IMC Chapter 2 - Complete Definitions Reference

🔎 Field lock: Add this to your cover sheet - "Definitions per IMC Chapter 2; if undefined, see IBC/IFC/IFGC/IPC; if still undefined, use commonly accepted meaning per IMC 201.4." This one-line aligns your reviewer, contractor, and AHJ to the same definition path.

Access (To) - That which enables a device, appliance, or equipment to be reached by ready access or by a means that first requires removal or movement of a panel or similar obstruction. See also Ready Access. Air - Air supplied to mechanical equipment and appliances for combustion, ventilation, cooling, and similar purposes. Standard air: 70 degrees F (21 degrees C) and 29.92 in. Hg (101.3 kPa). Air, Exhaust - Air being removed from any space, appliance, or equipment and conveyed directly to the atmosphere via openings or ducts.

Air, Makeup - Any combination of outdoor and transfer air intended to replace exhaust air and exfiltration. Air, Outdoor - Ambient air that enters a building through a ventilation system, through intentional openings for natural ventilation, or by infiltration. Air, Transfer - Air moved from one indoor space to another. Air Conditioning - Treatment of air to simultaneously control temperature, humidity, cleanness, and distribution to meet the requirements of a conditioned space.

Air Dispersion System - Any diffuser system designed to convey air within a room or space and diffuse air into that space while operating under positive pressure. Commonly constructed of fabric or plastic film. Air Distribution System - Any system of ducts, plenums, and air-handling equipment that circulates air within a space, including systems made up of one or more air-handling units. Air-Conditioning System - A system consisting of heat exchangers, blowers, filters, supply/exhaust/return ducts, and all apparatus installed in connection therewith.

Air-Handling Unit (AHU) - A blower or fan used for the purpose of distributing supply air to a room, space, or area. Alteration [A] - A change in a mechanical system that involves an extension, addition, or change to the arrangement, type, or purpose of the original installation. Ambulatory Care Facility [BG] - Buildings or portions thereof used to provide medical, surgical, psychiatric, nursing, or similar care on a less-than-24-hour basis to persons rendered incapable of self-preservation by the services provided.

Appliance - A device or apparatus manufactured and designed to utilize energy and for which this code provides specific requirements. Appliance, Existing - Any appliance regulated by this code that was legally installed prior to the effective date of this code, or for which a permit to install has been issued. Appliance, Vented - An appliance designed and installed so that all products of combustion are conveyed directly to the outdoor atmosphere through an approved chimney or vent system.

Appliance Type: High-Heat Appliance - Combustion products at the flue entrance exceed 2,000 degrees F (1093 degrees C) under normal operating conditions. Low-Heat Appliance (Residential Appliance) - Combustion products at the flue entrance are 1,000 degrees F (538 degrees C) or less under normal operating conditions. Medium-Heat Appliance - Combustion products at the flue entrance are more than 1,000 degrees F (538 degrees C) but not greater than 2,000 degrees F (1093 degrees C). Approved [A] - Acceptable to the code official.

Approved Agency [A] - An established and recognized organization regularly engaged in conducting tests, furnishing inspection services, or furnishing product evaluation or certification, as approved by the code official. Automatic Boiler - Any class of boiler equipped with the controls and limit devices specified in Chapter 10.

Boiler Room - A room primarily utilized for the installation of a boiler. Brazed Joint - A gastight joint obtained by joining metal parts with metallic mixtures or alloys that melt above 1,000 degrees F (538 degrees C) but below the melting temperature of the parts being joined. Brazing - A metal joining process using a nonferrous filler metal with a melting point above 1,000 degrees F (538 degrees C) but below the base metal. Filler is distributed by capillary attraction.

Breathing Zone - The region within an occupied space between planes 3 and 72 inches (76 and 1829 mm) above the floor and more than 2 feet (610 mm) from the walls or fixed air-conditioning equipment. BTU - British thermal unit: the quantity of heat required to raise the temperature of 1 pound (454 g) of water by 1 degrees F (0.56 degrees C). 1 Btu = 1055 J. Building [A] - Any structure utilized or intended for supporting or sheltering any occupancy.

Ceiling Radiation Damper [BF] - A listed device installed in a ceiling membrane of a fire-resistance-rated floor/ceiling or roof/ceiling assembly to limit automatically the radiative heat transfer through an air inlet/outlet opening. Classified for static systems (auto-shutdown on fire) or dynamic systems (continue to operate during fire). ⚠ CRD != fire damper. Chimney - A primarily vertical structure containing one or more flues for carrying gaseous products of combustion and air from a fuel-burning appliance to the outdoor atmosphere.

Factory-Built Chimney - A listed and labeled chimney composed of factory-made components, assembled per manufacturer's instructions and listing conditions. Masonry Chimney - A field-constructed chimney of solid masonry units, bricks, stones, or concrete. Metal Chimney - A field-constructed chimney of metal. Chimney Connector - A pipe that connects a fuel-burning appliance to a chimney. Clearance - The minimum distance through air between the heat-producing surface of mechanical appliance, device, or equipment and the surface of the combustible material or assembly.

