CMC · California Mechanical Code
What are low-water cutoff and combustion regulator requirements for boilers?
Boilers must not run without adequate water or flow: install a low‑water cutoff (or flow sensor for certain coil/water‑tube units) that shuts off the fuel per the manufacturer, and fit the combustion regulators the CMC requires — hot‑water boilers need two temperature regulators in series, steam boilers need a pressure regulator plus low‑water protection (see **§ 1008.1** and **§ 1009.1**).
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Boilers must be protected from operation when water level or flow is insufficient and must have the required combustion regulation devices. Specifically, hot‑water and steam boilers must have a low‑water cutoff (or an approved flow‑sensing device for certain coil/water‑tube boilers) per § 1008.1 . For combustion control, hot‑water‑heating boilers (not manually fired) need two temperature combustion regulators in series, and steam‑heating boilers (not manually fired) need a pressure combustion regulator plus a low‑water cutoff, per § 1009.1 .
The single most important rule: install a device that will shut off the fuel/energy source if boiler water level or required flow is too low, and fit the combustion regulator(s) required for the boiler type. (See § 1008.1 and § 1009.1.)
Requirements in detail
Low‑water cutoff (general requirements)
- What is required: Hot‑water boilers and steam boilers must be installed with a low‑water cutoff unless a permitted alternative is used. § 1008.1 .
- Alternative for coil/water‑tube with forced circulation: A flow‑sensing device in the outlet piping is permitted in lieu of a low‑water cutoff for a coil‑type boiler or a water‑tube boiler that requires forced circulation to prevent overheating. § 1008.1 .
- Installation and testing: The low‑water cutoff or flow sensor must be located/installed so as to prevent damage to the boiler and to permit testing of the fuel‑supply cutoff without draining the heating system. § 1008.1 .
- Setpoint: The low‑water cutoff must shut off the energy source at a water level setpoint in accordance with the boiler manufacturer’s instructions. § 1008.1 .
Combustion regulators and safety valves (general requirements)
- Hot‑water‑heating boilers (automatic): Two temperature combustion regulators in series are required for hot‑water‑heating boilers that are other than manually fired. § 1009.1(1) .
- Steam‑heating boilers (automatic): A pressure combustion regulator and a low‑water cutoff are required for steam‑heating boilers that are other than manually fired. § 1009.1(1) .
- Safety / relief valves: Boilers and pressure vessels must be provided with the required number, size, and capacity of safety or relief valves to ensure positive overpressure relief in accordance with nationally recognized standards; valves must be constructed, sealed, and installed per those standards. § 1009.1(2) .
Decision‑relevant table
| Boiler type / condition | Required device(s) | Installation notes / purpose | Code Reference |
|---|---|---|---|
| Hot‑water boiler (not manually fired) | Two temperature combustion regulators in series | Protects against overheating and provides staged/backup temperature control | § 1009.1(1) |
| Steam‑heating boiler (not manually fired) | Pressure combustion regulator + low‑water cutoff | Pressure regulator controls steam pressure; low‑water cutoff prevents dry‑firing | § 1009.1(1) and § 1008.1 |
| Hot‑water or steam boiler | Low‑water cutoff | Must shut off energy source at manufacturer‑specified water level; allow testing without draining | § 1008.1 |
| Coil‑type or water‑tube boiler requiring forced circulation | Flow‑sensing device (in outlet piping) instead of low‑water cutoff | Detects loss of flow that would cause overheating of coils/tubes | § 1008.1 |
| Any boiler/pressure vessel | Safety / relief valves sized per standards | Must ensure positive relief of overpressure; installed per nationally recognized standards | § 1009.1(2) |
Exceptions & special cases
- Coil‑type boilers and water‑tube boilers that require forced circulation may use a flow‑sensing device in the outlet piping in lieu of a low‑water cutoff; this is a permitted exception in § 1008.1 .
