CMC · California Mechanical Code
What is an 'Absorption Unit' and common refrigeration-definition terms?
An “Absorption Unit” in the California Mechanical Code is specifically an absorption refrigeration system that was factory‑assembled and factory‑tested before installation (see § 203.0). That factory‑assembled status determines which labeling, permitting fee bracket and refrigeration rules apply; field‑built absorption systems and other cooling equipment are treated differently by the code.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
An Absorption Unit is defined as an absorption refrigeration system that has been factory‑assembled and tested prior to its installation — that is the controlling definition in § 203.0. § 203.0 distinguishes factory‑assembled absorption units from other refrigeration equipment and is the anchor for how the CMC treats those pieces of equipment for labeling, permitting and exceptions.
The single most important thing: an “Absorption Unit” in the CMC is a factory‑assembled, factory‑tested absorption refrigeration system — if it wasn’t assembled and tested at the factory, it is not an “Absorption Unit” as defined in § 203.0.
Requirements in detail
Core definition (short)
- Absorption Unit — “An absorption refrigeration system that has been factory‑assembled and tested prior to its installation.” § 203.0.
How that definition is used (practical implications)
- Classification: Absorption equipment is treated separately from mechanical (compressor) refrigeration in the refrigeration chapter; the code places absorption systems under the refrigeration provisions (see references to absorption systems at § 220.0 and elsewhere).
- Labeling and nameplate: absorption equipment is subject to the labeling/identification rules that apply to refrigeration systems (see labeling requirements referenced elsewhere in the refrigeration chapter).
- Permit/fee buckets: absorption systems are listed explicitly in the permit fee Table 104.5 by capacity ranges (e.g., “not exceeding 100,000 Btu/h,” next bracket “exceeding 100,000 Btu/h and including 500,000 Btu/h,” etc.). Use the factory‑assembled status to determine whether the installed piece qualifies as an “absorption unit” for fee and permitting categories.
Decision‑relevant quick table
| Term | Decision‑relevant detail (what you check) | Code Reference |
|---|---|---|
| Absorption Unit | Must be an absorption refrigeration system that was factory‑assembled and factory‑tested prior to installation. If field‑assembled, it is not an “Absorption Unit.” | § 203.0 |
| Refrigeration System, Absorption | A heat‑operated closed refrigeration cycle where an absorbent absorbs the vaporized refrigerant (the system type definition used across refrigeration chapters). | § 220.0 (refrigeration definitions) |
| Permit fee bracket for absorption systems | Fees are tiered by Btu/h capacity — e.g., ≤ 100,000 Btu/h, > 100,000 Btu/h up to 500,000 Btu/h, etc.; use Table 104.5 to pick the correct bracket. | Table 104.5 (permit fees) |
Related definitional terms you will commonly see (short citations)
- Refrigeration System, Absorption — heat‑operated closed cycle using an absorbent to absorb the refrigerant vapor (§ 220.0).
- Cooling Unit / Cooling System / Condensing Unit / Self‑contained System — these mechanical/compressor terms are defined elsewhere in Chapter 2 and used to distinguish mechanical refrigeration from absorption equipment when applying other code rules (see Chapter 2 definitions).
Exceptions & special cases
- Lithium‑bromide absorption systems using water as the refrigerant are treated specially and are specifically noted as exceptions in refrigeration machinery room and related provisions (see refrigeration machinery rooms and exceptions at § 1106.1.2). Do not assume every absorption configuration is handled identically — check the exceptions in the refrigeration chapter.
- Portable cooling units and some small factory‑sealed systems have different definitions and exemptions; note that the portable cooling‑unit definition explicitly excludes an absorption unit (i.e., a portable cooling unit is not an absorption unit). Confirm the specific definition language in the Chapter 2 definitions when deciding which rules apply.
- Permit/fee application: Table 104.5 separates absorption systems by Btu/h capacity ranges; whether a particular piece of equipment is a factory‑assembled absorption unit will determine how it maps into those fee buckets.