Closed Combustion Solid-Fuel-Burning Appliance - A heat-producing appliance that employs a combustion chamber without openings other than the flue collar, fuel charging door, and adjustable combustion-air openings. Clothes Dryer - An appliance used to dry wet laundry by means of heat. Code [A] - These regulations, subsequent amendments, or any emergency rule lawfully adopted by the authority having jurisdiction. Code Official [A] - The officer or other designated authority charged with administration and enforcement of this code, or a duly authorized representative.

Combination Fire/Smoke Damper [BF] - A listed device installed in ducts and air transfer openings designed to close automatically upon detection of heat and resist passage of both flame and smoke. Operable automatically, by a smoke detection system, and from a fire command center where required. Combustible Assembly - Wall, floor, ceiling, or other assembly constructed of one or more component materials that are not noncombustible. Combustible Liquid [F] - A liquid with a closed cup flash point at or above 100 degrees F (38 degrees C).

Class II - Flash point >=100 degrees F (38 degrees C) and <140 degrees F (60 degrees C).

Class IIIA - Flash point >=140 degrees F (60 degrees C) and <200 degrees F (93 degrees C). Class IIIB - Flash point >=200 degrees F (93 degrees C). Combustible Material - Any material not defined as noncombustible. Combustion - Rapid oxidation of fuel accompanied by production of heat, or heat and light. Combustion Air - Air necessary for complete combustion of a fuel, including theoretical air and excess air. Combustion Chamber - The portion of an appliance within which combustion occurs.

Combustion Products - Constituents resulting from the combustion of a fuel with oxygen of the air, including inert gases but excluding excess air.

Commercial Cooking Appliances - Appliances used in a commercial food service establishment for heating or cooking food. Commercial food service is where food is prepared for sale or prepared at a scale not representative of domestic household cooking. Commercial Cooking Recirculating System - A self-contained system consisting of the exhaust hood, cooking equipment, filters, and fire suppression system. Captures cooking vapors and residues, removes contaminants from exhaust air, and recirculates air to the space. Commercial Kitchen Hoods: Backshelf Hood - Also called low-proximity or sidewall hood.

Front lower lip is low and set back from the appliance front. Always closed to the rear by a panel or wall. Double Island Canopy Hood - Placed over back-to-back appliances, open on all sides, overhanging both fronts and sides. Functions like two wall canopy hoods. Eyebrow Hood - Mounted directly to the appliance face above the opening, extending past the sides and overhanging the front to capture effluent. Pass-Over Hood - A free-standing backshelf hood constructed low enough to pass food over the top. Single Island Canopy Hood - Placed over a single appliance or appliance line, open on all sides.

More susceptible to cross drafts; requires greater exhaust airflow than wall-mounted canopy. Wall Canopy Hood - Mounted against a wall above a single appliance or line. The wall acts as a back panel, drawing makeup air across the front and increasing capture effectiveness. Compensating Hoods - Hoods with integral (built-in) makeup air supply. Makeup air can be supplied via short-circuit flow inside the hood, air curtain flow at the front face, or front-face discharge. Compressor - A specific machine, with or without accessories, for compressing a gas.

Compressor, Positive Displacement - A compressor in which increase in pressure is attained by changing the internal volume of the compression chamber. Compressor Unit - A compressor with its prime mover and accessories. Concealed Location - A location that cannot be accessed without damaging permanent parts of the building structure or finish surface. Spaces above, below, or behind readily removable panels or doors are NOT considered concealed. Condensate - The liquid that condenses from a gas (including flue gas) caused by a reduction in temperature.

Condenser - A heat exchanger designed to liquefy refrigerant vapor by removal of heat. Condensing Unit - A factory-made assembly of refrigeration components designed to compress and liquefy a specific refrigerant. Consists of one or more power-driven compressors, condensers, liquid receivers where required, and factory-supplied accessories. Conditioned Space - An area, room, or space enclosed within the building thermal envelope that is directly or indirectly heated or cooled.

Indirect conditioning occurs via openings to conditioned spaces, uninsulated walls/floors/ceilings, or uninsulated ducts/piping within the space. Construction Documents [A] - Written, graphic, and pictorial documents prepared or assembled for describing the design, location, and physical characteristics of the elements of a project necessary for obtaining a building permit. Shall be drawn to an appropriate scale. Control - A manual or automatic device designed to regulate the gas, air, water, or electrical supply to, or operation of, a mechanical system.

Conversion Burner - A burner designed to supply gaseous fuel to an appliance originally designed for another fuel. Cooking Appliance - See Commercial Cooking Appliances.

In Zone AO, the design flood elevation is the highest existing grade at the building's perimeter plus the depth number in feet specified on the map (or 2 feet if not specified). Design Working Pressure - The maximum allowable working pressure for which a specific part of a system is designed. Direct Evaporative Cooling - The evaporative cooling process where water evaporates directly into the air stream, reducing dry-bulb temperature and raising humidity level.

Direct Refrigeration System - A system in which the evaporator or condenser of the refrigerating system is in direct contact with the air or other substances to be cooled or heated. Direct Solar System - A solar thermal system in which the gas or liquid in the solar collector loop is not separated from the load. Direct-Vent Appliances [FG] - Appliances constructed and installed so that all air for combustion is derived from the outdoor atmosphere and all flue gases are discharged to the outdoor atmosphere.

