CMC · California Mechanical Code
When does Chapter 10 (Boilers and Pressure Vessels) apply — what is excluded?
Chapter 10 of the California Mechanical Code applies to boilers and pressure vessels unless the unit is specifically excluded by **§ 1001.1** — common exclusions include listed potable water heaters below **120 gallons / 200,000 Btu/h / 160 psi / 210°F**, small unfired vessels **≤ 5 cu ft** and **≤ 250 psi**, refrigeration vessels (Chapter 11), federally inspected units, and certain portable or fire‑code regulated containers. Verify the exact numeric thresholds in **§ 1001.1** when deciding which code applies.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Chapter 10 applies to the construction, installation, operation, repair, and alteration of boilers and pressure vessels, including low‑pressure boilers (which must also meet Section §904.0). The controlling provision is § 1001.1 — it sets the general scope and then lists specific exclusions. For quick planning, treat anything not listed in the exclusions of § 1001.1 as within Chapter 10 requirements.
The single most important rule: if your equipment is a boiler or pressure vessel and it is not expressly listed as excluded by § 1001.1, Chapter 10 applies.
Requirements in detail
Scope in plain language
- Chapter 10 covers boilers and pressure vessels for their full life‑cycle: construction, installation, operation, repair, and alteration. § 1001.1 is the controlling scope statement.
- Low‑pressure boilers are brought under Chapter 10 as well, with a cross‑reference to § 904.0.
Who / what is excluded (exceptions in § 1001.1)
The text of § 1001.1 lists nine exception categories. The most commonly encountered exclusions are summarized below; all items come directly from the exception list in § 1001.1.
Listed and approved potable water heaters with:
- nominal capacity not exceeding 120 gallons (454 L), and
- heat input not exceeding 200,000 Btu/h (58.6 kW), and
- used for hot water supply at pressure not exceeding 160 psi (1103 kPa) and temperature not exceeding 210°F (99°C) — these fall to the plumbing code instead of Chapter 10.
Pressure vessels used for unheated water supply (including tanks connected to sprinkler systems where air cushion is present).
Portable unfired pressure vessels and Interstate Commerce Commission (I.C.C.) containers.
Containers regulated by the fire code (e.g., containers for liquefied petroleum gases, bulk oxygen, medical gas).
Small unfired pressure vessels in common occupancies having:
- internal volume not exceeding 5 cubic feet (0.14 m³), and
- operating pressure not exceeding 250 psi (1724 kPa) — these are excluded from Chapter 10.
Pressure vessels used in refrigeration systems — those are handled by Chapter 11 instead of Chapter 10.
Pressure tanks used for telecom/power cable humidity control (coaxial, telephone, power cable humidity systems).
Equipment subject to regular federal inspection or federal licensing (i.e., federal jurisdiction).
Pressure vessels used in specific appliances that are covered by Chapter 9 (installation of specific appliances).
Decision table — which threshold matters?
| Decision dimension | Typical threshold / value | Excluded or Not? | Code Reference |
|---|---|---|---|
| Potable water heater nominal capacity | ≤ 120 gallons (454 L) | Excluded (if other limits met) | § 1001.1 |
| Potable water heater heat input | ≤ 200,000 Btu/h (58.6 kW) | Excluded (if other limits met) | § 1001.1 |
| Potable water heater pressure | ≤ 160 psi (1103 kPa) | Excluded (if other limits met) | § 1001.1 |
| Potable water heater temperature | ≤ 210°F (99°C) | Excluded (if other limits met) | § 1001.1 |
| Small unfired vessel volume | ≤ 5 cu ft (0.14 m³) | Excluded (if AND pressure ≤ 250 psi) | § 1001.1 |
| Small unfired vessel pressure | ≤ 250 psi (1724 kPa) | Excluded (if AND volume ≤ 5 cu ft) | § 1001.1 |
| Pressure vessels in refrigeration | Any size (handled by refrigeration chapter) | Excluded from Chapter 10 — use Chapter 11 | § 1001.1 (see Chapter 11 reference) |
| Federal inspection/licensing jurisdiction | N/A | Excluded from state Chapter 10 enforcement | § 1001.1 |
How to apply the exceptions (practical steps)
- Identify the equipment type: is it a boiler, pressure vessel, or a potable water heater? (Be sure to bold those terms in your project documents.)
- Check capacity, input, pressure, and temperature against the thresholds in § 1001.1 (see table above). If all relevant exception criteria are satisfied, Chapter 10 does not apply to that unit.
