CMC · California Mechanical Code
How are refrigeration systems classified (high-probability, low-probability)?
The California Mechanical Code sorts refrigeration systems by the chance a refrigerant leak would reach occupied spaces. If a leak can enter the occupied area the system is High‑Probability (examples: direct systems, some indirect open‑spray where refrigerant pressure exceeds secondary pressure); if it cannot, the system is Low‑Probability (examples: indirect closed, double indirect, or indirect open‑spray where the secondary pressure stays higher). See **§ 1103.2**, **§ 1103.2.1**, and **§ 1103.2.2** for the controlling rules.
Last reviewed: July 6, 2026
What the code requires
Refrigeration systems are classified by whether a refrigerant leak can enter an occupied (occupancy‑classified) space. The controlling provision is § 1103.2: systems that can send refrigerant into occupied space are High‑Probability, and those that cannot are Low‑Probability. See the specific definitions and the representative system types in § 1103.2.1 and § 1103.2.2.
Classify by the likelihood a refrigerant leak will reach occupied space: if it can, the system is High‑Probability; if it cannot, the system is Low‑Probability. § 1103.2 and § 1103.2.1 set the rule.
Requirements in detail
Key defined categories (first mentions bolded)
- § 1103.2 — Classification rule: classify systems by the probability a leak can enter an occupancy‑classified area.
- High‑Probability System (defined in § 1103.2.1) — a system whose design or component locations are such that a refrigerant leak will enter the occupied space; typical examples: direct system and indirect open spray system where the refrigerant can generate pressure more than the secondary coolant.
- Low‑Probability System (defined in § 1103.2.2) — a system whose design or component locations are such that a refrigerant leak cannot enter the occupied space; typical examples: indirect closed system, double indirect system, and indirect open spray when the secondary coolant pressure remains more than the refrigerant pressure in both operating and standby conditions.
Decision‑relevant dimensions (quick reference table)
| Decision factor | Values / test | Typical system outcome | Code Reference |
|---|---|---|---|
| Leak path to occupied space | Leak can reach occupied area → Yes / No | Yes → High‑Probability; No → Low‑Probability | § 1103.2 |
| System type | Direct system | High‑Probability (typical) | § 1103.2.1 |
| Indirect open spray — pressure relation | Refrigerant pressure > secondary coolant pressure | High‑Probability (typical) | § 1103.2.1 |
| Indirect open spray — pressure relation | Secondary coolant pressure > refrigerant pressure (operating & standby) | Low‑Probability (typical) | § 1103.2.2 |
| Indirect closed / double indirect | Closed or double barrier preventing refrigerant access to occupied air | Low‑Probability (typical) | § 1103.2.2 |
Notes:
- The code gives representative types — actual classification depends on the specific design and location of components (i.e., the practical leak path), not only the label on equipment. § 1103.2 and § 1103.2.1 describe this performance/likelihood approach.
How the pressure relationship matters
- For indirect open spray systems the relative pressures are decisive:
- If the refrigerant can produce pressure greater than the secondary coolant, a refrigerant release can be driven into the secondary circuit or air — this is a High‑Probability indicator per § 1103.2.1.
- If the secondary coolant pressure remains more than the refrigerant pressure in both operating and standby conditions, the refrigerant is not likely to be driven into the occupied space — this is a Low‑Probability indicator per § 1103.2.2.
Exceptions & special cases
- The chapter lists other occupancy‑based limits and requirements that affect where particular refrigerants or system types are permitted (see Table 1104.1 and Section 1104.0). For example, some occupancies limit what refrigerant groups may be used in High‑Probability systems. Consult § 1104.1 and Table 1104.1 for occupancy permissions.
- Use of A2L refrigerants in high‑probability human‑comfort systems has additional requirements (releasable charge limits, ventilation, sensors, listing, labeling) in § 1104.6.
- Higher‑flammability refrigerants (Groups A3, B3) are generally restricted — see § 1103.3 for prohibitions/approvals.
- Machinery‑room, ventilation, and refrigerant‑detector rules may be triggered by classification and refrigerant type; see § 1106 and specific subsections referenced from Chapter 11. (Relevant machinery‑room provisions and detector requirements are discussed elsewhere in Chapter 11.)
