/ Mechanical Reference
IMC Section 202 Definitions Glossary
Plain-English explanations of the International Mechanical Code's core definitions, written and reviewed by Masterbuild's licensed PE. Original wording, not a copy of the code text. English shown below; enable JavaScript for the searchable bilingual English/Spanish version with field notes on every term. Full build-out: 219 terms covering Section 202 General Definitions A through Z.
- Abrasive Materials. Particulate matter — such as alumina, bauxite, iron silicate, sand, or slag — that wears down duct and equipment surfaces at a moderate-to-high rate depending on concentration.
- Absorption System. A refrigeration system that pressurizes refrigerant by pumping a refrigerant-absorbent solution, then separates the two with heat, condenses and expands the refrigerant to produce cooling, and reabsorbs it to repeat the cycle.
- Access (To). The ability to reach a device, appliance, or equipment either directly (ready access) or by first removing a panel or similar obstruction.
- Air. Air supplied to mechanical equipment and appliances for combustion, ventilation, cooling, and similar purposes. Standard air is measured at 70°F and 29.92 inches of mercury.
- Air Conditioning. The simultaneous treatment of temperature, humidity, cleanliness, and distribution of air to meet the requirements of a conditioned space.
- Air Dispersion System. A diffuser system, often fabric or plastic film, designed to both convey and diffuse air into a room while operating under positive pressure.
- Air Distribution System. Any system of ducts, plenums, and air-handling equipment that circulates air within a space.
- Air, Exhaust. Air removed from a space, appliance, or equipment and conveyed directly to the outdoor atmosphere.
- Air-Conditioning System. A system consisting of heat exchangers, blowers, filters, and supply/exhaust/return ducts, plus any connected apparatus.
- Air-Handling Unit. A blower or fan used to distribute supply air to a room, space, or area.
- Air, Makeup. Any combination of outdoor air and transfer air intended to replace exhaust air and exfiltration.
- Air, Outdoor. Ambient air entering a building through a ventilation system, intentional natural-ventilation openings, or infiltration.
- Air, Transfer. Air moved from one indoor space to another.
- Alteration. A change to a mechanical system that extends, adds to, or changes the arrangement, type, or purpose of the original installation.
- Ambulatory Care Facility. A building or portion providing medical, surgical, psychiatric, nursing, or similar care on a less-than-24-hour basis to people incapable of self-preservation.
- Appliance. A device or apparatus, manufactured and designed to use energy, for which the code provides specific requirements.
- Appliance, Existing. Any appliance regulated by the code that was legally installed before the code's effective date, or for which a permit 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 / Medium-Heat / Low-Heat. Classified by flue-gas temperature at the flue entrance: high-heat above 2,000°F, medium-heat 1,000-2,000°F, low-heat 1,000°F or below.
- Approved. Acceptable to the code official.
- Approved Agency. An established, recognized organization regularly engaged in testing, inspection services, or product evaluation/certification, approved by the code official.
- Automatic Boiler. Any class of boiler equipped with the controls and limit devices specified in the code's boiler chapter.
- Balanced Ventilation System. A ventilation system that simultaneously supplies outdoor air and exhausts air, with supply and exhaust rates each within 10 percent of their average.
- Bathroom. A room containing a bathtub, shower, spa, or similar bathing fixture.
- Boiler. A closed heating appliance supplying hot water or steam for space heating, processing, or power. Low-pressure boilers operate at or below 15 psi steam / 160 psi water; high-pressure boilers exceed those pressures.
- Boiler Room. A room primarily used for the installation of a boiler.
- Brazed Joint / Brazing. A gastight joint made by joining metal parts with a nonferrous filler metal that melts above 1,000°F but below the base metal's melting point.
- Breathing Zone. The region of an occupied space between 3 and 72 inches above the floor and more than 2 feet from walls or fixed air-conditioning equipment.
- BTU. British thermal unit — the quantity of heat required to raise the temperature of 1 pound of water by 1°F.
- Building. Any structure used or intended for supporting or sheltering any occupancy.
