CMC · California Mechanical Code

What gauges, welding standards, and welder qualifications apply to boilers and pressure vessels?

Q: What gauges must a steam boiler have?

A steam boiler must have a pressure gauge and a water level glass , per § 1003.3 .

Q: Are damper blades allowed inside a gas‑fired boiler stack?

No. Operative dampers shall not be placed within a stack, flue, or vent of a gas‑fired boiler , unless the automatic‑boiler exception (prepurge, automatic draft control, interlock) applies. § 1003.4 .

Q: Which welding standard do I use for a pressure vessel?

The CMC requires welding by certified welders to nationally recognized standards ( § 1003.5 ) and requires pressure vessels to be constructed per ASME BPVC Section VIII.1 ( § 1002.1 ). Consult the ASME BPVC (and typically ASME Section IX for welder qualification) and the AHJ for the specific procedure/test requirements. § 1003.5 , § 1002.1 .

Q: Does § 1003.5 itself require ASME Section IX certification?

No — § 1003.5 requires certified welders and nationally recognized standards but does not explicitly name ASME Section IX; the specific qualification standard is found in the referenced construction code that applies to the vessel (see § 1002.1 ).

For homeowners: California’s mechanical code says steam boilers need a pressure gauge and water‑level glass, water boilers need a pressure and temperature gauge, automatic boilers need extra fuel/stack/windbox gauges as applicable, stack dampers on oil/solid‑fuel boilers may not close more than 80% of the stack area, and all welding on pressure vessels must be done by certified welders to nationally recognized standards; the CMC points you to ASME/NFPA construction codes for the detailed welding qualifications (check the AHJ and the ASME code referenced in § 1002.1).

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Mechanical Code requires specific gauges on boilers (different minimum instruments for steam boilers, water boilers, and automatic boilers) and limits how stack dampers may close on oil/solid‑fuel boilers — see § 1003.3 and § 1003.4. The CMC requires that welding on pressure vessels be performed by certified welders and follow nationally recognized standards — see § 1003.5. The CMC does not fully spell out which national welding standard (for example, ASME Section IX) must be used in § 1003.5, but Chapter 10 references ASME/NFPA construction standards that govern boilers and pressure vessels (see § 1002.1) and those referenced standards contain the detailed welding and welder‑qualification rules.

The essential rule: Provide the required pressure/level/temperature instruments for the boiler type, do not close a stack damper more than 80% on oil/solid‑fuel boilers, and use certified welders working to nationally recognized standards for pressure‑vessel welding. § 1003.3, § 1003.4, § 1003.5.

Requirements in detail

Gauges — what each boiler needs (CMC § 1003.3)

Steam boilers must have a pressure gauge and a water level glass. § 1003.3.
Water boilers must have a pressure gauge and a temperature gauge. § 1003.3.
Automatic boilers must be equipped, as applicable, with gauges for: oil temperature, oil suction pressure, high and low gas pressure, stack temperature, and windbox pressure. § 1003.3.

Decision‑relevant dimensions/values (quick reference)

Item	Required instrument(s)	When required / note	Code Reference
Steam boiler	Pressure gauge; water level glass	All steam boilers	§ 1003.3
Water boiler	Pressure gauge; temperature gauge	All water boilers	§ 1003.3
Automatic boilers	Oil temperature; oil suction pressure; high & low gas pressure; stack temperature; windbox pressure	As applicable to the automatic boiler controls/fuel type	§ 1003.3

Notes:

The CMC states the minimum gauges; manufacturers’ listings, the boiler’s listing/label, or the Authority Having Jurisdiction (AHJ) may require additional or more specific instrumentation (see § 1003.1 and related installation rules).

Stack dampers (CMC § 1003.4)

Stack dampers on oil‑ or solid‑fuel boilers shall not close off more than 80 percent of the stack area (i.e., at least 20% open area must remain when “closed” to prevent unsafe restriction). § 1003.4.
Operative dampers are prohibited inside stacks, flues, or vents of gas‑fired boilers. § 1003.4.
Exception: automatic boilers with prepurge, automatic draft control, and interlock are exempted from the operative‑damper prohibition. § 1003.4 (Exception).

Decision point example (stack damper math):

If stack internal area = 100 in², the damper may not close to less than 20 in² open (100 in² × 20% = 20 in²). § 1003.4.

Welding and welder qualifications (CMC § 1003.5 and related)

The CMC requires that welding on pressure vessels be performed by certified welders and in accordance with nationally recognized standards. § 1003.5.
The CMC’s Chapter 10 also establishes which construction standards apply to pressure vessels and boilers: pressure vessels — ASME BPVC Section VIII.1; boilers — ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85. Those referenced standards contain the detailed welding procedure, welder qualification, test methods, and acceptance criteria. § 1002.1.