Common mistakes
- Misreading “absorption system” vs “absorption unit”: designers and contractors sometimes treat any absorption system as an “Absorption Unit.” The code’s definition requires factory‑assembled and tested — field‑built absorption systems do not qualify as the defined “Absorption Unit” in § 203.0.
- Applying mechanical refrigeration rules without checking refrigerant/system classification: absorption systems are heat‑operated; some mechanical refrigeration provisions (compressor‑specific requirements) may not apply. Always confirm which chapter/section applies based on the system type (see § 220.0 for system types).
- Forgetting exceptions (lithium‑bromide/water): assume any absorption equipment is subject to the same machinery‑room rules — some absorption configurations are specifically excepted in machinery room requirements (see § 1106.1.2).
Worked example — concrete scenario applying the rule with numbers
Scenario: An owner is installing a factory‑assembled absorption chiller that the manufacturer shipped as a complete, factory tested package. The chiller nominal capacity is 120,000 Btu/h.
- Is it an “Absorption Unit”? — Yes, because it was factory‑assembled and tested prior to installation, matching the definition in § 203.0. That classification matters for labeling, permitting and which refrigeration rules apply.
- Permit/fee category — consult Table 104.5: the unit exceeds 100,000 Btu/h, so it falls into the next permit/fee bracket (the table lists absorption systems “not exceeding 100,000 Btu/h” as one bracket and the next bracket for “exceeding 100,000 Btu/h and including 500,000 Btu/h”). The installer should use that bracket when submitting permit paperwork. (See Table 104.5.)
- Machinery room/installation requirements — check refrigeration chapter provisions for absorption systems (including any special exceptions such as lithium‑bromide/water systems). For example, if the chiller used a lithium‑bromide/water arrangement there are special notes in the refrigeration machinery room sections; otherwise follow the refrigeration machinery room requirements that apply to absorption equipment.
Related provisions
- § 203.0 — Definitions (Absorption Unit) — primary controlling definition.
- § 220.0 — Refrigeration system definitions (including Refrigeration System, Absorption).
- Table 104.5 — Mechanical permit fee brackets (absorption system capacity buckets).
- § 307.4 — Labeling references for absorption equipment (labeling requirements referenced in index).
- § 1106.1.2 — Refrigeration machinery room exceptions (lithium‑bromide/water noted).
- Refrigeration chapter general rules (classification, safety groups, system probability): see § 1103.1 and related refrigeration requirements in the refrigeration chapter.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 104.5 High relevance — show source text
INDEX
© 2024 International Association of Plumbing and Mechanical Officials. All rights reserved. The copyright in this index is separate and distinct from the copyright in the document that it indexes. The licensing provisions set forth for the document are not applicable to this index. This index may not be reproduced in whole or in part by any means without the express written permission of IAPMO.
– A –
ABSORPTION SYSTEM
Cooling system . . . . . . . . . . . . . . . . . . . . . . . Chapter 11 Duct system . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 6