- The code requires the low‑water cutoff or flow sensor be installed so it can be tested without draining the system; if the installation cannot meet that testability requirement, the Authority Having Jurisdiction (AHJ) or manufacturer guidance becomes critical (see § 1008.1) .
- Note: § 1009.1 is written as retroactive for the requirements listed — meaning these combustion regulator requirements apply to existing installations as stated in the section. § 1009.1 .
Common mistakes
- Confusing a low‑water cutoff (level device) with a low‑water limit control or other limit/temperature devices — the code specifically requires a device that shuts off the fuel/energy source when level/flow is unsafe (see § 1008.1) .
- Omitting the two temperature combustion regulators in series for hot‑water heating boilers that are not manually fired; a single regulator is not compliance with § 1009.1(1) .
- Installing a flow sensor in a coil‑type boiler that does not truly rely on forced circulation — the flow‑sensing alternative is limited to coil‑type or water‑tube boilers that require forced circulation per § 1008.1; using it elsewhere may be noncompliant.
- Failing to size or install safety/relief valves per nationally recognized standards (ASME, etc.) — § 1009.1(2) requires valves of the required number, size, and capacity and that they be constructed/installed to recognized standards.
Worked example — concrete scenario
Scenario: You are replacing controls on a gas‑fired, automatic hot‑water heating boiler (not manually fired) in a small commercial building.
- Low‑water protection: Because this is a hot‑water boiler (not coil‑type requiring forced circulation), install a low‑water cutoff mounted and piped so it will shut off the energy source at a water level setpoint in accordance with the boiler manufacturer’s instructions and so the cutoff can be tested without draining the system, per § 1008.1 .
- Combustion regulators: Per § 1009.1(1), provide two temperature combustion regulators in series. Practically that means selecting two temperature limit/regulator devices compatible with the burner control and wiring them in series so that either device will interrupt fuel if the higher‑priority limit trips .
- Safety valves: Confirm existing safety/relief valves meet required capacity and are installed per nationally recognized standards as required by § 1009.1(2); replace or re‑rate if not compliant .
(Designer note: the code does not prescribe the numeric level setpoint — the cutoff must follow the boiler manufacturer’s instructions, so consult those instructions to set the device.)
Related provisions
- § 904.6 — Low‑water cutoff requirement in the Central Heating Boilers section (parallels § 1008.1)
- § 904.5 — Temperature or pressure limiting devices for steam and hot water boilers (related limit‑control requirements)
- § 1005.1 / § 1005.2 — Safety/relief valve discharge and discharge piping requirements (relates to installation of relief valves called for in § 1009.1(2))
- § 1007.1 — Gas‑pressure regulator requirements for gas‑fired boilers (related gas supply control devices)
- § 1010.1 — Clearance for access around boilers (relevant when installing or servicing low‑water cutoffs and regulators)
- § 1013.0 — Inspections and tests (useful for operational verification after installing controls)
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 1007.0 High relevance — show source text
1007.0 Gas-Pressure Regulators.
1007.1 General. An approved gas-pressure regulator shall be installed on gas-fired boilers where the gas supply pressure is exceeding that at which the main burner is designed to operate. A separate approved gas-pressure regulator shall be installed to regulate the gas pressure to the pilot or pilots.
2025 CALIFORNIA MECHANICAL CODE 219
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BOILERS AND PRESSURE VESSELS
1008.0 Low-Water Cutoff.
1008.1 General. Hot water boilers and steam boilers shall be installed with a low-water cutoff. A coil-type boiler or a water-tube boiler that requires forced circulation to prevent overheating of the coils or tubes shall be installed with a flowsensing device in the outlet piping in lieu of the low-water cutoff. The low-water cutoff or the flow sensing device shall be installed so as to prevent damage to the boiler and to permit testing of the fuel-supply cutoff without draining the heating system. The low-water cutoff shall shut off the energy source at a water level setpoint that is in accordance with the boiler manufacturer’s instructions.