- If the equipment is a refrigeration pressure vessel, consult Chapter 11 instead — Chapter 10 expressly excludes refrigeration vessels.
Exceptions & special cases
- Dual applicability: Low‑pressure boilers are explicitly stated to comply with Chapter 10 and Section §904.0, so don’t assume “low‑pressure” means excluded. § 1001.1 cross‑references §904.0.
- Overlapping codes: a water heater that meets the potable‑water‑heater exception is regulated under the plumbing code rather than Chapter 10; verify listing/approval and that all numeric limits are met.
- Federal vs. state: equipment under federal inspection/licensing is not enforced by the state Chapter 10 — confirm federal jurisdiction in writing. § 1001.1 contains this exclusion.
- Refrigeration systems: pressure vessels used within refrigeration are governed by Chapter 11 — see that chapter for relief‑device and volume thresholds applicable to refrigeration vessels. § 1001.1 directs you there.
Common mistakes
- Assuming any water heater is exempt. Only listed potable water heaters that meet all the numeric limits in § 1001.1 are excluded. Don’t drop a 150‑gallon or >200,000 Btu/h heater into the exception.
- Using the “≤5 cu ft / ≤250 psi” rule without checking occupancy and whether the vessel is unfired. The small‑vessel exclusion applies to unfired pressure vessels in the listed occupancies.
- Forgetting refrigeration exemptions. Pressure vessels in refrigeration are governed by Chapter 11 — applying Chapter 10 relief‑valve tables to a refrigeration vessel is a likely error.
- Ignoring federal jurisdiction. If the unit is regularly inspected by federal inspectors or federally licensed, state Chapter 10 enforcement may not apply. Confirm with the Authority Having Jurisdiction.
Worked example — concrete scenario
Scenario A — domestic water heater:
- Equipment: listed potable water heater for a multifamily unit.
- Manufacturer rating: 100 gallons, heat input 150,000 Btu/h, normal delivery pressure 120 psi, max temperature 180°F.
Analysis: All four numeric thresholds are under the limits in § 1001.1 (≤ 120 gallons, ≤ 200,000 Btu/h, ≤ 160 psi, ≤ 210°F). This unit is excluded from Chapter 10 and remains under the plumbing code. Cite: § 1001.1.
Scenario B — small unfired tank:
- Equipment: unfired pressure vessel in a retail store, internal volume 4.5 cu ft, maximum working pressure 200 psi.
Analysis: Both volume ≤ 5 cu ft and pressure ≤ 250 psi are satisfied, and the occupancy (mercantile) is listed in the exception, so this vessel is excluded from Chapter 10 per § 1001.1.
Scenario C — refrigeration receiver:
- Equipment: refrigeration receiver holding refrigerant with internal volume 8 cu ft.
Analysis: Pressure vessels used in refrigeration are not regulated by Chapter 10; they are handled by Chapter 11. Do not apply Chapter 10 relief‑valve rules to this vessel; consult Chapter 11 requirements. § 1001.1 directs you to Chapter 11.
Related provisions
- § 1001.2 — Boiler rooms and enclosures (boiler room requirements cross‑referenced to the California Building Code).
- § 1001.3 — Air for combustion and ventilation (see Chapter 7).
- § 1001.4 — Drainage (boiler room drainage and indirect discharge rules).
- § 1002.0 — Standards (ASME/NFPA standards that boilers and pressure vessels must meet).
- § 1003.0 — Detailed requirements (safety, controls, gauges, welding).
- § 1004.0 — Expansion tanks (capacity and installation rules).
- § 904.0 — (Referenced for low‑pressure boilers per § 1001.1) — see the code cross‑reference in § 1001.1.
- Chapter 11 (e.g., § 1113.2) — Pressure‑relief requirements for refrigeration pressure vessels — Chapter 10 excludes refrigeration vessels and points you to Chapter 11.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
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.