Permit Fees . . . . . . . . . . . . . . . . . . . . . . . . . Table 104.5
ABSORPTION UNIT
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
Labeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307.4
Permit Fees . . . . . . . . . . . . . . . . . . . . . . . . . Table 104.5
ACCEPTED ENGINEERING
PRACTICE . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0, 309.1
Oil supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D 112.1
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
HVAC system balancing . . . . . . . . . . . . . . . E 503.6.5.3
Pump head . . . . . . . . . . . . . . . . . . . . . . . . . E 503.4.5.1
Workmanship . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309.1
ACCESS PANELS
Air handling units . . . . . . . . . . . . . . . . . . . . . . . 1106.2.3
Appliances on roofs . . . . . . . . . . . . . . . . . . . . . . . 303.8
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
Ducts connected to
duct furnaces . . . . . . . . . . . . . . . . . . . . . . . . . . 905.4
Exhaust systems,
commercial kitchen . . . . . . . . . . . . . 510.1.5, 510.3.1,
510.3.6-510.3.7,
510.7.7, 514.4.9, 514.4.10
Exhaust systems, dryers (multistory) . . . . . . . . .504.4.6
CMC § 201.0 High relevance — show source text
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CHAPTER 2
DEFINITIONS
201.0 General.
201.1 Applicability. For the purpose of this code, the following terms have the meanings indicated in this chapter.
No attempt is made to define ordinary words, which are used in accordance with their established dictionary meanings, except where a word has been used loosely, and it is necessary to define its meaning as used in this code to avoid misunderstanding.
202.0 Definition of Terms.
202.1 General. The definitions of terms are arranged alphabetically according to the first word of the term.
203.0 – A –
Absorption Unit. An absorption refrigeration system that has been factory-assembled and tested prior to its installation.
Accepted Engineering Practice. That which conforms to technical or scientific-based principles, test, or standards that are accepted by the engineering profession.
Access Panel. A closure device used to cover an opening into a duct, an enclosure, equipment, or an appurtenance.
[NFPA 96:3.3.1]
Accessible. Where applied to a device, appliance, or equipment, “accessible” means having access thereto, but which first may require the removal of an access panel, door, or similar obstruction.
Accessible, Readily. Having a direct access without the necessity of removing a panel, door, or similar obstruction.
Accessory Dwelling Unit. [HCD 1 & HCD 2] An attached or detached residential dwelling unit that provides complete independent living facilities for one or more persons and is located on a lot with a proposed or existing primary residence. Accessory dwelling units shall include permanent provisions for living, sleeping, eating, cooking, and sanitation on the same parcel as the single-family or multifamily dwelling is or will be situated. (See Government Code Section 65852.2.)
Air, Class 1. Air with low contaminant concentration, low sensory-irritation intensity, and inoffensive odor. [ASHRAE 62.1:5.18.1]
Air, Class 2. Air with moderate contaminant concentration, mild sensory-irritation intensity, or mildly offensive odors. Class 2 air also includes air that is not necessarily harmful or objectionable, but that is inappropriate for transfer or recirculation to spaces used for different purposes. [ASHRAE 62.1:5.18.1]
Air, Class 3. Air with significant contaminant concentration, significant sensory-irritation intensity, or offensive odor.
[ASHRAE 62.1:5.18.1]
Air, Class 4. Air with highly objectionable fumes or gases or with potentially dangerous particles, bioaerosols, or gases, at concentrations high enough to be considered as harmful.
[ASHRAE 62.1:5.18.1]
Air, Combustion. See Combustion Air.
Air, Conditioned. Air that has been treated to achieve a desired level of temperature, humidity, or cleanliness.
CMC § 204.0 High relevance — show source text
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204.0
206.0
207.0
208.0
209.0
210.0
214.0
215.0
216.0
217.0
222.0
223.0
228.0
|||X|X|X|||||X|X|X|X|X|X|X||||||||| |Adopting Agency
Adopt Entire Chapter
Adopt Entire Chapter as
amended (amended sections
listed below)
Adopt only those sections
that are listed below
Chapter/Section
203.0
204.0
206.0
207.0
208.0
209.0
210.0
214.0
215.0
216.0
217.0
222.0
223.0
228.0
||||||||||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 2
DEFINITIONS
201.0 General.
201.1 Applicability. For the purpose of this code, the following terms have the meanings indicated in this chapter.
No attempt is made to define ordinary words, which are used in accordance with their established dictionary meanings, except where a word has been used loosely, and it is necessary to define its meaning as used in this code to avoid misunderstanding.
202.0 Definition of Terms.
202.1 General. The definitions of terms are arranged alphabetically according to the first word of the term.
203.0 – A –
Absorption Unit. An absorption refrigeration system that has been factory-assembled and tested prior to its installation.
Accepted Engineering Practice. That which conforms to technical or scientific-based principles, test, or standards that are accepted by the engineering profession.