Discrete Product - Noncontinuous, individual, distinct pieces such as electrical, plumbing, and mechanical products, and duct straps, fittings, registers, and pipe hangers. Draft - The pressure difference between the appliance or component and the atmosphere that causes continuous flow of air and combustion products through the gas passages to the atmosphere. Induced Draft - Pressure difference created by the action of a fan, blower, or ejector located between the appliance and the chimney or vent termination.

Natural Draft - Pressure difference created by a vent or chimney because of its height and the temperature difference between flue gases and the atmosphere. Draftstop - A material, device, or construction installed to restrict the movement of air within open spaces of concealed areas in building components such as crawl spaces, floor/ceiling assemblies, roof/ceiling assemblies, and attics. Drain-Back System - A solar thermal system in which the fluid in the solar collector loop is gravity drained from the collector into a holding tank under prescribed circumstances.

Drip - The container placed at a low point in a piping system to collect condensate from which the condensate is removable. Dry Cleaning Systems: Type I - Systems using Class I flammable liquid solvents (flash point below 100 degrees F / 38 degrees C). Type II - Systems using Class II combustible liquid solvents (flash point >=100 degrees F and <140 degrees F / 38 degrees C-60 degrees C). Type III - Systems using Class III combustible liquid solvents (flash point >=140 degrees F / 60 degrees C). Types IV and V - Systems using Class IV nonflammable liquid solvents.

Duct - A tube or conduit utilized for conveying air.

Air passages of self-contained systems are not construed as air ducts. Duct Furnace - A warm-air furnace normally installed in an air distribution duct to supply warm air for heating. Depends on a blower not furnished as part of the furnace for air circulation. Duct System - A continuous passageway for the transmission of air that, in addition to ducts, includes duct fittings, dampers, plenums, fans, and accessory air-handling equipment and appliances.

Ductless Mini-Split System - A heating and cooling system comprised of one or multiple indoor evaporator/air-handling units and an outdoor condensing unit connected by refrigerant piping and electrical wiring. Capable of cooling or heating one or more rooms without traditional ductwork. Dwelling [BG] - A building or portion thereof containing not more than two dwelling units. Dwelling Unit [A] - A single unit providing complete, independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking, and sanitation.

Electric Heating Appliance - An appliance that produces heat energy by application of electric power to resistance elements, refrigerant compressors, or dissimilar material junctions. Energy Recovery Ventilation System - Systems employing air-to-air heat exchangers to recover energy from or reject energy to exhaust air for the purpose of preheating, precooling, humidifying, or dehumidifying outdoor ventilation air prior to supplying it to a space.

Environmental Air - Air conveyed to or from occupied areas through ducts not part of the heating or air-conditioning system, such as ventilation for human usage, domestic kitchen range exhaust, bathroom exhaust, domestic clothes dryer exhaust, and parking garage exhaust. Equipment - Piping, ducts, vents, control devices, and other system components other than appliances that are permanently installed and integrated to provide control of environmental conditions for buildings. Also includes other systems specifically regulated in this code.

Equipment, Existing - Any equipment regulated by this code legally installed prior to the effective date, or for which a permit to install has been issued. 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 and appliances intended or installed for environmental cooling by an evaporative cooler from which conditioned air is distributed through ducts or plenums to the conditioned area.

Evaporator - That part of the system in which liquid refrigerant is vaporized to produce refrigeration.

Excess Air - The amount of air provided in addition to theoretical air to achieve complete combustion, preventing formation of dangerous products of combustion. Exfiltration - Uncontrolled outward air leakage from conditioned spaces through unintentional openings in ceilings, floors, and walls, caused by wind, stack effect, or imbalances between supply and exhaust airflow rates. Exhaust System - An assembly of connected ducts, plenums, fittings, registers, grilles, and hoods through which air is conducted from a space and exhausted to the outdoor atmosphere.

Extra-Heavy-Duty Cooking Appliance - Appliances utilizing open flame combustion of solid fuel at any time.

Factory-Built Fireplace - A listed and labeled fireplace and chimney system composed of factory-made components, assembled per manufacturer's instructions and listing conditions. Masonry Fireplace - A field-constructed fireplace composed of solid masonry units, bricks, stones, or concrete. Fireplace Stove - A free-standing, chimney-connected, solid-fuel-burning heater designed to be operated with fire chamber doors open or closed.

Flame Safeguard [FG] - A device that will automatically shut off the fuel supply to a main burner or group of burners when the means of ignition becomes inoperative and when flame failure occurs on the burner or group of burners. Flame Spread Index [BF] - The numerical value assigned to a material tested in accordance with ASTM E84 or UL 723. Flammable Liquids [F] - Any liquid with a flash point below 100 degrees F (38 degrees C) and vapor pressure not exceeding 40 psia (276 kPa) at 100 degrees F (38 degrees C).

Known as Class I liquids: Class IA - Flash point below 73 degrees F (23 degrees C) and boiling point below 100 degrees F (38 degrees C).