If you need authoritative definitions of types such as direct system, indirect closed, double indirect, or indirect open spray, those definitions are not reproduced in the retrieved snippets; consult the definitions section and ASHRAE/IIAR references cited in Chapter 11 for formal definitions.
Common mistakes
- Assuming a system labeled “indirect” is automatically Low‑Probability without checking the pressure relationships in the indirect spray loop. The code explicitly makes the pressure relation decisive for indirect open spray systems (§ 1103.2.1 / § 1103.2.2).
- Classifying only by equipment nameplate or marketing language (e.g., “closed loop”) instead of evaluating whether a leak can reach occupied space per § 1103.2.
- Forgetting downstream consequences: a High‑Probability classification can limit allowable refrigerant groups, require additional ventilation, sensors, or machinery‑room separation (see § 1104.1, § 1104.6). file
Worked example
Scenario A — rooftop condensing unit serving a retail sales floor:
- Equipment: a split DX system with evaporator coil and refrigerant piping inside the sales floor (no secondary loop).
- Assessment: this is a direct system (refrigerant is present in the occupied space a leak could reach) → classify as High‑Probability under § 1103.2.1. Consequence: occupancy‑based restrictions in Table 1104.1 and releasable charge limits apply. file
Scenario B — indirect open spray chilled‑water coil:
- Measured pressures: refrigerant side in the spray generator is normally 20 psi, secondary coolant loop is normally 40 psi (operating and standby).
- Assessment: because the secondary coolant pressure remains more than the refrigerant pressure in both operating and standby, the indirect open spray is a Low‑Probability system per § 1103.2.2. Consequence: the system is treated as low probability for classification and some stricter high‑probability limits may not apply (but check other Chapter 11 requirements).
Scenario C — indirect open spray where refrigerant pressure can exceed secondary pressure during some conditions:
- If refrigerant pressure can rise above the secondary coolant pressure (for example during startup or fault), the system becomes High‑Probability per § 1103.2.1 and must be treated accordingly.
Related provisions (quick list)
- § 1103.2 — Classification rule (primary controlling section).
- § 1103.2.1 — High‑Probability System definition and typical examples.
- § 1103.2.2 — Low‑Probability System definition and typical examples.
- § 1103.3 — Restrictions on higher‑flammability refrigerants.
- § 1104.1 and Table 1104.1 — System selection and occupancy permissions (how classification affects allowable refrigerant groups).
- § 1104.6 — Additional requirements for A2L refrigerants in high‑probability human‑comfort systems (RCLs, ventilation, sensors, listing).
- § 1106.x (machinery room requirements referenced from Chapter 11) — machinery‑room construction, detectors, and ventilation when required by classification or refrigerant type.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 1103.0 High relevance — show source text
where approved by the Authority Having Jurisdiction.
Exception: Lithium bromide absorption systems using water as the refrigerant.
1103.0 Classification.
1103.1 Classification of Refrigerants. Refrigerants shall be classified in accordance with Table 1102.3 or in accor dance with ASHRAE 34 where approved by the Authority Having Jurisdiction.
1103.1.1 Safety Group. Table 1102.3 classifies refrigerants by toxicity and flammability, and assigns safety groups using combinations of toxicity class and flammability class. For the purposes of this chapter, the refrigerant Groups A1, A2L, A2, A3, B1, B2L, B2, and B3 shall be considered to be individual and distinct safety groups, as shown in Table 1103.1.1. Each refrigerant is assigned into not more than one group.
TABLE 1103.1.1
REFRIGERANT SAFETY GROUP CLASSIFICATIONS
1103.2 Classification of Refrigeration Systems. Refrigeration systems shall be classified according to the degree of probability that a leakage of refrigerant will enter an occupancy-classified area in accordance with Section 1103.2.1 and Section 1103.2.2. [ASHRAE 15:5.2]
1103.2.1 High-Probability System. Systems in which the basic design, or the location of components, is such that a leakage of refrigerant from a failed connection, seal, or component will enter the occupied space shall be classified as high-probability systems. A typical high-probability system shall be one of the following:
(1) A direct system
(2) An indirect open spray system in which the refrigerant is capable of producing pressure that is more than the secondary coolant. [ASHRAE 15:5.2.1]
1103.2.2 Low-Probability System. Systems in which the basic design, or the location of the components, is such that a leakage of refrigerant from a failed connection, seal, or component cannot enter the occupied space shall be classified as low-probability systems. A typical low-probability system shall be one of the following:
(1) An indirect closed system
(2) Double indirect system
(3) An indirect open spray system. In a low-probability indirect open spray system, the secondary coolant pressure remains more than the refrigerant pressure in operating and standby conditions. [ASHRAE 15:5.2.2]
1103.3 Higher Flammability Refrigerants. Group A3 and B3 refrigerants shall not be used except where approved by the Authority Having Jurisdiction.
