CRC · California Residential Code

Which CRC chapters cover mechanical/HVAC (and which are NOT adopted)?

Q: My contractor referenced CRC Chapter 14 — is that authoritative?

Not at the state level. CRC Chapter 14 is not adopted (CRC directs you to the CMC). Ask the contractor to cite the corresponding CMC sections (and Energy Code where applicable) for the technical rules.

The CRC lists mechanical chapters, but California did not adopt CRC/IRC Chapters 12–14 for statewide technical HVAC rules; those chapters are explicitly noted as “not adopted” and the state refers users to the California Mechanical Code (CMC, Title 24, Part 4) for installation, clearances and equipment rules. The CRC still controls procedural items like inspection timing and permits (e.g., § R109.1 and § R109.1.2).

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Residential Code (CRC) shows the model IRC chapters for mechanical/HVAC but the State of California does not adopt those chapters for residential statewide enforcement. Specifically, the CRC Table of Contents states Chapter 12 Mechanical Administration, Chapter 13 General Mechanical System Requirements, and Chapter 14 Heating and Cooling Equipment and Appliances are not adopted in California — see the California Mechanical Code (CMC), Title 24, Part 4. See the CRC table-of-contents notes for these chapters and the CMC rule explaining how chapters may be marked “not adopted” § 1.1.11 .

The short rule: the CRC lists the mechanical/HVAC chapters, but the State replaces them — use the California Mechanical Code (CMC, Title 24, Part 4) for mechanical administration and equipment requirements (CRC says “not adopted; see CMC”).

Requirements in detail

Which chapters in the CRC are relevant (and what CRC says)

Chapter 12 — Mechanical Administration — not adopted; CRC directs users to the California Mechanical Code, Title 24, Part 4.
Chapter 13 — General Mechanical System Requirements — not adopted; see CMC.
Chapter 14 — Heating and Cooling Equipment and Appliances — not adopted; see CMC.

The CMC explains the adoption/format rule: when a model-code chapter is marked “Not adopted by the State of California” the state did not adopt that chapter as part of the CMC and it may be left for local adoption; see § 1.1.11 of the CMC (Format) for the official explanation. § 1.1.11 is the controlling CMC administrative provision on the format/adoption-by-chapter approach.

Decision table — when to use CRC (residential text) vs CMC (enforceable mechanical rules)

Decision question	If answer = Yes	Where to look	Code Reference
Is the subject the CRC chapter text for mechanical (Ch.12–14)?	Yes — but statewide CRC does not adopt those chapters	Use the CMC (Title 24, Part 4) for enforceable mechanical rules	CRC Table of Contents — Chapter notes
Does the local jurisdiction mention local adoption of IRC mechanical chapters?	If the local ordinance adopts IRC mechanical chapters	Follow local ordinance + CMC guidance for state-mandated items	CMC § 1.1.11 (format/adoption rules)
Is the work an inspection/permit item in the CRC (mechanical rough-in)?	Permits/inspections still required — CRC requires inspections for mechanical systems; but the technical/mechanical standards come from CMC	See CRC inspection sections (R109.1, R109.1.2) and CMC for technical requirements	§ R109.1 / § R109.1.2 — CRC (inspections) ; CMC § 1.1.11 (adoption rule)

Notes: the CRC still contains administrative inspection provisions (for permits and inspection scheduling) — those procedural CRC sections (e.g., § R109.1, § R109.1.2) remain relevant for how and when inspections occur, even though the mechanical technical requirements are in the CMC.

Exceptions & special cases

Local jurisdictions may adopt portions of the model IRC mechanical chapters locally (ordinance). If so, the local adoption governs in that jurisdiction unless it conflicts with state-adopted CMC provisions. The CMC explains this chapter-by-chapter adoption approach in § 1.1.11.
Energy-efficiency requirements for heating/cooling (equipment sizing, clearances, minimum efficiencies, etc.) are handled by the California Energy Code (Title 24, Part 6) and related CRC notes — see the CRC cross-reference to the California Energy Code and the Energy Code text (design temps, condensing unit clearance rules). For example, the Energy Code lists design temperatures (68°F heating / 75°F cooling) and an example clearance rule for condensing units.

If a required detail or numeric threshold is missing from the retrieved CRC text (for example, a specific equipment clearance or efficiency table that would normally be in a mechanical chapter), you must consult the CMC (and Part 6 for energy rules); the CRC explicitly directs you there. The CRC Table of Contents notes the non‑adoption and referral.

Common mistakes

Assuming the CRC chapters 12–14 contain the enforceable technical rules for mechanical/HVAC. (They do not — CRC explicitly marks them not adopted and points to the CMC.)
Quoting IRC/CRC mechanical specifications (e.g., duct construction, appliance clearances, combustion-air details) as if they are state law — instead, use the CMC and California Energy Code for the state-adopted technical provisions. See CMC § 1.1.11 for the adoption policy.
Forgetting CRC inspection rules: inspectors still use CRC procedural sections (for how inspections are requested and performed) — e.g., § R109.1 and § R109.1.2. Those remain applicable for inspection timing and permit process even though the technical standards are in the CMC.

Worked example — replacing a furnace in a 2,000 ft² single-family home

Scenario: homeowner replaces an existing gas furnace and outdoor condensing unit that serve a 2,000 ft² house.

Step 1 — Which code sets the technical requirements?

The CRC itself marks mechanical Chapters 12–14 as not adopted and redirects to the CMC for technical installation, clearances, and equipment rules. So do not rely on CRC Chapter 14 for technical requirements; use the CMC (Title 24, Part 4).

Step 2 — Inspections and permits

Permit application and inspection scheduling follow CRC procedural rules: see § R109.1 (inspections) and § R109.1.2 (plumbing, mechanical, gas and electrical systems inspection) for when rough and final inspections occur. Expect to pull a mechanical permit and schedule the rough and final inspections under those CRC procedures.

Step 3 — Numeric decisions you must make (examples grounded in Energy Code where applicable)

Equipment sizing method: use ACCA Manual J or an approved method — the California Energy Code requires building heating/cooling loads determined by acceptable methods; design indoor temperatures for sizing are 68°F heating and 75°F cooling. Use the Energy Code guidance for sizing validation.
Outdoor condensing-unit clearance: the Energy Code requires a minimum clearance of 5 feet from dryer exhaust outlets to the condensing unit (example mandatory clearance rule). Confirm the exact CMC/Manufacturer clearance in addition to this Energy Code requirement.

Putting numbers to the house:

If the Manual J determines the peak cooling load = 36,000 Btu/h (3 tons), select equipment that meets CMC/Manufacturer installation clearances and that complies with applicable Energy Code efficiency requirements (consult the CMC for installation and Part 6 for efficiency). The CRC itself will not supply the sizing tables — it refers you to the CMC and Energy Code.

Related provisions (CRC sections)

§ R109.1 — Inspections: on-site construction inspections procedure (CRC).
§ R109.1.2 — Plumbing, mechanical, gas and electrical systems inspection (CRC).
Part V — Mechanical — Note in CRC: Part V is not adopted; see California Mechanical Code, Title 24, Part 4. (CRC Table of Contents / Parts notes).
See also the California Energy Code (Title 24, Part 6) for space-conditioning sizing, design conditions and some installation requirements (design temperatures, condensing-unit clearances referenced above).

Code references

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

CRC § 207.1 High relevance — show source text
Exceptions:
1. Heat rejection devices included as an integral part of the equipment listed in Tables A6.207.1-A through A6.207.1-E.
2. Condenser fans serving multiple refrigerant circuits.
3. Condenser fans serving flooded condensers.
4. Up to [1] / 3 of the fans on a condenser or tower with multiple fans where the lead fans comply with the speed control requirement.
A6.207.2.3.3 Tower flow turndown. Open cooling towers configured with multiple condenser water pumps shall be designed so that all cells can be run in parallel with the larger of:
1. The flow that’s produced by the smallest pump or
2. 33 percent of the design flow for the cell.
A6.207.2.3.4 Limitation on centrifugal fan cooling towers. Open cooling towers with a combined rated capacity of 900 gpm and greater at 95°F condenser water return, 85°F condenser water supply and 75°F outdoor wet-bulb temperature shall use propeller fans and shall not use centrifugal fans.

Exceptions:
1. Cooling towers that are ducted (inlet or discharge) or have an external sound trap that requires external static pressure capability.
2. Cooling towers that meet the energy efficiency requirement for propeller fan towers in Section A6.207.1, Table A6.207.1-G.
APPENDIX A6.1-18 2025 CALIFORNIA GREEN BUILDING STANDARDS CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

APPENDIX A6.1 — VOLUNTARY STANDARDS FOR HEALTH FACILITIES [OSHPD 1, 2 & 4]

A6.207.2.4 Hydronic system measures.

A6.207.2.4.1 Hydronic variable flow systems. HVAC chilled and hot water pumping shall be designed for variable fluid flow and shall be capable of reducing pump flow rates to no more than the larger of: a) 50 percent or less of the design flow rate; or b) the minimum flow required by the equipment manufacturer for the proper operation of equipment served by the system.

Exceptions:
1. Systems that include no more than three control valves.
2. Systems having a total pump system power less than or equal to 1 [1] / 2 HP.
A6.207.2.4.2 Chiller isolation. When a chilled water plant includes more than one chiller, provisions shall be made so that flow through any chiller is automatically shut off when that chiller is shut off while still maintaining flow through other operating chiller(s). Chillers that are piped in series for the purpose of increased temperature differential shall be considered as one chiller.

A6.207.2.4.3 Boiler isolation. When a hot water plant includes more than one boiler, provisions shall be made so that flow through any boiler is automatically shut off when that boiler is shut off while still maintaining flow through other operating boiler(s).

A6.207.2.4.4 Chilled and hot water temperature reset controls. Chilled and hot water systems with a design capacity exceeding 500,000 Btu/hr supplying chilled or heated water (or both) shall include controls that automatically reset supply water temperatures as a function of representative building loads or outside air temperature.

Exception: Hydronic systems that use variable flow to reduce pumping energy in accordance with Section A6.207.2.4.1.