1009.0 Combustion Regulators – Safety Valves.
1009.1 General. The following requirements shall be retroactive:
(1) Hot-water-heating boilers, other than manually fired, shall be equipped with two temperature combustion regulators in series. Steam-heating boilers, other than manually fired, shall be equipped with a pressure combustion regulator and a low-water cutoff. (See Section 1008.0)
(2) Boilers and pressure vessels shall be provided with the required number, size, and capacity of safety or relief valves to ensure positive relief of overpressure in accordance with nationally recognized standards, as applicable. Valves so employed shall be constructed, sealed, and installed in accordance with nationally recognized standards, as applicable.
1010.0 Clearance for Access.
1010.1 General. Where boilers are installed or replaced, clearance shall be provided to allow access for inspection, maintenance, and repair. Passageways around all sides of boilers shall have an unobstructed width of not less than 18 inches (457 mm). Clearance for repair and cleaning shall be permitted to be provided through a door or access panel into another area, provided the opening is of sufficient size.
Exception: Subject to the approval of the Authority Having Jurisdiction, boilers shall be permitted to be installed with a side clearance of less than 18 inches (457 mm), provided that the lesser clearance does not inhibit inspection, maintenance, or repair.
1010.2 Power Boilers. Power boilers having a steam-generating capacity in excess of 5000 pounds per hour (lb/h) (0.6299 kg/s) or having a heating surface in excess of 1000 square feet (92.9 m [2] ) or input in excess of 5 000 000 Btu/h (1464 kW) shall have a clearance of not less than 7 feet (2134 mm) from the top of the boiler to the ceiling.
1010.3 Steam-Heating Boilers, Hot Water Boilers, and Power Boilers. Steam-heating boilers and hot-water-heating boilers that exceed one of the following limits:
(1) 5 000 000 Btu/h input (1464 kW)
CMC § 1005.3 High relevance — show source text
(3) Discharge pipe shall discharge independently by gravity through an air gap into the drainage system or outside of the building with the end of the pipe not exceeding 2 feet (610 mm) and not less than 6 inches (152 mm) above the ground and pointing downwards.
(4) Discharge in such a manner that does not cause personal injury or structural damage.
(5) No part of such discharge pipe shall be trapped or subject to freezing.
(6) The terminal end of the pipe shall not be threaded.
(7) Discharge from a relief valve into a water heater pan shall be prohibited.
(8) Discharge to a termination point that is readily visible.
1005.3 Splash Shield. Where the operating temperature exceeds 212°F (100°C), the discharge pipe shall be installed with a splash shield or centrifugal separator.
1005.4 Hazardous Discharge. Where the discharge from safety valves is capable of being hazardous, discharge of steam inside the boiler room, such discharge shall be discharged to the outside of the boiler room. Discharges from relief valves on industrial boilers shall be discharged to an approved location.
1005.5 Vacuum Relief Valve. Hot-water heating systems that are subjected to a vacuum while in operation or during shutdown shall be protected with a vacuum relief valve that complies with ANSI Z21.22/CSA 4.4. Where the piping configuration, equipment location, and valve outlets are located below the boiler elevation, the system shall be equipped with a vacuum relief valve at the highest point.
1006.0 Shutoff Valves.
1006.1 General. An approved manual shutoff valve shall be installed upstream of all control devices on the main burner of a gas-fired boiler. The takeoff point for the gas supply to the pilot shall be upstream of the gas shutoff valve of the main burner and shall be valved separately. A union or other approved means of disconnect shall be provided immediately downstream of these shutoff valves.
1007.0 Gas-Pressure Regulators.
1007.1 General. An approved gas-pressure regulator shall be installed on gas-fired boilers where the gas supply pressure is exceeding that at which the main burner is designed to operate. A separate approved gas-pressure regulator shall be installed to regulate the gas pressure to the pilot or pilots.