Exceptions:
(1) Laboratories with more than 100 square feet (9.29 m [2] ) of space per person.
(2) Industrial occupancies.
(3) Listed self-contained systems containing not more than 0.331 pounds (0.150 kg) of Group A3 refrigerant, provided that the equipment is installed in accordance with the listing and the manufacturer’s installation instructions. [ASHRAE 15:7.5.3]
1104.0 Requirements for Refrigerant and Refrigera- tion System Use.
CMC § 5.2.1 High relevance — show source text
(1) A direct system
(2) An indirect open spray system in which the refrigerant is capable of producing pressure that is more than the secondary coolant. [ASHRAE 15:5.2.1]
1103.2.2 Low-Probability System. Systems in which the basic design, or the location of the components, is such that a leakage of refrigerant from a failed connection, seal, or component cannot enter the occupied space shall be classified as low-probability systems. A typical low-probability system shall be one of the following:
(1) An indirect closed system
(2) Double indirect system
(3) An indirect open spray system. In a low-probability indirect open spray system, the secondary coolant pressure remains more than the refrigerant pressure in operating and standby conditions. [ASHRAE 15:5.2.2]
1103.3 Higher Flammability Refrigerants. Group A3 and B3 refrigerants shall not be used except where approved by the Authority Having Jurisdiction.
Exceptions:
(1) Laboratories with more than 100 square feet (9.29 m [2] ) of space per person.
(2) Industrial occupancies.
(3) Listed self-contained systems containing not more than 0.331 pounds (0.150 kg) of Group A3 refrigerant, provided that the equipment is installed in accordance with the listing and the manufacturer’s installation instructions. [ASHRAE 15:7.5.3]
1104.0 Requirements for Refrigerant and Refrigera- tion System Use.
1104.1 System Selection. Refrigeration systems shall be limited in application in accordance with Table 1104.1, and the requirements of Section 1104.0. 1104.2 Refrigerant Concentration Limit (RCL). The concentration of refrigerant in a complete discharge of an
Higher Flammability A3 B3 Flammable A2 B2 Lower Flammability A2L B2L No Flame Propagation
A1B1 Lower Toxicity Higher Toxicity 2025 CALIFORNIA MECHANICAL CODE 227
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REFRIGERATION
TABLE 1104.1 PERMISSIBLE REFRIGERATION SYSTEMS [1 ]
OCCUPANCY GROUP3 HIGH-PROBABILITY SYSTEM LOW PROBABILITY SYSTEM MACHINERY ROOM A-1 Group A1 or A2L4 only Any Any A-2 Group A1 or A2L4 only Any Any A-3 Group A1 or A2L4 only Any Any A-4 Group A1 or A2L4 only Any Any B Group A12 or A2L2,4 only Any Any E Group A1 or A2L4 only Any Any F-1 Group A12 or A2L2, CMC § 1101.0 High relevance — show source text
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226 2025 CALIFORNIA MECHANICAL CODE
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CHAPTER 11
REFRIGERATION
1101.0 General.
1101.1 Applicability. Part I governs the design, installation, and construction of refrigeration systems, equipment, refrigerant piping, pressure vessels, safety devices, replacement of parts, alterations, and substitution of different refrigerants. Part II governs the installation and construction of cooling
towers.
1101.2 Equipment. Equipment for refrigerant recovery, recycling, or both shall comply with UL 1963.
Part I – Refrigeration Systems.
1102.0 Refrigeration Systems.
1102.1 General. Refrigeration systems using a refrigerant other than ammonia shall comply with this chapter and ASHRAE 15. Refrigeration systems containing carbon dioxide as the refrigerant shall also comply with IIAR CO2.