- Ceiling Radiation Damper. A listed device in a ceiling membrane of a fire-resistance-rated floor/ceiling or roof/ceiling assembly that automatically limits radiative heat transfer through an air inlet/outlet opening.
- Chimney (Factory-Built / Masonry / Metal). A primarily vertical structure containing one or more flues that carries gaseous combustion products and air from a fuel-burning appliance to the outdoor atmosphere.
- Chimney Connector. A pipe that connects a fuel-burning appliance to a chimney.
- Clearance. The minimum air-measured distance between the heat-producing surface of a mechanical appliance, device, or equipment and the surface of combustible material or assembly.
- Closed Combustion Solid-Fuel-Burning Appliance. A heat-producing appliance whose combustion chamber has no openings other than the flue collar, fuel charging door, and adjustable combustion-air-control openings.
- Clothes Dryer. An appliance used to dry wet laundry by means of heat.
- Code. The regulations in force, including subsequent amendments and any emergency rules the administrative authority has lawfully adopted.
- Code Official. The officer or other designated authority charged with administering and enforcing the code, or a duly authorized representative.
- Combination Fire/Smoke Damper. A listed device in ducts and air transfer openings that closes automatically on heat detection and resists the passage of flame and smoke.
- Combustible Assembly. A wall, floor, ceiling, or other assembly built from one or more component materials that don't qualify as noncombustible.
- Combustible Liquid (Class II / IIIA / IIIB). A liquid with a closed-cup flash point at or above 100°F, subdivided into Class II (100-140°F), Class IIIA (140-200°F), and Class IIIB (200°F and above).
- Combustible Material. Any material not defined as noncombustible.
- Combustion. The rapid oxidation of fuel accompanied by the 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. The constituents resulting from burning a fuel with the oxygen in 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 Cooking Recirculating System. A self-contained system consisting of the exhaust hood, cooking equipment, filters, and fire suppression system that recirculates cleaned air back to the space instead of exhausting outdoors.
- Commercial Kitchen Hoods, Backshelf / Eyebrow / Pass-Over. Backshelf: a low front lip set back from the appliances. Eyebrow: mounted directly to an appliance face. Pass-Over: a free-standing backshelf-style hood low enough to pass food over the top.
- Commercial Kitchen Hoods, Single/Double Island Canopy / Wall Canopy. Island canopies are open on all sides over one or two appliance lines; wall canopies mount against a wall above an appliance line.
- Compensating Hoods. Hoods with an integral (built-in) makeup air supply delivered via short-circuit flow, air curtain, or front-face discharge.
- Compressor / Positive Displacement Compressor / Compressor Unit. A machine for compressing a gas; positive displacement increases pressure by changing internal chamber volume; a compressor unit adds the prime mover and accessories.
- Concealed Location. A location that cannot be accessed without damaging permanent parts of the building structure or finish surface.
- Condensate. The liquid that condenses from a gas (including flue gas) because of a temperature reduction.
- Condenser. A heat exchanger designed to liquefy refrigerant vapor by removing heat.
- Condensing Unit. A factory-made assembly of refrigeration components designed to compress and liquefy a specific refrigerant.
- Conditioned Space. An area enclosed within the building thermal envelope that is directly or indirectly heated or cooled.
- Construction Documents. The written, graphic, and pictorial documents prepared to describe a project's design, location, and physical characteristics, necessary to obtain a building permit.
- Control. A manual or automatic device designed to regulate the gas, air, water, or electrical supply to, or the operation of, a mechanical system.
- Conversion Burner. A burner designed to supply gaseous fuel to an appliance originally designed to use a different fuel.
- Damper / Volume Damper. A manually or automatically controlled device that regulates draft or the flow rate of air or combustion gases in a duct, appliance, vent connector, or chimney.
- Design Flood Elevation. The elevation of the design flood, including wave height, referenced to the datum on the community's legally designated flood hazard map.
- Design Working Pressure. The maximum allowable working pressure for which a specific part of a system is designed.
