CMC · California Mechanical Code
What is the maximum operating pressure inside buildings and when are higher pressures allowed?
Most indoor gas piping must not exceed 5 psi. Higher pressures are allowed only when the piping is welded or uses listed fittings, is in ventilated chases or exclusive industrial/boiler rooms, is temporary or agricultural, or is LP‑Gas handled per NFPA 58. The controlling text in the provided CMC files appears at § 1310.6 / § 1310.6.1 (also mirrored at CPC § 1208.4 / § 1208.4.1).
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The baseline rule is: the maximum operating pressure for fuel‑gas piping located inside buildings is 5 psi (34 kPa) unless specific construction or location conditions are met. The version of the California Mechanical Code text available to me does not contain § 1308.4 / § 1308.4.1 as requested; the equivalent provisions in the provided files are § 1310.6 and § 1310.6.1 (and the same language also appears in the California Plumbing Code at § 1208.4 / § 1208.4.1) — these are the controlling text I cite below.
The simplest rule: do not exceed 5 psi (34 kPa) inside a building unless the piping construction, installation location, or system type fits one of the enumerated exceptions in the code (see § 1310.6).
Requirements in detail
The numeric limit
- Maximum operating pressure: 5 psi (34 kPa) for fuel‑gas piping located inside buildings (unless an exception applies). § 1310.6.
When higher pressures are allowed (decision‑relevant list)
If any one of the listed conditions is true, piping inside a building may operate above 5 psi (34 kPa). The code lists these specific, alternative conditions; each is a separate allowance. § 1310.6.
| Decision factor / condition | What that means in plain language | Code Reference |
|---|---|---|
| Piping joints are welded or brazed | Permanently‑sealed joints that reduce leak risk. | § 1310.6(1) |
| Fittings listed to ANSI/CSA LC‑4 (CSA 6.32) | Use of fittings that are listed and installed per manufacturer instructions. | § 1310.6(2) |
| Flanged joints where pipe‑to‑flange connections are welded/brazed | Flanged joints acceptable only where mating connections are welded/brazed. | § 1310.6(3) |
| Piping in a ventilated chase / enclosed to prevent gas accumulation | Pipe runs within ventilated vertical chases or enclosures designed to avoid accumulation. | § 1310.6(4) |
| Piping located in exclusive industrial/research/warehouse/boiler & mechanical areas | Separate areas used exclusively for these functions permit higher pressures. | § 1310.6(5)(a–d) |
| Temporary piping for buildings under construction | Short‑term installations during construction are exempted. | § 1310.6(6) |
| Piping that serves agricultural appliances/equipment | Agricultural use piping inside buildings is excepted. | § 1310.6(7) |
| LP‑Gas piping > 20 psi that complies with NFPA 58 | Higher‑pressure LP‑Gas systems are governed by NFPA 58 (LP‑Gas Code). | § 1310.6(8) and § 1310.6.1 for very low temperature LP‑Gas notes |
Notes:
- Where the code text above appears identically in the California Plumbing Code, see § 1208.4 and § 1208.4.1 for the same allowances and the special LP‑Gas note.
How the list is used (practical decision steps)
- Start with the baseline: assume piping inside occupied building spaces must not exceed 5 psi. § 1310.6.
- Check each exception; if at least one applies to the piping installation (construction method, listed fittings, location in a designated room/chase, temporary, agricultural, or LP‑Gas meeting NFPA 58), the higher pressure may be permitted. § 1310.6.
- If relying on an exception that depends on listed fittings or welding/brazing, document the method/manufacturer instructions and make joints accessible for inspection as required by other code sections (see piping installation and testing rules).
Exceptions & special cases
- Special LP‑Gas (propane/propane‑butane) systems designed to operate below ‑5°F (‑21°C) require design measures to avoid liquid accumulation (either accommodate liquid or prevent vapor condensing back to liquid) — see § 1310.6.1 / § 1208.4.1.
- Appliance overpressure limits: piping serving appliances that are designed for low inlet pressures (≤ 14 in. WC / 3.5 kPa) are subject to tighter limits (see § 1310.7 for appliance overpressure protection — the code gives a 2 psig limit unless protected by overpressure device).
- The code may require ventilated chases to meet ventilation sizing rules (vent area tied to maximum pressure and pipe diameter) when relying on the ventilated‑chase exception; see chase ventilation and regulator venting requirements.
If you plan to use one of the exceptions as the basis for a higher operating pressure, be prepared to show compliance with the exact construction, listing, ventilation, or NFPA 58 requirements referenced in the code. The snippets I located show these allowances but other adjacent requirements (venting, testing, overpressure protection) are cross‑referenced elsewhere in the Chapter.
Common mistakes
- Relying on a “boiler room” or “mechanical room” location without confirming the room is used exclusively for those functions — the code exception requires exclusive use. § 1310.6(5).
- Assuming listed flexible fittings or common threaded fittings permit >5 psi — the code requires fittings listed to ANSI/CSA LC‑4 (CSA 6.32) and installed per the manufacturer for the exception to apply. § 1310.6(2).
- Forgetting overpressure protection: even where higher line pressure is permitted, appliances and equipment may have their own maximum inlet requirements and overpressure devices must be provided per other sections (e.g., appliance overpressure protection). § 1310.7 and § 1308.9.
- Citing the wrong section number: the text I found governing maximum operating pressure appears as § 1310.6 / § 1310.6.1 (and in the Plumbing Code at § 1208.4 / § 1208.4.1). The user‑requested § 1308.4 / § 1308.4.1 were not present in the provided files; always confirm the edition and table of contents for the adopted numbering in your jurisdiction.
Worked example — concrete scenario
Scenario: A designer proposes a natural‑gas piping system inside a small warehouse mechanical room that will operate at 10 psi to feed process burners.
Step 1 — Baseline check: 10 psi > 5 psi, so the baseline limit is exceeded and one of the code exceptions must apply. § 1310.6.
Step 2 — Evaluate exceptions:
- Is the piping jointed by welding or brazing? If yes → exception § 1310.6(1) applies (welded/brazed joints permit >5 psi).
- If not welded, are fittings listed to ANSI/CSA LC‑4 and installed per manufacturer? If yes → exception § 1310.6(2) applies.
- Is the location a separate area used exclusively for industrial processing or a boiler/mechanical room? If the mechanical room is used only for mechanical equipment (exclusive use), exception § 1310.6(5)(d) or (a) may apply.
Step 3 — Verify & document: Suppose the designer specifies welded steel piping (Schedule 40) with welded joints. That meets § 1310.6(1), so the higher operating pressure is permitted — but the installation must still meet all applicable testing, overpressure protection, and material requirements elsewhere in the code. § 1310.6(1) and related testing/overpressure sections.
Conclusion for example: With welded joints and proper testing and overpressure protection, the 10 psi system inside the mechanical room can be code‑compliant per § 1310.6(1).
Related provisions
- § 1310.6 — Maximum operating pressure in buildings (text located and used above).
- § 1310.6.1 — LP‑Gas systems operating below ‑5°F; design note for liquids/condensing.
- § 1208.4 / § 1208.4.1 — Same maximum operating pressure language in the California Plumbing Code (mirrors the allowances).
- § 1308.9 — Overpressure protection device requirements (pressure relief, monitor regulators, series regulators or automatic shutoffs).