1102.2 Ammonia Refrigeration Systems. Refrigeration systems using ammonia as the refrigerant shall comply with IIAR 2, IIAR 3, IIAR/ANSI 4, IIAR 5, and IIAR 6 and shall not be required to comply with this chapter.
1102.3 Refrigerants. The refrigerant used shall be of a type listed in Table 1102.3 or in accordance with ASHRAE 34
where approved by the Authority Having Jurisdiction.
Exception: Lithium bromide absorption systems using water as the refrigerant.
1103.0 Classification.
1103.1 Classification of Refrigerants. Refrigerants shall be classified in accordance with Table 1102.3 or in accor dance with ASHRAE 34 where approved by the Authority Having Jurisdiction.
1103.1.1 Safety Group. Table 1102.3 classifies refrigerants by toxicity and flammability, and assigns safety groups using combinations of toxicity class and flammability class. For the purposes of this chapter, the refrigerant Groups A1, A2L, A2, A3, B1, B2L, B2, and B3 shall be considered to be individual and distinct safety groups, as shown in Table 1103.1.1. Each refrigerant is assigned into not more than one group.
TABLE 1103.1.1
REFRIGERANT SAFETY GROUP CLASSIFICATIONS
1103.2 Classification of Refrigeration Systems. Refrigeration systems shall be classified according to the degree of probability that a leakage of refrigerant will enter an occupancy-classified area in accordance with Section 1103.2.1 and Section 1103.2.2. [ASHRAE 15:5.2]
1103.2.1 High-Probability System. Systems in which the basic design, or the location of components, is such that a leakage of refrigerant from a failed connection, seal, or component will enter the occupied space shall be classified as high-probability systems. A typical high-probability system shall be one of the following:
(1) A direct system
CMC § 1104.4 High relevance — show source text
Industrial occupancies. . . . . . . . . . . . . . . . . . . . . 1104.4
Institutional occupancies . . . . . . . . . . . . . . . . . . . 1104.3
Nonconnecting spaces . . . . . . . . . . . . . . . . . . . 1104.2.2
Refrigerated spaces . . . . . . . . . . . . . . . . . . . . . . 1104.4
Ventilated spaces . . . . . . . . . . . . . . . . . . . . . . . 1104.2.3
Volume calculation . . . . . . . . . . . . . . . . . . . . . . 1104.2.1
REFRIGERATION SYSTEM CLASSIFICATION
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220.0
High-probability systems. . . . . . . . . . . . . . . . . . 1103.2.1
Higher flammability refrigerants. . . . . . . . . . . . . . 1103.3
Low-probability . . . . . . . . . . . . . . . . . . . . . . . . . 1103.2.2
REFRIGERATION SYSTEMS
Absorption . . . . . . . . . . . . . . . . . . . . . . . . . 220.0, 307.4
Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 933.0
Attic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.3, 1105.9
Classification of . . . . . . . . . . . . . . . . . . . . . . . . . . 1103.2
Condensation . . . . . . . . . 310.6, 1105.7, 1105.10, 1109.9
Containing
hazardous fluids. . . . . . . . . . . . . . . . . . . . . . . . 1125.0
Defrost. . . . . . . . . . . . . . . . . . . . . . . . . . 1105.8, 1105.10
Discharge piping. . . . . . . . . . . . 1112.10, 1112.11, 1114.1
Duct furnaces used with . . . . . . . . . . . . . . . . . . . . 905.7
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108.2
Emergency shutoff. . . . . . . . . . . . . . . . . . . . . . . . 1108.3
Flaring device . . . . . . . . . . . . . . . . . . . . . 1114.1–1114.3
CMC § 1105.4 High relevance — show source text
Illumination and
service receptacles . . . . . . . . . . . . . . . . . . . . . 1105.4
Location of . . . . . . . . . . . . . . . . . . . . . . . 1104.2, 1105.0
Refrigeration recovery . . . . . . . . . . . . . . . . . . . . . 1101.2 Supports and anchorage. . . . . . . . . . . . . . . . . . . 1105.2
Testing of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1116.0 Valves. . . . . . . . . (see Valves, for refrigeration systems)
REFRIGERATION
MACHINERY ROOMS
A2L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1106.11
B2L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1106.11