CRC § 1.11.0. High relevance — show source text

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

APPENDIX A – RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SYSTEM DESIGN

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

Adopting Agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency	BSC	BSC- CG	SFM	1	2	1-AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopt Entire Chapter
Adopt Entire Chapter as amended (amended sections listed below)
Adopt only those sections that are listed below
Chapter/Section

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 387

388 2025 CALIFORNIA MECHANICAL CODE

APPENDIX A

RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SYSTEM DESIGN

(Loads, Equipment, Ducts) [ACCA]

The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.

The following Residential Plans Examiner Review Form for HVAC System Design (Loads, Equipment, Ducts), Form

390 2025 CALIFORNIA MECHANICAL CODE

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

APPENDIX B – PROCEDURES TO BE FOLLOWED TO PLACE GAS EQUIPMENT IN OPERATION

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

CRC § 1.11.0. High relevance — show source text

2025 CALIFORNIA MECHANICAL CODE 387

388 2025 CALIFORNIA MECHANICAL CODE

APPENDIX A

RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SYSTEM DESIGN

(Loads, Equipment, Ducts) [ACCA]

The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.

The following Residential Plans Examiner Review Form for HVAC System Design (Loads, Equipment, Ducts), Form

390 2025 CALIFORNIA MECHANICAL CODE

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

APPENDIX B – PROCEDURES TO BE FOLLOWED TO PLACE GAS EQUIPMENT IN OPERATION

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

Adopting Agency	BSC	BSC- CG	SFM	HCD	Col6	Col7	DSA	Col9	Col10	OSHPD	Col12	Col13	Col14	Col15	Col16	Col17	BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting Agency	BSC	BSC- CG	SFM	1	2	1-AC	AC	SS	SS/CC	1	1R	2	3	4	5	6	6	6	6	6	6	6	6	6
Adopt Entire Chapter	X									X	X	X	X	X	X	X
Adopt Entire Chapter as amended (amended sections listed below)
Adopt only those sections that are listed below
Chapter/Section

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 391

CRC § 503.4.6.3.1. High relevance — show source text
Each isolation area shall be controlled independently by a device meeting the requirements of Section E 503.4.6.3.1. For central systems and plants, controls and devices shall be provided to allow stable system and equipment operation for any length of time while serving only the smallest isolation area served by the system or plant.

Exceptions: Isolation devices and controls are not required for the following:

(1) Exhaust air and outdoor air connections to isolation zones where the fan system to which they connect is not more than 5000 ft [3] /min (2.3597 m [3] /s).

(2) Exhaust airflow from a single isolation zone of less than 10 percent of the design airflow of the exhaust system to which it

connects.

(3) Zones intended to operate continuously or intended to be inoperative only when all other zones are inoperative. [ASHRAE 90.1:6.4.3.3.4]

2025 CALIFORNIA MECHANICAL CODE 423

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APPENDIX E

E 503.4.6.3.5 Automatic Control of HVAC in Hotel/Motel Guest Rooms. Hotels and motels with more than 50 guest rooms shall be provided with automatic controls for the HVAC equipment serving each guest room capable of and configured according to the requirements in Section E 503.4.6.3.5.1. [ASHRAE 90.1:6.4.3.3.5]

E 503.4.6.3.5.1 Guest Room HVAC Set-Point Control. Within 30 minutes of all occupants leaving the guest room, HVAC set points shall be automatically raised by not less than 4°F (2°C) from the occupant set point in the cooling mode and automatically lowered by at least 4°F (2°C) from the occupant set point in the heating mode. When the guest room is unrented and unoccupied, HVAC set points shall be automatically reset to 80°F (27°C) or higher in the cooling mode and to 60°F (16°C) or lower in the heating mode. Unrented and unoccupied guest rooms shall be determined by either of the following:

(1) The guest room has been continuously unoccupied for up to 16 hours.

(2) A networked guest room control system indicates the guest room is unrented and the guest room is unoccupied for no more than 30 minutes.

Exceptions:

(1) A networked guest room control system shall be permitted to return the thermostat set points to their default occupied set points 60 minutes prior to the time the room is scheduled to be occupied.

(2) Cooling for humidity control shall be permitted during unoccupied periods.

E 503.4.6.4 Stair and Elevator Shaft Vent Dampers. Where stair and elevator shafts have vents, they shall be equipped with motorized dampers that are capable of and configured to automatically close during normal building operation and are interlocked to only open as required by fire and smoke detection systems, or by thermostatic control systems.
CRC § 0.293 High relevance — show source text

chilled-water, or hot-water system have DDC| |Alteration or addition|Air-handling system or fan coil|Where existing air-handling system(s) and fan-coil(s)
served by the same chilled- or hot-water plant have DDC| |Alteration or addition|New air-handling system and all new zones
served by the system|Individual systems with fan system bhp of 10 hp or more
and supplying more than three zones and more than 75 per-
cent of zones are new| |Alteration or addition|New or upgraded chilled-water plant|Where all chillers are new and plant design cooling capac-
ity is 300 000 Btu/h or more| |Alteration or addition|New or upgraded hot-water plant|Where all boilers are new and plant design heating capacity
is 300 000 Btu/h or more|

For SI units: 1000 British thermal units = 0.293 kW, 1 horsepower = 0.746 kW

2025 CALIFORNIA MECHANICAL CODE 427

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APPENDIX E

cation or DDC system accessible by operating or service personnel, or annunciated locally on zone thermostats. [ASHRAE 90.1:6.4.3.12]

E 503.4.7 HVAC System Construction and Insu- lation. HVAC Ducts shall be constructed in accordance with provisions contained in the SMACNA HVAC Duct Construction Standard. HVAC system construction and insulation shall comply with Section E 503.4.7.1 and Section E 503.4.7.2.1.

E 503.4.7.1 Insulation. Insulation required by this section shall be installed in accordance with industry-accepted standards. These requirements shall not apply to HVAC equipment. Insulation shall be protected from damage, including that due to sunlight, moisture, equipment maintenance, and wind, but not limited to the following:

(1) Insulation exposed to weather shall be suitable for outdoor service (e.g., protected by aluminum, sheet metal, painted canvas, or plastic cover). Cellular foam insulation shall be protected as above or painted with a coating that is water retardant and provides shielding from solar radiation that can cause degradation of the material.

(2) Insulation covering chilled-water piping, refrigerant suction piping, or cooling ducts located outside the conditioned space shall include a vapor retardant located outside the insulation (unless the insulation is inherently vapor retardant), all penetrations and joints of which shall be sealed. [ASHRAE 90.1:6.4.4.1.1]

E 503.4.7.1.1 Duct and Plenum Insula- tion. Supply and return ducts and plenums installed as part of an HVAC air distribution system shall be thermally insulated in accordance with Table E 503.7.2.

Exceptions:

(1) Factory-installed plenums, casings, or ductwork furnished as a part of HVAC equipment tested and rated in accordance with Section E 503.4 through Section E 503.4.4.1.

(2) Ducts or plenums located in heated spaces, semi-heated spaces, or cooled spaces.
CRC § 1220.4.2 High relevance — show source text
8|1220.4.2 – 1220.4.6| |1221.7|1221.6| |1308.2 – 1308.4.1|1308.3 – 1308.5.1| |Table 1308.3.1|Table 1308.4.1| |1308.4.2|1308.5.2| |1308.4.2.2 – 1308.6.4|1308.5.2.1 – 1308.7.3| |Table 1308.4.6.2|Table 1308.5.6.2| |1308.6.5 – 1308.13.1|1308.7.7 – 1308.14.1| |1312.1.2 – 1312.1.3|1312.1.1 – 1312.1.2| |Chapter 17|Appendix F| |Chapter 18|Chapter 17| |D 103.2|D 103.1| |E 503.5.6.7|E 503.5.6.6| |E 503.5.7.2 – E 503.5.7.6|E 503.5.7.1 – E 503.5.7.5| |Table E 503.5.7.2|Table E 503.5.7.1| |Table E 503.5.7.6|Table E 503.5.7.5| |Table E 503.5.10.1.2(1)|Table E 503.5.10(1)| |Table E 503.5.10.1.2(2)|Table E 503.5.10(2)| |E 503.5.10.1.2|E 503.5.10| |E 503.5.10.2 – E 503.5.10.2.2|E 503.5.10.1 – E 503.5.10.1.2| |E 503.5.12.1|E 503.5.12| |E 503.5.12.2|E 503.5.12.1| |E 503.6.5.4|E 503.6.5.4.1|

xxii 2025 CALIFORNIA MECHANICAL CODE

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Uniform Mechanical Code – 2024 Edition:

The Uniform Mechanical Code contains complete requirements for the installation and maintenance of heating, ventilating, cooking and refrigeration systems.

Uniform Mechanical Code Illustrated Training Manual:
CRC § 1215.0 High relevance — show source text
HYDRONIC SPACE HEATING . . . . . . . . . . . . . . . . . 1215.0

HYDRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 12

Auxiliary systems . . . . . . . . . . . . . . . . . . . . . . . . 1220.0

Appliances and equipment . . . . . . . . . . . . . . . . . 1207.0

Boilers . . . . . . . . . . . . . . . . . . 1207.2, 1207.2.1, 1207.2.2

Circulators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1208.0

Clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221.7

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210.0

Embedded piping and joints . . . . . . . . . . . . . . . . 1221.2

Expansion tanks . . . . . . . . . . . . . . . . . . . . . . . . . 1209.0

Hangers and supports. . . . . . . . . . . . . . . . . . . . . 1210.3

Heat emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1201.7

Heat pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207.5

Heat sources . . . . . . . . . . . . . . . . . . . . . . . . . . . 1203.1

Heat transfer fluid . . . . . . . . . . . . . . . . . . 1201.3, 1204.7

Identification of piping . . . . . . . . . . . . . . . . . . . . . 1204.0

Installation . . . . . . . . . . . . . . . . . . . . . . . 1205.0, 1221.0

Insulation. . . . . . . . . 1201.2, 1217.8.2, 1217.10, 1220.4.7

Joints and connections . . . . . . . . . . . . . . . . . . . . 1211.0

Materials . . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1

Protection of potable water supply . . . . . . . . . . . 1202.0

Radiant heating and cooling . . . . . . . . . . . . . . . . 1217.0

Snow melt systems . . . . . . . . . . . . . . . . 1220.4, 1220.0,

1217.8.2, Table 1220.4.2
CRC § 1.8.2 High relevance — show source text
1.8.2 Authority and Abbreviations.