Class IB - Flash point below 73 degrees F (23 degrees C) and boiling point at or above 100 degrees F (38 degrees C). Class IC - Flash point at or above 73 degrees F (23 degrees C) and below 100 degrees F (38 degrees C). Flammable Vapor or Fumes [F] - Mixtures of gases in air at concentrations equal to or greater than the LFL and less than or equal to the upper flammability limit (UFL). Flash Point [F] - The minimum temperature corrected to 14.7 psia (101 kPa) at which the application of a test flame causes the vapors of a sample to ignite under conditions specified by the test procedure.

Determined per ASTM D56, ASTM D93, or ASTM D3278.

Flexible Air Connector - A conduit for transferring air between an air duct or plenum and an air terminal unit, or between an air duct or plenum and an air inlet or outlet. Limited in use, length, and location. Floor Area, Net - The actual occupied area, not including unoccupied accessory areas or thicknesses of walls. Floor Furnace [FG] - A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting from such space.

Flue - A passageway within a chimney or vent through which gaseous combustion products pass. Flue Connection (Breeching) - A passage for conducting the products of combustion from a fuel-fired appliance to the vent or chimney. See also Chimney Connector and Vent Connector. Flue Gases [FG] - Products of combustion and excess air. Flue Liner (Lining) - A system or material used to form the inside surface of a flue in a chimney or vent, for the purpose of protecting the surrounding structure from combustion products and conveying combustion products without leakage.

Food-Grade Fluid - Potable water or a fluid containing additives listed in accordance with the Code of Federal Regulations, Title 21, Food and Drugs, Chapter 1 (Food and Drug Administration), Parts 174-186. Fuel Gas [FG] - Natural gas, manufactured gas, liquefied petroleum gas, or a mixture of these. Fuel Oil - Kerosene or any hydrocarbon oil having a flash point not less than 100 degrees F (38 degrees C). Fuel-Oil Piping System - A closed piping system that connects a combustible liquid from a source of supply to a fuel-oil-burning appliance.

Furnace - A completely self-contained heating unit designed to supply heated air to spaces remote from or adjacent to the appliance location. Furnace Room - A room primarily utilized for the installation of fuel-burning, space-heating, and water-heating appliances other than boilers. See also Boiler Room. Fusible Plug - A device arranged to relieve pressure by operation of a fusible member at a predetermined temperature.

Grease Duct - A duct serving a Type I hood, or cooking appliances equipped with integral down-draft exhaust systems that produce grease, to convey grease-laden air from the hood or cooking appliance directly to the outdoors. Ground Source Heat Pump Loop System - Piping buried in horizontal or vertical excavations or placed in a body of water for transporting heat transfer liquid to and from a heat pump. Includes closed loop systems (liquid recirculated) and open loop systems (liquid drawn from a well or other source).

Gypsum Board [BS] - A type of gypsum panel product consisting of a noncombustible core primarily of gypsum with paper surfacing. Gypsum Wallboard [BS] - A gypsum board used primarily as an interior surfacing for building structures.

Heat Transfer Liquid - The operating or thermal storage liquid in a mechanical system, including water or other liquid base and additives at the concentration present under operating conditions used to move heat from one location to another. Refrigerants are not included. Heavy-Duty Cooking Appliance - Includes electric under-fired broilers, electric chain (conveyor) broilers, gas under-fired broilers, gas chain (conveyor) broilers, gas open-burner ranges (with or without oven), electric and gas wok ranges, smokers, smoker ovens, and electric and gas over-fired (upright) broilers and salamanders.

High-Probability Systems - A refrigeration system in which the basic design or location of components is such that a leakage of refrigerant from a failed connection, seal, or component will enter an occupancy classified area other than the machinery room. High-Side Pressure - The parts of a refrigerating system subject to condenser pressure. Hood - An air intake device used to capture by entrapment, impingement, adhesion, or similar means, grease, moisture, heat, and similar contaminants before they enter a duct system. Type I Hood - A kitchen hood for collecting and removing grease vapors and smoke.

Equipped with a fire suppression system. Type II Hood - A general kitchen hood for collecting and removing steam, vapor, heat, odors, and products of combustion. Hydrogen Generating Appliance [FG] - A self-contained package or factory-matched packages of integrated systems for generating gaseous hydrogen using electrolysis, reformation, chemical, or other processes. Ignition Source - A flame, spark, or hot surface capable of igniting flammable vapors or fumes. Includes appliance burners, burner ignitors, and electrical switching devices.

Immediately Dangerous to Life or Health (IDLH) [F] - The concentration of airborne contaminants that poses a threat of death, immediate or delayed permanent adverse health effects, or effects that could prevent escape. Established by NIOSH based on both toxicity and flammability. Generally expressed in ppm v/v or mg/m3. Indirect Evaporative Cooling - The evaporative cooling process where water evaporates into a secondary air stream, removing heat from a primary air stream via a heat exchanger.

Indirect Refrigeration System - A system in which a secondary coolant cooled or heated by the refrigerating system is circulated to the air or substance to be cooled or heated. Closed System - Secondary fluid cooled or heated by refrigerating system, circulated within a closed circuit in indirect contact with the air or substance. Double-Indirect Open-Spray System - The secondary substance for an indirect open-spray system is heated or cooled by an intermediate coolant circulated from a second enclosure.