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220.0
General . . . . . . . . . . . . . . . . . . . . . . . . . . 1106.0, 1106.2
REFRIGERATION SPACES
Concentration limit. . . . . . . 1102.3, 1104.2, Table 1102.3
Industrial occupancies. . . . . . . . . . . . . . . . . . . . . 1104.4
Institutional occupancies . . . . . . . . . . . . . . . . . . . 1104.3
Nonconnecting spaces . . . . . . . . . . . . . . . . . . . 1104.2.2
Refrigerated spaces . . . . . . . . . . . . . . . . . . . . . . 1104.4
Ventilated spaces . . . . . . . . . . . . . . . . . . . . . . . 1104.2.3
Volume calculation . . . . . . . . . . . . . . . . . . . . . . 1104.2.1
REFRIGERATION SYSTEM CLASSIFICATION
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220.0
High-probability systems. . . . . . . . . . . . . . . . . . 1103.2.1
Higher flammability refrigerants. . . . . . . . . . . . . . 1103.3
Low-probability . . . . . . . . . . . . . . . . . . . . . . . . . 1103.2.2
REFRIGERATION SYSTEMS
Absorption . . . . . . . . . . . . . . . . . . . . . . . . . 220.0, 307.4
CMC § 1106.2.6. High relevance — show source text
(1) The space(s) containing the machinery is (are) separated from other occupancies by tight construction with tightfitting doors.
(2) Access is restricted to authorized personnel.
(3) Refrigerant detectors are installed with the sensing location and alarm level as required in refrigeration machinery rooms in accordance with Section 1106.2.6.
(4) Open flames and surfaces exceeding 800°F (427°C) shall not be permitted where a Group A2, B2, A3, or B3 refrigerant, is used.
(5) Electrical equipment that is in accordance with Class 1, Division 2, of NFPA 70 where the quantity of a Group A2, B2, A3, or B3 refrigerant in an independent circuit is capable of exceeding 25 percent of the lower flammability limit (LFL) upon release to the space based on the volume determined in accordance with Section 1104.2.1 through Section 1104.2.3.
(6) Refrigerant containing parts in systems exceeding 100 horsepower (74.6 kW) compressor drive power, except evaporators used for refrigeration or dehumidification, condensers used for heating, control and pressure-relief valves for either, low-probability pumps, and connecting piping, are located in a machinery room or outdoors.
[ASHRAE 15:7.2.2]
1104.5 Flammable Refrigerants. The total of Group A2, B2, A3, and B3 refrigerants, other than Group A2L and B2L refrigerants shall not exceed 1100 pounds (498.9 kg) without approval by the Authority Having Jurisdiction. Institutional Occupancies shall comply with Section 1104.3. Machinery rooms required in accordance with Section 1106.0 based on flammability shall be constructed and maintained in accordance with Section 1106.2.1 through Section 1106.2.6 and Section 1106.11 for Group A2L and B2L refrigerants. 1104.6 Group A2L Refrigerants for Human Comfort. High-probability systems using Group A2L refrigerants for human comfort applications shall comply with this section.
[ASHRAE 15:7.6]
1104.6.1 Refrigerant Concentration Limits. Occupied spaces shall comply with the releasable charge limitations of the equipment listing and ASHRAE 15. Unoccupied spaces with refrigerant containing equipment, not including continuous piping or tubing, shall comply with the releasable charge limitations of the equipment listing or Section 1104.6.4. {ASHRAE 15:7.6.1-7.6.1.2}
1104.6.2 Listing and Installation Requirements. Refrigeration systems shall be listed and shall be installed in accordance with listing, the manufacturer’s instructions, and any markings on the equipment restricting the installation. [ASHRAE 15:7.6.2]
1104.6.2.1 Nameplate. The nameplate required by Section 1115.5 shall include a symbol indicating that a flammable refrigerant is used, as specified by the product listing. [ASHRAE 15:7.6.2.1]
1104.6.2.2 Labeling. A label indicating a flammable refrigerant is used shall be placed adjacent to service ports and other locations where service involving components containing refrigerant is performed, as specified by the product listing.