1.8.2.1 General. The Department of Housing and Community Development is authorized by law to prom- ulgate and adopt building standards and regulations for several types of building applications. The applications under the authority of the Department of Housing and Community Development are listed in Sections 1.8.2.1.1 through 1.8.2.1.3.

1.8.2.1.1 Housing Construction.

Application – Hotels, motels, lodging houses, apart- ments, dwellings, dormitories, condominiums, shel- ters for homeless persons, congregate residences, employee housing, factory-built housing, and other types of dwellings containing sleeping accommoda- tions with or without common toilet or cooking facil- ities including accessory buildings, facilities, and uses thereto. Sections of this code which pertain to applications listed in this section are identified using the abbreviation “HCD 1.”

Enforcing Agency – Local building department or the Department of Housing and Community Devel- opment.

Authority Cited – Health and Safety Code Sections 17040, 17920.9, 17921, 17921.5, 17921.6, 17921.10, 17922, 17922.6, 17922.12, 17922.14, 17922.15, 17926, 17927, 17928, 17958.12, 18938.3, 18944.11, and 19990; and Government Code Section 12955.1.

References – Business and Professions Code Divi- sion 5; Health and Safety Code Sections 17000 through 17062.5, 17910 through 17995.5, 18200 through 18700, 18860 through 18874, 18938.6, 18941, 19890, 19891, 19892 and 19960 through 19997; Civil Code Sections 832, 1101.4, 1101.5, 1954.201, 1954.202 and 5551; and Government Code Sections 8698.4, 12955.1 and 12955.1.1. Cali- fornia Code of Regulations, Title 20, Sections 1605.1, 1605.3 and 1607.

1.8.2.1.2 Housing Accessibility.

Application – Covered multifamily dwellings as defined in Chapter 2 of the California Code of Regu- lations, Title 24, Part 2, also known as the California Building Code including, but not limited to, lodging houses, dormitories, timeshares, condominiums, shel- ters for homeless persons, congregate residences, apartments, dwellings, employee housing, factory- built housing, and other types of dwellings containing sleeping accommodations with or without common toilet or cooking facilities.
CRC § 150.2 High relevance — show source text
Exception 3 to Section 150.2(a): Space-conditioning system. When heating or cooling will be extended to an addition from the existing system(s), the existing heating and cooling equipment need not comply with Part 6. The heating system capacity must be adequate to meet the minimum requirements of CRC 303.10.

Exception 4 to Section 150.2(a): Space-conditioning system ducts. When any length of duct is extended from an existing duct system to serve the addition, the existing duct system and the extended duct shall meet the applicable requirements specified in Section 150.2(b)1Di and 150.2(b)1Dii.

Exception 5 to Section 150.2(a): Additions 1,000 square feet or less are not required to comply with the ventilation cooling requirements of Section 150.1(c)12.

Exception 6 to Section 150.2(a): Photovoltaic systems, as specified in Section 150.1(c)14, are not required for additions.
1. Prescriptive approach. Additions to existing buildings shall meet the following additional requirements: A. Additions that are greater than 700 square feet shall meet the requirements of Section 150.1(c), with the following modifications:
i. Extensions of existing wood-framed walls may retain the dimensions of the existing walls and shall install cavity insulation of R-15 in a 2 × 4 framing and R-21 in a 2 × 6 framing. ii. The maximum allowed fenestration area shall be the greater of 175 square feet or 20 percent of the addition floor area, and the maximum allowed west-facing fenestration area shall be the greater of 70 square feet or the requirements of Section 150.1(c).

iii. Alterations that add fenestration area shall have a maximum SHGC value of 0.23 in Climate Zone 15.

iv. When existing siding of a wood-framed wall is not being removed or replaced, cavity insulation of R-15 in a 2 × 4 framing and R-21 in a 2 × 6 framing shall be installed and continuous insulation is not required. v. Additions that consist of the conversion of existing spaces from unconditioned to conditioned space shall not be required to perform the following as part of QII: a. Existing window and door headers shall not be required to be insulated. b. Air sealing shall not be required when the existing air barrier is not being removed or replaced. B. Additions that are 700 square feet or less shall meet the requirements of Section 150.1(c), with the following modifications: i. Roof and ceiling insulation in a ventilated attic shall meet one of the following requirements: a. In Climate Zones 1, 2, 4, and 8 through 16, achieve an overall assembly U -factor not exceeding 0.025. In wood framed assemblies, compliance with U -factors may be demonstrated by installing insulation with an R -value of R-38 or greater. b. In Climate Zones 3, and 5 through 7, achieve an overall assembly U -factor not exceeding 0.031. In wood framed assemblies, compliance with U -factors may be demonstrated by installing insulation with an R value of R-30 or greater.

ii. Radiant barriers shall be installed in Climate Zones 2-15.

iii.
CRC § 9.2.2 High relevance — show source text
Entire Chapter||||||||||||||||||||||||| |Adopt Entire Chapter as
amended (amended sections
listed below)||||||||||||||||||||||||| |Adopt only those sections
that are listed below|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| |Chapter/Section||||||||||||||||||||||||| |1.9.2.2 & 1.9.2.2.1|||||||||X|||||||||||||||| |1.10.1 and subsections||||||||||X|X|||||||||||||| |1.10.2 and subsections||||||||||||X||||||||||||| |1.10.3 and subsections|||||||||||||X|||||||||||| |1.10.4 and subsections||||||||||||||X||||||||||| |1.10.5 and subsections|||||||||||||||X|||||||||| |1.10.6 and subsections||||||||||||||||X||||||||| |1.11.0 through 1.11.11|||X|||||||||||||||||||||| |1.12.0|||||||||||||||||||||||X|| |1.13.0||||||||||||||||||||X||||| |1.14.0||||||||||||||||||||||||X| |Division II –
Scope and Administration||||||||||||||||||||||||| |101.0 – 104.1||||||||||X|X|X|X|X|X|||||||||| |104.2 (Items 1 – 5)||||X|X|||||||||||||||||||| |104.3 – 107.0||||||||||X|X|X|X|X|X|||||||||| |104.4.3.1|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.

2 2025 CALIFORNIA MECHANICAL CODE

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

CHAPTER 1

ADMINISTRATION

DIVISION I CALIFORNIA ADMINISTRATION

1.1.0 General.
CRC § 2603.10 High relevance — show source text
2603.10

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REFERENCED STANDARDS

SDI Steel Deck Institute, 2661 Clearview Road #3, Allison Park, PA 15101

ANSI/SDI QA/QC—2022: Standard for Quality Control and Quality Assurance for Installation of Steel Deck

1705.2.3

ANSI/SDI SD—2022: Standard for Steel Deck

2208.1

SFM State of California, Department of Forestry and Fire Protection, Office of the State Fire Marshal, P.O. Box 944246, Sacramento, CA 94246-2460

12-3: Releasing Systems for Security Bars in Dwellings

1029.4

12-7-3: Fire-testing Furnaces

NA

12-7A-1: Exterior Wall Siding and Sheathing

703A.7, 707A.2

12-7A-2: Exterior Window

703A.7, 708A.2.1

12-7A-3: Under Eave

703A.7, 707A.8

12-7A-4: Decking:

703A.7, 709A.3

12-7A-4A: Decking Alternate Method A

703A.7, 709A.3

12-7A-5: Ignition Resistant Building Material

703A.7, 709A.3

12-8-100: Room Fire Tests for Wall and Ceiling Materials

NA

12-10-1: Power Operated Exit Doors

NA

12-10-2: Single Point Latching or Locking Devices

NA

12-10-3: Emergency Exit and Panic Hardware

NA

(The Office of the State Fire Marshal standards referred to above are found in the California Code of Regulations, Title 24, Part 12.):

SJI Steel Joist Institute, 140 Evans Street, Suite 203, Florence, SC 29501

SJI 100—2020: Standard Specification for K-Series, LH-Series, and DLH-Series Open Web Steel Joists and for Joist Girders

1604.3.3, 2207.1, 2207.2, 2207.3, 2207.4, 2207.5

SJI 200—2015: Standard Specification for CJ-Series Composite Steel Joists

1604.3.3, 2207.1, 2207.2, 2207.3, 2207.4, 2207.5

SPRI Single-Ply Roofing Industry, 465 Waverly Oaks Road, Suite 421, Waltham, MA 02452

ANSI/SPRI GT-1—2022: Test Standard for External Gutter Systems

1504.6.1, 1511.7.6.1

ANSI/SPRI RP-4—2019: Wind Design Standard for Ballasted Single-ply Roofing Systems