2025 CALIFORNIA MECHANICAL CODE 215
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216 2025 CALIFORNIA MECHANICAL CODE
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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 § 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 § 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 § 1102.3 Medium 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 § 926.4 Medium relevance — show source text
926.4, 1111.0, 1308.9.6
Relief devices . . . . . . . . . . . . . . . . 218.0, 904.7, 1112.0,
1113.0, 1115.4, C 109.1
Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D 113.6.2
Test, definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Vessel . . . . . . . . . . . . . . . . . . . . . . . .218.0, Chapter 10,
1113.0, 1117.0
Vessel, refrigerant . . . . . . . . . . . . .218.0, 1113.0, 1117.0
PRESSURE-RELIEF VALVE
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.0
Discharge . . . . . . . . . . 1005.2, 1112.10, 1112.11, 1206.2
Hydronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206.0
Pressure vessels . . . . . . . . . . . . . . . . . . 1005.0, 1113.0,
Refrigeration system. . . . . 1111.2, 1112.0, 1113.0, 1115.4
Steam and hot
water boilers (low pressure) . . . . . . . . . . . . . . . 904.7
PROFESSIONAL QUALIFICATIONS . . . . . . . .Appendix H
HVAC technicians . . . . . . . . . . . . . . . . . . . . . .H 102.5.3
Hydronic systems . . . . . . . . . . . . . . . . . . . . . .H 102.4.2
Infection control . . . . . . . . . . . . . . . . . . . . . . . . .H 102.5
Mechanical inspectors . . . . . . . . . . . . . . . . . .H 102.2.1
Mechanical plan examiners . . . . . . . . . . . . . .H 102.2.2
Residential mechanical service technicians . . .H 102.3
Solar water heaters . . . . . . . . . . . . . . . . . . . .H 102.4.1
Water management . . . . . . . . . . . . . . . . . . . . . .H 102.5
PROTECTION
Fire . . . . . . . . . . . . . . . . . . . . .506.8, 507.4.3.1, 510.3.7,
512.3.3, 513.2.1, 516.2.3,
516.5, 1108.1, 1406.2.1.4
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
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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 § 932.3 Medium 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 § 1.90 Medium relevance — show source text
RC.L|1.90 ×TDA + 7.08|1.90 ×TDA + 7.08| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Vertical Closed
Transparent (VCT)|38 (M)|≥32|VCT.SC.M|0.10 ×V + 0.86|0.10 ×V + 0.86| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Vertical Closed
Transparent (VCT)|0 (L)|<32|VCT.SC.L|0.29 ×V + 2.95|0.29 ×V + 2.95| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Vertical Closed
Solid (VCS)|38 (M)|≥32|VCS.SC.M|0.05 ×V + 1.36|0.05 ×V + 1.36| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Vertical Closed
Solid (VCS)|0 (L)|<32|VCS.SC.L|0.22 ×V + 1.38|0.22 ×V + 1.38| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Horizontal Closed
Transparent (HCT)|38 (M)|≥32|HCT.SC.M|0.06 ×V + 0.37|0.06 ×V + 0.37| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Horizontal Closed
Transparent (HCT)|0 (L)|<32|HCT.SC.L|0.08 ×V + 1.23|0.08 ×V + 1.23| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Horizontal Closed
Solid (HCS)|38 (M)|≥32|HCS.SC.M|0.05 ×V + 0.91|0.05 ×V + 0.91| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Horizontal Closed
Solid (HCS)|0 (L)|<32|HCS.SC.L|0.06 ×V + 1.12|0.06 ×V + 1.12| |Self-contained
commercial
refrigerators and
commercial
freezers with and
with outdoors|
Self-contained
(SC)|Service Over
Counter (SOC)|38 (M)|≥32|SOC.SC.M|0.52 ×TDA + 1.00|0.52 ×TDA + 1.CMC § 7-8 Medium relevance — show source text
- in.)|(ft. - in.)|(ft. - in.)**|
|12|Douglas
Fir-Larch|SS|7-8|12-1|15-11|20-3|24-8|7-8|12-1|15-11|20-3|24-0| |12|Douglas
Fir-Larch|#1|7-5|11-7|15-3|18-7|21-7|7-5|11-2|14-1|17-3|20-0| |12|Douglas
Fir-Larch|#2|7-3|11-3|14-3|17-5|20-2|7-1|10-5|13-2|16-1|18-8| |12|Douglas