Access Panel. A closure device used to cover an opening into a duct, an enclosure, equipment, or an appurtenance.
[NFPA 96:3.3.1]
Accessible. Where applied to a device, appliance, or equipment, “accessible” means having access thereto, but which first may require the removal of an access panel, door, or similar obstruction.
Accessible, Readily. Having a direct access without the necessity of removing a panel, door, or similar obstruction.
CMC § 14.7 Medium relevance — show source text
Flammability Classification. Refrigerants shall be classified for flammability in accordance with one of the following: Class 1. Refrigerants that do not show flame propagation where tested in air at 14.7 pound-force per square inch absolute (psia) (101 kPa) and 140°F (60°C). Class 2. Refrigerants having a lower flammability limit (LFL) of more than 0.00625 pound per cubic foot (lb/ft [3] ) (0.10012 kg/m [3] ) at 140°F (60°C), 14.7 psia (101 kPa), and a heat of combustion of less than 8169 British thermal units per pound (Btu/lb) (1.8988 E+07 J/kg).
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DEFINITIONS
Class 2L. Refrigerants having a lower flammability limit (LFL) of more than 0.00625 pound per cubic foot (lb/ft [3] ) (0.10012 kg/m [3] ) at 140°F (60°C), 14.7 psia (101 kPa), a heat of combustion of less than 8169 British thermal units per pound (Btu/lb) (1.8988 E+07 J/kg), and a maximum burning velocity of 3.9 inches per second (10 cm/s) where tested at 73.4°F (23°C) and 14.7 psia (101 kPa) in dry air. Class 3. Refrigerants that are highly flammable having a LFL of not more than 0.00625 lb/ft [3] (0.10012 kg/m [3] ) at 140°F (60°C) and 14.7 psia (101 kPa) or a heat of combustion not less than 8169 Btu/lb (1.8988 E+07 J/kg). Toxicity Classification. Refrigerants shall be classified for the toxicity in accordance with one of the following: Class A. Refrigerants have an occupational exposure limit (OEL) of not less than 400 parts per million (ppm). Class B. Refrigerants have an OEL of less than 400
ppm. Refrigeration Machinery Room. A room designed to house compressors and refrigerant pressure vessels. Refrigeration Room or Space. A room or space in which an evaporator or brine coil is located for the purpose of reducing or controlling the temperature within the room or space to less than 68°F (20°C). Refrigeration System, Absorption. A heat-operated closed refrigeration cycle in which a secondary fluid, the absorbent, absorbs a primary fluid, the refrigerant that has been vaporized in the evaporator. Refrigeration System, Direct. A system in which the evaporator or condenser of the refrigerating system is in direct contact with the air or other substances to be cooled or heated.
[ASHRAE 15:5.1.1]
Refrigeration System, Indirect. A system in which a secondary coolant cooled or heated by the refrigerating system is circulated to the air or other substance to be cooled or heated. Indirect systems are distinguished by the method of application given below.
CMC § 1104.4 Medium 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 § 0.00625 Medium relevance — show source text
** Refrigerants that are highly flammable having a LFL of not more than 0.00625 lb/ft [3] (0.10012 kg/m [3] ) at 140°F (60°C) and 14.7 psia (101 kPa) or a heat of combustion not less than 8169 Btu/lb (1.8988 E+07 J/kg). Toxicity Classification. Refrigerants shall be classified for the toxicity in accordance with one of the following: Class A. Refrigerants have an occupational exposure limit (OEL) of not less than 400 parts per million (ppm). Class B. Refrigerants have an OEL of less than 400
ppm. Refrigeration Machinery Room. A room designed to house compressors and refrigerant pressure vessels. Refrigeration Room or Space. A room or space in which an evaporator or brine coil is located for the purpose of reducing or controlling the temperature within the room or space to less than 68°F (20°C). Refrigeration System, Absorption. A heat-operated closed refrigeration cycle in which a secondary fluid, the absorbent, absorbs a primary fluid, the refrigerant that has been vaporized in the evaporator. Refrigeration System, Direct. A system in which the evaporator or condenser of the refrigerating system is in direct contact with the air or other substances to be cooled or heated.
