7.3]
1113.4 Parallel Pressure-Relief Devices. Two or more
pressure-relief devices in parallel to obtain the required capacity shall be considered as one pressure-relief device. The discharge capacity shall be the sum of the capacities required for each pressure vessel being protected.
1113.5 Discharge Capacity. The minimum required discharge capacity of the pressure-relief device or fusible plug for a pressure vessel shall be determined in accordance with ASHRAE 15.
1113.6 Three-Way Valve. Pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume shall use one or more rupture member(s) or dual pressure-relief valves where discharging to the atmosphere. Dual pressure-relief valves shall be installed with a three-way valve to allow testing or repair. Where dual relief valves are used, the valve shall comply with Section 1113.5.
Exception: A single relief valve shall be permitted on pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume where in accordance with the following conditions:
(1) The relief valves are located on the lowside of the sys tem.
(2) The vessel is provided with shutoff valves designed to allow pumpdown of the refrigerant charge of the pressure vessel.
(3) Other pressure vessels in the system are separately protected in accordance with Section 1113.1. [ASHRAE 15:9.7.2.3]
1114.0 Special Discharge Requirements.
CMC § 503.5.6.5 Medium relevance — show source text
covered by Section E 503.5.6.5 and having a fan nameplate electrical input power of less than 180 W or having a motor nameplate horsepower less than
1 / 12 hp (62.1 W) shall meet the fan efficacy requirements specified in ASHRAE 90.1. [ASHRAE 90.1:6.5.3.7]
E 503.5.6.7 Ventilation Design. The required minimum outdoor air rate is the larger of the minimum outdoor air rate or the minimum exhaust air rate
required by Chapter 4, ASHRAE 62.1, ASHRAE 62.2, ASHRAE/ASHE 170, or applicable codes or accreditation standards. Outdoor air ventilation systems shall comply with one of the following:
(1) Design minimum system outdoor air provided shall not exceed 135 percent of the required minimum outdoor air rate.
(2) Dampers, ductwork, and controls shall be provided that allow the system to supply no more than the required minimum outdoor air rate with a single setpoint adjustment.
(3) The system includes exhaust air energy recovery complying with Section E 503.5.10.1.
[ASHRAE 90.1:6.5.3.8]
E 503.5.6.8 Occupied-Standby Controls. Zones serving only rooms that are required to have automatic partial OFF or automatic full OFF lighting controls in accordance with ASHRAE 90.1, where the Chapter 4 or ASHRAE 62.1 occupancy category permits ventilation air to be reduced to zero when
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438 2025 CALIFORNIA MECHANICAL CODE
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APPENDIX E
TABLE E 503.5.6.5(1) MINIMUM AVERAGE FULL-LOAD EFFICIENCY FOR POLYPHASE SMALL ELECTRIC MOTORS* [ASHRAE 90.1: TABLE 10.8-3] Col2 Col3 Col4 FULL-LOAD EFFICIENCY, % FULL-LOAD EFFICIENCY, % FULL-LOAD EFFICIENCY, % FULL-LOAD EFFICIENCY, % NUMBER OF POLES OPEN MOTORS OPEN MOTORS OPEN MOTORS NUMBER OF POLES 2 4 6 SYNCHRONOUS SPEED (rpm) 3600 1800 1200 MOTOR SIZE (hp) EFFICIENCY, % EFFICIENCY, % EFFICIENCY, % 0.25 65.6 69.5 67.5 0.33 69.5 73.4 71.4 0.50 73.4 78.2 75.3 0.75 76.8 81.1 81.7 1 77.0 83.5 82.5 1.5 84.0 86.5 83.8 2 85.5 86.5 N/A 3 85.5 86.9 N/A For SI units: 1 horsepower = 0.746 kW
Frequently asked questions
Which boilers or pressure vessels are excluded from Chapter 10?
Chapter 10 lists specific exceptions in §1001.1 — small listed potable water heaters, certain unfired vessels, portable containers, federally inspected or licensed boilers, refrigeration pressure vessels (Chapter 11), and other limited‑volume vessels are excluded as described in §1001.1 .
What mandatory standards must I follow for boiler construction and pressure vessels?
Pressure vessels must be built per ASME BPVC Section VIII.1; boilers must comply with ASME BPVC Section I or IV or other listed standards such as NFPA 85, and fuel‑specific equipment must meet listing/installation standards (e.g., UL and NFPA references in §1002.0–§1002.5) .
What room provisions are required for boiler installations?
Boiler rooms must provide combustion and ventilation air per Chapter 7, have approved drainage for maintenance discharges, be mounted and anchored per §1001.4–§1001.6, and meet the California Building Code requirements for enclosures and clearances noted in §1001.2 .
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