Open-Spray System - Secondary coolant cooled or heated by the refrigerating system, circulated in direct contact with the air or substance. Vented Closed System - Secondary coolant cooled or heated by the refrigerating system and passed through a closed circuit, except that the evaporator or condenser is placed in an open or appropriately vented tank. Indirect Solar System - A solar thermal system in which the gas or liquid in the solar collector loop circulates between the solar collector and a heat exchanger, and such gas or liquid is not drained from the system or supplied to the load during normal operation.

Infiltration - Uncontrolled inward air leakage to conditioned spaces through unintentional openings, caused by wind, stack effect, or imbalances between supply and exhaust airflow rates. Interlock - A device actuated by another device with which it is directly associated, to govern succeeding operations of the same or allied devices. A circuit in which a given action cannot occur until after one or more other actions have taken place. Joint, Flanged - A joint made by bolting together a pair of flanged ends.

Joint, Flared - A metal-to-metal compression joint in which a conical spread is made on the end of a tube that is compressed by a flare nut against a mating flare. Joint, Plastic Adhesive - A joint made in thermoset plastic piping by the use of an adhesive substance that forms a continuous bond between the mating surfaces without dissolving either one. Joint, Plastic Heat Fusion - A joint made in thermoplastic piping by heating the parts sufficiently to permit fusion of the materials when pressed together.

Joint, Plastic Solvent Cement - A joint made in thermoplastic piping by the use of a solvent or solvent cement that forms a continuous bond between the mating surfaces. Joint, Soldered - A gastight joint obtained by joining metal parts with metallic mixtures or alloys that melt between 400 degrees F (204 degrees C) and 1,000 degrees F (538 degrees C). Joint, Welded - A gastight joint obtained by joining metal parts in molten state.

Labeled [A] - Equipment, materials, or products to which have been affixed a label, seal, symbol, or other identifying mark of a nationally recognized testing laboratory or approved agency that maintains periodic inspection of the production of the labeled items and whose labeling indicates either that the item meets identified standards or has been tested and found suitable for a specified purpose. Large-Diameter Ceiling Fan - A ceiling fan greater than 7 feet (2134 mm) in diameter. Also referred to as high-volume, low-speed (HVLS) fans.

Light-Duty Cooking Appliance - Includes gas and electric ovens (standard, bake, roasting, revolving, retherm, convection, combination convection/steamer, countertop conveyorized baking/finishing, deck, and pastry), electric and gas steam-jacketed kettles, pasta cookers, compartment steamers (pressure and atmospheric), and cheesemelters. Limit Control [FG] - A device responsive to changes in pressure, temperature, or level for turning on, shutting off, or throttling the gas supply to an appliance.

Limited Charge System - A system in which, with the compressor idle, the design pressure will not be exceeded when the refrigerant charge has completely evaporated. Listed [A] - Equipment, materials, products, or services included in a list published by an organization acceptable to the code official and concerned with evaluation of products or services, which maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that the item meets identified standards or has been tested and found suitable for a specified purpose.

Terms include: listed, certified, classified, or other terms determined appropriate by the listing organization. Living Space - Space within a dwelling unit utilized for living, sleeping, eating, cooking, bathing, washing, and sanitation purposes. Lower Explosive Limit (LEL) - See Lower Flammable Limit. Lower Flammable Limit (LFL) [F] - The minimum concentration of vapor in air at which propagation of flame will occur in the presence of an ignition source.

Lower Flammable Limit (Refrigerant) (LFL) - The minimum concentration of refrigerant at which a flame is capable of propagating through a homogeneous mixture of refrigerant and air under specific test conditions per ASHRAE 34. Low-Pressure Hot-Water-Heating Boiler - A boiler furnishing hot water at pressures not exceeding 160 psi (1103 kPa) and temperatures not exceeding 250 degrees F (121 degrees C). Low-Pressure Steam-Heating Boiler - A boiler furnishing steam at pressures not exceeding 15 psi (103 kPa).

Low-Probability Pump - A pump designed to prevent atmospheric release of the pumped fluid by one of the following: permanently sealed pump, pump incorporating a static seal, or pump incorporating not less than two sequential dynamic shaft seals that automatically shuts down upon failure of any seal. Low-Probability Systems - A refrigeration system in which the basic design or location of components is such that a leakage of refrigerant from a failed connection, seal, or component will not enter an occupancy-classified area other than the machinery room.

Low-Side Pressure - The parts of a refrigerating system subject to evaporator pressure.

Induced-Draft Venting System - A portion of a venting system using a fan or other mechanical means to cause removal of flue or vent gases under nonpositive static vent pressure. Power Venting System - A portion of a venting system using a fan or other mechanical means to cause removal of flue or vent gases under positive static vent pressure. Mechanical Equipment/Appliance Room - A room or space in which nonfuel-fired mechanical equipment and appliances are located. Mechanical Exhaust System - A system for removing air from a room or space by mechanical means.

Mechanical Joint - A connection between pipes, fittings, or pipes and fittings that is not welded, brazed, caulked, soldered, solvent cemented, or heat fused. A gas- or liquid-tight connection obtained by joining parts through positive holding mechanical construction such as flanged, screwed, clamped, or flared connections. Mechanical System - A system specifically addressed and regulated in this code, composed of components, devices, appliances, and equipment.