Important limitation from the text:

§ 1003.5 itself does not name the specific national standard (for example, ASME BPVC Section IX) for welder qualification; it defers to “nationally recognized standards.” To determine the precise qualification tests (bend, tensile, radiography, procedure specifications), consult the construction standard that governs the specific vessel (e.g., the ASME BPVC section referenced in § 1002.1) and the AHJ. § 1003.5, § 1002.1.

Quick guidance (how these interact in practice)

If a pressure vessel is required by § 1002.1 to be built to ASME BPVC Section VIII.1, then the vessel fabricator and welders must follow the welding procedures and welder qualifications that Section VIII (and its referenced Section IX) requires. While § 1003.5 in the CMC imposes the general requirement, the specific welding rules are found in the ASME code that the vessel must comply with.

Exceptions & special cases

Operative dampers are expressly not allowed in gas‑fired boiler stacks, except for automatic boilers that have prepurge, automatic draft control, and interlock — see the exception in § 1003.4.
The CMC lists many boiler and pressure‑vessel exceptions to Chapter 10 applicability (pools, certain small volumes, federally inspected vessels, listed potable water heaters, etc.) in § 1001.1 — if the vessel is excepted there, Chapter 10 gauge/welding rules may not apply. § 1001.1.
The CMC requires boilers/pressure vessels be constructed to referenced national standards (see § 1002.1); where the national standard has additional or different welding/gauge rules, those apply as the construction standard. § 1002.1.

Common mistakes

Assuming § 1003.5 names the specific welder‑qualification standard. It does not — it requires certified welders and nationally recognized standards, and the specific standard is usually the ASME code referenced in § 1002.1. Cite the ASME/NFPA standard that applies to the particular boiler/vessel. § 1003.5, § 1002.1.
Installing operative dampers in gas boiler stacks without verifying the automatic boiler exception — the rule prohibits dampers for gas‑fired boilers unless the exception conditions are met. § 1003.4.
Omitting required gauges on site because the installer relied only on manufacturer recommendations. The CMC establishes minimum gauge requirements that must be present; manufacturer/AHJ may require more. § 1003.3.
Assuming small or low‑pressure vessels are exempt — check § 1001.1 exceptions (volume and pressure limits) before deciding the CMC welding/gauge requirements don’t apply. § 1001.1.

Worked example — concrete scenario

Scenario: You are installing an oil‑fired automatic steam boiler with a stack whose internal area is 1,200 in².

Gauges — per § 1003.3:
- Because it is a steam boiler, install a pressure gauge and a water level glass. § 1003.3.
- Because it is an automatic boiler and oil‑fired, also provide oil temperature and oil suction pressure gauges, plus stack temperature and any other applicable automatic‑boiler gauges listed in § 1003.3. § 1003.3.
Stack damper — per § 1003.4:
- The damper may not close off more than 80% of the stack area. For 1,200 in² stack area, the minimum remaining open area when “closed” is 20% × 1,200 = 240 in². Do not design a damper that leaves less than 240 in². § 1003.4.
Welding — per § 1003.5 and scope § 1002.1:
- If the boiler/pressure components fall under ASME construction requirements in § 1002.1, require welding to the applicable ASME BPVC rules and have welders certified to the qualification scheme called for by that code. § 1003.5, § 1002.1.

Related provisions

§ 1002.1 — Construction standards required (ASME BPVC Section VIII.1 for pressure vessels; ASME BPVC Section I or IV or NFPA 85 for boilers).
§ 1001.1 — Exceptions to Chapter 10 applicability (small/unfired vessels, listed water heaters, etc.).
§ 1003.1 — General safety requirements and AHJ authority to require nationally recognized standards.
§ 1003.2 — Controls requirements for automatic boilers (ASME CSD‑1 or Table 1003.2.1 referenced).
§ 1004.3 — Expansion tank design that references ASME BPVC Section VIII.1 for tanks serving systems over 30 psi (shows where ASME BPVC appears elsewhere in Chapter 10).
§ 1013.1 – § 1013.7 — Inspection and test requirements for boilers and pressure vessels (operation permits and inspection frequency).

If you need: I can pull the exact CMC text blocks for any of these sections or show how the ASME BPVC/ASME IX wording typically maps to the CMC requirement — but note: § 1003.5 itself defers to nationally recognized standards and does not list the ASME IX language directly.

Code references

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

CMC § 1002.2.2 High relevance — show source text
1002.2.2 Installation. Tanks, piping, and valves for oil-burning boilers shall be installed in accordance with NFPA 31.

1002.3 Electric Boilers. Electric boilers shall be listed and

labeled in accordance with UL 834.

1002.4 Solid-Fuel-Fired Boilers. Solid-fuel-fired boilers shall comply with UL 2523 and shall be installed in accordance with the manufacturer’s installation instruc tions.

1002.5 Dual Purpose Water Heaters. Water heaters utilized for combined space- and water-heating applications shall comply with the standards referenced in Table 1203.2, and shall be installed in accordance with the manufacturer’s

installation instructions.

