CMC · California Mechanical Code
What controls and limit devices are required for automatic boilers?
Automatic boilers must be fitted with the specific safety and operating controls named in **§ 1003.2.1** — either by following **ASME CSD‑1** or by installing the devices listed in **Table 1003.2.1** (examples: two high‑limit controls with manual reset for many hot‑water boilers, a low‑water level cutoff or approved flow sensor, one flame‑failure device per burner, and required fuel‑shutoff interlocks). All devices must be listed/approved or accepted by the Authority Having Jurisdiction.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Automatic boilers must be fitted with approved electrical, mechanical, safety and operating controls; these controls must be either those called out in ASME CSD‑1 or the devices shown in Table 1003.2.1 — the California Mechanical Code makes this explicit in § 1003.2.1. The general approval/installation requirement for controls is set in § 1003.2.
The single most important rule: automatic boilers must have the specific safety and operating controls shown in the code (or meet ASME CSD‑1) — you cannot substitute them without approval. § 1003.2.1.
Requirements in detail
How the rules are set
- The basic approval/installation requirement: § 1003.2 requires required electrical, mechanical, safety, and operating controls to be approved by a recognized testing agency or accepted by the Authority Having Jurisdiction.
- The automatic‑boiler specific directive: § 1003.2.1 requires automatic boilers to be equipped with controls and limit devices in accordance with ASME CSD‑1 or Table 1003.2.1. The AHJ may approve alternate compliance for some solid‑fuel units.
Decision-relevant controls (summary table)
The table below collects the decision‑making dimensions (when you must provide a device, typical thresholds) and the specific CMC reference(s). This is a synthesis of the CMC text and Table 1003.2.1 footnotes.
| Control / limit device | When required / decision trigger | Minimum / required characteristic (decision value) | Code Reference |
|---|---|---|---|
| Approved controls and listed devices | All required electrical, mechanical, safety and operating controls for boilers | Devices must be approved/listed or accepted by AHJ | § 1003.2 |
| Choice of standard | For automatic boilers, follow ASME CSD‑1 or Table 1003.2.1 | Either ASME CSD‑1 compliance or the Table device set | § 1003.2.1 and Table 1003.2.1 |
| Two high‑temperature (high‑limit) controls | Automatic hot‑water heating, low‑pressure hot‑water heating, and power hot‑water boilers | Two high‑temperature limit controls; manual reset on controls; higher setting interlocked to shut off main fuel | Table text / commentary (see Table 1003.2.1 notes) |
| Low‑water level (or equivalent) | Automatic hot‑water, power boilers — to prevent damage from low water | One low‑water level limit control with manual reset, interlocked to shut off fuel; coil‑type boilers may use an approved low‑water flow sensing device instead | Table notes / §1003.3 commentary |
| Flame failure / flame proving device | Every automatic boiler burner | One flame failure device on each burner that proves ignition source presence (timing and allowed exceptions vary by boiler group and ignition type) | Table 1003.2.1 footnote and timing table |
| Fuel safety shutoff valves | Boiler groups C, D and H (and other group rules in Table) | Approved automatic‑reset safety shutoff valve for main burner; additional valve(s) required for some oil/gas pressures — interlocked to control devices | Table notes / footnotes in Table 1003.2.1 |
| Draft / combustion air interlocks | Forced/induced draft systems or gas power burners | Controls interlocked to shut off fuel on draft failure or low combustion airflow; single motor driving fan & oil pump may be exempt from separate control | Table 1003.2.1 notes |
| Start‑up / purge / low‑fire start | Boilers (groups C, D, H) with larger firing rates | Low‑fire start for > 400,000 Btu/h per combustion chamber (typically ~1/3 max firing rate) and specified purge air changes before ignition | Table notes / Table 1003.2.1 |
Notes on the table:
- The CMC places the detailed matrix of which devices apply to which boiler group, fuel and input ranges in Table 1003.2.1 — consult the Table for group‑by‑group specifics. The Table header and footnotes set timing, burner‑proofing, and special device rules.
- Many Table footnotes state timing limits for trial for pilot/main burner, exceptions for direct electric ignition and intermittent pilots, and other performance details — these are part of the required device function, not optional features.