- Direct Evaporative Cooling. A cooling process where water evaporates directly into the air stream, lowering the dry-bulb temperature while raising humidity.
- Direct Refrigeration System. A system in which the evaporator or condenser is in direct contact with the air or substance being cooled or heated, with no secondary coolant loop in between.
- Direct Solar System. A solar thermal system in which the gas or liquid in the solar collector loop is not separated from the load it serves.
- Direct-Vent Appliances. Appliances built and installed so all combustion air comes from outdoors and all flue gases discharge outdoors, with no air exchange with the indoor space.
- Discrete Product. Noncontinuous, individual, distinct pieces — such as electrical, plumbing, and mechanical products, and duct straps, fittings, registers, and pipe hangers.
- Draft / Induced Draft / Natural Draft. The pressure difference between an appliance and the atmosphere that drives combustion products through the vent, either fan-assisted (induced) or created by height and temperature difference alone (natural).
- Draftstop. A material, device, or construction installed to restrict air movement within concealed spaces in building components such as crawl spaces, floor/ceiling assemblies, and attics.
- Drain-Back System. A solar thermal system in which the collector-loop fluid gravity-drains from the collector into a holding tank under prescribed conditions, protecting the system from freeze damage.
- Drip. A container placed at a low point in a piping system to collect condensate, positioned so the collected condensate can be removed.
- Dry Cleaning Systems (Types I-V). Classified by solvent flammability, from Class I flammable liquid solvents (Type I) to Class IV nonflammable liquid solvents (Types IV/V).
- Duct / Duct System. A tube or conduit used to convey air; the duct system includes ducts plus fittings, dampers, plenums, fans, and accessory air-handling equipment.
- Duct Furnace. A warm-air furnace normally installed in an air distribution duct to supply heated air, relying on a blower not furnished as part of the furnace itself.
- Ductless Mini-Split System. A heating and cooling system with indoor evaporator/air-handling units connected to an outdoor condensing unit by refrigerant piping, without ductwork.
- Dwelling / Dwelling Unit. A building containing not more than two dwelling units; a dwelling unit provides complete, independent living facilities including permanent provisions for living, sleeping, eating, cooking, and sanitation.
- Electric Heating Appliance. An appliance that produces heat energy by applying electric power to resistance elements, refrigerant compressors, or dissimilar-material junctions.
- Energy Recovery Ventilation System. A system using air-to-air heat exchangers to recover or reject energy from exhaust air, preconditioning incoming outdoor ventilation air.
- Environmental Air. Air conveyed to or from occupied areas through ducts that are not part of the heating or air-conditioning system — kitchen, bathroom, dryer, and parking garage exhaust, for example.
- Equipment / Equipment, Existing. Piping, ducts, vents, control devices, and other permanently installed system components (other than appliances) that control environmental conditions in a building.
- Evaporative Cooler / Evaporative Cooling System. A device or system that reduces sensible heat by evaporating water into the airstream, with conditioned air distributed through ducts or plenums.
- Evaporator. The part of a refrigeration system where liquid refrigerant is vaporized to produce cooling.
- Excess Air. Air supplied beyond the theoretical amount needed for complete combustion, provided to prevent formation of dangerous combustion byproducts.
- Exfiltration. Uncontrolled outward air leakage from conditioned spaces through unintentional openings, caused by wind, stack effect, or supply/exhaust imbalances.
- Exhaust System. An assembly of connected ducts, plenums, fittings, registers, grilles, and hoods through which air is conducted from a space and discharged to the outdoors.
- Extra-Heavy-Duty Cooking Appliance. Appliances using open-flame combustion of solid fuel at any time — wood or charcoal-fired equipment, for example.
- Fire Damper. A listed device in ducts and air transfer openings that closes automatically on heat detection, restricting flame passage; classified static or dynamic.
- Fireplace / Factory-Built / Masonry / Fireplace Stove. An assembly with a hearth and noncombustible fire chamber for solid fuels, whether factory-made, field-built masonry, or a free-standing chimney-connected stove.