1504.5

ANSI/SPRI VF-1—2021: External Fire Design Standard for Vegetative Roofs
CRC § 110.2 High relevance — show source text
Compliance with the cooling-only perfor-
mance is required as defined in Notes b and c of Table 110.2-I.
h. Water-to-water heat pumps with a capacity less than 135,000 Btu/h are included in Table 110.2-B, Heat Pumps—Minimum Efficiency Requirements.
i. Source leaving liquid temperature.
1. The cooling evaporator liquid flow rate used for the heating rating for a reverse cycle air-to-water heat pump shall be the flow rate determined during the full-load cool-
ing rating.
2. The cooling evaporator liquid flow rate for the simultaneous cooling and heating and heat recovery liquid cooled chilling packages rating shall be the liquid flow rates
from the cooling operation full-load rating.
3. For heating-only fluid-to-fluid chiller packages, the evaporator flow rate obtained with an entering liquid temperature of 54°F and a leaving liquid temperature of 44°F
shall be used.
j. NA means the requirements are not applicable.|a. The size category is the full-load net refrigeration cooling mode capacity, which is the capacity of the evaporator available for cooling of the thermal load external to the chill-
ing package.
b. For air source heat pumps, compliance with both the 47°F and 17°F heating source outdoor air temperature (OAT) rating efficiency is required for heating.
c. Heating full-load rating conditions are at standard rating conditions defined in AHRI 550/590 (I-P), Table 4, which includes the impact of defrost for air source heating ratings.
d. For units that operate in both cooling and heating, compliance with both the cooling and heating efficiency is required.
e. For heat recovery heating chilling package applications where there is simultaneous cooling and heating, compliance with the heating performance heat recover COPHR is
only required at one of the four heating AHRI 550/590 (I-P) standard ratings conditions of Low, Medium, Hot-Water 1 or Hot-Water 2. Compliance with the cooling-only perfor-
mance is required as defined in Notes b and c of Table 110.2-I.
f. For liquid source heat recovery chilling packages that have capabilities for heat rejection to a heat recovery condenser and a tower condenser, the COPHR applies to operation
at full load with 100 percent heat recovery (no tower rejection). Units that only have capabilities for partial heat recovery shall meet the requirements of Table 110.2-D, Water
Chilling Packages—Minimum Efficiency Requirements.
g. For heat recovery heating chilling package applications where there is simultaneous cooling and heating, compliance with the heating performance heat recover COPHR is
only required at one of the four heating AHRI 550/590 (I-P) standard ratings conditions of Low, Medium, Hot-Water 1 or Hot-Water 2. Compliance with the cooling-only perfor-
mance is required as defined in Notes b and c of Table 110.2-I.
h. Water-to-water heat pumps with a capacity less than 135,000 Btu/h are included in Table 110.2-B, Heat Pumps—Minimum Efficiency Requirements.
i. Source leaving liquid temperature.
1. The cooling evaporator liquid flow rate used for the heating rating for a reverse cycle air-to-water heat pump shall be the flow rate determined during the full-load cool-
ing rating.
2. The cooling evaporator liquid flow rate for the simultaneous cooling and heating and heat recovery liquid cooled chilling packages rating shall be the liquid flow rates
from the cooling operation full-load rating.
3.
CRC § 1.9.1. High relevance — show source text
Sections of this code identified by the abbreviation “HCD 1-AC” require specific accommodations for persons with disabilities as defined in Chapter 2 of the California Building Code. The application of such provisions shall be in conjunction with other require- ments of the Building Standards Code and apply only to newly constructed covered multifamily dwellings as defined in Chapter 2 of the California Building Code. “HCD 1-AC” applications include, but are not limited to, the following: 1. All newly constructed covered multifamily dwellings as defined in Chapter 2 of the California Building Code. 2. New common use areas as defined in Chapter 2 of the California Building Code serving existing covered multifamily dwellings. 3. Additions to existing buildings, where the addition alone meets the definition of covered multifamily dwellings as defined in Chapter 2 of the California Building Code. 4. New common use areas serving new covered multifamily dwellings. 5. Where any portion of a building’s exterior is preserved, but the interior of the building is removed, including all structural portions of floors and ceilings, the building is considered a new building for determining the application of California Build- ing Code, Chapter 11A.

“HCD 1-AC” building standards generally do not apply to public use areas or public accommodations such as hotels and motels and public housing. Public use areas, public accommodations and public housing, as defined in Chapter 2 of the California Build- ing Code, are subject to the Division of the State Architect (DSA-AC) in Chapter 11B and are referenced in California Building Code Section 1.9.1.

Enforcing agency— Local building department or the Department of Housing and Community Development.

Authority cited— Health and Safety Code Sections 17040, 17920.9, 17921, 17921.5, 17921.6, 17921.10, 17922, 17922.6, 17922.12, 17922.14, 17926, 17927, 17928, 17958.12, 18938.3, 18944.11 and 19990; and Government Code Sections 12955.1 and 12955.1.1.

Reference— Health and Safety Code Sections 17000 through 17062.5, 17910 through 17995.5, 18200 through 18700, 18860 through 18874, 18938.6, 18941, 19890, 19891, 19892 and 19960 through 19997; Civil Code Sections 1101.4, 1101.5, 1954.201 and 1954.202; Government Code Sections 12955.1 and 12955.1.1; and California Code of Regulations, Title 20, Sections 1605.1, 1605.3 and 1607.

1.8.2.1.3 Permanent buildings in mobilehome parks and special occupancy parks.

Application— Permanent buildings, and permanent accessory buildings or structures, constructed within mobilehome parks and special occupancy parks that are under the control and ownership of the park operator. Sections of this code which pertain to applications listed in this section are identified using the abbreviation “HCD 2.”
CRC § 1.10.1 High relevance — show source text
Chapter 5A Prescriptive Compliance Method.

Chapter 5A provides details for the prescriptive compliance method for alteration, addition and change of occupancy of existing build- ings and structures regulated by the Department of Health Care Access and Information/Office of Statewide Hospital Planning and Development, which include hospitals and correctional treatment centers (applications listed in Sections 1.10.1 (OSHPD 1).

Chapter 6 Classification of Work.

Chapter 6 provides an overview of the Work Area Method and defines the different classifications of work including alterations, change of occupancy, additions and historic buildings. Detailed requirements for all of these are given in subsequent Chapters 7 through 11.

Chapter 7 Alterations—Level 1.

Chapter 7 provides the technical requirements for those existing buildings that undergo Level 1 alterations as described in Section 602, which includes replacement or covering of existing materials, elements, equipment or fixtures using new materials for the same purpose. This chapter is distinguished from Chapters 8 and 9 by only involving replacement of building components with new components with no reconfiguration of space.

Chapter 8 Alterations—Level 2.

A Level 2 alteration is an alteration involving space reconfiguration that could be up to and including 50 percent of the area of the building or addition of a new building system. Level 2 alterations also include the extension or addition of any system or equipment. The purpose of Chapter 8 is to provide detailed requirements and provisions to identify the required improvements in the existing building elements, means of egress, fire protection, structural systems, energy efficiency, and other building systems include electrical, mechanical and plumbing when a building is being altered.

Chapter 9 Alterations—Level 3.

Chapter 9 provides the technical requirements for those existing buildings that undergo Level 3 alterations. Level 3 alterations are those involving alterations that cover 50 percent of the aggregate area of the building. Under certain situations, this chapter also intends to improve the safety of certain building features beyond the work area and in other parts of the building where no alteration work might be taking place.

Chapter 10 Change of Occupancy.

The purpose of Chapter 10 is to address existing buildings that are subject to a change of occupancy. This chapter is an assembly of requirements to upgrade safety without having to comply fully as a new building. A change of occupancy classification is considered a change of occupancy, however, it will involve a higher level of regulation since the use of the building has made a more significant change.

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Chapter 11 Additions.

Chapter 11 provides the requirements for additions, which are considered new construction. The requirements focus on safely integrating the addition with the existing building. This includes issues such as limiting the overall height and area of the building where the addition is not separated by a fire wall.

Chapter 12 Historic Buildings —Reserved

Chapter 12 is not adopted by the State of California. Historic buildings and structures shall comply with Part 8, Title 24, California Code of Regulations.

Chapter 13 Performance Compliance Methods.

Chapter 13 allows for existing buildings to be evaluated to show that alterations or a change of occupancy, while not meeting new construction requirements, will provide a level of safety to demonstrate compliance. Provisions are based on a numerical scoring system involving 21 safety parameters where, when evaluated, such buildings must meet a minimum overall safety score.
CRC § R301.1 High relevance — show source text
Coordination of the I-Codes

The coordination of technical provisions allows the I-Codes to be used as a complete set of complementary documents. Individual codes can also be used in subsets or as stand-alone documents. Some technical provisions that are relevant to more than one subject area are duplicated in multiple model codes.

INTRODUCTION TO THE INTERNATIONAL RESIDENTIAL CODE

The IRC establishes minimum requirements for one- and two-family dwellings and townhouses using prescriptive provisions. It is founded on broad-based principles that make possible the use of new materials and new building designs. This 2024 edition is fully compatible with all of the International Codes® (I-Codes®) published by the ICC.

The IRC was created to serve as a complete, comprehensive code regulating the construction of single-family houses, two-family houses (duplexes) and buildings consisting of three or more townhouse units. All buildings within the scope of the IRC are limited to three stories above grade plane. For example, a four-story single-family house would fall within the scope of the IBC, not the IRC. The benefits of devoting a separate code to residential construction include the fact that the user need not navigate through a multitude of code provisions that do not apply to residential construction in order to locate that which is applicable. A separate code also allows for residential and nonresidential code provisions to be distinct and tailored to the structures that fall within the appropriate code’s scopes.

The IRC contains coverage for all components of a house or townhouse, including structural components, fireplaces and chimneys, thermal insulation, mechanical systems, fuel gas systems, plumbing systems and electrical systems.

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The IRC is a prescriptive-oriented (specification) code with some examples of performance code language. It has been said that the IRC is the complete cookbook for residential construction. Section R301.1, for example, is written in performance language, but states that the prescriptive requirements of the code will achieve such performance.

It is important to understand that the IRC contains coverage for what is conventional and common in residential construction practice. While the IRC will provide all of the needed coverage for most residential construction, it might not address construction practices and systems that are atypical or rarely encountered in the industry. Therefore, the IRC contains several references to other codes either as an alternative to the provisions of the IRC or where the IRC lacks coverage for a particular type of structure, design, system, appliance or method of construction. In other words, the IRC is meant to be all inclusive for typical residential construction and it relies on other codes only where alternatives are desired or where the code lacks coverage for the uncommon aspect of residential construction. Of course, the IRC constantly evolves to address new technologies and construction practices that were once uncommon, but are now common.

The IRC is unique in that much of it, including Chapters 3 through 9 and Chapters 34 through 43, is presented in an ordered format that is consistent with the normal progression of construction, starting with the design phase and continuing through the final trimout phase. This is consistent with the “cookbook” philosophy of the IRC.

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Arrangement and Format of the 2025 CRC

CRC § 34.5 High relevance — show source text

1 Table 50 is intended to be a reference between the transformer’s primary voltage and the type of primary system that it can be used on in the PG&E system.

