CMC · California Mechanical Code
Safety Controls, Gauges, Expansion Tanks, and Combustion Safety
This hub summarizes the CMC requirements for controls, gauges, expansion tanks, relief devices and combustion‑safety (air, venting, and flame safeguards) for boilers and hydronic/fuel‑burning systems.
Last reviewed: July 6, 2026
Overview
This area of the California Mechanical Code (CMC) covers the required safety and operating controls, instrumentation, pressure‑relief and expansion devices for boilers, pressure vessels, hydronic systems, and the combustion‑safety and venting requirements for fuel‑burning appliances. Key provisions appear in Chapter 10 (Boilers and Pressure Vessels) — including controls (§1003.2) and gauges (§1003.3) — and the expansion‑tank rules at §1004.0; hydronics expansion‑tank requirements are repeated in Chapter 12 (see §1209.0) .
Combustion safety (combustion air, venting, chimneys and appliance‑specific installation requirements) is addressed in Chapters 7–9 and in Appendix C (oil/liquid fuel installation and flame‑safeguard requirements). These sections require proof‑of‑air interlocks, prepurge and flame‑safeguard systems, interlocks for vent/stack dampers, and supervised startup and testing where applicable .
The CMC also ties installations to consensus standards and listings (for example ASME CSD‑1 for automatic boiler controls and ASME BPVC requirements for pressure vessels and certain expansion tanks), and it specifies sizing, mounting, pressure‑rating and discharge‑piping practices for relief devices and expansion tanks to prevent overpressure and hazardous discharge .
In this section
- How are expansion tanks sized and what are installation requirements for hot-water systems?
- What are low-water cutoff and combustion regulator requirements for boilers?
- What controls and limit devices are required for automatic boilers?
- What gauges, welding standards, and welder qualifications apply to boilers and pressure vessels?
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
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 § 3663.4 High relevance — show source text
(d) Programmed electronic flame safeguard including proven low-fire start, manual reset lockout, 100 percent shutoff (both pilot and main burner), and a separately supervised and proven pilot.
Flame-sensing systems utilizing a UV scanner shall prove pilot and interrupt ignition spark prior to main burner valves being energized.
(e) Two controls, one operating and one high limit, activated by temperature or pressure.
(f) Burners relying on mechanical means to provide air for combustion shall have actual proof-of-air interlock device.
(g) Power burners shall include proven prepurge of not less than 60 seconds at high-fire damper settings. This prepurge shall occur before every burner cycle, regardless of reason.
(h) Installations with dampered combustion air openings shall prove damper open position before trial for burner ignition.
(i) Vent dampers and flue dampers shall be interlocked to prevent burner ignition unless safely open.
(j) One high oil or liquid fuel-pressure interlock, reset from flame safeguard or manually.
(k) Where hot water or steam, two low water cutoffs.
(l) An atomizing medium proving switch.
(m) A low oil temperature switch for oil or liquid fuel requiring preheating.
(n) A high oil temperature interlock for oil or liquid fuel requiring preheating.
(o) A separate firing rate control valve.
(p) The burner oil pump shall automatically not operate or rotate while the alternate fuel is firing.
(q) A pressure-relief valve shall be provided between safety shutoff valves and between pump and safety valves where an integral valve is used with a pump.
(r) A separate relief device is required on each transfer
pump.
(s) One low oil or liquid fuel-pressure interlock reset from flame safeguard or manually.
(t) Burners with automatic controls, prepurge, proofof-closure, modulation, or postpurge shall not use relays external to the flame safeguard to accomplish these functions.
(5) More than 12 500 000 Btu/h (3663.4 kW) per burner inputs. These burners shall comply with the requirements of the appropriate standards listed in Chapter 18 and the following:
(a) One approved manual shutoff valve lever handle.
(b) One approved fuel-oil filter, installed on the supply piping.
(c) Two safety shutoff valves in series, one with proof of closure, with a combined flame failure response and valve closing time not to exceed 2 seconds with strainer directly before the valves.
(d) Programmed electronic flame safeguard including proven low-fire start, manual reset lockout, 100 percent shutoff (both pilot and main burner), and a separately supervised and proven pilot.
Flame-sensing systems utilizing a UV scanner shall prove pilot and interrupt ignition spark prior to main burner valves being energized.