2025 CALIFORNIA MECHANICAL CODE 217

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

BOILERS AND PRESSURE VESSELS

1003.0 Detailed Requirements.

1003.1 Safety Requirements. The construction of boilers and pressure vessels and the installation thereof shall be in accordance with minimum requirements for safety from structural and mechanical failure and excessive pressures as established by the Authority Having Jurisdiction in accordance with nationally recognized standards.

1003.2 Controls. Required electrical, mechanical, safety, and operating controls shall carry the approval of an approved testing agency or be accepted by the Authority Having Jurisdiction. Electrical controls shall be of such design and construction as to be suitable for installation in the environment

in which they are located.

1003.2.1 Automatic Boilers. Automatic boilers shall

be equipped with controls and limit devices in accordance with ASME CSD-1 or Table 1003.2.1.

The Authority Having Jurisdiction shall have the authority to approve solid-fuel-fired boilers that comply with the safety requirements for automatic gas fired boilers or oil fired boilers.

1003.3 Gauges. Steam boilers shall be provided with a pressure gauge and a water level glass. Water boilers shall be provided with a pressure gauge and a temperature gauge. Automatic boilers shall be equipped with the following gauges, as applicable :

(1) Oil temperature

(2) Oil suction pressure

(3) High and low gas pressure

(4) Stack temperature

(5) Windbox pressure

1003.4 Stack Dampers. Stack dampers on boilers fired with oil or solid fuel shall not close off more than 80 percent of the stack area. Operative dampers shall not be placed within a stack, flue, or vent of a gas-fired boiler.

Exception: Automatic boilers with prepurge, automatic draft control, and interlock.

1003.5 Welding. Welding on pressure vessels shall be done by certified welders in accordance with nationally recognized standards.

1004.0 Expansion Tanks.

1004.1 General. An expansion tank shall be installed in a hot-water-heating system as a means for controlling increased pressure caused by thermal expansion. Expansion tanks shall be of the closed or open type and securely fastened to or supported by the structure. Tanks shall be rated for the pressure of the system. Supports shall be capable of carrying twice the weight of the tank filled with water without placing a strain on connecting piping.

Hot-water-heating systems incorporating hot water tanks or fluid relief columns shall be installed to prevent freezing under normal operating conditions.
CMC § 1003.2.1. High relevance — show source text
be equipped with controls and limit devices in accordance with ASME CSD-1 or Table 1003.2.1.

The Authority Having Jurisdiction shall have the authority to approve solid-fuel-fired boilers that comply with the safety requirements for automatic gas fired boilers or oil fired boilers.

1003.3 Gauges. Steam boilers shall be provided with a pressure gauge and a water level glass. Water boilers shall be provided with a pressure gauge and a temperature gauge. Automatic boilers shall be equipped with the following gauges, as applicable :

(1) Oil temperature

(2) Oil suction pressure

(3) High and low gas pressure

(4) Stack temperature

(5) Windbox pressure

1003.4 Stack Dampers. Stack dampers on boilers fired with oil or solid fuel shall not close off more than 80 percent of the stack area. Operative dampers shall not be placed within a stack, flue, or vent of a gas-fired boiler.

Exception: Automatic boilers with prepurge, automatic draft control, and interlock.

1003.5 Welding. Welding on pressure vessels shall be done by certified welders in accordance with nationally recognized standards.

1004.0 Expansion Tanks.

1004.1 General. An expansion tank shall be installed in a hot-water-heating system as a means for controlling increased pressure caused by thermal expansion. Expansion tanks shall be of the closed or open type and securely fastened to or supported by the structure. Tanks shall be rated for the pressure of the system. Supports shall be capable of carrying twice the weight of the tank filled with water without placing a strain on connecting piping.

Hot-water-heating systems incorporating hot water tanks or fluid relief columns shall be installed to prevent freezing under normal operating conditions.

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]

(
CMC § 1002.3 High relevance — show source text
1002.3 Electric Boilers . . . . . . . . . . . . . . . 217

1002.4 Solid-Fuel-Fired Boilers . . . . . . . . 217

1002.5 Dual Purpose Water Heaters . . . . 217

1003.0 Detailed Requirements . . . . . . . . . 218

1003.1 Safety Requirements . . . . . . . . . . 218

1003.2 Controls . . . . . . . . . . . . . . . . . . . . 218

1003.3 Gauges . . . . . . . . . . . . . . . . . . . . . 218

1003.4 Stack Dampers . . . . . . . . . . . . . . . 218

1003.5 Welding. . . . . . . . . . . . . . . . . . . . . 218

1004.0 Expansion Tanks . . . . . . . . . . . . . 218

1004.1 General. . . . . . . . . . . . . . . . . . . . . 218

1004.2 Open-Type Expansion Tanks . . . . 218

1004.3 Closed-Type Systems . . . . . . . . . 218

1004.4 Minimum Capacity of ClosedType Tank. . . . . . . . . . . . . . . . . . . 218

Table 1004.4(1) Expansion Tank Capacities for Gravity Hot Water Systems . . . . . 219