- Flame Safeguard. A device that automatically shuts off fuel supply to a burner or group of burners when the ignition means fails or flame failure occurs.
- Flame Spread Index. The numerical value assigned to a material tested under ASTM E84 or UL 723, describing how quickly flame spreads across its surface.
- Flammable Liquids (Class I: IA, IB, IC). Liquids with a flash point below 100°F and vapor pressure not exceeding 40 psia at 100°F, subdivided by flash point and boiling point.
- Flammable Vapor or Fumes. A mixture of gases in air at concentrations between the lower and upper flammability limits.
- Flash Point. The minimum temperature, corrected to 14.7 psia, at which a test flame causes a sample's vapors to ignite under specified test conditions.
- Flexible Air Connector. A conduit for transferring air between a duct or plenum and an air terminal unit or inlet/outlet, limited in permitted use, length, and location.
- Floor Area, Net. The actual occupied area, not including unoccupied accessory areas or the thickness of walls.
- Floor Furnace. A completely self-contained furnace suspended from the floor of the space it heats, drawing combustion air from outside that space.
- Flue / Flue Connection / Flue Gases / Flue Liner. The passageway within a chimney or vent through which combustion products pass, along with the connecting breeching, the gases themselves, and the protective liner material.
- Food-Grade Fluid. Potable water or a fluid containing additives listed under 21 CFR Parts 174-186.
- Fuel Gas. Natural gas, manufactured gas, liquefied petroleum gas, or a mixture of these.
- Fuel Oil. Kerosene or any hydrocarbon oil with a flash point not less than 100°F.
- Fuel-Oil Piping System. A closed piping system connecting a combustible liquid supply source to a fuel-oil-burning appliance.
- Furnace / Furnace Room. A completely self-contained heating unit that supplies heated air remotely, housed in a room primarily used for fuel-burning, space-heating, and water-heating appliances.
- 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 with integral downdraft exhaust, that conveys grease-laden air directly to the outdoors.
- Ground Source Heat Pump Loop System. Piping buried in excavations, or placed in a body of water, that transports heat-transfer liquid to and from a heat pump — closed-loop or open-loop.
- Gypsum Board / Gypsum Wallboard. A panel product with a noncombustible gypsum core and paper surfacing, used primarily as interior surfacing for building structures.
- Gas Convenience Outlet. A permanently mounted, manually operated device for connecting and disconnecting an appliance or appliance connector to a gas supply piping system.
- Gas Piping. An installation of pipe, valves, or fittings used to convey fuel gas, not including the piping within an appliance.
- Gas Pressure Regulator. A device that reduces, controls, and maintains the pressure of gas downstream of the device at a value lower than the supply pressure.
- Gas Utilization Equipment. Equipment or an appliance that uses gas as a fuel or raw material to produce light, heat, power, refrigeration, or air conditioning.
- Grade. The finished ground level adjoining a building at all exterior walls.
- Grade Plane. A reference plane representing the average finished ground level adjoining a building at all exterior walls.
- Grease Duct System. A grease duct, including all fittings, transitions, access panels, and appurtenances, extending from a hood's collar to the exhaust fan or termination point.
- Grease Removal Device, Listed. A device listed for reducing grease carryover, typically installed in the duct or plenum ahead of the exhaust fan.
- Grease Reservoir. A device or system designed to collect grease at a hood, grease removal device, or exhaust duct termination.
- Hazardous Location. A location where fire or explosion hazards may exist due to flammable gases, vapors, liquids, combustible dusts, or fibers being present in ignitable quantities.
- Header. A pipe or manifold to which two or more branch pipes are connected, distributing or collecting flow across multiple circuits.
- Heat Exchanger. A device manufactured for transferring heat between two physically separated fluids, or between a fluid and a heat-producing element, without direct mixing.
- Heat Pump. A refrigeration system able to transfer heat into or out of a space or process, by reversing the refrigeration cycle to provide either heating or cooling.
- Heating and Cooling System. The equipment, distribution system, and terminal units that provide, collectively or individually, the heating or cooling of a building.