(e) Two controls, one operating and one high limit, activated by temperature or pressure.
(f) Burners relying on mechanical means to provide air for combustion shall have actual proof-of-air interlock device.
(g) Power burners must include proven prepurge of not less than 60 seconds at high-fire damper settings. This prepurge shall occur before every burner cycle, regardless of reason.
(h) Installations with dampered combustion air openings shall prove damper open position before trial for burner ignition.
(i) Vent dampers and flue dampers shall be interlocked to prevent burner ignition unless safely open.
(j) One high oil or liquid fuel-pressure interlock; reset from flame safeguard or manually.
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CMC § 1102.3 High 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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FORMAT OF THE UNIFORM MECHANICAL CODE
1102.3 lists the most commonly used refrigerants and is labeled by a number. The concentration limits provided in Table 1102.3 are useful for the quantity of refrigerant required to cool a volume of space safely.
A major milestone reached in the industry was the introduction of lower flammability refrigerants such as A2L and B2L. The industry’s concerns to address lower Global Warming Potential (GWP) refrigerants led to the development of these lower flammability refrigerants. Chapter 11 does not only include these lower flammability refrigerants in Table 1102.3, but it also contains specific A2L and B2L provisions to address the precautions necessary for the proper use of these products. In particular, high-probability systems using A2L refrigerants for human comfort applications are covered by provisions which include refrigerant concentration limits, mechanical ventilation, ignition sources, compressors and pressure vessels, and refrigerant sensors.
In addition, Chapter 11 addresses other minimum requirements for refrigeration systems such as refrigeration machinery rooms (including ventilation), relief valves, and pressure vessels. Apart from refrigerants, the chapter also addresses minimum requirements for systems that use other mediums such as ammonia and brine systems. For ammonia systems, such systems are required to comply with IIAR 2, IIAR 3, IIAR/ANSI 4, IIAR 5, and IIAR 6.
Chapter 12 Hydronics. Chapter 12 regulates hydronic systems that are part of heating, cooling, ventilation, and conditioning systems. Such piping systems include steam, hot water, radiant heating and cooling, chilled water, steam condensate, condenser water, ground source heat pump systems, snow and ice melt systems, ambient temperature loops, and district ambient temperature loops. Provisions within this chapter addressing ground source heat pumps and ambient temperature loops apply to the hydronic portions of the system. Geothermal energy systems, including ground source heat pumps and ambient temperature loops, are regulated by Chapter 17.
CMC § 3663.3 High relevance — show source text
(n) A high oil temperature interlock for oil or liquid fuel requiring preheating.
(o) The burner oil pump shall automatically not operate or rotate while the alternate fuel is firing.
(p) A pressure-relief valve shall be provided between safety shutoff valves and between pump and safety valves where an integral valve is used with a pump.
(q) A separate relief device is required on each transfer
pump.
(3) One million to 2 499 999 Btu/h (293 kW to 732 kW) input per burner.
(a) One approved manual shutoff valve lever handle.
(b) One approved fuel-oil filter, installed on the supply piping.
(c) Two safety shutoff valves in series with a combined flame failure response and valve closing time not to exceed 5 seconds with strainer directly before the valves.
(d) Programmed electronic flame safeguard including proven low-fire start, manual reset lockout, 100 percent shutoff (both pilot and main burner), and a separately supervised and proven pilot.
Flame-sensing systems utilizing a UV scanner shall prove pilot and interrupt ignition spark prior to main burner valves being energized.
(e) Two controls, one operating and one high limit, activated by temperature or pressure.
(f) Burners relying on mechanical means to provide air for combustion shall have actual proof-of-air interlock device.
(g) Power burners shall include proven prepurge of not less than 60 seconds at high-fire damper settings. This prepurge shall occur before every burner cycle, regardless of reason.
(h) Installations with dampered combustion air openings shall prove damper open position before trial for burner ignition.
(i) Vent dampers and flue dampers shall be interlocked to prevent burner ignition unless safely open.
(j) One high oil or liquid fuel-pressure interlock, reset from flame safeguard or manually.
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APPENDIX C
(k) Where hot water or steam, two low water cutoffs.
(l) An atomizing medium proving switch.
(m) A low oil temperature switch for oil or liquid fuel requiring preheating.
(n) A high oil temperature interlock for oil or liquid fuel requiring preheating.
