204.0 B – — 2025 California Mechanical Code
California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-10-19 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Mechanical Code (Title 24, Part 4) § 204.0 · Effective January 1, 2026 · Official source: Building Standards Commission
Backflow. The flow of water or other liquids, mixtures, or substances into the distributing pipes of a potable supply of water from sources other than its intended source.
Baffle Plate. An object placed in or near an appliance to change the direction or retard the flow of air, air-fuel mixtures, or flue gases. [NFPA 96:3.3.8]
Boiler. A closed vessel used for heating water or liquid, or for generating steam or vapor by direct application of heat from combustible fuels or electricity.
Boiler, Automatic. A boiler equipped with certain controls and limit devices.
Boiler, High-Pressure. A boiler for generating steam at gauge pressures in excess of 15 psig (103 kPa), or for heating water to a temperature in excess of 250°F (121°C) or at a gauge pressure in excess of 160 psig (gauge pressure of 1103 kPa). [NFPA 211:3.3.14.2]
Boiler, Hot-Water-Heating. A boiler having a volume exceeding 120 gallons (454 L), a heat input exceeding 200 000 Btu/h (58.6 kW), or an operating temperature exceeding 210°F (99°C) that provides hot water to be used externally to itself.
Boiler, Low-Pressure Hot-Water-Heating. A boiler furnishing hot water at pressures not exceeding 160 psig (1103 kPa) and at temperatures not exceeding 250°F (121°C).
Boiler, Low-Pressure Steam-Heating. A boiler furnishing steam at pressures not exceeding 15 psig (103 kPa).
Boiler, Miniature. A power boiler having an internal shell diameter of 16 inches (406 mm) or less, a gross volume of 5 cubic feet (0.14 m [3] ) or less, a heating surface of 20 square feet (1.86 m [2] ) or less (not applicable to electric boilers), and not exceeding 100 psig (689 kPa).
Boiler, Package. A class of boiler defined herein and shall be a boiler equipped and shipped complete with fuel-burning equipment, automatic controls and accessories, and mechanical draft equipment.
Boiler, Power. A boiler in which steam is generated at pressures exceeding 15 psig (103 kPa).
Boiler, Power Hot Water (High Temperature Water Boiler). A boiler used for heating water or liquid to a pressure exceeding 160 psig (1103 kPa) or to a temperature exceeding 250°F (121°C).
Boiler, Steam-Heating. A boiler operated at pressures not exceeding 15 psig (103 kPa) for steam.
Boiler, Water Heater or Hot-Water-Heating. An appliance designed primarily to supply hot water for domestic or commercial purposes and equipped with automatic controls limiting water temperature to a maximum of 210°F (99°C).
Boiler Room. A room where boilers are installed.
Bonding Conductor or Jumper. A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected. [NFPA 70:100(I)]
Borehole. A vertical or horizontal shaft typically cored, drilled or bored into the earth for geothermal system installations.
Breathing Zone. The region within an occupiable space between planes 3 inches and 72 inches (76 mm and 1829 mm) above the floor and exceeds 2 feet (610 mm) from the walls or fixed air-conditioning equipment. [ASHRAE 62.1:3]
Breathing Zone Outdoor Airflow. The outdoor airflow required in the breathing zone of the occupiable space or spaces in a ventilation zone.
Breeching. A metal connector for medium- and high-heat appliances.
Broiler. A general term including broilers, salamanders, barbecues, and other devices cooking primarily by radiated heat, excepting toasters. [NFPA 54:3.3.14]
BTU/H. The listed maximum capacity of any appliance, absorption unit, or burner expressed in British thermal units input per hour, unless otherwise noted.
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Building . [HCD 1 & HCD 2] Any structure used or intended for supporting or sheltering any use or occupancy.
Exceptions: “Building” shall not include the following:
(1) Any mobilehome as defined in Health and Safety Code Sec- tion 18008.
(2) Any manufactured home as defined in Health and Safety Code Section 18007.
(3) Any commercial modular as defined in Health and Safety Code Section 18001.8 or any special purpose commercial modular as defined in Health and Safety Code Section 18012.5.
(4) Any recreational vehicle as defined in Health and Safety Code Section 18010.
(5) Any multifamily manufactured home, as defined in Health and Safety Code Section 18008.7.
For additional information, see Health and Safety Code Sec- tion 18908.
Building Code. The building code that is adopted by this jurisdiction. [HCD 1, HCD 2, OSHPD 1, 1R, 2, 3, 4, 5, 6 & SFM] “Building Code” shall mean the California Build- ing Code, Title 24, Part 2. Building Official. See Authority Having Jurisdiction. For applications listed in Section 1.11.0 regulated by the Office of the State Fire Marshal “Building Official” is the officer charged with the administration and enforcement of this code, or a reg- ular deputy. See “Enforcing Agency.” For the State of Califor- nia, “Building Official” shall be the “Enforcing Agency” as specified in Section 1.11.0.
Burner, Automatic Boiler. A device to convey fuel into the combustion chamber in proximity to its combustion air supply so as to permit a stable, controlled heat release compatible with the burner design and that is equipped with an ignition system to reliably ignite the entire heat release surface of the burner assembly.
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