2025 CALIFORNIA MECHANICAL CODE 219
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BOILERS AND PRESSURE VESSELS
1008.0 Low-Water Cutoff.
1008.1 General. Hot water boilers and steam boilers shall be installed with a low-water cutoff. A coil-type boiler or a water-tube boiler that requires forced circulation to prevent overheating of the coils or tubes shall be installed with a flowsensing device in the outlet piping in lieu of the low-water cutoff. The low-water cutoff or the flow sensing device shall be installed so as to prevent damage to the boiler and to permit testing of the fuel-supply cutoff without draining the heating system. The low-water cutoff shall shut off the energy source at a water level setpoint that is in accordance with the boiler manufacturer’s instructions.
1009.0 Combustion Regulators – Safety Valves.
1009.1 General. The following requirements shall be retroactive:
CMC § 1009.0 High relevance — show source text
Combustion regulators . . . . . . . . . . . . . . . . . . . . 1009.0
Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003.2
Control diagram. . . . . . . . . . . . . . . . . . . . . . . . . . 1012.1
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.0
General requirements. . . . . . . . . . . . . . . . . . Chapter 10
In hydronic systems . . . . . . . . . . . . . . . . . . . . . . . 1207.2
Inspections and tests. . . . . . . . . . . . . . . . . . . . . . 1013.0
Low-water cutoff . . . . . . . . . . . . . . . . . . . . . . . . . 1008.0
Mounting of. . . . . . . . . . . . . . . . . . . . . . 1001.5, 1001.5.1
Operation and maintenance . . . . . . . . . . . . . . . . 1014.0
Permit Fees . . . . . . . . . . . . . . . . . . . . . . . . . Table 104.5
Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.0
Room . . . . . . . . . . . . . . . . . . . . . 204.0, 1001.2 , 1001.2.1
Venting of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1001.6
BOILER TYPES
Automatic . . . . . . . . . . . 204.0, 1003.2.1, Table 1003.2.1
1003.3, 1003.4
Central heating. . . . . . . . . . . . . . . . . . . . . . 303.2, 904.0
Condensing . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207.2.1
Electric . . . . . . . . . . . . . . . . . . . . . . 1002.3, E 503.5.7.3
High-pressure, definition . . . . . . . . . . . . . . . . . . . . 204.0
Low-pressure hot-water-heating,
definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.0
Low-pressure steam-heating,
definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.0
Miniature Boiler. . . . . . . . . . . . . . . . . . . . . 204.0, 1013.4
CMC § 904.5 High relevance — show source text
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INSTALLATION OF SPECIFIC APPLIANCES
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904.5 Temperature or Pressure Limiting Devices. Steam and hot water boilers, respectively, shall be provided with approved automatic limiting devices for shutting down the burner(s) to prevent boiler steam pressure or boiler water temperature from exceeding the maximum allowable working pressure or temperature. Safety limit controls shall not be used as operating controls. [NFPA 54:10.3.5]
904.6 Low-Water Cutoff. All water boilers and steam boilers shall be provided with an automatic means to shut off the fuel supply to the burner(s) if the boiler water level drops below the lowest safe water line. In lieu of the low-water cutoff, water tube or coil-type boilers that require forced circulation to prevent overheating and failure shall have an approved flow sensing device arranged to shut down the boiler when the flow rate is inadequate to protect the boiler against overheating. [NFPA 54:10.3.6]
904.7 Steam Safety and Pressure Relief Valves. Steam and hot water boilers shall be equipped, respectively, with listed or approved steam safety or pressure relief valves of appropriate discharge capacity and conforming with ASME requirements. A shutoff valve shall not be placed between the relief valve and the boiler or on discharge pipes between such valves and the atmosphere. [NFPA 54:10.3.7]