(o) The burner oil pump shall automatically not operate or rotate while the alternate fuel is firing.
(p) A pressure-relief valve shall be provided between safety shutoff valves and between pump and safety valves where an integral valve is used with a pump.
(q) A separate relief device is required on each transfer
pump.
(r) One low oil or liquid fuel-pressure interlock, reset from flame safeguard or manually.
(s) Burners with automatic controls, prepurge, proofof-closure, modulation, or postpurge shall not use relays external to the flame safeguard to accomplish these functions.
(4) Two million five hundred thousand to 12 499 999 Btu/h (733 kW to 3663.3 kW) per burner.
(a) One approved manual shutoff valve lever handle.
(b) One approved fuel-oil filter, installed on the supply piping.
(c) Two safety shutoff valves in series, with a combined flame failure response and valve closing time not to exceed 5 seconds with strainer directly before the valves.
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.
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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 § 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
California Mechanical Code Medium relevance — show source text
system to permit smooth light-off. This will normally be a rate of one-third of its maximum firing rate.
7 Boiler groups C, D, and H shall not permit pilot or main burner trial for ignition operation before a purging operation of sufficient duration to permit not less
than four complete air changes through the furnace, including a combustion chamber and the boiler passes. Where this is not readily determinable, five com plete air changes of the furnace, including combustion chamber up to the first pass, will be considered equivalent. An atmospheric gas burner with no mechan ical means of creating air movement or an oil burner that obtains two-thirds or more of the air required for combustion without mechanical means of creating
air movement shall not require purge by means of four air changes, so long as its secondary air openings are not provided with means of closing. Where such
burners have means of closing secondary air openings, a time delay shall be provided that puts these closures in a normally open position for four minutes
before an attempt for ignition. An installation with a trapped combustion chamber shall, in every case, be provided with a mechanical means of creating air
movement for purging. 8 An automatic hot-water-heating boiler, low-pressure hot-water-heating boiler, and power hot water boiler shall be equipped with two high-temperature limit
controls with a manual reset on the control, with the higher setting interlocked to shut off the main fuel supply, except that manual reset on the high-tem perature limit control shall not be required on an automatic package boiler not exceeding 400 000 Btu/h (117 kW) input and that has been approved by an
approved testing agency. An automatic hot-water heating, power boiler, and package hot-water supply boiler shall be equipped with one low-water level limit
control with a manual reset interlocked to shut off the fuel supply, so installed as to prevent damage to the boiler and to permit testing of the control with out draining the heating system, except on boilers used in Group R Occupancies of less than six units and in Group U Occupancies and further, except that
the low-water level limit control is not required on package hot-water supply boilers approved by a nationally recognized testing agency. However, a low water flow limit control installed in the circulating water line shall be permitted to be used instead of the low-water level limit control for the same purpose
on coil-type boilers. 9 An automatic low-pressure steam-heating boiler, small power boiler, and power steam boiler shall be equipped with two high-steam pressure limit controls
interlocked to shut off the fuel supply to the main burner with manual reset on the control, with the higher setting and two low-water-level limit controls,
one of which shall be provided with a manual reset device and independent of the feed water controller. Coil-type flash steam boilers shall be permitted to
use two high-temperature limit controls, one of which shall be manually reset in the hot water coil section of the boiler instead of the low-water level limit
control.
10 Boiler groups C, D, and H shall use an approved automatic reset safety shutoff valve for the main burner fuel shutoff, which shall be interlocked to the pro gramming control devices required. On oil burners where the safety shutoff valve will be subjected to pressures in excess of 10 psi (69 kPa) where the burner
is not firing, a second safety shutoff valve shall be provided in series with the first. Boiler groups C and D using gas in excess of 1 psi (7 kPa) pressure or
having a trapped combustion chamber or employing horizontal fire tubes shall be equipped with two approved safety shutoff valves, one of which shall be
an automatic reset type, one of which shall be permitted to be used as an operating control, and both of which shall be interlocked to the limit-control devices
CMC § 1211.2.2 Medium relevance — show source text
1211.2.2 Polyethylene (PE) Plastic Pipe/Tubing. Polyethylene pipe and tubing bends shall have a bend radius in accordance with Table 1211.2.2. When a fitting or flange connection is present in the pipe bend, the minimum bend radius shall be one hundred times the pipe outside diameter (OD) for a distance of five times the pipe diameter on either side of the fitting location.