- § 1310.7 — Appliance overpressure protection and the 2 psig appliance limit where applicable.
- See the Chapter 13 (Fuel Gas Piping) table of contents for other related installation, chase ventilation, and testing requirements that intersect with higher‑pressure installations.
Note on citations and numbering: you asked for § 1308.4 / § 1308.4.1 specifically. The file set you provided does not contain those exact section numbers; the governing text for maximum operating pressure in the available CMC file is at § 1310.6 / § 1310.6.1, and the same language is mirrored in the California Plumbing Code at § 1208.4 / § 1208.4.1. I have quoted and cited the sections that are present in the uploaded documents rather than inventing or assuming other numbering.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 1310.5.1 High relevance — show source text
1310.5.1 Pressure Reduction. Where pressure reduction is required in branch connections for compliance with Section 1310.6, such reduction shall take place either inside the chase or immediately adjacent to the outside wall of the chase. Regulator venting and downstream overpressure protection shall comply with Section 1308.6.4 and Section 1308.7. The regulator shall be accessible for service and repair, and vented in accordance with one of the following:
(1) Where the fuel gas is lighter than air, regulators equipped with a vent limiting means shall be permitted to be vented into the chase. Regulators not equipped with a vent limiting means shall be permitted to be vented either directly to the outdoors or to a point within the top 1 foot (305 mm) of the chase.
(2) Where the fuel gas is heavier than air, the regulator vent shall be vented only directly to the outdoors.
[NFPA 54:7.4.1]
1310.5.2 Chase Construction. Chase construction
shall comply with local building codes with respect to fire resistance and protection of horizontal and vertical openings. [NFPA 54:7.4.2]
1310.5.3 Ventilation. A chase shall be ventilated to the
outdoors and only at the top. The opening(s) shall have a minimum free area [in square inches (square meters)] equal to the product of one-half of the maximum pressure in the piping [in pounds per square inch (kilopas
cals)] times the largest nominal diameter of that piping
[in inches (millimeters)], or the cross-sectional area of the chase, whichever is smaller. Where more than one fuel gas piping system is present, the free area for each system shall be calculated and the largest area used.
[NFPA 54:7.4.3]
1310.6 Maximum Operating Pressure in Buildings. The maximum operating pressure for any piping systems located inside buildings shall not exceed 5 psi (34 kPa) unless one or more of the following conditions are met:
(1) The piping joints are welded or brazed.
(2) The piping is joined by fittings listed to CSA/ANSI LC 4/CSA 6.32 and installed according to the manufacturer’s installation instructions.
(3) The piping joints are flanged and all pipe-to-flange connections are made by welding or brazing.
(4) The piping is located in a ventilated chase or otherwise enclosed for protection against accidental gas accumulation.
(5) The piping is located inside buildings or separate areas of buildings used exclusively for one of the following:
(a) Industrial processing or heating
(b) Research
(c) Warehousing
(d) Boiler or mechanical rooms
(6) The piping is a temporary installation for buildings under construction.
(7) The piping serves appliances or equipment used for agricultural purposes.
(8) The piping system is an LP-Gas piping system with an operating pressure greater than 20 psi (138 kPa) and complies with NFPA 58. [NFPA 54:5.4.4]
1310.6.1 LP-Gas Systems Operating Below -5°F (-21°C). LP-Gas systems designed to operate below 5°F (-21°C) or with butane or a propane-butane mix shall be designed to either accommodate liquid LP-Gas or to prevent LP-Gas vapor from condensing back into a liquid. [NFPA 54:5.4.5]
CMC § 7.4.3 High relevance — show source text
[NFPA 54:7.4.3]
1310.6 Maximum Operating Pressure in Buildings. The maximum operating pressure for any piping systems located inside buildings shall not exceed 5 psi (34 kPa) unless one or more of the following conditions are met:
(1) The piping joints are welded or brazed.
(2) The piping is joined by fittings listed to CSA/ANSI LC 4/CSA 6.32 and installed according to the manufacturer’s installation instructions.
(3) The piping joints are flanged and all pipe-to-flange connections are made by welding or brazing.
(4) The piping is located in a ventilated chase or otherwise enclosed for protection against accidental gas accumulation.
(5) The piping is located inside buildings or separate areas of buildings used exclusively for one of the following:
(a) Industrial processing or heating
(b) Research
(c) Warehousing
(d) Boiler or mechanical rooms
(6) The piping is a temporary installation for buildings under construction.
(7) The piping serves appliances or equipment used for agricultural purposes.
(8) The piping system is an LP-Gas piping system with an operating pressure greater than 20 psi (138 kPa) and complies with NFPA 58. [NFPA 54:5.4.4]
1310.6.1 LP-Gas Systems Operating Below -5°F (-21°C). LP-Gas systems designed to operate below 5°F (-21°C) or with butane or a propane-butane mix shall be designed to either accommodate liquid LP-Gas or to prevent LP-Gas vapor from condensing back into a liquid. [NFPA 54:5.4.5]
1310.7 Appliance Overpressure Protection. The maximum operating pressure for piping systems serving appliances designed to operate at 14 inches water column (3.5 kPa) inlet pressure or less shall be 2 pounds-force per square inch gauge (psig) (14 kPa) unless an over pressure protection device designed to limit pressure at the appliance to 2 psig (14 kPa) upon failure of the line gas pressure regulator is installed. 1310.8 Gas Pipe Turns. Changes in direction of gas pipe shall be made by the use of fittings, factory bends, or field bends. [NFPA 54:7.5]
1310.8.1 Metallic Pipe. Metallic pipe bends shall comply with the following:
(1) Bends shall be made only with bending tools and procedures intended for that purpose.
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FUEL GAS PIPING
(2) All bends shall be smooth and free from buckling, cracks, or other evidence of mechanical damage.
(3) The longitudinal weld of the pipe shall be near the neutral axis of the bend.
(4) Pipe shall not be bent through an arc of more than 90 degrees.
(5) The inside radius of a bend shall be not less than 6 times the outside diameter of the pipe. [NFPA 54:7.5.1]
1310.8.2 Plastic Pipe. Plastic pipe bends shall comply with the following:
(1) The pipe shall not be damaged, and the internal diameter of the pipe shall not be effectively reduced.
(2) Joints shall not be located in pipe bends.
CMC § 1208.3.1 High relevance — show source text
1208.3.1 Maximum Gas Demand. The volumetric flow rate of gas to be provided shall be the sum of the maximum input of the appliances served. The volumetric flow rate of gas to be provided shall be adjusted for altitude where the installation is above 2000 feet (610 m). [NFPA 54:5.3.2.1 – 5.3.2.2] Where the input rating is not indicated, the gas supplier, appliance manufacturer, or a qualified agency shall be contacted, or the rating from Table 1208.3.1 shall be used for estimating the volumetric flow rate of gas to be supplied.
The total connected hourly load shall be used as the basis for piping sizing, assuming all appliances are operating at full capacity simultaneously.
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FUEL GAS PIPING
the inlet connection of all appliances served shall be such that the supply pressure at each appliance inlet is greater than or equal to the minimum pressure required by the appliance. [NFPA 54:5.3.4]
1208.4 Maximum Operating Pressure in Buildings. The maximum operating pressure for any piping systems located inside buildings shall not exceed 5 psi (34 kPa) unless one or more of the following conditions are met:
(1) The piping joints are welded or brazed.