904.7.1 Discharge. Relief valves shall be piped to discharge near the floor. [NFPA 54:10.3.7.1]
904.7.2 Size. The entire discharged piping shall be at least the same size as the relief valve discharge piping.
[NFPA 54:10.3.7.2]
904.7.3 End Connections. Discharge piping shall not contain threaded end connection at its termination point.
[NFPA 54:10.3.7.3]
904.8 Refrigeration Coils. The installation of refrigeration coils shall comply with the following requirements:
(1) A refrigeration coil shall not be installed in conjunction with a forced air furnace where circulation of cooled air is provided by the furnace blower, unless the blower has
sufficient capacity to overcome the external static pressure resistance imposed by the duct system and refrigeration coil at the air flow rate for heating or cooling, whichever is greater.
(2) Furnaces shall not be located upstream from refrigeration coils, unless the refrigeration coil is designed or equipped so as not to develop excessive temperature or
pressure.
(3) Refrigeration coils shall be installed in parallel with or on the downstream side of central furnaces to avoid condensation in the heating element, unless the furnace has been specifically listed for downstream installation. With a parallel flow arrangement, the dampers or other means used to control flow of air shall be sufficiently tight to prevent any circulation of cooled air through the furnace.
(4) Means shall be provided for disposal of condensate and to prevent dripping of condensate on the heating element.
[NFPA 54:10.3.9]
904.9 Cooling Units Used with Heating Boilers. Boilers, where used in conjunction with refrigeration systems, shall be installed so that the chilled medium is piped in parallel with the heating boiler with appropriate valves to prevent the chilled medium from entering the heating boiler.
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 High 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 § 1102.3 High relevance — show source text
Allowable quantities . . . . . . . . . . . . . . . . . . Table 1102.3
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.0
– B –
BAFFLE PLATE . . . . . . . . . . . . . . . . . . . . 204.0, 509.2.2.1,
509.2.2.3, 513.2.4.2, 515.1.1.4
BALANCING, HVAC . . . . . . . . . . . . . . . . . . . 314.0, E 502.3
E 503.6.5.3–E 503.6.5.3.2
BLEED LINES . . . . . . . . . . . . . . . . . . . . . . . 902.15, 1308.14
BOARD OF APPEALS . . . . . . . . . . . . . . . . . . . . . . . . . 107.0
BOILER
Clearance for access. . . . . . . . . . . . . . . . . . . . . . 1010.0
Clearance for connectors . . . . . . . . . . . . Table 802.7.3.3
Closet or alcove installation . . . . . . . . . . . . . . . . . 303.2
Combustion regulators . . . . . . . . . . . . . . . . . . . . 1009.0
Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003.2
Control diagram. . . . . . . . . . . . . . . . . . . . . . . . . . 1012.1
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.0
General requirements. . . . . . . . . . . . . . . . . . Chapter 10
In hydronic systems . . . . . . . . . . . . . . . . . . . . . . . 1207.2
Inspections and tests. . . . . . . . . . . . . . . . . . . . . . 1013.0
Low-water cutoff . . . . . . . . . . . . . . . . . . . . . . . . . 1008.0
Mounting of. . . . . . . . . . . . . . . . . . . . . . 1001.5, 1001.5.1
Operation and maintenance . . . . . . . . . . . . . . . . 1014.0
Permit Fees . . . . . . . . . . . . . . . . . . . . . . . . . Table 104.5
Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.0
CMC § 901.1 High relevance — show source text
901.1 Applicability. . . . . . . . . . . . . . . . . . 199