Table 1004.4(2) Expansion Tank Capacities for Forced Hot Water Systems . . . . . 219

1005.0 Safety or Relief Valve Discharge . . 219

1005.1 General. . . . . . . . . . . . . . . . . . . . . 219

1005.2 Discharge Piping . . . . . . . . . . . . . 219

1005.3 Splash Shield . . . . . . . . . . . . . . . . 219

1005.4 Hazardous Discharge . . . . . . . . . . 219

1005.5 Vacuum Relief Valve . . . . . . . . . . 219

1006.0 Shutoff Valves . . . . . . . . . . . . . . . 219

1006.1 General. . . . . . . . . . . . . . . . . . . . . 219

1007.0 Gas-Pressure Regulators . . . . . . . 219

1007.1 General. . . . . . . . . . . . . . . . . . . . . 219

1008.0 Low-Water Cutoff . . . . . . . . . . . . . 220

1008.1 General. . . . . . . . . . . . . . . . . . . . . 220

1009.0 Combustion Regulators Safety Valves . . . . . . . . . . . . . . . . 220

1009.1 General. . . . . . . . . . . . . . . . . . . . . 220

1010.0 Clearance for Access . . . . . . . . . . 220

1010.1 General. . . . . . . . . . . . . . . . . . . . . 220
CMC § 5.1.10.5.1.2 High relevance — show source text
ASME Boiler and Pressure Vessel Code on each tube size diameter. [NFPA 99:5.1.10.5.1.2, 5.1.10.5.1.3] 1322.1.2 Welding Procedure Specification. Each welder shall qualify to a welding procedure specification (WPS) for each tube diameter. [NFPA 99:5.1.10.5.1.4] 1322.1.3 Purging of Joints. GTAW autogenous orbital welded joints shall be purged during welding with a commercially available mixture of 75 percent helium (+/- 5 percent) and 25 percent argon (+/- 5 percent).

[NFPA 99:5.1.10.5.1.5] 1322.1.4 Shield Gas. The shield gas shall be as required in Section 1322.1.3. [NFPA 99:5.1.10.5.1.6] 1322.1.5 Test Coupons. Test coupons shall be welded and inspected, as a minimum, at the start of work and every 4 hours thereafter, or when the machine is idle for more than 30 minutes, and at the end of the work period. Test coupons shall be inspected on the I.D. and O.D. by a qualified quality control inspector. Test coupons shall also be welded at change of operator, weld head, welding power supply, or gas source. [NFPA 99:5.1.10.5.1.7 – 5.1.10.5.1.9] 1322.2 Welding for Stainless Tube. Stainless tube shall be welded using metal inert gas (MIG) welding, tungsten inert gas (TIG) welding, or other welding techniques suited to joining stainless tube. [NFPA 99:5.1.10.5.2.1]

1322.2.1 Qualifications. Welders shall be qualified to Section IX of the ASME Boiler and Pressure Vessel Code. [NFPA 99:5.1.10.5.2.2]

1322.3 Memory Metal Fittings. Memory metal fittings having a temperature rating not less than 1000°F (538°C) and a pressure rating not less than 300 psi (2068 kPa) shall be permitted to be used to join copper or stainless steel tube. Memory metal fittings shall be installed by qualified technicians in accordance with the manufacturer’s instructions. [NFPA 99:5.1.10.6.1, 5.1.10.6.2]

1322.4 Axially Swaged Fittings. Axially swaged fittings providing metal-to-metal seals, suitable for service at 300 psig (2070 kPa) and able to withstand a temperature of 1000°F (538°C) and that, when complete, are permanent and nonseparable shall be permitted to be used to join copper or stainless steel tube. Axially swaged fittings shall be installed by qualified technicians in accordance with the manufacturer’s instructions. [NFPA 99:5.1.10.7.1, 5.1.10.7.2]

1322.5 Threaded Fittings. Threaded fittings shall meet the following criteria:

(1) They shall be limited to connections for pressure and vacuum indicators, alarm devices, gas-specific demand check fittings, and source equipment on the source side of the source valve.
CMC § 1324.5 High relevance — show source text
(5) Cracks in the tube or component.

(6) Cracks in the braze filler metal.

(7) Failure of the joint to hold the test pressure under the installer-performed initial pressure test (see Section 1324.5 through Section 1324.5.1.2) and standing pressure test (see Section 1324.5.4 or Section 1324.5.5).