(2) The piping is joined by fittings listed to ANSI LC 4/CSA 6.32 and installed according to the manufacturer’s installation instructions.
(3) The piping joints are flanged and all pipe-to-flange connections are made by welding or brazing.
(4) The piping is located in a ventilated chase or otherwise enclosed for protection against accidental gas accumulation.
(5) The piping is located inside buildings or separate areas of buildings used exclusively for one of the following:
(a) Industrial processing or heating
(b) Research
(c) Warehousing
(d) Boiler or mechanical rooms
(6) The piping is a temporary installation for buildings under construction.
(7) The piping serves appliances or equipment used for agricultural purposes.
(8) The piping system is an LP-Gas piping system with an operating pressure greater than 20 psi (138 kPa) and complies with NFPA 58. [NFPA 54:5.4.4]
1208.4.1 LP-Gas Systems Operating Below -5°F (-21°C). LP-Gas systems designed to operate below 5°F (-21°C) or with butane or a propane-butane mix shall be designed to either accommodate liquid LP-Gas or to prevent LP-Gas vapor from condensing back into a liquid. [NFPA 54:5.4.5]
1208.5 Acceptable Piping Materials and Joining Methods. Materials used for piping systems shall comply with the requirements of Section 1208.5.1 through Section 1208.5.6.3. {NFPA 54:5.5.1.1}
1208.5.1 Used Materials. Pipe, fittings, valves, or other materials shall not be used again unless they are free of foreign materials and have been ascertained to be adequate for the service intended. [NFPA 54:5.5.1.2]
CMC § 1308.8 High relevance — show source text
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TABLE OF CONTENTS
1308.8 Pressure Limitation
Requirements . . . . . . . . . . . . . . . . 281
1308.9 Overpressure Protection Devices. . . . . . . . . . . . . . . . . . . . . 281
1308.10 Backpressure Protection . . . . . . . 282
1308.11 Low-Pressure Protection . . . . . . . 282
1308.12 Shutoff Valves . . . . . . . . . . . . . . . 282
Table 1308.12 Manual Gas Valve Standards. . . . 282
1308.13 Expansion and Flexibility . . . . . . . 282
1308.14 Pressure Regulator and Pressure Control Venting . . . . . . . 282
1309.0 Excess Flow Valve . . . . . . . . . . . . 283
1309.1 General. . . . . . . . . . . . . . . . . . . . . 283
1310.0 Gas Piping Installation . . . . . . . . . 283
1310.1 Piping Underground . . . . . . . . . . . 283
1310.2 CSST Piping Systems . . . . . . . . . 284
1310.3 Installation of Aboveground Piping . . . . . . . . . . . . . . . . . . . . . . 284
Table 1310.3.5.1 Support of Piping . . . . . . . . . . . . . 285
1310.4 Concealed Piping in Buildings . . . 285
1310.5 Piping in Vertical Chases . . . . . . . 286
1310.6 Maximum Operating Pressure in Buildings . . . . . . . . . . . . . . . . . . 286
1310.7 Appliance Overpressure Protection . . . . . . . . . . . . . . . . . . . 286
1310.8 Gas Pipe Turns. . . . . . . . . . . . . . . 286
1310.9 Drips and Sediment Traps . . . . . . 287
1310.10 Outlets . . . . . . . . . . . . . . . . . . . . . 287
1310.11 Manual Gas Shutoff Valves . . . . . 287
1310.12 Prohibited Devices . . . . . . . . . . . . 288
1310.13 Systems Containing Gas-Air Mixtures Outside the Flammable
Range . . . . . . . . . . . . . . . . . . . . . . 288
1310.14 Systems Containing Flammable Gas-Air Mixtures. . . . . . . . . . . . . . 288
1311.0 Electrical Bonding and Grounding. . . . . . . . . . . . . . . . . . . 289
1311.1 Pipe and Tubing other than CSST . . . . . . . . . . . . . . . . . . . . . . 289
1311.2 Bonding of CSST Gas Piping . . . . 289
1311.3 Arc-Resistant Jacketed CSST . . . 289
CMC § 1310.4 Medium relevance — show source text
1310.4 Concealed Piping in Buildings . . . 285
1310.5 Piping in Vertical Chases . . . . . . . 286
1310.6 Maximum Operating Pressure in Buildings . . . . . . . . . . . . . . . . . . 286
1310.7 Appliance Overpressure Protection . . . . . . . . . . . . . . . . . . . 286
1310.8 Gas Pipe Turns. . . . . . . . . . . . . . . 286
1310.9 Drips and Sediment Traps . . . . . . 287
1310.10 Outlets . . . . . . . . . . . . . . . . . . . . . 287
1310.11 Manual Gas Shutoff Valves . . . . . 287
1310.12 Prohibited Devices . . . . . . . . . . . . 288
1310.13 Systems Containing Gas-Air Mixtures Outside the Flammable
Range . . . . . . . . . . . . . . . . . . . . . . 288
1310.14 Systems Containing Flammable Gas-Air Mixtures. . . . . . . . . . . . . . 288
1311.0 Electrical Bonding and Grounding. . . . . . . . . . . . . . . . . . . 289
1311.1 Pipe and Tubing other than CSST . . . . . . . . . . . . . . . . . . . . . . 289
1311.2 Bonding of CSST Gas Piping . . . . 289
1311.3 Arc-Resistant Jacketed CSST . . . 289
1311.4 Prohibited Use . . . . . . . . . . . . . . . 289
1311.5 Lightning Protection System. . . . . 289
1311.6 Electrical Circuits . . . . . . . . . . . . . 289
1311.7 Electrical Connections . . . . . . . . . 289
1312.0 Appliance and Equipment Connections to Building Piping. . . 289
1312.1 Connecting Appliances and Equipment . . . . . . . . . . . . . . . . . . 289
2025 CALIFORNIA MECHANICAL CODE
1312.2 Suspended Low-Intensity Infrared Tube Heaters . . . . . . . . . 290
1312.3 Use of Nonmetallic Gas Hose
Connectors . . . . . . . . . . . . . . . . . . 290
1312.4 Injection (Bunsen) Burners . . . . . . 290
1312.5 Connection of Portable and
Mobile Industrial Appliances. . . . . 290
1312.6 Appliance Shutoff Valves and Connections. . . . . . . . . . . . . . 291
1312.7 Quick-Disconnect Devices . . . . . . 291
1312.8 Gas Convenience Outlets. . . . . . . 291
1312.9 Sediment Trap . . . . . . . . . . . . . . . 291
1312.10 Installation of Piping . . . . . . . . . . . 291
1312.11 Liquefied Petroleum Gas Facilities and Piping . . . . . . . . . . . 291
CMC § 1004.4 Medium relevance — show source text
[Equation 1004.4(1)]
Vt (forced-type) = [(0.00041] [t] [ - 0.0466) ] [V][s]
(P P a a
Pf Po )
[Equation 1004.4(2)]
Vt (diaphragm-type) = [(0.00041] [t] [ - 0.0466) ] [V][s]
– [P][f]
[1]
( Po )
Where:
Vt = Minimum volume of expansion tank, gallons. Vs = Volume of system, not including expansion tank, gallons.
t = Average operating temperature, °F.