062111 Page 20 of 26 Rev. #27: 03-25-22

UG-1: Transformers Greenbook Application of Underground Distribution Transformers EDM

Pictorial Index

1	Col2

Box Style Front View (doors removed)	Front View (hinged top open) Clam Shell Three-Phase Cabinet
Clam Shell Single-Phase Cabinet Front View (hinged top open)	1-Wire Cabinet 2-Wire Cabinet 3-Wire Cabinet Front Views (hinged tops open) Single-Phase - Style Dead-Front
	Style MTP and Duplex Style DF
Figure 1 Single-Phase, Pad-Mount Transformers for Loop or Radial Application	Figure 1 Single-Phase, Pad-Mount Transformers for Loop or Radial Application

Rev. #27: 03-25-22 062111 Page 21 of 26

UG-1: Transformers Greenbook Application of Underground Distribution Transformers EDM

Pictorial Index (continued)	Col2
Front View (doors removed) Style IIA	Style IID 75 − 300 kVA Front View (doors removed) CL Fuses Interlocked With Switch
Style IIB 225 − 1,000 kVA Front View (doors removed)	Front View (doors removed) Bayonet Fuses Style IIE 75 − 2,500 kVA
Style IIC 1,500 − 2,500 kVA Front View (doors removed)	Style IIF 300 − 2,500 kVA Bayonet Fuses

Figure 2 Three-Phase, Pad-Mount Transformers for Loop or Radial Application

CRC § 101.4 High relevance — show source text
When adopted by a state agency, the provisions of this code shall be enforced by the appropriate enforcing agency, but only to the extent of authority granted to such agency by statute.
1. State-owned buildings, including buildings constructed by the Trustees of the California State University, and to the extent permitted by California law, buildings designed and constructed by the Regents of the University of California and regulated by the Building Standards Commission. See Section 103 for additional scoping provisions.
2. Energy efficiency standards regulated by the California Energy Commission.
3. All residential buildings constructed throughout the State of California, including but not limited to, hotels, motels, lodging houses, apartments, dwellings, dormitories, condominiums, shelters for homeless persons, congregate residences, employee housing, factory-built housing and other types of dwellings containing sleeping accommodations with or without common toilets or cooking facilities regulated by the Department of Housing and Community Development. See Section 104 for additional scoping provisions.
4. Public elementary and secondary schools, and community college buildings regulated by the Division of the State Architect. See Section 105 for additional scoping provisions.
5. Qualified historical buildings and structures and their associated sites regulated by the State Historical Building Safety Board within the Division of the State Architect.
6. General acute care hospitals, acute psychiatric hospitals, skilled nursing and/or intermediate care facilities, clinics licensed by the Department of Public Health and correctional treatment centers regulated by the Office of Statewide Health Planning and Development. See Section 106 for additional scoping provisions.
7. Graywater systems regulated by the Department of Water Resources and the Department of Housing and Community Development.
8. Green building standards for occupancies where no state agency has authority or expertise, adopted by the California Building Standards Commission. See Section 103 for additional scoping provisions.
101.4 Appendices. Provisions contained in the appendices of this code are not mandatory unless specifically adopted by a city, county, or city and county in compliance with Health and Safety Code Sections 18930 and 18941.5, respectively, for Building Standards Law; Health and Safety Code Section 17950 for State Housing Law; and Health and Safety Code Section 13869.7 for Fire Protection Districts. See Section 101.7 of this code.

101.5 Referenced codes and standards. The codes and standards referenced elsewhere in this code shall be considered part of the requirements of this code to the prescribed extent of each such reference.

101.5.1 Building. The provisions of the California Building Code, California Residential Code and California Existing Building Code, as applicable, shall apply to the construction, alteration, movement, enlargement, replacement, repair, use and occupancy, location, maintenance, removal and demolition of every structure or any appurtenances connected or attached to such buildings or structures.

101.5.2 Electrical. The provisions of the California Electrical Code shall apply to the installation of electrical systems, including but not limited to, alterations, repair, replacement, equipment, appliances, fixtures, fittings and appurtenances thereto.

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ADMINISTRATION

101.5.3 Mechanical. The provisions of the California Mechanical Code shall apply to the installation, alterations, repair and replacement of mechanical systems, including equipment, appliances, fixtures, fittings and/or appurtenances, including ventilating, heating, cooling, air-conditioning and refrigeration systems, incinerators and other energy-related systems.
CRC § 212.0 High relevance — show source text
Intermittent Pilot. A pilot that burns during light-off and while the main burner is firing, and that is shut off with the main burner.

Interrupted Pilot. A pilot that burns during light-off and that is shut off during normal operation of the main burner.

212.0 – J –

Joint, Brazed. A joint obtained by joining of metal parts with alloys that melt at temperatures exceeding 840°F (449°C) but less than the melting temperature of the parts being joined.

Joint, Compression. A multipiece joint with cup-shaped threaded nuts that, when tightened, compress tapered sleeves so that they form a tight joint on the periphery of the tubing they connect.

Joint, Flanged. One made by bolting together a pair of flanged ends.

Joint, Flared. A metal-to-metal compression joint in which a conical spread is made on the end of a tube that is compressed by a flare nut against a mating flare.

Joint, Heat Fusion. A joint used in some thermoplastic systems to connect the pipe to fittings or pipe lengths directly to one another (butt-fusion). This method of joining pipe to fittings includes butt-fusion, socket-fusion, electro-fusion, and saddle-fusion. This method of welding involves the application of heat and pressure to the components, allowing them to fuse together forming a bond between the pipe and fitting.

Joint, Mechanical. General form for gastight or liquid-tight joints obtained by the joining of parts through a positive holding mechanical construction.

Joint, Press-Connect. A permanent mechanical joint consisting of an elastomeric seal or an elastomeric seal and cor

rosion-resistant grip ring. The joint is made with a pressing tool and jaw or ring approved by the fitting manufacturer.

Joint, Soldered. A joint obtained by the joining of metal parts with metallic mixtures or alloys that melt at a temperature up to and including 840°F (449°C).

Joint, Welded. A gastight joint obtained by the joining of metal parts in the plastic molten state.

213.0 – K –

No definitions.

214.0 – L –

Labeled. Equipment or materials bearing a label of a listing agency (accredited conformity assessment body). See Listed (Third Party Certified). [HCD 1 & HCD 2] “Labeled” means equipment or materials to which has been attached a label, symbol or other identifying mark of an organization, approved by the Department, that maintains a periodic inspection program of production of labeled products, instal- lations, equipment, or materials and by whose labeling the manufacturer indicates compliance with appropriate stan- dards or performance in a specified manner. LEL (Lower Explosive Limit). See LFL.
CRC § 2-550 High relevance — show source text
″|3′-2″|4′-3″|3′-8″|3′-1″|2′-7″|2′-0″| |2-550S162-68|6′-5″|5′-10″|5′-3″|4′-9″|4′-4″|5′-5″|4′-9″|4′-3″|3′-9″|3′-4″| |2-800S162-33|—|—|—|—|—|—|—|—|—|—| |2-800S162-43|2′-6″|—|—|—|—|—|—|—|—|—| |2-800S162-54|6′-1″|5′-5″|4′-10″|4′-3″|3′-9″|4′-11″|4′-3″|3′-8″|3′-0″|2′-5″| |2-800S162-68|7′-8″|6′-11″|6′-3″|5′-9″|5′-2″|6′-5″|5′-9″|5′-1″|4′-6″|4′-0″| |2-1000S162-43|2′-10″|—|—|—|—|—|—|—|—|—| |2-1000S162-54|6′-7″|5′-10″|5′-3″|4′-9″|4′-3″|5′-4″|4′-9″|4′-1″|3′-5″|2′-9″| |2-1000S162-68|8′-8″|7′-10″|7′-2″|6′-6″|5′-11″|7′-4″|6′-6″|5′-9″|5′-1″|4′-6″| |2-1200S162-54|5′-6″|4′-10″|4′-4″|3′-11″|3′-7″|4′-5″|3′-11″|3′-6″|3′-2″|2′-11″| |2-1200S162-68|9′-7″|8′-8″|7′-11″|7′-2″|6′-6″|8′-1″|7′-2″|6′-4″|5′-8″|5′-0″| |For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa, 1 pound per square inch = 6.895 kPa, 1 ksi = 1,000 psi = 6.895 MPa.
a.
CRC § 150.0 High relevance — show source text
Closable metal or glass doors covering the entire opening of the firebox; and 2. A combustion air intake to draw air from the outside of the building, which is at least 6 square inches in area and is equipped with a readily accessible, operable and tight-fitting damper or combustion-air control device; and Exception to Section 150.0(e)2: An outside combustion-air intake is not required if the fireplace will be installed over concrete slab flooring and the fireplace will not be located on an exterior wall. 3. A flue damper with a readily accessible control. Exception to Section 150.0(e)3: When a gas log, log lighter or decorative gas appliance is installed in a fireplace, the flue damper shall be blocked open if required by the CMC or the manufacturer’s installation instructions.

(f) Slab edge insulation. Material used for slab edge insulation shall meet the following minimum specifications:
1. Water absorption rate for the insulation material alone without facings no greater than 0.3 percent when tested in accordance with Test Method A – 24-Hour-Immersion of ASTM C272.
2. Water vapor permeance no greater than 2.0 perm/inch when tested in accordance with ASTM E96.
3. Concrete slab perimeter insulation shall be protected from physical damage and ultraviolet light deterioration.
4. Insulation for a heated slab floor shall meet the requirements of Section 110.8(g).
(g) Vapor retarder.
1. In Climate Zones 1–16, the earth floor of unvented crawl space shall be covered with a Class I or Class II vapor retarder. This requirement shall also apply to controlled ventilation crawl space for buildings complying with the Exception to Section 150.0(d).
2. In Climate Zones 14 and 16, a Class I or Class II vapor retarder shall be installed on the conditioned space side of all insulation in all exterior walls, vented attics and unvented attics with air-permeable insulation.
(h) Space-conditioning equipment.
1. Building cooling and heating loads. Building heating and cooling loads shall be determined using a method based on any one of the following: A. The ASHRAE Handbook, Equipment Volume, Applications Volume and Fundamentals Volume; or B. The SMACNA Residential Comfort System Installation Standards Manual; or
C. The ACCA Manual J.