- High-Probability System. A refrigeration system in which failure of a refrigerant-containing part exposed to an occupied space would allow refrigerant to enter that space.
- Hood, Type I. A kitchen hood for collecting and removing grease-laden vapors and smoke, required over appliances that griddle, fry, broil, or produce similar grease-laden vapors.
- Hood, Type II. A hood for collecting steam, vapor, heat, or odors, not required to meet grease-hood construction standards, used over non-grease-producing appliances.
- Hot Water Boiler. A closed vessel in which water is heated for uses other than potable water heating, by combustion of fuel or electric heating elements.
- Humidifier. A device or assembly used to add moisture to air.
- Hydronic Piping. Piping used to convey liquid used for heat transfer in heating or cooling systems.
- Ignition Source. A flame, spark, or hot surface capable of igniting flammable vapors or fumes.
- Indirect Refrigeration System. A system in which a secondary coolant, cooled or heated by the refrigerant, is circulated to the space or process, keeping the refrigerant itself out of the occupied space.
- Indirect Waste Pipe. A waste pipe (such as a condensate line) that discharges through an air gap into a trapped fixture or receptor rather than connecting directly to the sanitary system.
- Infiltration. Air leakage into a building through unintentional openings, driven by wind, stack effect, or mechanical system pressure imbalances.
- Insulation. A material used to reduce the transfer of heat, applied to piping, ductwork, or equipment.
- Interlock. A device or control arrangement that requires the state of one component to be verified before allowing another component to operate.
- Kitchen, Commercial. A room or space intended for the preparation of food, containing one or more pieces of commercial cooking equipment.
- Labeled. Equipment or materials bearing a label, symbol, or identifying mark of an approved agency that conducts periodic inspection of production.
- Limit Control. A device responsive to changes in pressure, temperature, or liquid level, used to keep a supervised condition within a predetermined range.
- Liquefied Petroleum Gas (LP-Gas). Material composed predominantly of propane, propylene, butane, or butylenes, gaseous at normal atmospheric conditions but stored/transported as a pressurized liquid.
- Listed. Equipment, materials, or services on a list published by an organization acceptable to the code official, that maintains periodic inspection of production.
- Living Space. Space within a dwelling unit used for living, sleeping, eating, or cooking, excluding bathrooms, closets, halls, and storage/utility spaces.
- Makeup Air. Air provided to replace air being exhausted from a space, ensuring balanced pressure between supply and exhaust.
- Mechanical Draft System. A venting system using a fan or blower to induce draft, classified forced draft or induced draft.
- Mechanical Exhaust System. A power-driven device with associated ducts and equipment used to remove air from a portion of a building.
- Mechanical Joint. A joint between pipe and fittings that is not welded, soldered, brazed, or solvent-cemented; assembled by compression, threading, or grooving.
- Mechanical System. A system specifically addressed and regulated by the mechanical code, including equipment, appliances, fixtures, and appurtenances.
- Medium-Heat Appliance. A fuel-burning appliance capable of maintaining refractory-chamber temperatures between 2,000°F and 2,500°F at the flue entrance.
- Modular Boiler. A boiler composed of two or more separately fired sections, factory-assembled and shipped as a unit, with a single group operating control.
- Motor. A device that converts electrical energy into rotating mechanical energy to drive equipment such as fans, pumps, and compressors.
- Negative Pressure. A condition where air pressure within a space is lower than the surrounding area, typically because exhaust airflow exceeds supply airflow.
- Noncombustible Material. A material that, when tested per the applicable standard, does not ignite, burn, support combustion, or release flammable vapors.
- Occupiable Space. A room or enclosed space designed for human occupancy in which occupants perform work or other activities.
- Offset. A vent or chimney configuration that changes direction, deviating from a straight vertical run.
- Outdoor Air. Air taken from the outdoors, not previously circulated within a building.
- Outdoor Opening. An opening in a building's exterior envelope through which outdoor air can enter or be discharged, including louvers, grilles, and combustion air openings.
- Piping System. Pipe, tubing, fittings, valves, and other components assembled to convey a fluid, gas, or vapor.