Required interlocks and electrical practice
- Controls and limit device systems must be properly grounded and normally operate at not more than 150 volts (with limited exceptions for reuse of existing 220 V equipment approved by the building official). Control circuits must interrupt the ungrounded side and be provided with a readily accessible manual disconnect. (Table commentary / related CMC text)
Exceptions & special cases
- ASME CSD‑1 compliance is an accepted alternative to following Table 1003.2.1; either path meets the CMC requirement for automatic boiler controls. § 1003.2.1.
- Some package boilers approved by a nationally recognized testing agency (and below certain input thresholds) may be exempt from manual‑reset requirements on the high‑temperature limit (see Table notes and the package‑boiler exception). The Table/notes identify these package‑boiler exceptions.
- Coil‑type or flash steam boilers: where forced circulation is required, an approved flow sensing device may be substituted for a low‑water level cutoff to protect against overheating.
- The Authority Having Jurisdiction (AHJ) has latitude to accept alternate arrangements or approve solid‑fuel boilers to comply with the gas/oil automatic boiler safety requirements when appropriate. § 1003.2.1.
If a specific Table entry or footnote is needed for a particular boiler group, refer to Table 1003.2.1 directly — the table assigns devices by fuel type, boiler group, and input (Btu/h) ranges.
Common mistakes
- Treating a safety limit as an operating control. The code explicitly forbids using safety limit controls as normal operating controls — safety limits must only shut the boiler down when unsafe conditions occur. (See Table/notes and related boiler control text.)
- Omitting a required manual reset where the Table/notes require it (e.g., one of the high‑limit controls or the low‑water level limit on many automatic boilers). Verify the package‑boiler exception before omitting manual reset.
- Not providing one flame‑failure device per burner (the Table footnotes require flame proving per burner, with certain ignition‑type exceptions).
- Failing to interlock draft/air‑flow devices to fuel shutoff on forced‑draft systems — a common oversight on retrofit installations.
- Reusing existing control equipment at higher voltages without AHJ approval — the CMC limits normal control voltage and requires interrupting the ungrounded conductor.
Worked example — concrete scenario
Scenario: You are installing an automatic hot‑water heating boiler with a rated input of 350,000 Btu/h (package boiler).
What the CMC requires (apply § 1003.2.1 / Table 1003.2.1):
- Follow ASME CSD‑1 or the device list in Table 1003.2.1 for an automatic hot‑water boiler. § 1003.2.1.
- Provide two high‑temperature limit controls, both manual reset, with the higher setting interlocked to shut off the main fuel. This is required for automatic hot‑water heating boilers per the CMC text and Table notes. (If the boiler is a listed package unit below the input exception, confirm whether the manual‑reset requirement is waived by the manufacturer’s listing.)
- Provide one low‑water level limit control with manual reset, interlocked to shut off fuel (unless the boiler is an approved package hot‑water supply boiler where the low‑water limit is not required). Testability without draining the system is also specified.
- Provide a flame failure device that proves the presence of ignition at the burner — one per burner per the Table footnote.
- Ensure all controls are approved/listed or accepted by the AHJ and the control wiring meets the grounding/voltage practices described in the code.
Bottom line for this 350,000 Btu/h boiler: expect two high‑limit controls (manual reset), one low‑water limit (manual reset) unless covered by a package‑boiler listing exception, flame proving per burner, and the usual interlocks and approvals — all per § 1003.2.1 and Table 1003.2.1.
Related provisions
- § 1003.2 — General controls requirement (approval/listing and electrical suitability).
- § 1003.2.1 — Automatic boilers must follow ASME CSD‑1 or Table 1003.2.1.
- Table 1003.2.1 — Matrix of controls and limit devices by boiler group, fuel, and input; includes footnotes for timing, flame proving and special device rules.
- § 1003.3 — Required gauges for automatic boilers (pressure, temperature, oil/gas pressures, stack temperature, etc.).
- Related electrical/control practice and grounding limits (control voltage, manual disconnect): (CMC text commentary near Chapters 10 & Table notes).
If you need the exact device list for a particular boiler group and fuel/input range, I can extract the specific rows and footnotes from Table 1003.2.1 and show which devices apply to that exact boiler classification. The CMC Table contains group‑by‑group assignments and the timing/performance footnotes that control how devices must operate.