[NFPA 99:5.1.10.4.7.4] 1321.12.4 Defective Brazed Joints. Brazed joints that are identified as defective under the conditions of Section 1321.12.3(2) or Section 1321.12.3(5) shall be replaced. [NFPA 99:5.1.10.4.7.5]

Brazed joints that are identified as defective under the conditions of Section 1321.12.3(1), Section 1321.12.3(3), Section 1321.12.3(4), Section 1321.12.3(6) or Section 1321.12.3(7) shall be permitted to be repaired, except that no joint shall be reheated more than once before being replaced. [NFPA 99:5.1.10.4.7.6]

1322.0 Welded Joints.

1322.1 Welded Joints Procedure. Welded joints for medical gas and medical-surgical vacuum systems shall be permitted to be made using a gas tungsten arc welding (GTAW) autogenous orbital procedure. [NFPA 99:5.1.10.5.1.1]

1322.1.1 Welder Qualification Procedure. The GTAW autogenous orbital procedure and the welder qualification procedure shall be qualified in accordance with Section IX of the ASME Boiler and Pressure Vessel Code. Welder qualification procedures shall include a bend test and a tensile test in accordance with Section IX of the

ASME Boiler and Pressure Vessel Code on each tube size diameter. [NFPA 99:5.1.10.5.1.2, 5.1.10.5.1.3] 1322.1.2 Welding Procedure Specification. Each welder shall qualify to a welding procedure specification (WPS) for each tube diameter. [NFPA 99:5.1.10.5.1.4] 1322.1.3 Purging of Joints. GTAW autogenous orbital welded joints shall be purged during welding with a commercially available mixture of 75 percent helium (+/- 5 percent) and 25 percent argon (+/- 5 percent).

[NFPA 99:5.1.10.5.1.5] 1322.1.4 Shield Gas. The shield gas shall be as required in Section 1322.1.3. [NFPA 99:5.1.10.5.1.6] 1322.1.5 Test Coupons. Test coupons shall be welded and inspected, as a minimum, at the start of work and every 4 hours thereafter, or when the machine is idle for more than 30 minutes, and at the end of the work period. Test coupons shall be inspected on the I.D. and O.D. by a qualified quality control inspector. Test coupons shall also be welded at change of operator, weld head, welding power supply, or gas source.
CMC § 938.1 High relevance — show source text
938.1 General. . . . . . . . . . . . . . . . . . . . . 214

939.0 Sauna Heaters . . . . . . . . . . . . . . . 214

939.1 Electric Sauna Heaters. . . . . . . . . 214

CHAPTER 10 BOILERS AND

PRESSURE VESSELS . . . . . . . . 215

1001.0 General. . . . . . . . . . . . . . . . . . . . . 217

1001.1 Applicability. . . . . . . . . . . . . . . . . . 217

1001.2 Boiler Rooms and Enclosures . . . 217

1001.3 Air for Combustion

and Ventilation . . . . . . . . . . . . . . . 217

1001.4 Drainage . . . . . . . . . . . . . . . . . . . . 217

1001.5 Mounting. . . . . . . . . . . . . . . . . . . . 217

xxxvii

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TABLE OF CONTENTS

1001.6 Chimneys or Vents . . . . . . . . . . . . 217

1002.0 Standards . . . . . . . . . . . . . . . . . . . 217

1002.1 General. . . . . . . . . . . . . . . . . . . . . 217

1002.2 Oil-Burning Boilers . . . . . . . . . . . . 217

1002.3 Electric Boilers . . . . . . . . . . . . . . . 217

1002.4 Solid-Fuel-Fired Boilers . . . . . . . . 217

1002.5 Dual Purpose Water Heaters . . . . 217

1003.0 Detailed Requirements . . . . . . . . . 218

1003.1 Safety Requirements . . . . . . . . . . 218

1003.2 Controls . . . . . . . . . . . . . . . . . . . . 218

1003.3 Gauges . . . . . . . . . . . . . . . . . . . . . 218

1003.4 Stack Dampers . . . . . . . . . . . . . . . 218

1003.5 Welding. . . . . . . . . . . . . . . . . . . . . 218

1004.0 Expansion Tanks . . . . . . . . . . . . . 218

1004.1 General. . . . . . . . . . . . . . . . . . . . . 218

1004.2 Open-Type Expansion Tanks . . . . 218

1004.3 Closed-Type Systems . . . . . . . . . 218

1004.4 Minimum Capacity of ClosedType Tank. . . . . . . . . . . . . . . . . . . 218

Table 1004.4(1) Expansion Tank Capacities for Gravity Hot Water Systems . . . . . 219

Table 1004.4(2) Expansion Tank Capacities for Forced Hot Water Systems . . . . . 219
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 § 1102.3 Medium relevance — show source text
Chapter 10 Boilers and Pressure Vessels. Chapter 10 regulates the construction, installation, operation, repair, and alteration of boilers and pressure vessels. The safety provisions within this chapter address controls and limit devices for automatic boilers, methods of determining expansion tank capacities, discharge piping, relief valves, shutoff valves, gas-pressure and combustion regulators, and inspections and tests. Potable water heaters are free from the requirements of Chapter 10 as they are within the scope of the Uniform Plumbing Code (UPC).