[ASHRAE 15:5.1.1]
Refrigeration System, Indirect. A system in which a secondary coolant cooled or heated by the refrigerating system is circulated to the air or other substance to be cooled or heated. Indirect systems are distinguished by the method of application given below. [ASHRAE 15:5.1.2] Double Indirect Open Spray System. A system in which the secondary substance for an indirect open spray system is heated or cooled by the secondary coolant circulated from a second enclosure. [ASHRAE 15:5.1.2.2] Indirect Closed System. A system in which a secondary coolant passes through a closed circuit in the air or other substance to be cooled or heated. [ASHRAE 15:5.1.2.3] Indirect Open Spray System. A system in which a secondary coolant is in direct contact with the air or other substance to be cooled or heated. [ASHRAE 15:5.1.2.1] Refrigeration System, Mechanical. A combination of interconnected refrigerant-containing parts constituting one closed refrigerant circuit in which a refrigerant is circulated for the purpose of extracting heat and in which a compressor(s) is/are used for compressing the refrigerant vapor.
Refrigeration System, Self-Contained. A complete factory-assembled and tested system that is shipped in one or more sections and has no refrigerant-containing parts that are joined in the field by other than companion or block valves.
Registered Design Professional. An individual who is registered or licensed by the laws of the state to perform such design work in the jurisdiction.
Relief Valve, Vacuum. A device which automatically opens or closes for relieving a vacuum with the system, depending on whether the vacuum is above or below a predetermined value.
Removable. Capable of being transferred to another location with a limited application of effort and tools. [NFPA 96:3.3.42]
Replacement Air. See Air, Makeup.
CMC § 0.016 Medium relevance — show source text
0179|0.016|26|0.0217|0.019| |27|0.0164|0.014|27|0.0202|0.017| |28|0.0149|0.013|28|0.0187|0.016| |—|—|—|29|0.0172|0.014| |—|—|—|30|0.0157|0.013|
For SI units: 1 inch = 25.4 mm
- The thickness of the sheets set forth in the code correspond to the thickness shown under these columns. They are the approximate minimum thicknesses
and are based on the following references:
Carbon Sheet Steel—Thickness 0.071 inch (1.803 mm) and over:
ASTM A 568, Table 3, Thickness Tolerances of Hot-Rolled Sheet (Carbon Steel).
Carbon Sheet Steel—Thickness less than 0.071 inch (1.803 mm):
ASTM A 568, Table 23, Thickness Tolerances of Cold-Rolled Sheet (Carbon and High-Strength Low Alloy).
Galvanized Sheet Steel—All thicknesses:
ASTM A 653, Table 4, Thickness Tolerances of Hot-Dip Galvanized Sheet.
Minimum thickness is the difference between the thickness equivalent of each gauge and the maximum negative tolerance for the widest rolled width.
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INDEX
© 2024 International Association of Plumbing and Mechanical Officials. All rights reserved. The copyright in this index is separate and distinct from the copyright in the document that it indexes. The licensing provisions set forth for the document are not applicable to this index. This index may not be reproduced in whole or in part by any means without the express written permission of IAPMO.
– A –
ABSORPTION SYSTEM
Cooling system . . . . . . . . . . . . . . . . . . . . . . . Chapter 11 Duct system . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 6
Permit Fees . . . . . . . . . . . . . . . . . . . . . . . . . Table 104.5
ABSORPTION UNIT
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
Labeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307.4
Permit Fees . . . . . . . . . . . . . . . . . . . . . . . . . Table 104.5
ACCEPTED ENGINEERING
PRACTICE . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0, 309.1
Oil supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D 112.1
CMC § 1106.1.2 Medium relevance — show source text
1106.1.2 Equipment. Direct- and indirect-fired absorption equipment is used.
Exception: Direct and indirect-fired lithium bromide absorption systems using water as the refrigerant.