Medium-Duty Cooking Appliance - Includes electric discrete element ranges (with or without oven), electric and gas hot-top ranges, electric and gas griddles, double-sided griddles, electric and gas fryers (open deep fat, donut, kettle, and pressure fryers), electric and gas conveyor pizza ovens, electric and gas tilting skillets (braising pans), and electric and gas rotisseries. Modular Boiler - A steam or hot-water-heating assembly consisting of a group of individual boilers (modules) intended to be installed as a unit without intervening stop valves.

Maximum input per module: 400,000 Btu/h (117,228 W) gas, 3 gph (11.4 L/h) oil, or 115 kW electric. Natural Draft System - A venting system designed to remove flue or vent gases under nonpositive static vent pressure entirely by natural draft. Natural Ventilation - The movement of air into and out of a space through intentionally provided openings such as windows and doors, or through nonpowered ventilators.

Net Occupiable Floor Area - The floor area of an occupiable space defined by the inside surfaces of its walls, excluding shafts, column enclosures, and other permanently enclosed, inaccessible, and unoccupiable areas. Obstructions such as furnishings and storage racks are NOT deducted from the space area. No-Flow Condition (Solar) - A condition where thermal energy is not transferred from a solar thermal collector by means of flow of a heat transfer fluid.

Nonabrasive/Abrasive Materials - Nonabrasive particulate in high concentrations, moderately abrasive particulate in low and moderate concentrations, and highly abrasive particulate in low concentrations, such as alfalfa, asphalt, plaster, gypsum, and salt. Noncombustible Material - A material that passes ASTM E136. Nonfood-Grade Fluid - Any fluid that is not designated as a food-grade fluid. Occupancy [A] - The purpose for which a building, or portion thereof, is utilized or occupied.

Occupational Exposure Limit (OEL) - The time-weighted average (TWA) concentration for a normal 8-hour workday and 40-hour workweek to which nearly all workers can be repeatedly exposed without adverse effect, based on the OSHA PEL, ACGIH TLV-TWA, TERA OARS WEEL, or consistent value. Occupiable Space - An enclosed space intended for human activities, excluding spaces intended primarily for other purposes such as storage rooms and equipment rooms that are only intended to be occupied occasionally and for short periods of time.

Offset (Vent) - A combination of approved bends that make two changes in direction bringing one section of the vent out of line but into a line parallel with the other section. Outdoor Air - Air taken from the outdoors, and therefore not previously circulated through the system. Outdoor Opening - A door, window, louver, or skylight openable to the outdoor atmosphere. Outlet - A threaded connection or bolted flange in a piping system to which a gas-burning appliance is attached. Panel Heating - A method of radiant space heating in which heat is supplied by large heated areas of room surfaces.

The heating element usually consists of warm water piping, warm air ducts, or electrical resistance elements embedded in or located behind ceiling, wall, or floor surfaces. Peer Review [A] - An independent and objective technical review conducted by an approved third party. Pellet Fuel-Burning Appliance - A closed-combustion, vented appliance equipped with a fuel-feed mechanism for burning processed pellets of solid fuel of a specified size and composition. Piping - Refers to either pipe or tubing, or both. Pipe - A rigid conduit of iron, steel, copper, copper-alloy, or plastic.

Tubing - Semirigid conduit of copper, copper-alloy, aluminum, plastic, or steel. Plastic, Thermoplastic - A plastic capable of being repeatedly softened by increase of temperature and hardened by decrease of temperature. Plastic, Thermosetting - A plastic capable of being changed into a substantially infusible or insoluble product when cured under application of heat or chemical means. Plenum - An enclosed portion of the building structure, other than an occupiable space being conditioned, that is designed to allow air movement and thereby serve as part of an air distribution system.

⚠ Triggers material limits (plenum-rated), wiring/insulation ratings, and fire/smoke coordination. Pollution-Control Unit (PCU) - Manufactured equipment installed in a grease exhaust duct system for the purpose of extracting smoke, grease particles, and odors from the exhaust flow by means of a series of filters. Portable Fuel Cell Appliance - A fuel cell generator of electricity that is not fixed in place. Utilizes a cord and plug connection to a grid-isolated load and has an integral fuel supply. Power Boiler - See Boiler. Premises [A] - A lot, plot, or parcel of land, including any structure thereon.

Press-Connect Joint - A permanent mechanical joint incorporating an elastomeric seal or an elastomeric seal and corrosion-resistant grip or bite ring. Made with a pressing tool and jaw or ring approved by the fitting manufacturer. Pressure, Field Test - A test performed in the field to prove system tightness. Pressure Relief Device - A pressure-actuated valve or rupture member designed to relieve excessive pressure automatically. Pressure Relief Valve - A pressure-actuated valve held closed by a spring or other means and designed to relieve pressure automatically in excess of the device's setting.