Pa = Atmospheric pressure, pounds per square inch. Pf = Fill pressure, pounds per square inch. Po = Maximum operating pressure, pounds per square inch.
For SI units: 1 gallon = 3.785 L
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BOILERS AND PRESSURE VESSELS
TABLE 1004.4(1) EXPANSION TANK CAPACITIES FOR GRAVITY HOT WATER SYSTEMS [1]
INSTALLED EQUIVALENT
DIRECT RADIATION2
(square feet)TANK CAPACITY
(gallons)
Up to 35018
Up to 45021
Up to 65024
Up to 90030
Up to 110035
Up to 140040
Up to 16002 to 30
Up to 18002 to 30
Up to 20002 to 35
Up to 24002 to 40 For SI units: 1 gallon = 3.785 L, 1 square foot = 0.0929 m [2]
Notes: 1 Based on a two-pipe system with an average operating water temperature of 170°F (77°C), using cast-iron column radiation with a heat emission rate of 150 British thermal units per square foot hour [Btu/(ft [2] - h)] (473 W/m [2] ) equivalent direct radiation. 2 For systems that exceed 2400 square feet (222.9 m 2 ) of installed equivalent direct water radiation, the required capacity of the cushion tank shall be increased on the basis of 1 gallon (4 L) tank capacity per 33 square feet (3.1 m [2] ) of additional equivalent direct radiation.
TABLE 1004.4(2) EXPANSION TANK CAPACITIES FOR FORCED HOT WATER SYSTEMS [1]
CMC § 1208.0 Medium relevance — show source text
1208.0 Gas Piping System Design, Materials, and Components. 1208.1 Installation of Piping System. Where required by the Authority Having Jurisdiction, a piping sketch or plan shall be prepared before proceeding with the installation. The plan shall show the proposed location of piping, the size of different branches, the various load demands, and the location of the point of delivery. [NFPA 54:5.1.1] 1208.1.1 Addition to Existing System. When additional appliances are being connected to a gas piping system, the existing piping shall be checked to determine whether it has adequate capacity. If the capacity of the system is determined to be inadequate for the additional appliances, the existing system shall be enlarged as required, or separate gas piping of adequate capacity shall be provided. [NFPA 54:5.1.2] 1208.2 Interconnections Supplying Separate Users. Where two or more meters, or two or more service regulators where meters are not provided, are located on the same premises and supply separate users, the gas piping systems shall not be interconnected on the outlet side of the meters or service regulators. [NFPA 54:5.2.1] 1208.2.1 Interconnections for Standby Fuels. Where a supplementary gas for standby use is connected downstream from a meter or a service regulator where a meter is not provided, equipment to prevent backflow shall be installed. A three-way valve installed to admit the standby supply and at the same time shut off the regular supply shall be permitted to be used for this purpose.
[NFPA 54:5.2.2.1 – 5.2.2.2] 1208.3 Sizing of Gas Piping Systems. Gas piping systems shall be of such size and so installed as to provide a supply of gas sufficient to meet the maximum demand and supply gas to each appliance inlet at not less than the minimum supply pressure required by the appliance. [NFPA 54:5.3.1]
1208.3.1 Maximum Gas Demand. The volumetric flow rate of gas to be provided shall be the sum of the maximum input of the appliances served. The volumetric flow rate of gas to be provided shall be adjusted for altitude where the installation is above 2000 feet (610 m). [NFPA 54:5.3.2.1 – 5.3.2.2] Where the input rating is not indicated, the gas supplier, appliance manufacturer, or a qualified agency shall be contacted, or the rating from Table 1208.3.1 shall be used for estimating the volumetric flow rate of gas to be supplied.
The total connected hourly load shall be used as the basis for piping sizing, assuming all appliances are operating at full capacity simultaneously.
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FUEL GAS PIPING
the inlet connection of all appliances served shall be such that the supply pressure at each appliance inlet is greater than or equal to the minimum pressure required by the appliance. [NFPA 54:5.3.4]
1208.4 Maximum Operating Pressure in Buildings. The maximum operating pressure for any piping systems located inside buildings shall not exceed 5 psi (34 kPa) unless one or more of the following conditions are met:
(1) The piping joints are welded or brazed.
CMC § 1313.1.6 Medium relevance — show source text
1313.1.6 Test Medium. The test medium shall be air, nitrogen, carbon dioxide, or an inert gas. Oxygen shall not be used as a test medium. [NFPA 54:8.1.2]
1313.2 Test Preparation. Test preparation shall comply with Section 1313.2.1 through Section 1313.2.6.
1313.2.1 Pipe Joints. Pipe joints, including welds, shall be left exposed for examination during the test.
Exception: Covered or concealed pipe end joints that have been previously tested in accordance with this code.
[NFPA 54:8.1.3.1]
1313.2.2 Expansion Joints. Expansion joints shall be provided with temporary restraints, if required, for the additional thrust load under test. [NFPA 54:8.1.3.2]
1313.2.3 Appliances and Equipment. Appliances and equipment that are not to be included in the test shall be either disconnected from the piping or isolated by blanks, blind flanges, or caps. Flanged joints at which blinds are inserted to blank off other equipment during the test shall not be required to be tested. [NFPA 54:8.1.3.3] 1313.2.4 Designed for Operating Pressures Less than Test Pressure. Where the piping system is connected to appliances or equipment designed for operating pressures of less than the test pressure, such appliances or equipment shall be isolated from the piping system by disconnecting them and capping the outlet(s). [NFPA 54:8.1.3.4]
1313.2.5 Designed for Operating Pressures Equal to or Greater than Test Pressure. Where the piping system is connected to appliances or equipment designed for operating pressures equal to or greater than the test pressure, such appliances or equipment shall be isolated from the piping system by closing the individual appliance or equipment shutoff valve(s). [NFPA 54:8.1.3.5] 1313.2.6 Safety. All testing of piping systems shall be performed in a manner that protects the safety of employees and the public during the test. [NFPA 54:8.1.3.6]
1313.3 Test Pressure. This inspection shall include an air, CO2, or nitrogen pressure test, at which time the gas piping shall stand a pressure of not less than 10 psi (69 kPa) gauge pressure. Test pressures shall be held for a length of time satisfactory to the Authority Having Jurisdiction but in no case less than 15 minutes with no perceptible drop in pressure. For welded piping, and for piping carrying gas at pressures in excess of 14 inches water column (3.5 kPa) pressure, the test pressure shall be not less than 60 psi (414 kPa) and shall be continued for a length of time satisfactory to the Authority Having Jurisdiction, but in no case for less than 30 minutes.
For CSST carrying gas at pressures in excess of 14 inches water column (3.5 kPa) pressure, the test pressure shall be 30 psi (207 kPa) for 30 minutes. These tests shall be made using air, CO2, or nitrogen pressure and shall be made in the presence of the Authority Having Jurisdiction. Necessary apparatus for conducting tests shall be furnished by the permit holder.
CMC § 1220.4.2 Medium 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:
CMC § 58.6 Medium relevance — show source text
Appliance, Portable Heating. A heating appliance designed for environmental heating that may have a self
32 2025 CALIFORNIA MECHANICAL CODE
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DEFINITIONS
200 000 Btu/h (58.6 kW), or an operating temperature exceeding 210°F (99°C) that provides hot water to be used externally to itself.