CMC § 933.0 High relevance — show source text
Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 933.0
Attic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.3, 1105.9
Classification of . . . . . . . . . . . . . . . . . . . . . . . . . . 1103.2
Condensation . . . . . . . . . 310.6, 1105.7, 1105.10, 1109.9
Containing
hazardous fluids. . . . . . . . . . . . . . . . . . . . . . . . 1125.0
Defrost. . . . . . . . . . . . . . . . . . . . . . . . . . 1105.8, 1105.10
Discharge piping. . . . . . . . . . . . 1112.10, 1112.11, 1114.1
Duct furnaces used with . . . . . . . . . . . . . . . . . . . . 905.7
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108.2
Emergency shutoff. . . . . . . . . . . . . . . . . . . . . . . . 1108.3
Flaring device . . . . . . . . . . . . . . . . . . . . . 1114.1–1114.3
High probability. . . . . . . . . . . . . . . . . . . . . . . . . 1103.2.1
Highside, definition . . . . . . . . . . . . . . . . . . . . . . . . 210.0
Human comfort . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.1
Labeling. . . . . . . . . . . . . . . . . . . . . . 307.3, 307.4, 1115.3
2025 CALIFORNIA MECHANICAL CODE 587
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INDEX
Low probability . . . . . . . . . . . . . . . . . . . . . . . . . 1103.2.2
Lowside, definition. . . . . . . . . . . . . . . . . . . . . . . . . 214.0
Machinery room. . . . . . . . . . . . . . . . . . . . 220.0, 1106.0,
1107.0, 1115.3
Maintenance and operation . . . . . . . . . . . . . . . . . 1118.0
Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . 220.0, 933.3
Mechanical system, definition . . . . . . . . . . . . . . . . 220.0
CMC § 1103.2.1 High relevance — show source text
High probability. . . . . . . . . . . . . . . . . . . . . . . . . 1103.2.1
Highside, definition . . . . . . . . . . . . . . . . . . . . . . . . 210.0
Human comfort . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.1
Labeling. . . . . . . . . . . . . . . . . . . . . . 307.3, 307.4, 1115.3
2025 CALIFORNIA MECHANICAL CODE 587
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INDEX
Low probability . . . . . . . . . . . . . . . . . . . . . . . . . 1103.2.2
Lowside, definition. . . . . . . . . . . . . . . . . . . . . . . . . 214.0
Machinery room. . . . . . . . . . . . . . . . . . . . 220.0, 1106.0,
1107.0, 1115.3
Maintenance and operation . . . . . . . . . . . . . . . . . 1118.0
Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . 220.0, 933.3
Mechanical system, definition . . . . . . . . . . . . . . . . 220.0
Mechanical ventilation . . . . . . . . . . . . . . . . . . . . . 1107.0
Permissible . . . . . . . . . . . . . . . . . . . . . . . . Table 1104.1
Pressure-limiting devices . . . . . . . . . . . . . . . . . . . 1111.0
Pressure-relief devices . . . . . . . . . . . . . . 1112.0, 1112.9,
1112.10, 1112.11
1113.4, 1113.5, 1115.4
Probability . . . . . . . . . . . . . . . 1103.2, 1103.2.1, 1103.2.2
Protection from
mechanical damage . . . . . . . . . . . . . . . . . . . 1109.4.1
Requirements for . . . . . . . . . . . . . . . . . . . . . . . . . 1104.0
Self-contained mechanical
refrigeration systems . . . . . . . . . . . . . . . . . . . . . 933.3
Self-contained refrigerators
and freezers . . . . . . . . . . . . . . . . . . . . . . . . . . . 933.1
Unit coolers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 933.2
Ventilation of room . . . . . . . . . . . . . . . . . . 1105.5, 1107.0
CMC § 1104.1 High relevance — show source text
1104.1 System Selection. Refrigeration systems shall be limited in application in accordance with Table 1104.1, and the requirements of Section 1104.0. 1104.2 Refrigerant Concentration Limit (RCL). The concentration of refrigerant in a complete discharge of an
Higher Flammability A3 B3 Flammable A2 B2 Lower Flammability A2L B2L No Flame Propagation
A1B1 Lower Toxicity Higher Toxicity 2025 CALIFORNIA MECHANICAL CODE 227
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REFRIGERATION
TABLE 1104.1 PERMISSIBLE REFRIGERATION SYSTEMS [1 ]
