206.0 – D –

Damper. A valve or plate for controlling draft or the flow of gases, including air. [NFPA 211:3.3.52]

Ceiling Radiation Damper. A listed device installed in a ceiling membrane of a fire-resistance-rated floorceiling or roof-ceiling assembly to automatically limit the radiative heat transfer through an air inlet/outlet opening. [NFPA 5000:3.3.140.1]

Combination Fire/Smoke Damper. An automaticclosing metal assembly consisting of one or more louvers, blades, slats, or vanes that closes upon detection of heat or smoke as to restrict the passage of flame and smoke.

Corridor Damper. An automatic closing metal assembly consisting of one or more louvers, blades, slats, or vanes that closes upon detection of heat or smoke as to restrict the passage of flame and smoke used where air ducts penetrate horizontal openings in fire-resistancerated corridors.

Fire Damper. An automatic-closing metal assembly consisting of one or more louvers, blades, slats, or vanes that closes upon detection of heat so as to restrict the passage of flame.

Smoke Damper. A damper arranged to seal off airflow automatically through a part of an air duct system so as to restrict the passage of smoke.

Volume Damper. A device that, when installed, will restrict, retard, or direct the flow of air in any duct, or the products of combustion in any heat-producing equipment, its vent connector, vent, or chimney.

Department. [HCD 1 & HCD 2] “Department” means the Department of Housing and Community Development.

Design Flood Elevation. The elevation of the “design flood,” including wave height, relative to the datum specified on the community’s legally designated flood hazard map. In areas designated as Zone AO, the design flood elevation is the elevation of the highest existing grade of the building’s perimeter plus the depth number (in feet) specified on the flood hazard map. In areas designated as Zone AO where a depth number is not specified on the map, the depth number is taken as being equal to 2 feet (610 mm).

Detection Devices. Electrical, pneumatic, thermal, mechanical, or optical sensing instruments, or subcomponents of such instruments, whose purpose is to cause an automatic action upon the occurrence of some preselected event. [NFPA 96:3.3.17] In the context of this document, the event in question could be excessive temperature or flame, and the action could be the operation of a fire-extinguishing system.

Dips. Depression or cup like places in horizontal duct runs in which liquids could accumulate.

Direct Exchange (DX). A ground-source heat pump that circulates a refrigerant through a closed-loop system. Also known as direct expansion unit or direct expansion system.

Direct Gas-Fired Nonrecirculating Heating and Forced Ventilation Appliances for Commercial and Industrial Application. A nonrecirculating direct gas-fired heating and forced ventilation appliance in which all the products of combustion generated by the appliance are released into the outdoor airstream being heated. [NFPA 54:3.3.56.2]

Direct Gas-Fired Recirculating Heating and Forced Ventilation Appliances for Commercial and Indus- trial Application. A recirculating direct gas-fired heating and forced ventilation appliance in which all of the products of combustion generated by the appliance are released into the airstream being heated. [NFPA 54:3.3.56.4]

Discharge. The final portion of a duct or pipe where the product being conveyed is emptied or released from confinement; the termination point of the pipe or duct. [NFPA 96:3.3.18]

Discrete Products in Plenums. Individual, distinct products which are non-continuous such as pipe hangers, duct registers, duct fittings, and duct straps.

District Heating Plant. A power boiler plant designed to distribute hot water or steam to users located off the premises.

Draft Hood. A nonadjustable device built into an appliance, or made a part of the vent connector from an appliance, that is designed to:

(1) Provide for the ready escape of the flue gases from the appliance in the event of no draft, backdraft, or stoppage beyond the draft hood.

(2) Prevent a backdraft from entering the appliance.

(3) Neutralize the effect of stack action of the chimney or gas vent upon the operation of the appliance. [NFPA 54:3.3.30]

Driver Building. One or more building(s) or facility(ies) that determined the upper and lower temperature limits of hot fluid or cold fluid delivery system.

Dual Purpose Water Heater. An appliance intended to be a heat source for both space heating and domestic hot water applications.

Duct. A tube or conduit for transmission of air, fumes, vapors, or dust. This definition shall not include:

(1) A vent, vent connector, or chimney connector.

(2) A tube or conduit wherein the pressure of the air exceeds 1 psi (7 kPa).

(3) The air passages of listed self-contained systems.

Duct, Environmental Air. Ducting used for conveying air at temperatures not exceeding 250°F (121°C) to or from occupied areas of any occupancy through other than heating or air-conditioning systems, such as ventilation for human usage, domestic kitchen range exhaust, bathroom exhaust ducts, locker room exhaust ducts, shower room exhaust ducts, janitor’s closet exhaust ducts, and domestic-type clothes dryer exhaust ducts.

Duct, Grease. A containment system for the transportation of air and grease vapors that is designed and

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36 2025 CALIFORNIA MECHANICAL CODE

DEFINITIONS

Electrical Code. The National Electrical Code promulgated by the National Fire Protection Association, as adopted by this jurisdiction. [HCD 1 & HCD 2] Whenever the term “Electrical Code” is used in this code, it shall mean the Cal- ifornia Electrical Code, Title 24, Part 3.

Emergency Alarm System. A system intended to provide notification and warning of abnormal conditions and summon appropriate aid.

Emergency Control Station. An approved location on the premises where signals from emergency equipment are received.

Enforcing Agency. [HCD 1, HCD 2, SFM, OSHPD 1, 1R, 2, 3, 4, 5 & 6] “Enforcing Agency” is the designated department or agency as specified by statute and regulation.

Energy Recovery Ventilation (ERV) System. A device intended to provide outdoor ventilation air, and in the process transfer energy between the intake and exhaust airstreams for the purpose of preheating, precooling, humidifying, or dehumidifying outdoor ventilation air prior to supplying such air to a conditioned space.

Engineering Methods. Design methods that rely on the application of mathematics, sciences, empirical evidence, and engineering principles. [NFPA 54:3.3.34]

Equipment. A general term including materials, fittings, devices, appliances, and apparatus used as part of or in connection with installations regulated by this code.

Evaporative Cooler. A device used for reducing the sensible heat of air for cooling by the process of evaporation of water into an airstream.

Evaporative Cooling System. Equipment intended or installed for the purpose of environmental cooling by an evaporative cooler from which the conditioned air is distributed through ducts or plenums to the conditioned space or zone.

Evaporator. Part of a refrigeration system in which liquid refrigerant is vaporized to produce refrigeration.

Excess Flow Valve (EFV). A valve designed to activate when the fuel gas passing through it exceeds a prescribed flow rate. [NFPA 54:3.3.98.3]

Expansion Tank. A vessel used to protect closed systems from excessive pressure.