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1208.2 Mounting. The circulator or pump shall be installed in such a way that strain from the piping is not transferred to the circulator or pump housing. The circulator or pump shall be permitted to be directly connected to the piping, provided the piping is supported on each side of the circulator or pump. Where the installation of a circulator or pump will cause strain on the piping, the circulator or pump shall be installed on a mounting bracket or base plate or securely fastened to or supported by the structure with approved fastening devices. Where means for controlling vibration of a circulator or pump is required, an approved means for support and restraint shall be provided. 1208.3 Sizing. The selection and sizing of a circulator or pump shall be based on all of the following: (1) Loop or system head pressure, feet of head (m) (2) Capacity, gallons per minute (L/s) (3) Maximum and minimum temperature, °F (°C) (4) Maximum working pressure, pounds per square inch (kPa) (5) Fluid type
1209.0 Expansion Tanks. 1209.1 General. An expansion tank shall be installed in each closed hydronic system to control system pressure due to thermal expansion and contraction. Expansion tanks shall be of the closed type. Expansion tanks shall be rated for the pressure of the system. 1209.2 Installation. Expansion tanks shall be accessible for maintenance and shall be installed in accordance with the manufacturer’s installation instructions. Each expansion tank shall be equipped with a shutoff device that will remain open during operation of the hydronic system. Valve handles shall be locked open or removed to prevent from being inadvertently shut off. Provisions shall be made for draining the tank without emptying the system. Expansion tanks shall be securely fastened to or supported by the structure. 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. 1209.3 Closed-Type Tanks. Closed-type expansion tanks 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.
1209.4 Sizing. Expansion tanks shall be sized to accept the full expansion volume of the fluid in the system. The minimum capacity of a closed-type expansion tank shall be sized in accordance with Section 1004.4.
1210.0 Materials.
1210.1 Piping, Tubing, and Fittings. Hydronic pipe and tubing shall comply with the applicable standards referenced in Table 1210.1 and shall be approved for use based on the intended purpose. Materials shall be rated for the operating
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CMC § 1204.1 Medium relevance — show source text
1204.1 General. . . . . . . . . . . . . . . . . . . . . 258
1204.2 Color and Information . . . . . . . . . . 258
1204.3 Potable Water. . . . . . . . . . . . . . . . 258
1204.4 Nonpotable Water. . . . . . . . . . . . . 258
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TABLE OF CONTENTS
Table 1204.3 Minimum Length of Color Field and Size of Letters. . . . . . . . 258
1204.5 Location of Piping Identification . . . 258
1204.6 Flow Directions . . . . . . . . . . . . . . . 258
1204.7 Heat Transfer Fluid. . . . . . . . . . . . 258
1204.8 Identification of Chemical
Additives . . . . . . . . . . . . . . . . . . . . 258
1205.0 Installation, Testing, and Inspection . . . . . . . . . . . . . . . . . . . 258
1205.1 Operating Instructions . . . . . . . . . 258
1205.2 Pressure Testing . . . . . . . . . . . . . 258
1205.3 Flushing . . . . . . . . . . . . . . . . . . . . 259
1206.0 Pressure and Safety Devices . . . . 259
1206.1 General. . . . . . . . . . . . . . . . . . . . . 259
1206.2 Discharge Piping . . . . . . . . . . . . . 259
1207.0 Heating Appliances and Equipment . . . . . . . . . . . . . . . . . . 259
1207.1 General. . . . . . . . . . . . . . . . . . . . . 259
1207.2 Boilers. . . . . . . . . . . . . . . . . . . . . . 259
1207.3 Dual Purpose Water Heaters . . . . 259
1207.4 Solar Heat Collector Systems. . . . 259
1207.5 Heat Pumps . . . . . . . . . . . . . . . . . 259
1208.0 Circulators and Pumps . . . . . . . . . 259
1208.1 General. . . . . . . . . . . . . . . . . . . . . 259
1208.2 Mounting. . . . . . . . . . . . . . . . . . . . 260
1208.3 Sizing . . . . . . . . . . . . . . . . . . . . . . 260
1209.0 Expansion Tanks . . . . . . . . . . . . . 260
1209.1 General. . . . . . . . . . . . . . . . . . . . . 260
1209.2 Installation . . . . . . . . . . . . . . . . . . 260
1209.3 Closed-Type Tanks . . . . . . . . . . . 260
CMC § 610.4. Medium relevance — show source text
** Where static water pressure in the water supply piping exceeds 80 psi (552 kPa), an approved-type pressure regulator preceded by an adequate strainer shall be installed and the static pressure reduced to 80 psi (552 kPa) or less. Pressure regulators for potable water distribution systems shall comply with ASSE 1003 or AWWA C530. Pressure regulator(s) equal to or exceeding 1 [1] ⁄ 2 inches (40 mm) shall not require a strainer. Such regulator(s) shall control the pressure to water outlets in the building unless otherwise approved by the Authority Having Jurisdiction. Each such regulator and strainer shall be accessibly located aboveground or in a vault equipped with a properly sized and sloped boresighted drain to daylight, shall be protected from freezing, and shall have the strainer readily accessible for cleaning without removing the regulator or strainer body or disconnecting the supply piping. Pipe size determinations shall be based on 80 percent of the reduced pressure where using Table 610.4.