OCCUPANCY GROUP3 HIGH-PROBABILITY SYSTEM LOW PROBABILITY SYSTEM MACHINERY ROOM A-1 Group A1 or A2L4 only Any Any A-2 Group A1 or A2L4 only Any Any A-3 Group A1 or A2L4 only Any Any A-4 Group A1 or A2L4 only Any Any B Group A12 or A2L2,4 only Any Any E Group A1 or A2L4 only Any Any F-1 Group A12 or A2L2,4 only Any Any F-2 Any2 Any Any H-1 Any Any Any H-2 Any Any Any H-3 Any Any Any H-4 Group A1 or A2L4 only Any Any H-5 Group A1 or A2L4 only Any Any I-1 None Any Any I-2 Group A1 or A2L4 only Any Any I-3 None Any Any I-4 Group A1 or A2L4 only Any Any M Group A12 or A2L2,4 only Any Any R-1 Group A1 or A2L4 only Any Any R-2 Group A1 or A2L4 only Any Any R-3 Group A1 or A2L4 only Any Any R-4 Group A1 or A2L4 only Any Any S-1 Group A12 or A2L2,4 only Any Any S-2 Any2 Any Any U Any Any Any Notes: 1 See Section 1104.0. 2 A refrigerant shall be permitted to be used within a high-probability system where the room or space is in accordance with Section 1104.4. 3 Occupancy classifications are defined in the building code. 4 See Section 1104.6 for requirements applicable to A2L equipment.
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
2025 CALIFORNIA MECHANICAL CODE xv
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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 § 1104.6.4 Medium relevance — show source text
1104.6.4 Mechanical Ventilation. When the releasable charge of the refrigeration system exceeds the refrigerant concentration limit specified in Section 1104.6.1, the refrigerant charge and ventilation air flow shall be in accordance with the equipment listing and ASHRAE 15. 1104.6.5 Compressors and Pressure Vessels Located Indoors. For refrigeration compressors and pressure vessels located in an indoor space that is accessible only during service and maintenance, the refrigerant charge shall be in accordance with the equipment listing and ASHRAE 15 .
1104.6.6 Refrigerant Sensors. Refrigerant sensors required by Section 1104.6.2 shall meet the following requirements:
(1) Refrigerant sensors shall be evaluated by the testing laboratory as part of the equipment listing.
(2) Refrigerant sensors shall be located such that refrigerant will be detected if the refrigerating system is operating or not operating.
(a) For refrigerating systems that are connected to the occupied space through ductwork, refrigerant sensors shall be located within the listed equipment.
(b) For refrigerating systems that are directly connected to the occupied space without ductwork, the refrigerant sensor shall be located in the equipment in accordance with the equipment listing. Additional remote refrigerant sensors shall be permitted within the occupied space when included as part of the equipment mitigation system according to manufacturer’s instructions. {ASHRAE 15:7.6.5}
1104.7 Applications for Human Comfort and for Non- industrial Occupancies. In nonindustrial occupancies, Group A2, A3, B1, B2L, B2, and B3 refrigerants shall not be used in high-probability systems for human comfort. Use of Group A2L refrigerants used in high-probability systems for human comfort shall be in accordance with Section 1104.6.
1104.8 Refrigerant Type and Purity. Refrigerants shall be of a type specified by the equipment manufacturer. Unless otherwise specified by the equipment manufacturer, refrigerants used in new equipment shall be of purity in accordance with AHRI 700.
1104.8.1 Recovered Refrigerants. Recovered refrigerants shall not be reused except in the system from which they were removed, or as provided in Section 1104.8.2 or Section 1104.8.3. When contamination is evident by discoloration, odor, acid test results, or system history, recovered refrigerants shall be reclaimed in accordance with Section 1104.8.3 before reuse. [ASHRAE 15:7.5.1.4]
1104.8.2 Recycled Refrigerants. Recycled refrigerants shall not be reused except in systems using the same refrigerant and lubricant designation and belonging to the same owner as the systems from which they were removed. Where contamination is evident by discoloration, odor, acid test results, or system history, recycled refrigerants shall be reclaimed in accordance with Section 1104.8.3.
Exception: Drying shall not be required in order to use recycled refrigerants where water is the refrigerant, is used as an absorbent or is a deliberate additive.