- Plenum. An enclosed portion of the building structure, other than an occupiable space, designed to allow air movement as part of an air distribution system.
- Plume. The visible or invisible column of flue gases discharged from a vent or chimney termination into the outdoor atmosphere.
- Pneumatic Piping. Piping used to convey compressed air for control or power purposes.
- Positive Pressure. A condition where air pressure within a space is higher than the surrounding area, typically because supply airflow exceeds exhaust airflow.
- Potable Water. Water free from impurities present in amounts sufficient to cause disease or harmful physiological effects.
- Pressure-Relief Device. A device designed to open automatically and relieve excess pressure, protecting a vessel or system from overpressure conditions.
- Pressure Vessel. A closed container designed to hold gases or liquids at a pressure substantially different from ambient pressure.
- Process Fluids. Any liquid or gas used in a research, commercial, or industrial process, distinct from water or fluids used solely for space heating or cooling.
- Public Space. A space accessible to the general public, as distinguished from spaces restricted to employees, tenants, or authorized personnel.
- Purge. To clear a piping system, combustion chamber, or vent of air, gas, or combustion products before startup or after shutdown.
- Qualified Agency. A person, firm, or corporation approved by the code official to inspect, test, adjust, or install a specific piece of equipment or system.
- Radiant Heater. A heater designed to transfer heat primarily by radiation to objects and occupants in a space, rather than by heating the air directly.
- Ready Access (To). Access that does not require removal of a panel, door, or similar obstruction, or the use of a portable ladder or similar equipment.
- Receiver. A vessel permanently connected to a refrigeration system by piping, used to store liquid refrigerant.
- Refrigerant. A substance used to produce refrigeration by absorbing heat as it expands or evaporates.
- Refrigerant Compressor. A specific machine, with or without accessories, for compressing a given refrigerant vapor.
- Refrigerant Piping. Piping used to convey refrigerant from one component of a refrigerating system to another.
- Refrigerant Safety Classification. A two-part classification (toxicity Class A/B; flammability Class 1/2/3) assigned to a refrigerant based on standardized testing.
- Refrigerated Room. A room or space cooled below the ambient temperature by refrigeration equipment as part of its intended use.
- Refrigeration System. A combination of interconnected refrigerant-containing parts constituting one closed refrigerant circuit.
- Registered Design Professional. An individual legally registered or licensed to practice their respective design profession per the jurisdiction's statutory requirements.
- Relief Valve, Pressure. A pressure-actuated valve designed to relieve excess pressure automatically and reseat once normal pressure is restored.
- Return Air. Air removed from a conditioned space and returned to a heating, cooling, or ventilating system for reconditioning or exhaust.
- Riser. A vertical pipe or run of piping that conveys fluid, gas, or vapor upward from one level of a building to another.
- Roof-Mounted Equipment. Equipment installed on a roof, typically requiring a curb, structural support, and weatherproofing.
- Room Air Conditioner. An encased, self-contained assembly designed for mounting in a window, through a wall, or as a console, cooling a single room without ductwork.
- Safety Controls. Devices designed to protect against unsafe conditions by shutting down or limiting equipment operation.
- Sealed Combustion System. A combustion system in which all combustion air is piped from outdoors and all flue gases discharge outdoors, sealed from the appliance's surrounding space.
- Sediment Trap. A device installed in fuel gas piping ahead of an appliance's gas controls, trapping dirt and foreign material before it reaches the appliance.
- Sensible Heat. Heat that results in a measurable temperature change, as distinguished from latent heat.
- Shaft. An enclosed space extending through one or more stories of a building, connecting openings on successive floors.
- Single Duct System. An air distribution system using one duct system to convey either heated or cooled air, but not both simultaneously.
- Smoke Damper. A listed device in ducts and air transfer openings, designed to resist passage of air and smoke, controlled by a smoke detection system.
- Smoke Detector. A listed device that detects products of combustion, used within air distribution systems to shut down fans and/or actuate smoke dampers.