902.0 General. . . . . . . . . . . . . . . . . . . . . 199
902.1 Nonindustrial Appliances . . . . . . . 199
902.2 Combustion Air from Bedroom
or Bathroom . . . . . . . . . . . . . . . . . 199
902.3 Added or Converted Appliances. . 199
902.4 Type of Gas(es) . . . . . . . . . . . . . . 199
902.5 Safety Shutoff Devices for Unlisted LP-Gas Appliances Used Indoors . . . . . . . . . . . . . . . . 199
902.6 Fuel Input Rate . . . . . . . . . . . . . . . 199
902.7 Use of Air or Oxygen Under Pressure . . . . . . . . . . . . . . . . . . . . 199
902.8 Appliance Support . . . . . . . . . . . . 199
902.9 Flammable Vapors . . . . . . . . . . . . 199
902.10 Solid-Fuel-Burning Appliances . . . 199
902.11 Combination of Appliances and Equipment . . . . . . . . . . . . . . . 199
902.12 Protection of Gas Appliances from Fumes or Gases Other
than Products of Combustion . . . . 199
902.13 Process Air . . . . . . . . . . . . . . . . . . 200
902.14 Gas Appliance Pressure Regulators . . . . . . . . . . . . . . . . . . 200
902.15 Bleed Lines for Diaphragm-Type Valves. . . . . . . . . . . . . . . . . . . . . . 200
903.0 Air-Conditioning Appliances . . . . . 200
903.1 Electric Air Conditioners . . . . . . . . 200
903.2 Gas-Fired Air Conditioners
and Heat Pumps. . . . . . . . . . . . . . 200
903.3 Packaged Terminal Air Conditioners . . . . . . . . . . . . . . . . . 200
904.0 Central Heating Boilers and Furnaces. . . . . . . . . . . . . . . . . . . . 200
904.1 Application . . . . . . . . . . . . . . . . . . 200
2025 CALIFORNIA MECHANICAL CODE
904.2 Location . . . . . . . . . . . . . . . . . . . . 201
904.3 Clearance . . . . . . . . . . . . . . . . . . . 201
904.4 Assembly and Installation. . . . . . . 201
904.5 Temperature or Pressure Limiting Devices . . . . . . . . . . . . . . 202
904.6 Low-Water Cutoff . . . . . . . . . . . . . 202
904.7 Steam Safety and Pressure Relief Valves. . . . . . . . . . . . . . . . . 202
904.8 Refrigeration Coils . . . . . . . . . . . . 202
CMC § 1005.0 High relevance — show source text
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
1010.2 Power Boilers . . . . . . . . . . . . . . . . 220
1010.3 Steam-Heating Boilers, Hot Water Boilers, and Power Boilers. . 220
1010.4 Package Boilers, Steam-Heating Boilers, and Hot-Water-Heating Boilers. . . . . . . . . . . . . . . . . . . . . . 220
1011.0 Boilers, Stokers, and Steam
Generators . . . . . . . . . . . . . . . . . . 220
xxxviii
1011.1 General. . . . . . . . . . . . . . . . . . . . . 220
1012.0 Operating Adjustments and Instructions . . . . . . . . . . . . . . . . . . 220
1012.1 General. . . . . . . . . . . . . . . . . . . . . 220
1013.0 Inspections and Tests. . . . . . . . . . 220
1013.1 General. . . . . . . . . . . . . . . . . . . . . 220
1013.2 Operating Permit . . . . . . . . . . . . . 221
1013.3 Maintenance Inspection . . . . . . . . 221
1013.4 Power and Miniature Boilers. . . . . 221
1013.5 Steam-Heating and WaterHeating Boilers . . . . . . . . . . . . . . . 221
CMC § 904.2.1 Medium relevance — show source text
obtained from the outdoors. The closet shall be for the exclusive use of the central heating furnace or low-pressure boiler.
(2) Central heating furnaces and low-pressure boilers shall be of the direct vent type.
904.2.1 Self-Closing Doors. Self-closing doors shall swing easily and freely, and shall be equipped with a self-closing device to cause the door to close and latch each time it is opened. The closing mechanism shall not have a hold-open feature.
904.2.2 Gasketing. Gasketing on gasketed doors or frames shall be furnished in accordance with the published listings of the door, frame, or gasketing material manufacturer.