Boiler, Low-Pressure Hot-Water-Heating. A boiler furnishing hot water at pressures not exceeding 160 psig (1103 kPa) and at temperatures not exceeding 250°F (121°C).
Boiler, Low-Pressure Steam-Heating. A boiler furnishing steam at pressures not exceeding 15 psig (103 kPa).
Boiler, Miniature. A power boiler having an internal shell diameter of 16 inches (406 mm) or less, a gross volume of 5 cubic feet (0.14 m [3] ) or less, a heating surface of 20 square feet (1.86 m [2] ) or less (not applicable to electric boilers), and not exceeding 100 psig (689 kPa).
Boiler, Package. A class of boiler defined herein and shall be a boiler equipped and shipped complete with fuel-burning equipment, automatic controls and accessories, and mechanical draft equipment.
Boiler, Power. A boiler in which steam is generated at pressures exceeding 15 psig (103 kPa).
Boiler, Power Hot Water (High Temperature Water Boiler). A boiler used for heating water or liquid to a pressure exceeding 160 psig (1103 kPa) or to a temperature exceeding 250°F (121°C).
Boiler, Steam-Heating. A boiler operated at pressures not exceeding 15 psig (103 kPa) for steam.
Boiler, Water Heater or Hot-Water-Heating. An appliance designed primarily to supply hot water for domestic or commercial purposes and equipped with automatic controls limiting water temperature to a maximum of 210°F (99°C).
Boiler Room. A room where boilers are installed.
Bonding Conductor or Jumper. A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected. [NFPA 70:100(I)]
Borehole. A vertical or horizontal shaft typically cored, drilled or bored into the earth for geothermal system installations.
Breathing Zone. The region within an occupiable space between planes 3 inches and 72 inches (76 mm and 1829 mm) above the floor and exceeds 2 feet (610 mm) from the walls or fixed air-conditioning equipment. [ASHRAE 62.1:3]
Breathing Zone Outdoor Airflow. The outdoor airflow required in the breathing zone of the occupiable space or spaces in a ventilation zone.
Breeching. A metal connector for medium- and high-heat appliances.
Broiler. A general term including broilers, salamanders, barbecues, and other devices cooking primarily by radiated heat, excepting toasters. [NFPA 54:3.3.14]
BTU/H. The listed maximum capacity of any appliance, absorption unit, or burner expressed in British thermal units input per hour, unless otherwise noted.
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CMC § 0.120 Medium relevance — show source text
fastener**
horizontal spacing| |CLADDING FASTENER
THROUGH FOAM
SHEATHING INTO:|CLADDING FASTENER
TYPE AND MINIMUM SIZEc|CLADDING FASTENER
VERTICAL SPACING
(INCHES)|Cladding weight:|Cladding weight:|Cladding weight:|Cladding weight:|Cladding weight:|Cladding weight:|Cladding weight:|Cladding weight:| |CLADDING FASTENER
THROUGH FOAM
SHEATHING INTO:|CLADDING FASTENER
TYPE AND MINIMUM SIZEc|CLADDING FASTENER
VERTICAL SPACING
(INCHES)|**3 **
psf|11
psf|18
psf|25
psf|**3 **
psf|11
psf|18
psf|25
psf| |Wood Framing
(minimum 11/4- inch
penetration)b|0.120" diameter nail|6|3.00|1.70|0.90|0.55|3.00|1.05|0.50|DR| |Wood Framing
(minimum 11/4- inch
penetration)b|0.120" diameter nail|8|3.00|1.20|0.60|DR|3.00|0.70|DR|DR| |Wood Framing
(minimum 11/4- inch
penetration)b|0.120" diameter nail|12|3.00|0.70|DR|DR|2.15|DR|DR|DR| |Wood Framing
(minimum 11/4- inch
penetration)b|0.131" diameter nail|6|4.00|2.15|1.20|0.75|4.00|1.35|0.70|DR| |Wood Framing
(minimum 11/4- inch
penetration)b|0.131" diameter nail|8|4.00|1.55|0.80|DR|4.00|0.90|DR|DR| |Wood Framing
(minimum 11/4- inch
penetration)b|0.131" diameter nail|12|4.00|0.90|DR|DR|2.70|0.50|DR|DR| |Wood Framing
(minimum 11/4- inch
penetration)b|0.162" diameter nail|6|4.00|3.55|2.05|1.40|4.00|2.25|1.25|0.80| |Wood Framing
(minimum 11/4- inch
penetration)b|0.162" diameter nail|8|4.00|2.55|1.45|0.95|4.00|1.60|0.85|0.50| |Wood Framing
(minimum 11/4- inch
penetration)b|0.162" diameter nail|12|4.00|1.60|0.85|0.50|4.00|0.95|DR|DR| |For SI: 1 inch = 25.CMC § 304.8 Medium relevance — show source text
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
1112.12.5 Simultaneous Operation. When outlets of two or more relief devices or fusible plugs, which are
TABLE 1112.12.4
ATMOSPHERIC PRESSURE AT NOMINAL INSTALLATION ELEVATION ( Pa )
[ASHRAE 15: TABLE 9-2]
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
244 2025 CALIFORNIA MECHANICAL CODE
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REFRIGERATION
1113.2 Type of Protection. Pressure vessels with an internal gross volume of 3 cubic feet (0.1 m [3] ) or less shall use one or more pressure relief devices or a fusible plug. Pressure vessels of more than 3 cubic feet (0.1 m [3] ) but less than 10 cubic feet (0.28 m [3] ) internal gross volume shall use one or more pressure relief devices. Fusible plugs shall not be used.
[ASHRAE 15:9.7.2.1, 9.7.2.2]
1113.3 Discharging into Lowside of System. For pressure-relief valves discharging into the lowside of the system, a single relief valve (not rupture member) of the required relieving capacity shall not be used on vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume except under the conditions permitted in Section 1112.11.3. [ASHRAE 15:9.7.3]
1113.4 Parallel Pressure-Relief Devices. Two or more
pressure-relief devices in parallel to obtain the required capacity shall be considered as one pressure-relief device. The discharge capacity shall be the sum of the capacities required for each pressure vessel being protected.
1113.5 Discharge Capacity. The minimum required discharge capacity of the pressure-relief device or fusible plug for a pressure vessel shall be determined in accordance with ASHRAE 15.
1113.6 Three-Way Valve. Pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume shall use one or more rupture member(s) or dual pressure-relief valves where discharging to the atmosphere. Dual pressure-relief valves shall be installed with a three-way valve to allow testing or repair. Where dual relief valves are used, the valve shall comply with Section 1113.5.
Exception: A single relief valve shall be permitted on pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume where in accordance with the following conditions:
(1) The relief valves are located on the lowside of the sys tem.
(2) The vessel is provided with shutoff valves designed to allow pumpdown of the refrigerant charge of the pressure vessel.