- Solar Thermal Collector. A device designed to absorb solar radiation and convert it into thermal energy for heating water, air, or other fluids.
- Solvent Cementing. A joining method for certain plastic piping materials using a solvent cement that chemically fuses pipe and fitting surfaces.
- Spillage. The escape of combustion products from an appliance's draft hood, barometric draft regulator, or vent connector into the room rather than up the vent.
- Split-System Air Conditioner. A factory-matched central air conditioning system with an outdoor condensing unit and indoor evaporator coil or air handler, connected by refrigerant piping.
- Standby Boiler. A boiler not normally in service, maintained ready for use to supplement or replace another boiler.
- Steam. Water in its vaporous phase, converted from liquid water by the addition of heat.
- Steam Boiler. A closed vessel in which steam is generated by combustion of fuel or electric heating elements, for use external to itself.
- Supply Air. Air delivered to a conditioned space through ductwork or a distribution system, from an outdoor air intake or recirculated return air.
- Tank. A vessel used for the storage of liquids, distinguished from a pressure vessel by not being designed to hold contents at a pressure substantially above ambient.
- Temperature Relief Valve. A temperature-actuated valve designed to open automatically at a predetermined temperature to protect a vessel or system.
- Testing Agency. An organization determined by the code official to possess the required equipment, staff qualifications, and experience to conduct specified tests.
- Thermostat. An automatic control device responsive to temperature, used to maintain a desired temperature by cycling heating or cooling equipment.
- Toxic Gas. A gas classified as highly toxic or toxic based on standardized acute toxicity testing.
- Transfer Air. Air moved from one interior space to another, typically through a transfer grille, duct, or undercut door.
- Vent, Type L. A listed and labeled factory-made vent tested and identified for use with oil-burning appliances listed for this venting type.
- Underfloor Air Distribution System. A ventilation approach using the cavity beneath a raised access floor as a supply air plenum, delivering air through floor-mounted diffusers.
- Unit Heater. A self-contained, fuel-burning or electric heating appliance with an integral fan, for suspended or floor mounting, that heats a space directly without ductwork.
- Unusually Tight Construction. Construction meeting specified air leakage and vapor retarder criteria, indicating an envelope tight enough that combustion air can't be assumed to infiltrate naturally.
- Vapor Barrier (Vapor Retarder). A material or assembly that adequately retards the transmission of water vapor, typically on the warm side of insulated piping or assemblies.
- Vapor Recovery System. A system designed to capture and recover vapors released during storage, transfer, or dispensing of a volatile liquid.
- Variable Air Volume (VAV) System. An air distribution system that varies supply air volume while maintaining a relatively constant supply temperature, using modulating terminal boxes.
- Vehicle Repair Garage. A building or portion used for repair, servicing, or fueling of self-propelled vehicles, including associated flammable/combustible liquid or gas storage.
- Vent. A pipe or conduit of factory-made components, listed and labeled for venting an appliance, conducting flue gases to the outdoor atmosphere.
- Vent Connector. The pipe or duct that connects a fuel-fired appliance to a vent or chimney.
- Vent Damper Device, Automatic. A listed device in the venting system of an appliance that automatically opens the venting system during operation and closes it when off.
- Vent Gases. Products of combustion from fuel-fired appliances, plus excess and dilution air, present in the venting system above the draft hood.
- Ventilation. The process of supplying and removing air, by natural or mechanical means, to or from a space.
- Ventilation Air. That portion of supply air consisting of outdoor air plus any recirculated air treated to maintain acceptable indoor air quality.
- Waste Heat Boiler. A boiler that derives its heat energy from recovered exhaust gases or waste heat of another process, rather than dedicated fuel combustion.
- Water Heater. An appliance designed primarily to supply hot water for domestic or commercial purposes, distinct from a boiler used for space heating.
- Zone. A space or group of spaces within a building with sufficiently similar heating/cooling requirements that a single controlling device can adequately control conditions.
Need this checked against your project?
This glossary is general reference. For a determination tied to your drawings, equipment schedule, or AHJ, send the project background and get a written scope.
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