Fir-Larch|#3|5-10|8-6|10-9|13-2|15-3|5-5|7-10|10-0|12-2|14-1| |12|Hem-Fir|SS|7-3|11-5|15-0|19-2|23-4|7-3|11-5|15-0|19-2|23-4| |12|Hem-Fir|#1|7-1|11-2|14-8|18-1|21-0|7-1|10-10|13-9|16-9|19-5| |12|Hem-Fir|#2|6-9|10-8|14-0|17-2|19-11|6-9|10-3|13-0|15-10|18-5| |12|Hem-Fir|#3|5-10|8-6|10-9|13-2|15-3|5-5|7-10|10-0|12-2|14-1| |12|Southern
Pine|SS|7-6|11-10|15-7|19-11|24-3|7-6|11-10|15-7|19-11|24-3| |12|Southern
Pine|#1|7-3|11-5|15-0|18-2|21-7|7-3|11-4|14-5|16-10|20-0| |12|Southern
Pine|#2|6-11|10-6|13-4|15-10|18-8|6-6|
- in.)|(ft. - in.)|(ft. - in.)**|
|12|Douglas
California Mechanical Code Medium relevance — show source text
2
5
10
15
20|190
182
224
277
325
374|1053
708
692
666
640
616|573
468
457
437
419
400|238
227
279
339
393
448|1379
914
896
866
838
810|750
611
596
570
549
526|326
309
381
457
526
592|1751
1146
1126
1092
1060
1028|927
754
734
702
677
651|473
443
547
646
730
808|2631
1689
1665
1626
1587
1550|1346
1098
1074
1037
1005
973| |30|0
2
5
10
15
20
30|184
175
215
265
312
360
461|1168
823
806
777
750
723
670|647
533
521
501
481
461
426|229
219
269
327
379
433
541|1542
1069
1049
1017
985
955
895|852
698
684
662
638
615
574|312
296
366
440
507
570
704|1971
1346
1324
1287
1251
1216
1147|1056
863
846
821
794
768
720|454
424
524
620
702
780
937|2996
1999
1971
1927
1884
1841
1759|1545
1308
1283
1243
1205
1166
1101| |50|0
2
5CMC § 101.2.2 Medium relevance — show source text
CFC—25: California Fire Code
101.2.2, 101.4.2, 301.3.1, 302.2, 307.1, 308.1, 802.2.1, 802.2.3, 803.2.3, 803.4.1.1, 803.4.1.2, 803.4.1.3, 803.4.1.4, 803.4.1.5, 803.4.1.6, Table 804.5.1.1(1), 904.1.5, 1011.6.1.1, 1303.1.2, 1305.2.8.1, 1305.2.14, 1305.2.14.1, 1401.2, 1501.1, 1501.5, 1502.1, 1502.1.1, 1502.2, 1502.3, 1504.1, 1507.1, 1507.2
CMC—25: California Mechanical Code
302.2, 702.7, 807.1, 902.1.1, 1008.1, 1305.2.7.1, 1305.2.8, 1305.2.8.1
CPC—25: California Plumbing Code
302.2, 408.1, 702.7, 1009.1, 1009.2, 1009.3, 1009.5, 1302.1.6, 1503.1
16-4 2025 CALIFORNIA EXISTING BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
REFERENCED STANDARDS
CRC—25: California Residential Code
101.2, 101.4.1, 104.3.1, 109.3.3, 109.3.10, 302.2, 307.1, 308.1, 401.3, 402.1, 405.2.6, 502.2, 502.3, 502.4, 503.2, 503.3, 503.11, 505.2, 505.3, 507.3, 701.3, 702.4, 702.5, 706.2, 708.1, 805.2, 806.4, 809.1, 906.2, 907.1, 1011.2.1, 1103.1, 1103.2, 1103.3, 1104.1, 1201.4, 1302.1.2, 1302.1.3, 1302.1.3, 1303.1.3, 1401.2, 1402.1, 1402.2, 1402.2.1, 1402.3, 1402.4, 1402.5, 1402.6
ICC 300—2023: ICC Standard on Bleachers, Folding and Telescopic Seating and Grandstands
301.1.1, 401.1.1, 1401.1.1
ICC A117.1—2017: Accessible and Usable Buildings and Facilities
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
244 2025 CALIFORNIA MECHANICAL CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
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.
Frequently asked questions
When is a potable water heater covered by Chapter 10 instead of the plumbing code?
If the potable water heater exceeds any of the limits in § 1001.1 — capacity > 120 gallons, heat input > 200,000 Btu/h, pressure > 160 psi, or temperature > 210°F — it is not excluded and Chapter 10 applies. § 1001.1
Are small receiver tanks in refrigeration covered by Chapter 10?
No. Pressure vessels used in refrigeration systems are handled by Chapter 11, not Chapter 10, per § 1001.1. Consult Chapter 11 for relief‑device and sizing rules.
Does a 6 cu ft unfired pressure vessel at 100 psi fall under Chapter 10?
Yes — the small‑vessel exception in § 1001.1 requires volume ≤ 5 cu ft and pressure ≤ 250 psi; a 6 cu ft vessel exceeds the volume threshold and therefore is within Chapter 10.
If equipment is federally inspected is Chapter 10 enforcement waived?
Equipment subject to regular federal inspection or licensed by federal authorities is excluded by § 1001.1; verify federal jurisdiction and document it with the Authority Having Jurisdiction.
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