Pressure vessels store large amounts of energy and must comply with ASME Boiler and Pressure Vessel Code (BPVC) Section VIII.1. The stored energy must be contained to prevent disastrous failures. Boilers must comply with ASME BPVC Section I, ASME BPVC Section IV, or NFPA 85. Installing a safety relief valve and expansion tank prevents pressures in the tank from exceeding the design threshold.

Chapter 11 Refrigeration. Chapter 11 regulates the design, installation, and construction requirements of refrigeration systems and the installation and construction of cooling towers. Refrigeration is a method used for achieving heat transfer to cool spaces. Refrigerants are the most common medium used to transfer the heat energy from the low-temperature level to the high-temperature level. Table

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1102.3 lists the most commonly used refrigerants and is labeled by a number. The concentration limits provided in Table 1102.3 are useful for the quantity of refrigerant required to cool a volume of space safely.

A major milestone reached in the industry was the introduction of lower flammability refrigerants such as A2L and B2L. The industry’s concerns to address lower Global Warming Potential (GWP) refrigerants led to the development of these lower flammability refrigerants. Chapter 11 does not only include these lower flammability refrigerants in Table 1102.3, but it also contains specific A2L and B2L provisions to address the precautions necessary for the proper use of these products. In particular, high-probability systems using A2L refrigerants for human comfort applications are covered by provisions which include refrigerant concentration limits, mechanical ventilation, ignition sources, compressors and pressure vessels, and refrigerant sensors.

In addition, Chapter 11 addresses other minimum requirements for refrigeration systems such as refrigeration machinery rooms (including ventilation), relief valves, and pressure vessels. Apart from refrigerants, the chapter also addresses minimum requirements for systems that use other mediums such as ammonia and brine systems. For ammonia systems, such systems are required to comply with IIAR 2, IIAR 3, IIAR/ANSI 4, IIAR 5, and IIAR 6.

Chapter 12 Hydronics. Chapter 12 regulates hydronic systems that are part of heating, cooling, ventilation, and conditioning systems. Such piping systems include steam, hot water, radiant heating and cooling, chilled water, steam condensate, condenser water, ground source heat pump systems, snow and ice melt systems, ambient temperature loops, and district ambient temperature loops. Provisions within this chapter addressing ground source heat pumps and ambient temperature loops apply to the hydronic portions of the system. Geothermal energy systems, including ground source heat pumps and ambient temperature loops, are regulated by Chapter 17.
CMC § 1001.3 Medium relevance — show source text
1001.3 Air for Combustion and Ventilation. Air for combustion and ventilation shall be provided in accordance with Chapter 7.

1001.4 Drainage. For heating or hot-water-supply boiler applications, the boiler room shall be equipped with a floor drain or other approved means for disposing of the accumulation of liquid wastes incident to cleaning, recharging, and routine maintenance. No steam pipe shall be directly connected to a part of a plumbing or drainage system, nor shall a water having a temperature above 140°F (60°C) be discharged under pressure directly into a part of a drainage system. Pipes from boilers shall discharge by means of indirect waste piping as determined by the Authority Having Jurisdiction or the boiler manufacturer’s instructions.

1001.5 Mounting. Equipment shall be set or mounted on a level base capable of supporting and distributing the weight contained thereon. Boilers, tanks, and equipment shall be securely anchored to the structure. Equipment requiring vibration isolation shall be installed as designed by a registered design professional and approved by the Authority Having Jurisdiction.

1001.5.1 Floors. Boilers shall be mounted on floors of noncombustible construction unless listed for mounting on combustible flooring. 1001.6 Chimneys or Vents. Boilers shall be connected to a chimney or vent, as provided for other fuel-burning equipment in Chapter 8 of this code.

1002.0 Standards.

1002.1 General. Pressure vessels shall be constructed and designed in accordance with the ASME Boiler & Pressure Vessel Code (BPVC) Section VIII.1. Boilers shall be constructed, designed, and installed in accordance with one of the following: (1) ASME BPVC Section I (2) ASME BPVC Section IV (3) NFPA 85 1002.2 Oil-Burning Boilers. Oil-burning boilers shall comply with Section 1002.2.1 and Section 1002.2.2. 1002.2.1 Listing & Labeling. Oil-burning boilers shall be listed and labeled in accordance with UL 726.

1002.2.2 Installation. Tanks, piping, and valves for oil-burning boilers shall be installed in accordance with NFPA 31.

1002.3 Electric Boilers. Electric boilers shall be listed and

labeled in accordance with UL 834.

1002.4 Solid-Fuel-Fired Boilers. Solid-fuel-fired boilers shall comply with UL 2523 and shall be installed in accordance with the manufacturer’s installation instruc tions.