An approved expansion tank shall be installed in the cold water distribution piping downstream of each such regulator to prevent pressure exceeding 80 psi from developing due to thermal expansion. Expansion tanks used in potable water systems intended to supply drinking water shall comply with NSF/ANSI/CAN 61. The expansion tank shall be properly sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions and listing. Systems designed by a licensed plumbing contractor or registered design professionals shall be permitted to use approved pressure relief valves in lieu of expansion tanks provided such relief valves have a maximum pressure relief setting of 100 psi (689 kPa) or less. 608.3 Expansion Tanks, and Combination Tempera- ture and Pressure-Relief Valves. A water system provided with a check valve, backflow preventer, or other normally closed device that prevents dissipation of building pressure back into the water main, independent of the type of water heater used, shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Prepressurized water expansion tanks shall comply with IAPMO/ANSI Z1088. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions.
A water system containing storage water heating equipment shall be provided with an approved, listed, adequately sized combination temperature and pressure-relief valve, except for listed nonstorage instantaneous heaters having an inside diameter of not more than 3 inches (80 mm). Each such approved combination temperature and pressure-relief valve shall be installed on the water-heating device in an approved location based on its listing requirements and the manufacturer’s installation instructions. Each such combination temperature and pressure-relief valve shall be provided with a drain in accordance with Section 608.5.
CMC § 607.5 Medium relevance — show source text
installation instructions. Such vent shall be screened with a cor rosion-resistant material of not less than number 24 mesh.
607.5 Overflow. Tanks shall have not less than a 16 square inch (0.01 m [2] ) overflow that is screened with a corrosionresistant material of not less than number 24 mesh.
607.6 Valves. Pressurized tanks shall be provided with a listed pressure-relief valve installed in accordance with the manufacturer’s installation instructions. The relief valve shall be discharged in accordance with Section 608.5. Where a potable water supply tank is located above the fixtures, appliances, or system components it serves, it shall be equipped with a vacuum relief valve that complies with ANSI Z21.22/CSA 4.4.
608.0 Water Pressure, Pressure Regulators, Pres- sure Relief Valves, and Vacuum Relief Valves. 608.1 Inadequate Water Pressure. Where the water pressure in the main or other source of supply will not provide a residual water pressure of not less than 15 pounds force per square inch (psi) (103 kPa), after allowing for friction and other pressure losses, a tank and a pump or other means that will provide said 15 psi (103 kPa) pressure shall be installed. Where fixtures, fixture fittings, or both are installed that, require a residual pressure exceeding 15 psi (103 kPa), that minimum residual pressure shall be provided.
608.2 Excessive Water Pressure. Where static water pressure in the water supply piping exceeds 80 psi (552 kPa), an approved-type pressure regulator preceded by an adequate strainer shall be installed and the static pressure reduced to 80 psi (552 kPa) or less. Pressure regulators for potable water distribution systems shall comply with ASSE 1003 or AWWA C530. Pressure regulator(s) equal to or exceeding 1 [1] ⁄ 2 inches (40 mm) shall not require a strainer. Such regulator(s) shall control the pressure to water outlets in the building unless otherwise approved by the Authority Having Jurisdiction. Each such regulator and strainer shall be accessibly located aboveground or in a vault equipped with a properly sized and sloped boresighted drain to daylight, shall be protected from freezing, and shall have the strainer readily accessible for cleaning without removing the regulator or strainer body or disconnecting the supply piping. Pipe size determinations shall be based on 80 percent of the reduced pressure where using Table 610.4.