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
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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 § 1104.3 High relevance — show source text
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
required. Boiler groups C and D using gas in excess of 1 psi (7 kPa) pressure shall be provided with a permanent and ready means for making periodic tight ness checks of the main fuel safety shutoff valves.
11 Control and limit device systems shall be grounded with operating voltage not to exceed 150 volts, except that, upon approval by the building official, exist ing control equipment to be reused in an altered boiler control system shall be permitted to use 220 volts single phase with one side grounded, provided such
voltage is used for all controls. Control and limit devices shall interrupt the ungrounded side of the circuit. A readily accessible means of manually discon necting the control circuit shall be provided with controls so arranged that where they are de-energized, the burner shall be inoperative.
2025 CALIFORNIA MECHANICAL CODE 223
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224 2025 CALIFORNIA MECHANICAL CODE
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 11 – REFRIGERATION
(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
|Adopting Agency
Adopt Entire Chapter
Adopt Entire Chapter as
amended (amended sections
listed below)
Adopt only those sections
that are listed below
Chapter/Section
1104.3 Exception
1108.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
2025 CALIFORNIA MECHANICAL CODE xv
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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 § 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 § 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.
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 § 0.8 High relevance — show source text
the main burner, except that boiler groups A, B, E, F, and G, which are equipped with direct electric ignition, shall monitor the main burner, and boiler
groups using interrupted pilots shall monitor the main burner after the prescribed limited trial and ignition periods. Boiler group A, equipped with continu ous pilot, shall accomplish 100 percent shutoff within 90 seconds upon pilot flame failure. The use of intermittent pilots in boiler group C is limited to
approved burner units.
3 In boiler groups B, C, and D a 90 second main burner flame failure limit shall be permitted to be applied where continuous pilots are provided on manufac turer assembled boiler-burner units that have been approved by an approved testing agency in accordance with nationally recognized standards approved by
the building official. Boiler groups F and G equipped to re-energize their ignition systems within 0.8 second after main burner flame failure will be permit ted 30 seconds for group F or 15 seconds for group G to re-establish their main burner flames.
4 Boiler groups C and D shall have controls interlocked to accomplish a non-recycling fuel shutoff upon high or low gas pressure, and boiler groups F, G, and
H using steam or air for fuel atomization shall have controls interlocked to accomplish a nonrecycling fuel shutoff upon low atomizing steam or air pressure.
Boiler groups F, G, and H equipped with a preheated oil system shall have controls interlocked to provide fuel shutoff upon low oil temperature.
5 Automatic boilers shall have controls interlocked to shut off the fuel supply in the event of draft failure where forced or induced draft fans are used or, in the
event of low combustion airflow, where a gas power burner is used. Where a single motor directly driving both the fan and the oil pump is used, a separate
control is not required.
6 Boiler groups C, D, and H, where firing in excess of 400 000 Btu/h (117 kW) per combustion chamber, shall be provided with low fire start of its main burner
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
CMC § 2025 High relevance — show source text
Chapter 7 Combustion Air. Chapter 7 regulates combustion air requirements for ventilation and dilution of flue gases for appliances installed in buildings. Fuel-gas appliances not regulated by chapter include direct vent appliances and Type I clothes dryers. Makeup air requirements for Type I clothes dryers are located in Chapter 5. Chapter 7 provides acceptable methods for supplying satisfactory combustion air to ensure proper combustion. Combustion air can be supplied by using indoor combustion air or by introducing the air from the outdoors.
Combustion is the rapid oxidation of fuel to release energy. The oxygen required to release the energy from the fuel normally comes from the air. Incomplete combustion of fuel occurs when inadequate oxygen is provided to the appliance. Combustion is needed to provide ventilation cooling for the casing and internal controls. When a lack of oxygen occurs, some of the carbon is not oxidized, and carbon monoxide forms.
Chapter 8 Chimneys and Vents. Chapter 8 regulates the installation, design, and construction of venting systems for fuel-burning appliances. The provisions addressed within this chapter follow procedures an installer would use to design or evaluate a venting system. Many requirements apply to the design and construction of venting systems, chimneys, installation of gas vents, and the sizing of venting system for a Category I appliance. Sizing venting systems require rigorous engineering calculations. However, the venting sizing requirements and sizing tables in this chapter already perform the calculations for the benefit of the end user.