1106.1.3 A1 System. An A1 system having an aggregate combined compressor horsepower of 100 (74.6 kW) or more is used.
1106.1.4 A1 Refrigerant. The system contains other than a Group A1 refrigerant.
Exceptions:
(1) Lithium bromide absorption systems using water as the refrigerant.
(2) Systems containing less than 300 pounds (136.1 kg) of refrigerant R-123 and located in an approved exterior location.
Refrigeration machinery rooms shall house refrigerant-containing portions of the system other than the piping and evaporators permitted by Section 1104.4, discharge piping required of this chapter, and cooling towers regulated by Part II of this chapter, and their essential piping.
1106.2 Refrigeration Machinery Room, General Requirements. Where a refrigeration system is located indoors and a machinery room is required in accordance with Section 1106.1, the machinery room shall be in accordance with Section 1106.2.1 through Section 1106.2.9.1.
1106.2.1 Access. Machinery rooms shall not be prohibited from housing other mechanical equipment unless specifically prohibited elsewhere in this chapter. A machinery room shall be so dimensioned that parts are accessible with space for service, maintenance, and operations. There shall be clear head room of not less than
7.25 feet (2210 mm) below equipment situated over passageways. [ASHRAE 15:8.11.1]
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REFRIGERATION
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1106.2.2 Openings. Each refrigeration machinery room shall have a tight-fitting door or doors opening outward, self-closing where they open into the building and adequate in number to ensure freedom for persons to escape in an emergency. With the exception of access doors and panels in air ducts and air-handling units in accordance with Section 1106.2.3, there shall be no openings that will permit passage of escaping refrigerant to other parts of the building. [ASHRAE 15:8.11.2]
1106.2.3 Airflow. There shall be no airflow to or from an occupied space through a machinery room unless the air is ducted and sealed in such a manner as to prevent any refrigerant leakage from entering the airstream. Access doors and panels in ductwork and air-handling units shall be gasketed and tight fitting. [ASHRAE 15:8.11.3]
1106.2.4 Restricted Access. Access to the refrigeration machinery room shall be restricted to authorized personnel. Doors shall be clearly marked, or permanent signs shall be posted at each entrance to indicate this restriction. [ASHRAE 15:8.11.4]
**1106.2.5 Detectors and Alarms.
CMC § 3.3.39 Medium relevance — show source text
[NFPA 96:3.3.39]
Plenum. An air compartment or chamber including uninhabited crawl space areas above a ceiling or below a floor, including air spaces below raised floors of computer/data processing centers or attic spaces, to one or more ducts are connected and that forms part of either the supply-air, return-air, or exhaust-air system, other than the occupiable space being conditioned.
Plumbing Code. The Uniform Plumbing Code (UPC) promulgated by the International Association of Plumbing and Mechanical Officials (IAPMO), as adopted by this jurisdiction. [HCD 1 & HCD 2] Whenever the term “Plumbing Code” is used in this code, it shall mean the California Plumb- ing Code, Title 24, Part 5.
Portable Cooling Unit. A self-contained refrigerating system, not over 3 horsepower (hp) (2.2 kW) rating that has been factory assembled and tested, installed without supply-air ducts and without connecting any refrigerant-containing parts. This definition shall not include an absorption unit.
Portable Evaporative Cooler. An evaporative cooler that discharges the conditioned air directly into the conditioned space or zone without the use of ducts and can be readily transported from place to place without dismantling any portion thereof.
Portable Ventilating Equipment. Ventilating equipment that can be readily transported from place to place without dismantling a portion thereof and that is not connected to a duct.
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DEFINITIONS
Power Boiler Plant. One or more power steam boilers or power hot water boilers and connecting piping and vessels within the same premises.