An approved expansion tank shall be installed in the cold water distribution piping downstream of each such regulator to prevent pressure exceeding 80 psi from developing due to thermal expansion. Expansion tanks used in potable water systems intended to supply drinking water shall comply with NSF/ANSI/CAN 61. The expansion tank shall be properly sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions and listing. Systems designed by a licensed plumbing contractor or registered design professionals shall be permitted to use approved pressure relief valves in lieu of expansion tanks provided such relief valves have a maximum pressure relief setting of 100 psi (689 kPa) or less. 608.3 Expansion Tanks, and Combination Tempera- **ture and Pressure-Relief Valves.
CMC § 1209.2 Medium relevance — show source text
Expansion tanks shall be of the closed type. Expansion tanks shall be rated for the pressure of the system. 1209.2 Installation. Expansion tanks shall be accessible for maintenance and shall be installed in accordance with the manufacturer’s installation instructions. Each expansion tank shall be equipped with a shutoff device that will remain open during operation of the hydronic system. Valve handles shall be locked open or removed to prevent from being inadvertently shut off. Provisions shall be made for draining the tank without emptying the system. Expansion tanks shall be securely fastened to or supported by the structure. 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. 1209.3 Closed-Type Tanks. Closed-type expansion tanks 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.
1209.4 Sizing. Expansion tanks shall be sized to accept the full expansion volume of the fluid in the system. The minimum capacity of a closed-type expansion tank shall be sized in accordance with Section 1004.4.
1210.0 Materials.
1210.1 Piping, Tubing, and Fittings. Hydronic pipe and tubing shall comply with the applicable standards referenced in Table 1210.1 and shall be approved for use based on the intended purpose. Materials shall be rated for the operating
260 2025 CALIFORNIA MECHANICAL CODE
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HYDRONICS
TABLE 1210.1
MATERIALS FOR HYDRONIC SYSTEM PIPING, TUBING, AND FITTINGS
MATERIAL STANDARDS Col3 MATERIAL PIPING/TUBING FITTINGS Copper/Copper Alloy ASTM B42, ASTM B43, ASTM B75,
ASTM B88, ASTM B135, ASTM B2512,
ASTM B302, ASTM B447ASME B16.15, ASME B16.18, ASME B16.22,
ASME B16.23, ASME B16.24, ASME B16.26,
ASME B16.29, ASME B16.51, ASSE 1061,
ASTM F3226, IAPMO PS 117Ductile Iron AWWA C115/A21.15,
AWWA C151/A21.51AWWA C110/A21.101,
AWWA C153/A21.53Steel ASTM A53, ASTM A106, ASTM A254 ASME B16.5, ASME B16.9,
ASME B16.11, ASTM A420, ASTM F3226,
IAPMO IGC 353, IAPMO PS 117Stainless Steel ASTM A269, ASTM A312,
ASTM A554, ASTM A778ASTM F1476, ASTM F1548, ASTM F3226,
IAPMO IGC 353,
Frequently asked questions
When is an expansion tank required?
An expansion tank is required where thermal expansion can raise system pressure — e.g., in hot‑water‑heating systems and closed hydronic systems; the CMC requires tanks sized, rated and supported for system pressure and provides minimum sizing methods at §1004.0 and §1004.4 (and hydronics detail at §1209.0) .
What gauges and safety controls must boilers have?
Steam boilers must have a pressure gauge and a water‑level glass; water boilers must have a pressure and temperature gauge. Automatic boilers and larger burners must also be equipped with listed safety and flame‑safeguard controls, proof‑of‑closure/proof‑of‑air interlocks, and required shutoff and relief devices as set out in §1003.2–§1003.3 and Appendix C (C109) .
What are the CMC’s core combustion‑safety requirements?
Combustion air supply and dilution requirements are in Chapter 7 and venting/chimney rules are in Chapter 8; installations must provide adequate combustion air, proper venting, interlocks for dampers and proven flame‑safeguard controls (including prepurge and supervised startup where required) to prevent incomplete combustion and CO hazards .
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