Combustion appliances produce products of incomplete combustion, including potentially harmful carbon monoxide (CO). It is desirable to vent these products to the outdoors. Although the gas is clean-burning fuel, the products of combustion must not be allowed to collect within a building.
Chapter 9 Installation of Specific Appliances. Chapter 9 regulates the minimum requirements for the design, construction and installation of specific appliances. The provisions address the minimum requirements for gas-fired appliances, oil-fired appliances, wood-fired appliances, and electric-type appliances. In addition to the requirements of this chapter, appliances are also required to comply with the general requirements of Chapter 3.
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
CMC § 1010.2 High relevance — show source text
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
1013.6 Automatic Steam-Heating Boilers. . . . . . . . . . . . . . . . . . . . . . 221
1013.7 Unfired Pressure Vessels . . . . . . . 221
1014.0 Operation and Maintenance of
Boilers and Pressure Vessels. . . . 221
1014.1 General. . . . . . . . . . . . . . . . . . . . . 221
Table 1003.2.1 Controls and Limit Devices for
Automatic Boilers . . . . . . . . . . . . . 222
CHAPTER 11 REFRIGERATION . . . . . . . . . . . . 225
1101.0 General. . . . . . . . . . . . . . . . . . . . . 227
1101.1 Applicability. . . . . . . . . . . . . . . . . . 227
1101.2 Equipment . . . . . . . . . . . . . . . . . . 227
Part I Refrigeration Systems . . . . . . . . 227
1102.0 Refrigeration Systems . . . . . . . . . 227
1102.1 General. . . . . . . . . . . . . . . . . . . . . 227
1102.2 Ammonia Refrigeration Systems . . 227
1102.3 Refrigerants . . . . . . . . . . . . . . . . . 227
1103.0 Classification . . . . . . . . . . . . . . . . 227
1103.1 Classification of Refrigerants . . . . 227
CMC § 1003.2.1 High relevance — show source text
**
BTU/H|0 - 400 000|400 001 -
2 500 000|2 500 001 -
5 000 000|Over
5 000 000|0 - 400 000|400 001 -
1 000 000|1 000 001 -
3 000 000|Over
3 000 000|All|12 500 000
or more|Any| |FUEL|FUEL|FUEL|Gas|Gas|Gas|Gas|Oil|Oil|Oil|Oil|Electric|Gas, Oil
and/or
Coal|Heat
Recovery
Steam
Generator| |BOILER
GROUP|BOILER
GROUP|BOILER
GROUP|A|B|C|D|E|F|G|H|K|L|M|222 2025 CALIFORNIA MECHANICAL CODE
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BOILERS AND PRESSURE VESSELS
FOOTNOTES FOR TABLE 1003.2.1 (continued)
1 Fuel input shall be determined by one of the following:
The burner input shall not exceed the input shown on the burner nameplate or as otherwise identified by the manufacturer.
The nominal boiler rating, as determined by the building official, plus 25 percent.
2 Automatic boilers shall have one flame failure device on each burner, which shall prove the presence of an ignition source at the point where it will ignite
the main burner, except that boiler groups A, B, E, F, and G, which are equipped with direct electric ignition, shall monitor the main burner, and boiler
groups using interrupted pilots shall monitor the main burner after the prescribed limited trial and ignition periods. Boiler group A, equipped with continu ous pilot, shall accomplish 100 percent shutoff within 90 seconds upon pilot flame failure. The use of intermittent pilots in boiler group C is limited to
approved burner units.
3 In boiler groups B, C, and D a 90 second main burner flame failure limit shall be permitted to be applied where continuous pilots are provided on manufac turer assembled boiler-burner units that have been approved by an approved testing agency in accordance with nationally recognized standards approved by
the building official. Boiler groups F and G equipped to re-energize their ignition systems within 0.8 second after main burner flame failure will be permit ted 30 seconds for group F or 15 seconds for group G to re-establish their main burner flames.