Pressure Vessels - Closed containers, tanks, or vessels designed to contain liquids or gases, or both, under pressure. Pressure Vessels - Refrigerant - Any refrigerant-containing receptacle in a refrigerating system, excluding evaporators where each separate section does not exceed 0.5 cubic foot (0.014 m3) of refrigerant-containing volume, regardless of inside dimensions, evaporator coils, controls, headers, pumps, and piping. Pressure-Limiting Device - A pressure-responsive mechanism designed to stop automatically the operation of the pressure-imposing element at a predetermined pressure.

Protective Assembly (Reduced Clearance) - Any noncombustible assembly that is labeled or constructed in accordance with Table 308.4.2 and is placed between combustible materials or assemblies and mechanical appliances, devices, or equipment, for the purpose of reducing required airspace clearances. Purge - To clear of air, water, or other foreign substances. Push-Fit Joints - A type of mechanical joint consisting of elastomeric seals and corrosion-resistant tube grippers. May be permanent or removable, depending on the design.

Receiver, Liquid - A vessel permanently connected to a refrigeration system by inlet and outlet pipes for storage of liquid refrigerant. Recirculated Air - Air removed from a conditioned space and intended for reuse as supply air. Reclaimed Refrigerants - Refrigerants reprocessed to the same specifications as new refrigerants by means including distillation, and chemically analyzed to verify that the specifications have been met. Reclaiming usually implies the use of processes available only at a reprocessing or manufacturing facility.

Recovered Refrigerants - Refrigerants removed from a system in any condition without necessarily testing or processing them. Recycled Refrigerants - Refrigerants from which contaminants have been reduced by oil separation, removal of noncondensable gases, and single or multiple passes through devices that reduce moisture, acidity, and particulate matter, such as replaceable core filter driers. Usually performed at the field job site or a local service shop. Refrigerant - The fluid used for heat transfer in a refrigeration system that undergoes a change of state to absorb heat.

Refrigerant Designation - The unique identifying alphanumeric value or refrigerant number assigned to an individual refrigerant and published in ASHRAE 34. Refrigerant Safety Group Classification - The alphanumeric designation that indicates both the toxicity and flammability classifications of refrigerants in accordance with ASHRAE 34. Flammability Classification: Class 1 - No flame propagation. Class 2 - Low flammability. Class 2L - Low flammability and low burning velocity. Class 3 - High flammability. Toxicity Classification: Class A = low toxicity. Class B = high toxicity.

Refrigeration Capacity Rating - 1 horsepower (0.75 kW), 1 ton, or 12,000 Btu/h (3.5 kW) shall all mean the same quantity. Refrigeration Machinery Room - See Machinery Room. Refrigeration System - A combination of interconnected parts in which a refrigerant is enclosed and circulated for the purpose of extracting then rejecting heat. Refrigeration System, Absorption - A heat-operated, closed-refrigeration cycle in which a secondary fluid (the absorbent) absorbs a primary fluid (the refrigerant) that has been vaporized in the evaporator.

Direct System - The evaporator is in direct contact with the material or space refrigerated, or is located in air-circulating passages communicating with such spaces. Indirect System - A brine coil cooled by the refrigerant is circulated to the material or space refrigerated, or is used to cool the air so circulated. Refrigeration System, Self-Contained - A complete factory-assembled and tested system shipped in one or more sections, without refrigerant-containing parts joined in the field other than by companion or block valves.

Refrigeration System Classification - Systems classified according to the degree of probability that leaked refrigerant from a failed connection, seal, or component will enter an occupied area. Registered Design Professional [A] - An individual registered or licensed to practice their respective design profession as defined by the statutory requirements of the professional registration laws of the state or jurisdiction in which the project is to be constructed. Return Air - Air removed from an approved conditioned space or location and recirculated or exhausted.

Return Air System - An assembly of connected ducts, plenums, fittings, registers, and grilles through which air from the space or spaces to be heated or cooled is conducted back to the supply unit. See also Supply Air System. Room Heater, Vented [FG] - A free-standing heating unit burning solid or liquid fuel for direct heating of the space in and adjacent to that in which the unit is located. Safety Valve - A valve that relieves pressure in a steam boiler by opening fully at the rated discharge pressure. Spring-pop type.

Self-Contained Equipment - Complete, factory-assembled and tested, heating, air-conditioning, or refrigeration equipment installed as a single unit, with all working parts, complete with motive power, in an enclosed unit of said machinery. Shaft [BF] - An enclosed space extending through one or more stories of a building, connecting vertical openings in successive floors, or floors and the roof. Shaft Enclosure [BF] - The walls or construction forming the boundaries of a shaft.

Sleeping Unit [A] - A room or space in which people sleep, which can also include permanent provisions for living, eating, and either sanitation or kitchen facilities but not both. Such rooms and spaces that are also part of a dwelling unit are not sleeping units. Smoke Damper [BF] - A listed device installed in ducts and air transfer openings designed to resist the passage of smoke. Installed to operate automatically, controlled by a smoke detection system, and where required, capable of being positioned from a fire command center.

Smoke-Developed Index [BF] - A numerical value assigned to a material tested in accordance with ASTM E84. Solar Thermal System - A system that converts solar radiation to thermal energy for use in heating or cooling. Solid Fuel (Cooking Applications) - Applicable to commercial food service operations only. Any bulk material such as hardwood, mesquite, charcoal, or briquettes combusted to produce heat for cooking operations. Source Capture System - A mechanical exhaust system designed and constructed to capture air contaminants at their source and exhaust such contaminants to the outdoor atmosphere.