Exception: Where acceptable to the Authority Having Jurisdiction, gasketing of noncombustible or limitedcombustible material shall be permitted to be applied to the frame, provided closing and latching of the door are not inhibited.
904.3 Clearance. Central heating furnaces and low-pressure boilers shall be provided with clearances in accordance with Section 904.3.1 through Section 904.3.7.
904.3.1 Listed Units. Listed central heating furnaces and low-pressure boilers shall be installed with clearances in accordance with the terms of their listings and the manufacturer’s installation instructions. {NFPA 54:10.3.3.1}
904.3.2 Unlisted Units. Unlisted central heating furnaces and low-pressure boilers shall be installed with clearances from combustible material not less than those specified in Table 904.3.2. [NFPA 54:10.3.3.2]
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INSTALLATION OF SPECIFIC APPLIANCES
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904.5 Temperature or Pressure Limiting Devices. Steam and hot water boilers, respectively, shall be provided with approved automatic limiting devices for shutting down the burner(s) to prevent boiler steam pressure or boiler water temperature from exceeding the maximum allowable working pressure or temperature. Safety limit controls shall not be used as operating controls. [NFPA 54:10.3.5]
904.6 Low-Water Cutoff. All water boilers and steam boilers shall be provided with an automatic means to shut off the fuel supply to the burner(s) if the boiler water level drops below the lowest safe water line. In lieu of the low-water cutoff, water tube or coil-type boilers that require forced circulation to prevent overheating and failure shall have an approved flow sensing device arranged to shut down the boiler when the flow rate is inadequate to protect the boiler against overheating. [NFPA 54:10.3.6]
904.7 Steam Safety and Pressure Relief Valves. Steam and hot water boilers shall be equipped, respectively, with listed or approved steam safety or pressure relief valves of appropriate discharge capacity and conforming with ASME requirements. A shutoff valve shall not be placed between the relief valve and the boiler or on discharge pipes between such valves and the atmosphere. [NFPA 54:10.3.7]
904.7.1 Discharge. Relief valves shall be piped to discharge near the floor. [NFPA 54:10.3.7.1]
California Mechanical Code Medium relevance — show source text
does not meet the
criteria for Category 1 or Category 2.| |Aerosol|Aerosol|Level 2|Those with a total chemical heat of combustion that is
less than or equal to 8,600 Btu/lb (20 kJ/g).|H223, Category 2; Flammable aerosol. Pressurized
container: May burst if heated:
1.
Any aerosol that dispenses a spray that, based
on the results of the ignition distance test, does
not meet the criteria for Category 1, and which
has:
a.
A heat of combustion of ≥ 20 kJ/g.
b.
A heat of combustion of < 20 kJ/g along
with an ignition distance of ≥ 15 cm; or
c.
A heat of combustion of < 20 kJ/g and an
ignition distance of < 15 cm along with
either, in the enclosed space ignition test
a time:
i. A time equivalent of ≤ 300 s/m3; or
ii. A deflagration density of ≤ 300
g/m3; or
2.
Any aerosol that dispenses a foam that, based
on the results of the aerosol foam flammability
test, does not meet the criteria for Category 1,
and which has a flame height of ≥ 4 cm and a
flame duration of ≥ 2 s.| |Aerosol|Aerosol|Level 3|Those with a total chemical heat of combustion that is
greater than 13,000 Btu/lb (30 kJ/g).|H222, Category 1; Extremely flammable aerosol. Pres-
surized container: May burst if heated:
1.
Any aerosol that contains ≥ 85% flammable
components (by mass) and has a heat of
combustion of ≥ 30 kJ/g.
2.
Any aerosol that dispenses a spray that, in the
ignition distance test, has an ignition distance
of ≥ 75 cm.
3.
Any aerosol that dispenses a foam that, in the
foam flammability test, has:
a.
A flame height of ≥ 20 cm and a flame
duration of ≥ 2 s.
b.