(3) Other pressure vessels in the system are separately protected in accordance with Section 1113.1. [ASHRAE 15:9.7.2.3]
1114.0 Special Discharge Requirements.
CMC § 8.8 Medium relevance — show source text
**
HOURS| |ITEM CODE|DEPTH|CONSTRUCTION DETAILS|LOAD|TIME|PRE-BMS-92|BMS-92|POST-BMS-92|POST-BMS-92|POST-BMS-92| |B-11-RC-1|11″|24″ wide × 11″ deep reinforced concrete “T”
beam (3290 psi); details: see Note 5 figure.|8.8 tons|4 hrs
2 min|||7|1, 2, 14|4| |B-10-RC-2|10″|24″ wide × 10″ deep reinforced concrete “T”
beam (4370 psi); details: see Note 6 figure.|8.8 tons|1 hr
53
min|||7|1, 3|13/4| |B-10-RC-3|101/2″|24″ wide × 101/2″ deep reinforced concrete
“T” beam (4450 psi); details: see Note 7
figure.|8.8 tons|2 hrs
40
min|||7|1, 3|22/3| |B-11-RC-4|11″|24″ wide × 11″ deep reinforced concrete “T”
beam (2400 psi); details: see Note 8 figure.|8.8 tons|3 hrs
32
min|||7|1, 3, 14|31/2| |B-11-RC-5|11″|24″ wide × 11″ deep reinforced concrete “T”
beam (4250 psi); details: see Note 9 figure.|8.8 tons|3 hrs
3 min|||7|1, 3, 14|3| |B-11-RC-6|11″|Concrete flange: 4″ deep × 2' wide (4895 psi)
concrete; concrete beam: 7″ deep × 61/2″
wide; “I” beam reinforcement; 10″ × 41/2″ ×
25 lbs R.S.J.; 1″ cover on flanges; flange rein-
forcement:3/8″ diameter bars at 6″ pitch
parallel to “T”; 1/4″ diameter bars perpendic-
ular to “T”; beam reinforcement: 4″ × 6″ No.
13 SWG wire mesh; span: 11' restrained;
details: see Note 10 figure.|10 tons|6 hrs|||7|1, 4|6| |B-11-RC-7|11″|Concrete flange: 6″ deep × 1' 61/2″ wide (3525
psi) concrete; concrete beam: 5″ deep × 8″
wide precast concrete blocks 83/4″ long; “I”
beam reinforcement; 7″ × 4″ × 16 lbs R.S.J.California Mechanical Code Medium relevance — show source text
2
5
10
15
20|190
182
224
277
325
374|1053
708
692
666
640
616|573
468
457
437
419
400|238
227
279
339
393
448|1379
914
896
866
838
810|750
611
596
570
549
526|326
309
381
457
526
592|1751
1146
1126
1092
1060
1028|927
754
734
702
677
651|473
443
547
646
730
808|2631
1689
1665
1626
1587
1550|1346
1098
1074
1037
1005
973| |30|0
2
5
10
15
20
30|184
175
215
265
312
360
461|1168
823
806
777
750
723
670|647
533
521
501
481
461
426|229
219
269
327
379
433
541|1542
1069
1049
1017
985
955
895|852
698
684
662
638
615
574|312
296
366
440
507
570
704|1971
1346
1324
1287
1251
1216
1147|1056
863
846
821
794
768
720|454
424
524
620
702
780
937|2996
1999
1971
1927
1884
1841
1759|1545
1308
1283
1243
1205
1166
1101| |50|0
2
5CMC § 7.11 Medium relevance — show source text
80|7.11|7.35|7.71|7.97|8.16| |45|75|30|6.71|6.99|7.21|7.55|7.78|7.96| |44|75|31|6.61|6.89|7.09|7.40|7.61|7.77| |43|75|32|6.52|6.79|6.98|7.26|7.45|7.60| |42|75|33|6.43|6.69|6.87|7.13|7.31|7.44| |41|75|34|6.33|6.60|6.77|7.02|7.18|7.30| |46|80|34|6.33|6.60|6.77|7.02|7.18|7.30| |40|75|35|6.23|6.50|6.68|6.91|7.06|7.17| |45|80|35|6.23|6.50|6.68|6.91|7.06|7.17| |44|80|36|6.13|6.41|6.58|6.81|6.95|7.05| |43|80|37|6.02|6.31|6.49|6.71|6.85|6.94| |42|80|38|5.90|6.21|6.40|6.61|6.75|6.84| |41|80|39|5.77|6.11|6.30|6.52|6.65|6.74| |46|85|39|5.77|6.11|6.30|6.52|6.65|6.74| |40|80|40|5.63|6.00|6.20|6.43|6.56|6.65| |45|85|40|5.63|6.00|6.20|6.43|6.56|6.65| |44|85|41|5.47|5.87|6.10|6.33|6.47|6.55| |43|85|42|5.30|5.74|5.98|6.24|6.37|6.46| |42|85|43|5.11|5.60|5.86|6.13|6.28|6.37| |41|85|44|4.90|5.44|5.72|6.02|6.17|6.27| |40|85|45|4.68|5.26|5.58|5.90|6.07|6.17| |Condenser DT2|Condenser DT2|Condenser DT2|14.04|11.23|9.36|7.02|5.62|4.68| |1. LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2.CMC § 7.47 Medium relevance — show source text
15|7.47|7.72|8.10|8.37|8.58| |45|75|30|7.05|7.35|7.58|7.93|8.18|8.36| |44|75|31|6.95|7.23|7.45|7.77|8.00|8.16| |43|75|32|6.85|7.13|7.33|7.63|7.83|7.98| |42|75|33|6.75|7.03|7.22|7.49|7.68|7.82| |41|75|34|6.65|6.93|7.12|7.37|7.55|7.67| |46|80|34|6.65|6.93|7.12|7.37|7.55|7.67| |40|75|35|6.55|6.83|7.01|7.26|7.42|7.54| |45|80|35|6.55|6.83|7.01|7.26|7.42|7.54| |44|80|36|6.44|6.73|6.92|7.15|7.30|7.41| |43|80|37|6.32|6.63|6.82|7.05|7.19|7.30| |42|80|38|6.20|6.53|6.72|6.95|7.09|7.19| |41|80|39|6.06|6.42|6.62|6.85|6.99|7.08| |46|85|39|6.06|6.42|6.62|6.85|6.99|7.08| |40|80|40|5.91|6.30|6.52|6.76|6.89|6.98| |45|85|40|5.91|6.30|6.52|6.76|6.89|6.98| |44|85|41|5.75|6.17|6.403|6.66|6.79|6.89| |43|85|42|5.57|6.03|6.28|6.55|6.70|6.79| |42|85|43|5.37|5.88|6.16|6.44|6.59|6.69| |41|85|44|5.15|5.71|6.01|6.33|6.49|6.59| |40|85|45|4.91|5.53|5.86|6.20|6.37|6.48| |Condenser DT2|Condenser DT2|Condenser DT2|14.04|11.23|9.36|7.02|5.62|4.68| |1. LIFT = Entering Condenser Water Temperature (°F) – Leaving Chilled Water Temperature (°F)
2.CMC § 1308.8 Medium relevance — show source text
have a flow capacity such that the pressure in the protected system is maintained at or below the limits specified in Section 1308.8 under the following conditions:
(1) The line pressure regulator for which the relief valve is providing overpressure protection has failed wide
open.