Exception 1 to Section 150.0(h)1: Block loads, the total load for all rooms combined that are served by the central equipment, may be used for the purpose of system sizing for additions. 2. Design conditions. Design conditions shall be determined in accordance with the following: A. For the purpose of sizing the space-conditioning (HVAC) system, the indoor design temperatures shall be 68°F for heating and 75°F for cooling. B. Outdoor design conditions shall be selected from one of the following: i. Reference Joint Appendix JA2, which is based on data from the ASHRAE Climatic Data for Region X; or ii. The ASHRAE Handbook, Fundamentals Volume; or

iii. The ACCA Manual J.

C. The outdoor design temperatures for heating shall be no lower than the 99.0 percent Heating Dry Bulb or the Heating Winter Median of Extremes values.

D. The outdoor design temperatures for cooling shall be no greater than the 1.0 percent Cooling Dry Bulb and Mean Coincident Wet Bulb values.
1. Outdoor condensing units. A. **Clearances.
CRC § 5003.1.2 High relevance — show source text
Exempted materials and conditions listed in this table are required to comply with provisions of this code that are not based on exceeding maximum allowable quantities in
Section 5003.|

5003.1.2 Conversion. Where quantities are indicated in pounds and where the weight per gallon of the liquid is not provided to the fire code official, a conversion factor of 10 pounds per gallon (1.2 kg/L) shall be used.

5003.1.3 Quantities not exceeding the maximum allowable quantity per control area. The storage, use and handling of hazardous materials in quantities not exceeding the maximum allowable quantity per control area indicated in Tables 5003.1.1(1) through 5003.1.1(4) shall be in accordance with Sections 5001 and 5003.

5003.1.4 Quantities exceeding the maximum allowable quantity per control area. The storage and use of hazardous materials in quantities exceeding the maximum allowable quantity per control area indicated in Tables 5003.1.1(1) through 5003.1.1(4) shall be in accordance with this chapter.

5003.2 Systems, equipment and processes. Systems, equipment and processes utilized for storage, dispensing, use or handling of hazardous materials shall be in accordance with Sections 5003.2.1 through 5003.2.9.

5003.2.1 Design and construction of containers, cylinders and tanks. Containers, cylinders and tanks shall be designed and constructed in accordance with approved standards. Containers, cylinders, tanks and other means used for containment of hazardous materials shall be of an approved type. Pressure vessels not meeting DOTn requirements for transportation shall comply with the ASME Boiler and Pressure Vessel Code.

5003.2.2 Piping, tubing, valves and fittings. Piping, tubing, valves, and fittings conveying hazardous materials shall be designed and installed in accordance with ASME B31.1 or other approved standards, and shall be in accordance with Sections 5003.2.2.1 and 5003.2.2.2.

5003.2.2.1 Design and construction. Piping, tubing, valves, fittings and related components used for hazardous materials shall be in accordance with the following:
1. Piping, tubing, valves, fittings and related components shall be designed and fabricated from materials that are compatible with the material to be contained and shall be of adequate strength and durability to withstand the pressure, structural and seismic stress and exposure to which they are subject.
2. Piping and tubing shall be identified in accordance with ASME A13.1 to indicate the material conveyed.
3. Manual valves or automatic remotely activated fail-safe emergency shutoff valves shall be installed on supply piping and tubing and provided with ready access at the following locations: 3.1. The point of use. 3.2. The tank, cylinder or bulk source.
4. Manual emergency shutoff valves and controls for remotely activated emergency shutoff valves shall be clearly visible, provided with ready access and identified in an approved manner.
5. Backflow prevention or check valves shall be provided where the backflow of hazardous materials could create a hazardous condition or cause the unauthorized discharge of hazardous materials.
Exceptions:
1. Piping for inlet connections designed to prevent backflow.
2. Piping for pressure relief devices.
CRC § 10005-4026. High relevance — show source text
IES Illuminating Engineering Society, 120 Wall St. Fl 17, New York, NY 10005-4026.

IEST Institute of Environmental Sciences and Technology, 1827 Walden Office Square, Suite 400, Schaumburg, IL 60173.

IGSHPA International Ground Source Heat Pump Association, 1723 W. Tyler Ave. Stillwater, OK 74078.

IIAR International Institute of Ammonia Refrigeration, 1001 N. Fairfax Street, Suite 503, Alexandria, VA 22314.

ISO International Organization for Standardization, 1 ch. de la Voie-Creuse, Casa Postale 56, CH-1211 Geneva 20, Switzerland.

MSS Manufacturers Standardization Society of the Valve and Fittings Industry, 127 Park Street NE, Vienna, VA 22180.

NAIMA North American Insulation Manufacturers Association, Inc., 11 Canal Center Plaza #103, Alexandria, VA 22314.

NEBB National Environmental Balancing Bureau, 8575 Grovemont Circle, Gaithersburg, MD 20877.

NFPA National Fire Protection Association, 1 Batterymarch Park, Quincy, MA 02169-7471.

NGWA National Ground Water Association, 601 Dempsey Road, Westerville, Ohio 43081-8978.

NSF NSF International, 789 N. Dixboro Road, Ann Arbor, MI 48105.

SAE Society of Automotive Engineers, 400 Commonwealth Drive, Warrendale, PA 15096.

SMACNA Sheet Metal and Air Conditioning Contractors National Association, 4201 Lafayette Center Drive, Chantilly, VA 20151-1219.

UL Underwriters Laboratories, Inc., 333 Pfingsten Road, Northbrook, IL 60062.

384 2025 CALIFORNIA MECHANICAL CODE

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APPENDICES

The appendices are intended to supplement the provisions of the installation requirements of this code. The definitions in Chapter 2 are also applicable to the appendices.

TABLE OF CONTENTS

»

»

Appendix A Page

Residential Plans Examiner Review Form for HVAC System Design..............................................................387

Appendix B

Procedures to be Followed to Place Gas Equipment in Operation..................................................................391

Appendix C

Installation and Testing of Oil (Liquid) Fuel-Fired Equipment ..........................................................................395

Appendix D

Fuel Supply: Manufactured/Mobile Home Parks and Recreational Vehicle Parks ..........................................403

Appendix E

Sustainable Practices ......................................................................................................................................411

Appendix F

Sizing of Venting Systems and Outdoor Combustion and Ventilation Opening Design ..................................533

Appendix G

Example Calculation of Outdoor Air Rate........................................................................................................545

Appendix H

Professional Qualifications ..............................................................................................................................549

Appendix I

Indoor Horticultural Facilities ..........................................................................................................................553

Appendix J

Clean Air Delivery............................................................................................................................................559

2025 CALIFORNIA MECHANICAL CODE 385

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386 2025 CALIFORNIA MECHANICAL CODE

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CRC § 995-3019 High relevance — show source text
The Uniform Mechanical Code provides consumers with complete requirements for the installation and maintenance of heating, ventilating, cooling, and refrigeration systems, while, at the same time, allowing latitude for innovation and new technologies. The public at large is invited and encouraged to take part in IAPMO’s open consensus code development process. This code is updated every three years. The Uniform Mechanical Code is dedicated to all those who, in working to achieve “the ultimate mechanical code,” have unselfishly devoted their time, effort, and personal funds to create and maintain this, the finest mechanical code in existence today.

The Uniform Mechanical Code updates every three years in revision cycles that begin twice each year that takes two years to complete.

Each revision cycle advances according to a published schedule that includes final dates for all major events and contains four basic steps as follows:
1. Proposal Stage;
2. Comment Stage;
3. Association Technical Meeting;
4. Council Appeals and Issuance of Code.
IAPMO develops “full consensus” codes built on a foundation of maximum participation and agreement by a broad range of interests. This philosophy has led to producing technically sound codes that promote health and safety, yet do not stifle design or development.

It is important to stress that the process remains committed to the principles of consensus code development where consensus Technical Committees and Correlating Committees revise codes. The public and membership are offered multiple opportunities to debate, provide input and raise concerns through Amending Motions at the annual Assembly Consideration Session. Anyone may submit an appeal related to the issuance of a document through the IAPMO Standards Council.

The 2024 Uniform Mechanical Code is supported by the Mechanical Contractors Association of America (MCAA), the Plumbing-Heating-Cooling Contractors National Association (PHCC-NA), the United Association (UA), and the World Plumbing Council (WPC). The presence of these logos, while reflecting support, does not imply any ownership of the copyright to the UMC, which is held exclusively by IAPMO. Further, the logos of these associations indicate the support of IAPMO’s open consensus process being used to develop IAPMO’s codes and standards.

2025 CALIFORNIA MECHANICAL CODE xi

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FOREWORD

The addresses of the organizations are as follows: ASSE – 18927 Hickory Creek Drive, Suite 220 • Mokena, IL 60448 • (708) 995-3019 MCAA – 1385 Piccard Drive • Rockville, MD 20850 • (301) 869-5800 PHCC-NA – 180 S Washington Street, Suite 100 • Falls Church, VA 22040-6808 • (800) 533-7694 RPA – 18927 Hickory Creek Drive, Suite 220 • Mokena, IL 60448 • (877) 427-6601 UA – Three Park Place • Annapolis, MD 21401 • (410) 269-2000 WPC – Auf der Mauer 11 • 8021 Zurich, Switzerland • Secretariat@worldplumbing.org

CRC § 90.1 High relevance — show source text

[ASHRAE 90.1: TABLE 6.4.3.4.3]

Col1	OUTDOOR AIR INTAKE (CFM/ft2)	Col3	EXHAUST/RELIEF (CFM/ft2)	Col5
CLIMATE ZONE	NONMOTORIZED1	MOTORIZED	NONMOTORIZED3	MOTORIZED
0, 1, 2	0, 1, 2	0, 1, 2	0, 1, 2	0, 1, 2
Any height	20	4	20	4
3	3	3	3	3
Any height	20	10	20	10
4, 5B, 5C	4, 5B, 5C	4, 5B, 5C	4, 5B, 5C	4, 5B, 5C
Fewer than three stories	204	10	20	10
Three or more stories	204	10	204	10
5A, 6, 7, 8	5A, 6, 7, 8	5A, 6, 7, 8	5A, 6, 7, 8	5A, 6, 7, 8
Fewer than three stories	204	4	20	4
Three or more stories	204	4	204	4

For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.00047 m [3] /s, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ], 1 inch water gauge = 0.249 kPa

Notes:

1 When tested in accordance with AMCA 500D.

2 Dampers smaller than 12 inches (305 mm) in height, width, or diameter need not be tested but shall be of the same design and construction as the smallest tested damper meeting the listed leakage rate requirement.