A flame height of ≥ 4 cm and a flame
duration of ≥ 7 s.| |Combustible
liquid|Combustible
liquid|—|A liquid having a closed cup flash point at or above
100°F (38°C).CMC § 10-8 Medium relevance — show source text
000|10-8|12-6|9-8|10-0|9-0|8-2|7-7|6-4|6-2| |24|2-#4
1-#6|60,000|12-11|15-2|11-9|12-2|11-0|9-11|9-3|7-8|7-6| |24|2-#5|40,000|15-2|17-9|13-9|14-3|12-10|11-7|10-10|9-0|8-9| |24|2-#5|60,000|18-4|21-6|16-7|17-3|15-6|14-0|13-1|10-4|10-0| |24|2-#6|40,000|18-0|21-1|16-4|16-11|14-10|12-9|11-8|9-2|8-11| |24|2-#6|60,000|21-7|25-4|19-2|20-4|17-2|14-9|13-4|10-4|10-0| |24|Center distance_A_k, l|Center distance_A_k, l|4-6|6-2|3-8|4-0|3-3|2-8|2-3|1-7|1-6| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square inch = 6.895 kPa, 1 pound per square foot = 0.0479 kPa, Grade 40 = 280 MPa, Grade 60 = 420 MPa.
a. See Table R608.3 for tolerances permitted from nominal thickness.
b. Table values are based on concrete with a minimum specified compressive strength of 2,500 psi. See Note j.
c. Table values are based on uniform loading. See Section R608.8.2 for lintels supporting concentrated loads.
d. Deflection criterion is_L_/240, where_L_ is the clear span of the lintel in inches, or1/2 inch, whichever is less.
e. Linear interpolation is permitted between ground snow loads and between lintel depths.
f. DR indicates design required.
g. Lintel depth,D, is permitted to include the available height of wall located directly above the lintel, provided that the increased lintel depth spans the entire length of the
lintel.
h. Stirrups shall be fabricated from reinforcing bars with the same yield strength as that used for the main longitudinal reinforcement.
i. Allowable clear span without stirrups applicable to all lintels of the same depth,D. Top and bottom reinforcement for lintels without stirrups shall be not less than the least
amount of reinforcement required for a lintel of the same depth and loading condition with stirrups. All other spans require stirrups spaced at not more than_d_/2.
j. Where concrete with a minimum specified compressive strength of 3,000 psi is used, clear spans for lintels without stirrups shall be permitted to be multiplied by 1.05.
Frequently asked questions
What if my boiler is a coil‑type used for domestic hot water rather than space heating — do I still need a low‑water cutoff?
If the coil‑type boiler (or water‑tube boiler) requires forced circulation to avoid overheating, you may use an approved flow‑sensing device in the outlet piping in lieu of a low‑water cutoff per § 1008.1. Otherwise install a low‑water cutoff.
Do existing boilers have to be retrofitted with these combustion regulators?
§ 1009.1 states the listed combustion regulator requirements are retroactive, so the obligation is set forth in that section; verify the specific retroactivity/application with the AHJ.
Who determines the low‑water cutoff setpoint?
The low‑water cutoff must shut off the energy source at a setpoint in accordance with the boiler manufacturer’s instructions — the manufacturer’s instructions determine the numeric setpoint; the installer must follow them. § 1008.1
Can a safety limit be used as an operating control in lieu of the combustion regulators required by § 1009.1?
No. Safety limit devices are intended to shut down burners to prevent exceedance of allowed temperature or pressure and are not to be used as operating controls; combustion regulator requirements in § 1009.1 are separate. See related limit control language in § 904.5.
Where must relief valve discharge terminate?
Discharge piping for relief valves must be sized and routed to discharge safely (near the floor, not trapped, not threaded at the terminal end, and so as not to cause injury or damage) per Sections covering safety/relief valve discharge (see § 1005.1–§ 1005.4). These requirements apply to the valves required by § 1009.1(2).
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California Mechanical Code