(2) The gas pressure at the inlet of the line pressure regulator for which the relief valve is providing overpressure protection is not less than the regulator’s normal operating inlet pressure. [NFPA 54:5.8.2.5]
1308.9 Overpressure Protection Devices. Overpressure protection devices shall be one of the following:
(1) Pressure relief valve.
(2) Monitor regulator.
(3) Series regulator installed upstream from the line regulator and set to continuously limit the pressure on the inlet of the line regulator to the maximum values specified by Section 1308.8 or less.
(4) Automatic shutoff device installed in series with the line pressure regulator and set to shut off when the pressure on the downstream piping system reaches the maximum values specified by Section 1308.8 or less. This device shall be designed so that it will remain closed until manually reset. [NFPA 54:5.8.3.1]
1308.9.1 Separate Devices. The devices in Section 1308.9 shall be installed either as an integral part of the service or line pressure regulator or as separate units. Where separate overpressure protection devices are installed, they shall comply with Section 1308.9.2 through Section 1308.9.7. [NFPA 54:5.8.3.2]
1308.9.2 Construction and Installation. All overpressure protection devices shall meet the following requirements:
(1) Be constructed of materials so that the operation of the device is not impaired by corrosion of external parts by the atmosphere or of internal parts by the gas.
(2) Be designed and installed so they can be operated to determine whether the valve is free. The devices shall also be designed and installed so they can be tested to determine the pressure at which they operate and be examined for leakage when in the closed position. [NFPA 54:5.8.4]
1308.9.3 External Control Piping. External control piping shall be designed and installed so that damage to the control piping of one device does not render both the regulator and the overpressure protective device inoperative. [NFPA 54:5.8.5]
1308.9.4 Setting. Each pressure limiting or pressure relieving device shall be set so that the gas pressure supplied to the connected appliance(s) does not exceed the limits specified in Section 1308.8 and Section 1308.8.1.
[NFPA 54:5.8.6]
1308.9.5 Unauthorized Operation. Where unauthorized operation of any shutoff valve could render a pres
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2025 CALIFORNIA MECHANICAL CODE 281
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FUEL GAS PIPING
TABLE 1308.12
MANUAL GAS VALVE STANDARDS
[NFPA 54: TABLE 5.11]
CMC § 1004.2 Medium relevance — show source text
1004.2 Open-Type Expansion Tanks. Open type expansion tanks shall be located not less than 3 feet (914 mm) above the highest point of the system. Such tanks shall be sized based on the capacity of the system. An overflow with a diameter of not less than one-half the size of the supply or not less than 1 inch (25 mm) in diameter shall be installed at the top of the tank. The overflow shall discharge through an air gap into the drainage system.
1004.3 Closed-Type Systems. Closed-type systems shall have an airtight tank or other approved air cushion that will be consistent with the volume and capacity of the system, and shall be designed for a hydrostatic test pressure of two and one-half times the allowable working pressure of the system. Expansion tanks for systems designed to operate at more than 30 pounds-force per square inch (psi) (207 kPa) shall comply with ASME BPVC Section VIII.1. Provisions shall be made
for draining the tank without emptying the system.
1004.4 Minimum Capacity of Closed-Type Tank. The minimum capacity for a gravity-type hot water system expansion tank shall be in accordance with Table 1004.4(1). The minimum capacity for a forced-type hot water system expansion tank shall be in accordance with Table 1004.4(2) or Equation 1004.4(1). The minimum capacity for a diaphragmtype hot water system expansion tank shall be in accordance with Table 1004.4(2) or Equation 1004.4(2).
[Equation 1004.4(1)]
Vt (forced-type) = [(0.00041] [t] [ - 0.0466) ] [V][s]
(P P a a
Pf Po )
[Equation 1004.4(2)]
Vt (diaphragm-type) = [(0.00041] [t] [ - 0.0466) ] [V][s]
– [P][f]
[1]
( Po )
Where:
Vt = Minimum volume of expansion tank, gallons. Vs = Volume of system, not including expansion tank, gallons.
t = Average operating temperature, °F.
Pa = Atmospheric pressure, pounds per square inch. Pf = Fill pressure, pounds per square inch. Po = Maximum operating pressure, pounds per square inch.
For SI units: 1 gallon = 3.785 L
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BOILERS AND PRESSURE VESSELS
TABLE 1004.4(1) EXPANSION TANK CAPACITIES FOR GRAVITY HOT WATER SYSTEMS [1]
CMC § 1305.2.3.3 Medium relevance — show source text
2, 1305.2.3.3, 1305.2.4.1, 1305.2.5, 1305.2.5.1, 1305.2.6, 1305.2.7.1, 1305.2.8, 1305.2.9, 1305.2.9.1, 1305.2.10, 1305.2.10.1, 1305.2.11, 1305.2.11.1, 1305.2.12.1, 1305.2.13, Table 1305.2.15, 1305.2.15.1, 1305.2.16.1, 1305.2.17, 1305.2.17.1, 1305.2.18, 1305.2.18.1, 1305.2.19, Table 1305.2.19, 1305.2.20, 1305.2.20.1, 1307.1.1, 1401.2, 1402.1, 1402.2, 1402.2.1, 1402.3, 1402.4, 1402.5, 1402.6, 1501.5, 1504.1.1, 1504.1.4.1, 1504.1.7, 1509.1, 1509.3, 1510.1
CEC — 25 : California Energy Code
302.2, 702.7, 708.1, 809.1, 907.1, 1104.1
CFC—25: California Fire Code
101.2.2, 101.4.2, 301.3.1, 302.2, 307.1, 308.1, 802.2.1, 802.2.3, 803.2.3, 803.4.1.1, 803.4.1.2, 803.4.1.3, 803.4.1.4, 803.4.1.5, 803.4.1.6, Table 804.5.1.1(1), 904.1.5, 1011.6.1.1, 1303.1.2, 1305.2.8.1, 1305.2.14, 1305.2.14.1, 1401.2, 1501.1, 1501.5, 1502.1, 1502.1.1, 1502.2, 1502.3, 1504.1, 1507.1, 1507.2
CMC—25: California Mechanical Code
302.2, 702.7, 807.1, 902.1.1, 1008.1, 1305.2.7.1, 1305.2.8, 1305.2.8.1
CPC—25: California Plumbing Code
302.2, 408.1, 702.7, 1009.1, 1009.2, 1009.3, 1009.5, 1302.1.6, 1503.1
California Mechanical Code Medium relevance — show source text
|100 psf|1 hr
23 min|||7|1, 2|11/3| |F/C-4-RC-9|4″|4″ deep (4370 psi);1/4″ reinforcement bars
at 6″ pitch with3/4″ cover;1/4″ main rein-
forcement bars at 4″ pitch perpendicular
with1/2″ cover; 13′1″ span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-10|4″|4″ thick (5140 psi) deck;1/4″ reinforce-
ment bars at 71/2″ pitch with7/8″ cover;3/8″
main reinforcement bars at 33/4″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|140 psf|1 hr
16 min|||7|1, 5|11/4| |F/C-4-RC-11|4″|4″ thick (4000 psi) concrete deck;
3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.; flush
with top surface; 4″ × 6″ x 13 SWG mesh
reinforcement 1″ from bottom of slab; 6′6″
span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-12|4″|4″ deep (2380 psi) concrete deck;
3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.; flush
with top surface; 4″ × 6″ x 13 SWG mesh
reinforcement 1″ from bottom surface;
6′6″ span restrained.|150 psf|1 hr
3 min|||7|1, 2|1| |F/C-4-RC-13|41/2″|41/2″ thick (5200 psi) deck;1/4″ reinforce-
ment bars at 71/4″ pitch with7/8″ cover;3/8″
main reinforcement bars at 33/4″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|140 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-14|41/2″|41/2″ deep (2525 psi) concrete deck;1/4″
reinforcement bars at 71/2″ pitch with7/8″
cover;3/8″ main reinforcement bars at
33/8″ pitch perpendicular with1/2″ cover;
13′1″ span restrained.|150 psf|42 min|||7|1, 5|2/3| |F/C-4-RC-15|41/2″|41/2″ deep (4830 psi) concrete deck;
11/2″ × No.CMC § 9.9 Medium relevance — show source text
Exception: Pressure limiting devices are not required for listed factory-sealed systems containing less than 22 pounds (9.9 kg) of Group A1 refrigerant. [ASHRAE 15:9.9.1] 1111.2 Setting. Pressure limiting devices shall be set in accordance with one the following:
(1) For positive displacement compressors:
(a) When systems are protected by a highside pressure relief device, the compressor’s pressure limiting device shall be set not more than 90 percent of the operating pressure for the highside pressure relief device.