1002.5 Dual Purpose Water Heaters. Water heaters utilized for combined space- and water-heating applications shall comply with the standards referenced in Table 1203.2, and shall be installed in accordance with the manufacturer’s

installation instructions.

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1003.0 Detailed Requirements.

1003.1 Safety Requirements. The construction of boilers and pressure vessels and the installation thereof shall be in accordance with minimum requirements for safety from structural and mechanical failure and excessive pressures as established by the Authority Having Jurisdiction in accordance with nationally recognized standards.
CMC § 2.1 Medium relevance — show source text
2.1_||||||||||X|X|X|X|X|X||||||||||

This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.

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1001.0 General.

1001.1 Applicability. The requirements of this chapter shall apply to the construction, installation, operation, repair, and alteration of boilers and pressure vessels. Low-pressure boilers shall comply with this chapter and Section 904.0.

Exceptions:

(1) Listed and approved potable water heaters with a nominal capacity not exceeding 120 gallons (454 L) and having a heat input not exceeding 200 000 British thermal units per hour (Btu/h) (58.6 kW) used for hot water supply at a pressure not exceeding 160 pounds-force per square inch (psi) (1103 kPa) and at temperatures not exceeding 210°F (99°C), in accordance with the plumbing code.

(2) Pressure vessels used for unheated water supply, including those containing air that serves as a cushion and is compressed by the introduction of water and tanks connected to sprinkler systems.

(3) Portable unfired pressure vessels and Interstate Commerce Commission (I.C.C.) containers.

(4) Containers for liquefied petroleum gases, bulk oxygen, and medical gas that are regulated by the fire code.

(5) Unfired pressure vessels in business, factory, hazardous, mercantile, residential, storage, and utility occupancies having a volume not exceeding 5 cubic feet (0.14 m [3] ) and operating at pressures not exceeding 250 psi (1724 kPa).

(6) Pressure vessels used in refrigeration systems shall comply with Chapter 11.

(7) Pressure tanks used in conjunction with coaxial cables, telephone cables, power cables, and other similar humidity control systems.

(8) A boiler or pressure vessel subject to regular inspection by federal inspectors or licensed by federal authorities.

(9) Pressure vessels used in specific appliances shall comply with Chapter 9.

1001.2 Boiler Rooms and Enclosures. Boiler rooms and enclosures shall comply with the California Building Code .

1001.2.1 [OSHPD 1, 1R, 2, 3, 4 & 5] In no case shall boiler room volume or clearances be reduced below those required by the conditions of the boiler listing. The boiler and the boiler room ventilation system, including fans, con- trols, and damper motors shall be on essential power when required by Section 321.0. The ventilation system shall either operate continuously, or, if interlocked with the boiler(s) it shall not interfere with the proper boiler oper- ation. Listed boilers shall be installed with clearances in accordance with the manufacturer’s instructions.
CMC § 1012.0 Medium relevance — show source text
1012.0 Operating Adjustments and Instructions. 1012.1 General. Hot water boiler installations, upon completion, shall have controls set, adjusted, and tested by the installing contractor. A complete control diagram of a permanent legible type, together with complete boiler operating instructions, shall be furnished by the installer for each installation.

1013.0 Inspections and Tests. 1013.1 General. An installation for which a permit is required shall not be put into service until it has been inspected and approved by the Authority Having Jurisdiction.

It shall be the duty of the owner or his authorized representative to notify the Authority Having Jurisdiction that the installation is ready for inspection and test. It also shall be the duty of the owner or his authorized representative to post in a conspicuous position on the installation a notice in substantially the following form: “WARNING! THIS INSTALLATION HAS NOT BEEN INSPECTED AND APPROVED

BY THE AUTHORITY HAVING JURISDICTION AND

SHALL NOT BE COVERED OR CONCEALED UNTIL SO INSPECTED AND APPROVED,” and it shall be unlawful for anyone other than the Authority Having Jurisdiction to remove such notice. The Authority Having Jurisdiction shall require such tests as it deems necessary to determine that the installation is in accordance with the provision of this section. Such tests shall be made by the owner or his authorized representative in the presence of the Authority Having Jurisdiction.

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Exception: On installations designed and supervised by a registered design professional, the Authority Having Jurisdiction shall have the authority to permit inspection and testing by such registered design professional.

Where the owner or his authorized representative requests inspection of a boiler prior to its installation, the Authority Having Jurisdiction shall make such inspection. 1013.2 Operating Permit. It shall be unlawful to operate a boiler or pressure vessel without first obtaining a valid operating permit to do so from the Authority Having Jurisdiction. Such permit shall be displayed in a conspicuous place adjacent to the boiler or vessel. The operating permit shall not be issued until the equipment has been inspected and approved by the Authority Having Jurisdiction.