3 Nonmotorized dampers smaller than 24 inches (610 mm) in height, width, or diameter shall be permitted to have a leakage rate of 40 CFM/ft 2 [0.203 (m 3 /s)/m 2 ].

4 Where permitted by Section E 503.4.6.4.1, exception 2.

2025 CALIFORNIA MECHANICAL CODE 425

APPENDIX E

(2) Systems serving zones where humidity levels are required to be maintained with precision of not more than ±5 percent relative humidity to comply with applicable codes or accreditation standards or as approved by the Authority Having Jurisdiction.

[ASHRAE 90.1:6.4.3.6.2]

CRC § 50-2023 High relevance — show source text
NSF/ANSI/CAN 50-2023e Equipment and Chemicals for Swimming Pools, Spas, Hot Tubs, and Other Recreational Water Facilities

Available from: NSF International

PO Box 130140 Ann Arbor, MI 48113 (735) 769-8010

RESIDENTIAL ENERGY SERVICES NETWORK

ANSI/RESNET/ICC 380-2019 Standard for Testing Airtightness of Building Enclosures, Dwelling Unit, and Sleeping Unit Enclosures, Airtightness of Heating and Cooling Air Distribution Systems, and Airflow of Mechanical Ventilation Systems (2019)

Available from: Residential Energy Services Network, Inc. (RESNET) P.O. Box 4561 Oceanside, CA 92052-4561 http://resnet.us/

SAE INTERNATIONAL

SAE J1772_201710 SAE Electric Vehicle and Plug in Hybrid Electric Vehicle Conductive Charge Coupler

SHEET METAL AND AIR-CONDITIONING CONTRACTORS’ NATIONAL ASSOCIATION

Residential Comfort System Installation Standards, Eighth Edition-2016

ANSI/SMACNA 006-2006 HVAC Duct Construction Standards—Metal and Flexible, Third Edition - 2005

Available from: Sheet Metal and Air-Conditioning Contractors’ National Association (SMACNA) 4201 Lafayette Center Drive Chantilly, VA 20151-1209 (703) 803-2980

www.smacna.org

UNDERWRITERS LABORATORIES / UL

UL 181-2013 (R2021) Standard for Safety Factory-Made Air Ducts and Connectors

UL 181A-2013 (R2021) Standard for Safety Closure Systems for Use with Rigid Air Ducts

UL 181B-2013 (R2021) Standard for Safety Closure Systems for Use with Flexible Air Ducts and Air Connectors

UL 723-2018 (R2023) Standard for Safety Test for Surface Burning Characteristics of Building Materials

UL 727-2018 Standard for Safety Oil-Fired Central Furnaces

UL 731-2018 (R2021) Standard for Safety Oil-Fired Unit Heaters

UL 1077-2015 (R2021) Standard for Safety Supplementary Protectors for Use in Electrical Equipment

UL 1574-2004 (R2023) Standard for Safety Track Lighting Systems

UL 1598-2021 Standard for Safety Luminaires

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ANSI/NFRC 400-2023

Available from:

Procedure for Determining Fenestration Product Air Leakage

National Fenestration Rating Council 6035 Ivy Lane, Suite 140 Greenbelt, MD 20770 (301) 589-1776 www.NFRC.org Email: info@nfrc.org

STANDARDS AND DOCUMENTS REFERENCED IN THE ENERGY CODE

UL 1741-2021 Standard for Safety Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources

ANSI/CAN/UL 1973-2022 Standard for Safety Batteries for Use in Stationary and Motive Auxiliary Power Applications

UL 2108-2015 (R2023) Standard for Safety Low Voltage Lighting Systems

UL 8750-2015 (R2022) Standard for Safety Light Emitting Diode (LED) Equipment for Use in Lighting Products

ANSI/CAN/UL 9540-2023 Standard for Safety Energy Storage Systems and Equipment
CRC § 11.1.2 High relevance — show source text
(1) At the rate of 4 percent for each 1000 feet (305 m) above sea level before selecting appropriately sized appliances.

(2) As permitted by the Authority Having Jurisdiction.

(3) In accordance with the manufacturer’s installation instructions. [NFPA 54:11.1.2]

B 102.0 Primary Air Adjustment. B 102.1 General. The primary air for injection (Bunsen)type burners shall be adjusted for proper flame characteristics in accordance with the appliance manufacturer’s instructions. After setting the primary air, the adjustment means shall be secured in position. [NFPA 54:11.2]

B 103.0 Safety Shutoff Devices.

B 103.1 General. Where a safety shutoff device is provided, it shall be checked for proper operation and adjustment in accordance with the appliance manufacturer’s instructions. Where the device does not turn off the gas supply in the event of pilot outage or other ignition malfunction, the device shall be serviced or replaced with a new device. [NFPA 54:11.3]

B 104.0 Automatic Ignition.

B 104.1 General. Appliances supplied with means for automatic ignition shall be checked for operation within the parameters provided by the manufacturer. Any adjustments made shall be in accordance with the manufacturer’s instal lation instructions. [NFPA 54:11.4]

B 105.0 Protective Devices.

B 105.1 General. Where required by the manufacturer’s installation instructions, all protective devices furnished with the appliance such as a limit control, fan control to blower,

temperature and pressure relief valve, low-water cutoff device, or manual operating features, shall be checked for operation within the parameters provided by the manufacturer. Any adjustments made shall be in accordance with the manufacturer’s installation instructions. [NFPA 54:11.5]

B 106.0 Checking the Draft.

B 106.1 General. Draft hood-equipped appliances shall be checked to verify that there is no draft hood spillage after 5 minutes of main burner operation. [NFPA 54:11.6]

B 107.0 Operating Instructions.

B 107.1 General. Operating instructions shall be furnished and shall be left in a prominent position near the appliance for use by the consumer. [NFPA 54:11.7]

2025 CALIFORNIA MECHANICAL CODE 393

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394 2025 CALIFORNIA MECHANICAL CODE

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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

APPENDIX C – INSTALLATION AND TESTING OF OIL (LIQUID) FUEL-FIRED EQUIPMENT (Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
CRC § 2025 Medium relevance — show source text
Chapter 9 Roof Assemblies.

Chapter 9 regulates the design and construction of roof assemblies. A roof assembly includes the roof deck, vapor retarder, substrate or thermal barrier, insulation, vapor retarder and roof covering. This chapter provides the requirement for wind resistance of roof coverings.

The types of roof covering materials and installation regulated by Chapter 9 are: asphalt shingles, clay and concrete tile, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shakes and shingles, built-up roofs, metal roof panels, modified bitumen roofing, thermoset and thermoplastic single-ply roofing, sprayed polyurethane foam roofing, liquid applied coatings and photovoltaic shingles. Chapter 9 also provides requirements for roof drainage, flashing, above deck thermal insulation, rooftop-mounted photovoltaic systems and recovering or replacing an existing roof covering.

Chapter 10 Chimneys and Fireplaces.

Chapter 10 contains requirements for the safe construction of masonry chimneys and fireplaces and establishes the standards for the use and installation of factory-built chimneys, fireplaces and masonry heaters. Chimneys and fireplaces constructed of masonry rely on prescriptive requirements for the details of their construction; the factory-built type relies on the listing and labeling method of approval. Chapter 10 provides the requirements for seismic reinforcing and anchorage of masonry fireplaces and chimneys.

Chapter 11 [RE] Energy Efficiency.

Chapter 11 is not adopted in California. See California Energy Code, Title 24, Part 6.

Chapter 12 Mechanical Administration.

Chapter 12 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 13 General Mechanical System Requirements.

Chapter 13 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 14 Heating and Cooling Equipment and Appliances.

Chapter 14 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 15 Exhaust Systems.

Chapter 15 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 16 Duct Systems.

Chapter 16 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 17 Combustion Air.

Chapter 17 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 18 Chimneys and Vents.

Chapter 18 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 19 Special Appliances, Equipment and Systems.

Chapter 19 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 20 Boilers and Water Heaters.

Chapter 20 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

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Chapter 21 Hydronic Piping.

Chapter 21 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 22 Special Piping and Storage Systems.

Chapter 22 is not adopted in California. See California Mechanical Code, Title 24, Part 4.

Chapter 23 Solar Thermal Energy Systems.
CMC § 2025 Medium relevance — show source text
Energy Systems| |16|

Stationary Power Plants| |17|

Geothermal Energy Systems and Ambient Temperature Loops| |18|

Referenced Standards| |Appendix A|
Residential Plans Examiner Review Form for HVAC System Design| |Appendix B|
Procedures to be Followed to Place Gas Equipment in Operation| |Appendix C|
Installation and Testing of Oil (Liquid) Fuel-Fired Equipment| |Appendix D|

Fuel Supply: Manufactured/Mobile Home Parks and Recreational Vehicle
Parks| |Appendix E|
Sustainable Practices| |Appendix F|

Sizing of Venting Systems and Outdoor Combustion and Ventilation
Opening Design| |Appendix G|
Example Calculation of Outdoor Air Rate| |Appendix H|

Professional Qualifications| |Appendix I|

Indoor Horticultural Facilities| |Appendix J|

Clean Air Delivery| |Useful Tables|Useful Tables|

2025 CALIFORNIA MECHANICAL CODE xiii

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

FORMAT OF THE UNIFORM MECHANICAL CODE

The following is a summary of the scope and intent of the provisions addressed within the chapters and appendices of the Uniform Mechanical Code :

Chapter 1 Administration. Chapter 1 regulates the application, enforcement, and administration of subsequent requirements of the code. As well as establishing the scope of the code, this chapter is concerned with enforcing the requirements contained in the body of the code. A mechanical code, as with any other code, is intended to be adopted as a legally enforceable document to safeguard health, safety, property, and public welfare. The code cannot be effective without satisfactory provisions for its administration and enforcement. The Authority Having Jurisdiction is to review the proposed and completed work and decide whether a mechanical system conforms to the code requirements. As a public servant, the Authority Having Jurisdiction enforces the code in an unbiased proper manner. The design professional is responsible for the design of a safe mechanical system. The contractor is responsible for installing the system in accordance with the plans.