(b) When systems are not protected by a highside pressure relief device, the compressor’s pressure limiting device shall be set not more than the system’s highside design pressure.
(2) For nonpositive displacement compressors:
(a) When systems are protected by a highside pressure relief device, the compressor’s pressure limiting device shall be set not more than 90 percent of the operating pressure for the highside pressure relief device.
(b) When systems are protected by a lowside pressure relief device that is only subject to lowside pressure, and is provided with a permanent relief path between the systems’ highside and lowside, without intervening valves, the compressor’s pressure limiting device shall be set not more than the systems’ highside design pressure. [ASHRAE 15:9.9.2]
1111.3 Location. Stop valves shall not be installed between the pressure imposing element and pressure limiting devices serving compressors. [ASHRAE 15:9.9.3] 1111.4 Emergency Stop. Activation of a pressure-limiting device shall stop the action of the pressure-imposing element.
[ASHRAE 15:9.9.4]
240 2025 CALIFORNIA MECHANICAL CODE
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REFRIGERATION
1112.0 Pressure-Relief Devices.
1112.1 General. Refrigeration systems shall be protected by a pressure-relief device or other approved means to safely relieve pressure due to fire or abnormal conditions. [ASHRAE 15:9.4.1] 1112.2 Positive Displacement Compressor. A positive displacement compressor with a stop valve in the discharge connection shall be equipped with a pressure-relief device that is sized, and with a pressure setting, in accordance with the compressor manufacturer to prevent rupture of the compressor or to prevent the pressure from increasing to more than 10 percent above the maximum allowable working pressure of any other component located in the discharge line between the compressor and the stop valve or in accordance with Section 1113.5, whichever is larger. The pressure-relief device shall discharge into the low-pressure side of the system or in accordance with Section 1112.11.
Exception: Hermetic refrigerant motor-compressors that are listed and have a displacement not more than 50 cubic feet per minute (1.42 m [3] /min).
The relief device(s) shall be sized based on compressor flow at the following conditions:
(1) For compressors in single-stage systems and high-stage compressors of other systems, the flow shall be calculated based on 50°F (10°C) saturated suction temperature at the compressor suction.
CMC § 1.11.0. Medium relevance — show source text
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 273
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274 2025 CALIFORNIA MECHANICAL CODE
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CHAPTER 13
FUEL GAS PIPING
1301.0 Scope of Gas Piping.
1301.1 Applicability. The regulations of this chapter shall govern the installation of fuel gas piping in or in connection with a building, structure or within the property lines of premises up to 5 pounds-force per square inch (psi) (34 kPa) for natural gas and 10 psi (69 kPa) for undiluted propane, other than service pipe.
1302.0 Coverage of Piping System.
1302.1 General. Coverage of piping systems shall extend from the point of delivery to the appliance connections. For other than undiluted liquefied petroleum gas (LP-Gas) systems, the point of delivery shall be the outlet of the service meter assembly or the outlet of the service regulator or service shutoff valve where no meter is provided. For undiluted LP-Gas systems, the point of delivery shall be considered to be the outlet of the final pressure regulator, exclusive of line gas regulators where no meter is installed. Where a meter is installed, the point of delivery shall be the outlet of the meter.
[NFPA 54:1.1.1.1(A)]
1302.2 Piping System Requirements. Requirements for piping systems shall include design, materials, components, fabrication, assembly, installation, testing, inspection, operation, and maintenance. [NFPA 54:1.1.1.1(E)]
1302.3 Applications. This chapter shall not apply to the following items:
(1) Portable LP-Gas appliances and equipment of all types that are not connected to a fixed fuel piping system.
(2) Installation of appliances such as brooders, dehydrators, dryers, and irrigation equipment used for agricultural
purposes.
(3) Raw material (feedstock) applications except for piping to special atmosphere generators.
(4) Oxygen-fuel gas cutting and welding systems.
(5) Industrial gas applications using such gases as acetylene and acetylenic compounds, hydrogen, ammonia, carbon monoxide, oxygen, and nitrogen.
(6) Petroleum refineries, pipeline compressor or pumping stations, loading terminals, compounding plants, refinery tank farms, and natural gas processing plants.
(7) Large integrated chemical plants or portions of such plants where flammable or combustible liquids or gases are produced by chemical reactions or used in chemical reactions.
(8) LP-Gas installations at utility gas plants.
(9) Liquefied natural gas (LNG) installations.
(10)Fuel gas piping in electric utility power plants.
(11)Proprietary items of equipment, apparatus, or instruments such as gas-generating sets, compressors, and calorime ters.
(12)LP-Gas equipment for vaporization, gas mixing, and gas manufacturing.
Frequently asked questions
Can a gas piping system inside a dwelling be run at 10 psi if it uses welded joints?
Yes — if the piping joints are welded or brazed, the code permits operating pressures above 5 psi; you must still comply with all other applicable installation, testing, and overpressure protection provisions. § 1310.6(1).
If I use listed ANSI/CSA LC‑4 fittings, do I still need welded joints?
No — listed fittings installed per the manufacturer are an alternate exception that allows higher pressures without welded joints. Document the fittings and follow the manufacturer’s installation instructions. § 1310.6(2).
Does the ventilated chase option require specific ventilation sizing?
Yes — the code references ventilated chase ventilation requirements (chase venting and regulator venting are covered elsewhere); if you rely on the ventilated‑chase exception you must meet the chase ventilation provisions. § 1310.6(4) and related chase ventilation language.
Are LP‑Gas systems treated differently?
Yes — LP‑Gas piping operating above 20 psi (138 kPa) must comply with NFPA 58; there is also a special note for LP‑Gas intended to operate below ‑5°F (‑21°C). § 1310.6(8) and § 1310.6.1.
What if an appliance requires a very low inlet pressure?
Appliances that are designed for low inlet pressures are protected by appliance‑overpressure rules — the code limits piping pressures for such appliances (see § 1310.7 for the 2 psig appliance limit unless protected by an overpressure device).
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