Power Ventilator, Dryer Exhaust Duct. A fan used to boost airflow through a clothes dryer duct.
PP. Polypropylene.
Pressure, Design. The maximum allowable pressure for which a specific part of a system is designed. Pressure, Design (Refrigeration). The maximum allowable pressure for which a specific part of a refrigeration system is designed.
Pressure, Field Test. A test performed in the field to prove system tightness.
Pressure-Imposing Element. A device or portion of the equipment used for the purpose of increasing the pressure of the refrigerant vapor.
Pressure-Limiting Device. A pressure-responsive mechanism designed to automatically stop the operation of the pressure-imposing element at a predetermined pressure.
Pressure-Relief Device. A pressure-actuated valve or rupture member or fusible plug designed to automatically relieve excessive pressure.
Pressure Test. The minimum gauge pressure to which a specific system component is subjected under test condition. Pressure Vessel (Unfired). A closed container, having a nominal internal diameter exceeding 6 inches (152 mm) and a volume exceeding 1 [1] ⁄ 2 cubic feet (0.04 m [3] ), for liquids, gases, vapors subjected to pressures exceeding 15 psi (103 kPa), or steam under a pressure.
Pressure Vessel, Refrigerant. A refrigerant-containing receptacle that is a portion of a refrigeration system, but shall not include evaporators, headers, or piping of certain limited size and capacity.
CMC § 4.83 Medium relevance — show source text
** The part of the system designed to liquefy refrigerant vapor by removal of heat. Condensing Appliance. An appliance that condenses part of the water vapor generated by the burning of hydrogen in fuels.
Condensing Unit. A mechanical refrigeration system, consisting of one or more power-driven compressors, condensers, liquid receivers where provided, and the regularly furnished accessories that have been factory assembled and tested prior to its installation.
Conditioned Space. An area, room, space, or zone being heated or cooled by an appliance or equipment.
Confined Space. A room or space having a volume less than 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m [3] /kW) of the aggregate input rating of all fuel-burning appliances installed in that space. {NFPA 96:3.3.47.2}
Construction Documents. Plans, specifications, written, graphic, and pictorial documents prepared or assembled for describing the design, location, and physical characteristics of the elements of a project necessary for obtaining a permit.
Continuous Enclosure. A recognized architectural or mechanical component of a building having a fire resistance rating as required for the structure and whose purpose is to enclose the vapor removal duct for its full length to its termination point outside the structure without any portion of the enclosure having a fire resistance rating less than the required value. [NFPA 96:3.3.22.1]
Continuous Pilot. A pilot that burns without turndown throughout the entire period that the boiler is in service, whether or not the main burner is firing.
Continuous Weld. A metal-joining method that produces a product without visible interruption or variation in quality.
[NFPA 96:3.3.15] For the purpose of the definition, it specifically includes the exhaust compartment of hoods and welded joints of exhaust ducts, yet specifically does not include filter support frames or appendages inside hoods.
Conversion Burner, Gas. A unit consisting of a burner and its controls utilizing gaseous fuel for installation in an appliance originally utilizing another fuel. [NFPA 54:3.3.16.2]
Cooling. Air cooling to provide a room or space temperature of 68°F (20°C) or above.
Cooling System. All of the equipment, ducts and components, including associated refrigeration, intended or installed for the purpose of cooling air by mechanical means and discharging such air into any room or conditioned space. This definition shall not include an evaporative cooler.
Cooling Unit. A self-contained refrigeration system that has been factory assembled tested, and installed with or without conditioned air and ducts, without connecting any refrigerant-containing parts. This definition shall not include a portable cooling unit or an absorption unit.
Copper Alloy. A homogenous mixture of two or more metals in which copper is the primary component, such as brass and bronze.
Crawl Space. In a building, an area accessible by crawling, having a clearance less than human height, for access to plumbing or wiring, storage, etc.
CSST. An acronym for corrugated stainless steel tubing.