Exception: The operation of steam-heating boilers, low-pressure hot-water-heating boilers, hot water supply boilers, and pressure vessels in residential occupancies of less than six dwelling units and utility occupancies. 1013.3 Maintenance Inspection. The Authority Having Jurisdiction shall inspect boilers and pressure vessels operated under a permit in accordance with ASHRAE/ACCA 180 at such intervals as deemed necessary, but not less frequently than in accordance with Section 1013.4 through Section 1013.7.

1013.4 Power and Miniature Boilers. Power boilers and miniature boilers shall be inspected externally annually. Where construction and operating conditions permit, they shall be subject to inspection internally annually. 1013.5 Steam-Heating and Water-Heating Boilers. Steam-heating boilers and hot-water-heating boilers shall be inspected externally annually. Where construction and operating conditions permit, they shall also be subject to inspection internally annually. 1013.6 Automatic Steam-Heating Boilers. Automatic steam-heating boilers shall be inspected externally biennially. Where construction and operating conditions permit, they shall be subject to inspection internally biennially.

CMC § 1014.0 Medium relevance — show source text

Where subject to corrosion and construction permits, they shall be subject to inspection internally biennially.

Inspection of boilers and pressure vessels covered by insurance shall be permitted to be made by employees of the insuring company holding commissions from the National Board of Boiler and Pressure Vessel Inspectors, subject to approval of the Authority Having Jurisdiction. Approved insuring company inspectors shall make reports on prescribed forms on inspections authorized by the Authority Having Jurisdiction. The reports shall be filed in the Authority Having Jurisdiction office. Company inspectors shall notify the Authority Having Jurisdiction of suspension of insurance because of dangerous conditions, new insurance in effect, and discontinuance of insurance

coverage.

1014.0 Operation and Maintenance of Boilers and Pressure Vessels.

1014.1 General. Boilers and pressure vessels shall be operated and maintained in accordance with requirements for pro

tection of the public established by the Authority Having Jurisdiction in accordance with nationally recognized standards.

The Authority Having Jurisdiction shall notify the owner or authorized representative of defects or deficiencies and properly corrected. Where such corrections are not made, or where the operation of the boiler or pressure vessel is deemed unsafe by the Authority Having Jurisdiction, they shall have the authority to revoke the permit to operate the boiler or pressure vessel. Where the operation of a boiler or pressure vessel is deemed by the Authority Having Jurisdiction to constitute an immediate danger, the pressure on such boiler or pressure vessel shall be permitted to be relieved at the owner’s cost and the boiler or pressure vessel shall not thereafter be operated without the approval of the Authority Having Jurisdiction.

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CONTROL AND LIMIT DEVICE SYSTEM DESIGN11	Col2	Col3	Required	Required	Required	Required	Required	Required	Required	Required	Required	Per NFPA 85	Per NFPA 85
APPROVED FUEL SHUT- OFF10	APPROVED FUEL SHUT- OFF10	APPROVED FUEL SHUT- OFF10	Not Required	Not Required	Required	Required	Not Required	Not Required	Not Required	Required	Not Required	Per NFPA 85	Per NFPA 85
STEAM PRESSURE AND LOW WATER LIMIT CON- TROLS9	STEAM PRESSURE AND LOW WATER LIMIT CON- TROLS9	STEAM PRESSURE AND LOW WATER LIMIT CON- TROLS9	Required	Required	Required	Required	Required	Required	Required	Required	Required	Per ASME Power Boiler Code,

Frequently asked questions

What gauges must a steam boiler have?

A steam boiler must have a pressure gauge and a water level glass, per § 1003.3.

Are damper blades allowed inside a gas‑fired boiler stack?

No. Operative dampers shall not be placed within a stack, flue, or vent of a gas‑fired boiler, unless the automatic‑boiler exception (prepurge, automatic draft control, interlock) applies. § 1003.4.

Which welding standard do I use for a pressure vessel?

The CMC requires welding by certified welders to nationally recognized standards (§ 1003.5) and requires pressure vessels to be constructed per ASME BPVC Section VIII.1 (§ 1002.1). Consult the ASME BPVC (and typically ASME Section IX for welder qualification) and the AHJ for the specific procedure/test requirements. § 1003.5, § 1002.1.

Does § 1003.5 itself require ASME Section IX certification?

No — § 1003.5 requires certified welders and nationally recognized standards but does not explicitly name ASME Section IX; the specific qualification standard is found in the referenced construction code that applies to the vessel (see § 1002.1).

If a boiler is “listed,” do I still need the gauges in § 1003.3?

Yes — § 1003.3 gives minimum gauge requirements. However, listed equipment and manufacturer instructions may require additional or different instrumentation; follow the listing/manufacturer and the AHJ. § 1003.3, § 1001.2.

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Safety Controls, Gauges, Expansion Tanks, and Combustion Safety

California Mechanical Code