Chapter 2 Definitions. To maintain consistency and encourage the use of common terminology, Chapter 2 establishes definitions to provide clarity of terms and promote the use of a common language throughout the code. Understanding definitions within the context of their application enables greater collaboration, efficiency, standardization, and interpretation in applying and enforcing terms used throughout the code. Codes are technical documents, and every term can impact the meaning of the code text. Terms not defined have a normally accepted meaning.

Chapter 3 General Regulations. Chapter 3 regulates the general requirements, not specific to other chapters, for installing mechanical systems. Many regulations are not specific mechanical requirements but relate to the overall mechanical system. This chapter contains safety requirements for appliance location and installation, appliance and system access, condensate disposal, clearances to combustibles, and return or outside air used in mechanical systems. Listing method of approval, based on applicable nationally recognized standards for the safe and proper installation of mechanical systems, is essential to ensure protection of public health, safety, and welfare. These safety requirements provide protection for piping, tubing, materials, and structures, including provisions for installation practices addressing stress and strain, sleeving, and hanger support.

CMC § 2025 Medium relevance — show source text

Text that is extracted pursuant to IAPMO’s Extract Guidelines, but outside of the regular revision process is denoted with the use of the source document in the margin. This text is not fully processed by IAPMO in accordance with ANSI’s public announcement consensus requirements for an American National Standard (ANS) nor approved by ANSI’s Board of Standards Review. The next revision cycle processes such text in accordance with those requirements.

xii 2025 CALIFORNIA MECHANICAL CODE

FORMAT OF THE UNIFORM MECHANICAL CODE

The format of the Uniform Mechanical Code (UMC) arranges each chapter in accordance with a specific subject matter. However, Chapter 3 is dedicated to general requirements that are applicable to every chapter. The subject matters are divided as follows:

CHAPTERS	SUBJECTS
1	Administration
2	Definitions
3	General Regulations
4	Ventilation Air
5	Exhaust Systems
6	Duct Systems
7	Combustion Air
8	Chimneys and Vents
9	Installation of Specific Appliances
10	Boilers and Pressure Vessels
11	Refrigeration
12	Hydronics
13	Fuel Gas Piping
14	Process Piping
15	Solar Energy Systems
16	Stationary Power Plants
17	Geothermal Energy Systems and Ambient Temperature Loops
18	Referenced Standards
Appendix A	Residential Plans Examiner Review Form for HVAC System Design
Appendix B	Procedures to be Followed to Place Gas Equipment in Operation
Appendix C	Installation and Testing of Oil (Liquid) Fuel-Fired Equipment
Appendix D	Fuel Supply: Manufactured/Mobile Home Parks and Recreational Vehicle Parks
Appendix E	Sustainable Practices
Appendix F	Sizing of Venting Systems and Outdoor Combustion and Ventilation Opening Design
Appendix G	Example Calculation of Outdoor Air Rate
Appendix H	Professional Qualifications
Appendix I	Indoor Horticultural Facilities
Appendix J	Clean Air Delivery
Useful Tables	Useful Tables

2025 CALIFORNIA MECHANICAL CODE xiii

FORMAT OF THE UNIFORM MECHANICAL CODE

The following is a summary of the scope and intent of the provisions addressed within the chapters and appendices of the Uniform Mechanical Code :

Chapter 1 Administration. Chapter 1 regulates the application, enforcement, and administration of subsequent requirements of the code. As well as establishing the scope of the code, this chapter is concerned with enforcing the requirements contained in the body of the code.

CRC § 12.5 Medium relevance — show source text
5|12.5|12.5|8.0|6.8| |C
(townhouses
only)||10|NP|4.5|4.5|3.0|2.6| |C
(townhouses
only)||20|NP|9.0|9.0|6.0|5.1| |C
(townhouses
only)||30|NP|13.5|13.5|9.0|7.7| |C
(townhouses
only)||40|NP|18.0|18.0|12.0|10.2| |C
(townhouses
only)||50|NP|22.5|22.5|15.0|12.8| |C
(townhouses
only)||10|NP|6.0|6.0|4.5|3.8| |C
(townhouses
only)||20|NP|12.0|12.0|9.0|7.7| |C
(townhouses
only)||30|NP|18.0|18.0|13.5|11.5| |C
(townhouses
only)||40|NP|24.0|24.0|18.0|15.3| |C
(townhouses
only)||50|NP|30.0|30.0|22.5|19.1| |D0||10|NP|2.8|2.8|1.8|1.6| |D0||20|NP|5.5|5.5|3.6|3.1| |D0||30|NP|8.3|8.3|5.4|4.6| |D0||40|NP|11.0|11.0|7.2|6.1| |D0||50|NP|13.8|13.8|9.0|7.7| |D0||10|NP|5.3|5.3|3.8|3.2| |D0||20|NP|10.5|10.5|7.5|6.4| |D0||30|NP|15.8|15.8|11.3|9.6| |D0||40|NP|21.0|21.0|15.0|12.8| |D0||50|NP|26.3|26.3|18.8|16.0| |D0||10|NP|7.3|7.3|5.3|4.5| |D0||20|NP|14.5|14.5|10.5|9.0| |D0||30|NP|21.8|21.8|15.8|13.4| |D0||40|NP|29.0|29.0|21.0|17.9| |D0||50|NP|36.3|36.3|26.3|22.3|

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WALL CONSTRUCTION

|TABLE R602.10.
CRC § 2025 Medium relevance — show source text
Chapter 6 also regulates exterior windows and doors installed in walls. This chapter contains criteria for the performance of exterior windows and doors and includes provisions for testing and labeling, garage doors, windborne debris protection and anchorage details.

Chapter 7 Wall Covering.

Chapter 7 contains provisions for the design and construction of interior and exterior wall coverings. This chapter establishes the various types of materials, materials standards and methods of application permitted for use as interior coverings, including interior plaster, gypsum board, ceramic tile, wood veneer paneling, hardboard paneling, wood shakes and wood shingles. Chapter 7 also contains requirements for the use of vapor retarders for moisture control in walls.

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Exterior wall coverings provide the weather-resistant exterior envelope that protects the building’s interior from the elements. Chapter 7 provides the requirements for wind resistance and water-resistive barrier for exterior wall coverings. This chapter prescribes the exterior wall coverings as well as the water-resistive barrier required beneath the exterior materials. Exterior wall coverings regulated by this section include aluminum, stone and masonry veneer, wood, hardboard, particleboard, wood structural panel siding, wood shakes and shingles, exterior plaster, steel, vinyl, fiber cement and exterior insulation finish systems.

Chapter 8 Roof-Ceiling Construction.

Chapter 8 regulates the design and construction of roof-ceiling systems. This chapter contains two roof-ceiling framing systems: wood framing and cold-formed steel framing. Allowable span tables are provided to simplify the selection of rafter and ceiling joist size for wood roof framing and cold-formed steel framing. Chapter 8 also provides requirements for the application of ceiling finishes, the proper ventilation of concealed spaces in roofs (e.g., enclosed attics and rafter spaces), unvented attic assemblies and attic access.

Chapter 9 Roof Assemblies.

Chapter 9 regulates the design and construction of roof assemblies. A roof assembly includes the roof deck, vapor retarder, substrate or thermal barrier, insulation, vapor retarder and roof covering. This chapter provides the requirement for wind resistance of roof coverings.

The types of roof covering materials and installation regulated by Chapter 9 are: asphalt shingles, clay and concrete tile, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shakes and shingles, built-up roofs, metal roof panels, modified bitumen roofing, thermoset and thermoplastic single-ply roofing, sprayed polyurethane foam roofing, liquid applied coatings and photovoltaic shingles. Chapter 9 also provides requirements for roof drainage, flashing, above deck thermal insulation, rooftop-mounted photovoltaic systems and recovering or replacing an existing roof covering.

Chapter 10 Chimneys and Fireplaces.

Chapter 10 contains requirements for the safe construction of masonry chimneys and fireplaces and establishes the standards for the use and installation of factory-built chimneys, fireplaces and masonry heaters. Chimneys and fireplaces constructed of masonry rely on prescriptive requirements for the details of their construction; the factory-built type relies on the listing and labeling method of approval. Chapter 10 provides the requirements for seismic reinforcing and anchorage of masonry fireplaces and chimneys.

Chapter 11 [RE] Energy Efficiency.

Chapter 11 is not adopted in California. See California Energy Code, Title 24, Part 6.

Chapter 12 Mechanical Administration.

Frequently asked questions

Who enforces the mechanical rules for residential HVAC in California?

State-level technical mechanical rules for residential buildings are enforced via the California Mechanical Code (CMC), Title 24, Part 4. The CRC explicitly marks its mechanical chapters not adopted and points users to the CMC.

If the CRC chapters aren’t adopted, do I still need a permit?

Yes. The CRC contains procedural/administrative inspection rules (e.g., § R109.1, § R109.1.2) that govern permits and inspections; the technical installation requirements come from the CMC.

Can a city require the IRC mechanical chapters instead of the CMC?

A local jurisdiction may adopt additional or different provisions by ordinance (local adoption). However, state-adopted requirements in the CMC and the Energy Code take precedence for matters the state has adopted; see CMC § 1.1.11 for the chapter-adoption policy.

Where do I find equipment-efficiency rules and sizing methods?

Equipment efficiency and several mandatory sizing/installation rules are in the California Energy Code (Title 24, Part 6) and the CMC. The CRC directs users to the Energy Code for energy matters. Design temperatures (68°F heating / 75°F cooling) and related sizing guidance are in the Energy Code.

My contractor referenced CRC Chapter 14 — is that authoritative?

Not at the state level. CRC Chapter 14 is not adopted (CRC directs you to the CMC). Ask the contractor to cite the corresponding CMC sections (and Energy Code where applicable) for the technical rules.

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