2025 CALIFORNIA MECHANICAL CODE 35
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
DEFINITIONS
206.0 – D –
CMC § 1105.4 Medium 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 § 104.5 Medium relevance — show source text
26 2025 CALIFORNIA MECHANICAL CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
DIVISION II SCOPE AND ADMINISTRATION
TABLE 104.5
MECHANICAL PERMIT FEES
Permit Issuance
For the issuance of each permit..................................................................................................................................._____ [1 ]
For issuing each supplemental permit for which the original permit has not expired or been canceled or finalized..................................................................................................................................................................._____ [1]
Unit Fee Schedule
- Furnaces:
For the installation or relocation of each forced-air or gravity-type furnace or burner, including ducts and vents attached to such appliance, not exceeding 100 000 British thermal units per hour (Btu/h)..........................................................................................................................................._____ [1 ]
For the installation or relocation of each forced-air or gravity-type furnace or burner, including ducts and vents attached to such appliance, exceeding 100 000 Btu/h................................................_____ [1 ]
For the installation or relocation of each floor furnace, including vent..............................................................._____ [1 ]
For the installation or relocation of each suspended heater, recessed wall heater, or floor-mounted unit heater ................................................................................................................................_____ [1]
- Appliance Vents:
For the installation, relocation, or replacement of each appliance vent installed and not included in an appliance permit .........................................................................................................................._____ [1]
- Repairs or Additions:
For the repair of, alteration of, or addition to each heating appliance, refrigeration unit, cooling unit, absorption unit, or each heating, cooling, absorption, or evaporative cooling, system including installation of controls regulated by this code ........................................................................._____ [1]
- Boilers, Compressors, and Absorption Systems:
For the installation or relocation of each boiler or compressor, not exceeding 3 horsepower (hp), or each absorption system not exceeding 100 000 Btu/h......................................................_____ [1 ]
For the installation or relocation of each boiler or compressor exceeding 3 hp, not exceeding 15 hp, or each absorption system exceeding 100 000 Btu/h and including 500 000 Btu/h ................................._____ [1 ]
For the installation or relocation of each boiler or compressor exceeding 15 hp, not exceeding 30 hp, or each absorption system exceeding 500 000 Btu/h, not exceeding 1 000 000 Btu/h............................._____ [1 ]
For the installation or relocation of each boiler or compressor exceeding 30 hp, not exceeding 50 hp, or for each absorption system exceeding 1 000 000 Btu/h, not exceeding 1 750 000 Btu/h............................................................................................................................._____ [1] For the installation or relocation of each boiler or compressor exceeding 50 hp, or each absorption system exceeding 1 750 000 Btu/h........................................................................................_____ [1]
- Air Handlers:
For each air-handling unit not exceeding 10 000 cubic feet per minute (CFM), including ducts attached thereto........................................................................................................................_____ [1, 2]
- Evaporative Coolers: For each air-handling unit exceeding 10 000 CFM ....
Frequently asked questions
What exactly makes a system an “Absorption Unit” instead of just an absorption system?
An “Absorption Unit” must be a factory‑assembled absorption refrigeration system that was factory‑tested before installation — that factory‑assembly/test requirement is the defining point in § 203.0.
If an absorption system is field‑assembled, do the same rules and fees apply?
No — field‑assembled absorption systems are not the defined “Absorption Unit.” For permitting and fee classification you must check whether the equipment meets the factory‑assembled requirement and then use Table 104.5 and the refrigeration chapter rules.
Does a portable cooling unit ever count as an Absorption Unit?
No — the portable cooling unit definition explicitly does not include an absorption unit; check the Chapter 2 definitions to confirm which definition controls in your case.
Are lithium‑bromide absorption chillers handled the same as other absorption units?
Some lithium‑bromide absorption systems using water as the refrigerant are treated as exceptions in refrigeration machinery room rules — consult the refrigeration machinery room provisions (e.g., § 1106.1.2) before assuming identical treatment.
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