[ASHRAE 15:7.5.1.5]
1104.8.3 Reclaimed Refrigerants. Used refrigerants shall not be reused in a different owner’s equipment unless tested and found to be in accordance with the
CMC § 503.5.7.7 Medium relevance — show source text
E 503.5.7.7 Chilled-Water Coil Selection.
Chilled-water cooling coils shall be selected to provide a 15°F (8°C) or higher temperature difference between leaving and entering water temperatures and a minimum of 57°F (14°C) leaving water temperature at design conditions.
Exceptions:
(1) Chilled-water cooling coils that have an air-side pressure drop exceeding 0.70 inch of water (0.17 kPa) when rated at 500 feet per minute (2.54 m/s) face velocity and dry conditions (no condensation).
(2) Individual fan-cooling units with a design supply airflow rate 5000 cubic feet per minute (ft [3] /min) (2.36 m [3] /s) and less.
(3) Constant-air-volume systems.
(4) Coils selected at the maximum temperature difference allowed by the chiller.
(5) Passive coils (no mechanically supplied airflow).
(6) Coils with design entering chilled-water temperatures of 50°F (10°C) and higher.
(7) Coils with design entering air dry-bulb temperatures of 65°F (18°C) and lower. [ASHRAE 90.1:6.5.4.7]
E 503.5.8 Heat Rejection Equipment. Section E 503.5.8 through Section E 503.5.9 applies to heat-rejection equipment used in comfort cooling systems, such as air-cooled condensers, dry coolers, open-circuit cooling towers, closed-circuit cooling towers, and evaporative condensers.
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(3) Water temperature reset is not required where valve position is used to comply with Section E 503.5.7. [ASHRAE 90.1:6.5.4.4]
E 503.5.7.5 Hydronic (Water Loop) Heat Pump and Water-Cooled Unitary Air Condi- tioners. Hydronic heat pumps and water-cooled unitary air-conditioners shall have a two-position automatic valve interlocked to shut off water flow
when the compressor is off.
Exception: Units employing fluid economizers.
[ASHRAE 90.1:6.5.4.5.1]
E 503.5.7.5.1 Controls. Hydronic heat pumps and water-cooled unitary air-conditioners having a total pump system power exceeding 5 hp (3.7 kW) shall have controls, devices, or both (such as variable speed control) that will result in pump motor demand of not more than 30 percent of design wattage at 50 percent of design water flow. [ASHRAE 90.1:6.5.4.5.2]
E 503.5.7.6 Pipe Sizing. Chilled-water and condenser-water piping shall be designed such that the design flow rate in each piping segment shall not exceed the values listed in Table E 503.5.7.6 for the
appropriate total annual hours of operation. Piping size selections for systems that operate under variable flow conditions (e.g., modulating two-way control valves at coils) and that contain variable-speed pump motors shall be permitted to be made from the “Variable Flow/Variable Speed” columns. All others shall be made from the “Other” columns.
Exceptions:
Frequently asked questions
What is the single decisive test for classifying a system high vs. low probability?
Whether a refrigerant leak from a failed connection, seal, or component can enter the occupied (occupancy‑classified) space — if it can, classify High‑Probability; if it cannot, classify Low‑Probability (see § 1103.2, § 1103.2.1, § 1103.2.2).
Is a direct system always High‑Probability?
Yes — a direct system is listed as a typical High‑Probability system in § 1103.2.1. However, always confirm by evaluating the actual leak path and occupancy.
How do I treat an indirect open spray system?
Check the pressure relationship: if the refrigerant can produce pressure greater than the secondary coolant → High‑Probability; if the secondary coolant pressure remains higher in operating and standby → Low‑Probability (§ 1103.2.1 / § 1103.2.2).
Do classification results affect what refrigerants I can use?
Yes. Classification influences which refrigerant groups and quantities are permitted in a space (see Table 1104.1 and § 1104.1), and may trigger additional requirements (e.g., A2L provisions in § 1104.6). file
Where can I find formal definitions for "direct", "indirect closed", "double indirect", etc.?
Those formal definitions and the referenced standards (ASHRAE 15, IIAR) appear elsewhere in Chapter 11 and referenced standards; they are not included in the code snippets retrieved here — consult the definitions and ASHRAE/IIAR text cited by Chapter 11 for the formal language.
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