4 Boiler groups C and D shall have controls interlocked to accomplish a non-recycling fuel shutoff upon high or low gas pressure, and boiler groups F, G, and
H using steam or air for fuel atomization shall have controls interlocked to accomplish a nonrecycling fuel shutoff upon low atomizing steam or air pressure.
Boiler groups F, G, and H equipped with a preheated oil system shall have controls interlocked to provide fuel shutoff upon low oil temperature.
5 Automatic boilers shall have controls interlocked to shut off the fuel supply in the event of draft failure where forced or induced draft fans are used or, in the
event of low combustion airflow, where a gas power burner is used. Where a single motor directly driving both the fan and the oil pump is used, a separate
control is not required.
CMC § 904.2.1 High 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]
CMC § 1013.7 High relevance — show source text
1013.7 Unfired Pressure Vessels . . . . . . . 221
1014.0 Operation and Maintenance of
Boilers and Pressure Vessels. . . . 221
1014.1 General. . . . . . . . . . . . . . . . . . . . . 221
Table 1003.2.1 Controls and Limit Devices for
Automatic Boilers . . . . . . . . . . . . . 222
CHAPTER 11 REFRIGERATION . . . . . . . . . . . . 225
1101.0 General. . . . . . . . . . . . . . . . . . . . . 227
1101.1 Applicability. . . . . . . . . . . . . . . . . . 227
1101.2 Equipment . . . . . . . . . . . . . . . . . . 227
Part I Refrigeration Systems . . . . . . . . 227
1102.0 Refrigeration Systems . . . . . . . . . 227
1102.1 General. . . . . . . . . . . . . . . . . . . . . 227
1102.2 Ammonia Refrigeration Systems . . 227
1102.3 Refrigerants . . . . . . . . . . . . . . . . . 227
1103.0 Classification . . . . . . . . . . . . . . . . 227
1103.1 Classification of Refrigerants . . . . 227
Table 1103.1.1 Refrigerant Safety Group Classifications. . . . . . . . . . . . . . . . 227
1103.2 Classification of Refrigeration Systems . . . . . . . . . . . . . . . . . . . . 227
1103.3 Higher Flammability Refrigerants . . . . . . . . . . . . . . . . . 227
1104.0 Requirements for Refrigerant and Refrigeration System Use . . . 227
1104.1 System Selection . . . . . . . . . . . . . 227
1104.2 Refrigerant Concentration Limit (RCL) . . . . . . . . . . . . . . . . . . 227
Table 1104.1 Permissible Refrigeration Systems . . . . . . . . . . . . . . . . . . . . 228
1104.3 Institutional Occupancies . . . . . . . 229
1104.4 Industrial Occupancies and Refrigerated Rooms . . . . . . . . . . . 229
1104.5 Flammable Refrigerants . . . . . . . . 229
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TABLE OF CONTENTS
1104.6 Group A2L Refrigerants for Human Comfort . . . . . . . . . . . . . . 229
110.4.7 Applications for Human Comfort and for Nonindustrial
Occupancies. . . . . . . . . . . . . . . . . 230
1104.8 Refrigerant Type and Purity . . . . . 230
1104.9 Changing Refrigerants . . . . . . . . . 231
Frequently asked questions
What does "automatic boiler" mean for these requirements?
An automatic boiler in the CMC context is a boiler that starts and stops automatically and requires safety and operating controls; the controls requirement is stated in § 1003.2.1.
Can I follow ASME CSD‑1 instead of Table 1003.2.1?
Yes — § 1003.2.1 allows compliance by meeting ASME CSD‑1 instead of using the Table. The AHJ must accept the method chosen.
Are low‑water flow devices allowed instead of low‑water level cutoffs?
Yes — for coil‑type boilers that require forced circulation, an approved low‑water flow sensing device may be used instead of a low‑water‑level limit to protect the boiler.
Do all boilers need two high‑temperature limits?
Not all boilers in all configurations — but automatic hot‑water heating, low‑pressure hot‑water heating, and power hot‑water boilers are required to have two high‑temperature limit controls with manual reset (with some package boiler exceptions explained in the Table/notes).
Is flame proving required for each burner?
Yes — the Table footnotes require one flame failure/flame proving device on each burner, subject to specific ignition‑type exceptions and timing requirements in the Table notes.
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