Stationary Fuel Cell Power Plant [FG] - A self-contained package or factory-matched packages constituting an automatically operated assembly of integrated systems for generating useful electrical energy and recoverable thermal energy that is permanently connected and fixed in place. Steam Bath Equipment - Includes steam bath generators, combination room and steam generator systems, and steam bath cabinets intended for high-humidity concentrated heating at elevated temperatures for personal bathing. Steam-Heating Boiler - A boiler operated at pressures not exceeding 15 psi (103 kPa) for steam.

Stop Valve - A shutoff valve for controlling the flow of liquid or gases. Story [BG] - That portion of a building included between the upper surface of a floor and the upper surface of the floor next above, except that the topmost story is that portion included between the upper surface of the topmost floor and the ceiling or roof above. Strength, Ultimate - The highest stress level that the component will tolerate without rupture.

Supply Air - Air delivered to each space supplied by the air distribution system, provided for ventilating, heating, cooling, humidification, dehumidification, and other similar purposes. Supply Air System - An assembly of connected ducts, plenums, fittings, registers, and grilles through which air, heated or cooled, is conducted from the supply unit to the spaces to be heated or cooled. See also Return Air System.

Third-Party Certified [P] - Certification obtained by the manufacturer indicating that the function and performance characteristics of a product or material have been determined by testing and ongoing surveillance by an approved third-party certification agency. Assertion of certification is in the form of identification in accordance with the requirements of the third-party certification agency. Third-Party Tested [P] - Procedure by which an approved testing laboratory provides documentation that a product, material, or system conforms to specified requirements.

TLV-TWA (Threshold Limit Value-Time-Weighted Average) - The time-weighted average concentration of a refrigerant or other chemical in air for a normal 8-hour workday and 40-hour workweek to which nearly all workers are repeatedly exposed without adverse effects, as adopted by the American Conference of Government Industrial Hygienists (ACGIH). Toilet Room - A room containing a water closet and frequently a lavatory, but not a bathtub, shower, spa, or similar bathing fixture.

Transition Fittings, Plastic to Steel - An adapter for joining plastic pipe to steel pipe, providing a permanent, pressure-tight connection between two materials that cannot be joined directly. Unit Heater [FG] - A self-contained appliance of the fan type, designed for the delivery of warm air directly into the space in which the appliance is located. Unvented Alcohol Fuel-Burning Decorative Appliance - A stationary, self-contained appliance intended to be directly or indirectly secured to a wall or floor and not intended for duct connection.

Burns alcohol; made in a manufacturing facility for delivery to the installation site. Vent - A pipe or other conduit composed of factory-made components, containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance. Pellet Vent - A vent listed and labeled for use with listed pellet-fuel-burning appliances. Type L Vent - A vent listed and labeled for use with oil-burning appliances listed for Type L vents, and gas-fired appliances listed for Type B vents.

Vent Connector - The pipe that connects an approved fuel-fired appliance to a vent. Vent Damper Device, Automatic - A device intended for installation in the venting system, in the outlet of an individual automatically operated fuel-burning appliance, designed to open the venting system automatically when the appliance is in operation and to close it automatically when the appliance is in standby or shutdown. Ventilation - The natural or mechanical process of supplying conditioned or unconditioned air to, or removing such air from, any space.

Ventilation Air - That portion of supply air that comes from the outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air within a designated space. Venting System [FG] - A continuous open passageway from the flue collar of an appliance to the outdoor atmosphere for the purpose of removing flue or vent gases. Usually composed of a vent or chimney and vent connector, assembled to form the open passageway. Water Heater - Any heating appliance or equipment that heats potable water and supplies such water to the potable hot water distribution system.

Zone - One occupiable space or several occupiable spaces with similar occupancy classification (see Table 403.3.1.1), occupant density, zone air distribution effectiveness, and zone primary airflow rate per unit area.

Code Path: IMC Chapter 2 (Section 202 Master Definitions) -> Section 201.2 (Cross-Reference Hierarchy) -> IBC/IFC when term is absent. Use Section 202 as the primary term lookup before citing any technical section.

Section 202 is the controlling definition set for all IMC-regulated systems and equipment.

Where a term appears in both IMC Chapter 2 and IFGC/IPC, the IMC definition controls for mechanical systems.

Definitions with [A], [BF], [F], [FG], [BS], or [P] brackets indicate code-specific origin - confirm jurisdiction adoption.

Check: Before You Submit

Confirm all bracketed terms on the permit set match the adopting jurisdiction's currently adopted code edition.

Verify the equipment schedule uses the Chapter 2 definition of 'appliance' vs. 'equipment' consistently throughout.

Confirm plenum areas are labeled per the Section 202 plenum definition before applying material limitations.

Review Risk:

Using a term from a different code edition or a model code the jurisdiction has not adopted is a common redline source.

Defining equipment in the schedule differently than the code defines it creates a mismatched compliance basis.

Failing to apply the Flash Point classification when specifying flammable or combustible liquids near mechanical equipment.