HVAC Abbreviations
Common shorthand found on nameplates, proposals, wiring diagrams and service reports.
View abbreviations โAn extensive plain-English reference for the equipment, parts, fittings, controls, tools, measurements and trade terms commonly used by HVAC mechanics, suppliers, contractors and homeowners.
This glossary includes homeowner terminology as well as the parts and language commonly encountered at supply houses, on service trucks, in equipment manuals and during installation and repair work.
Common shorthand found on nameplates, proposals, wiring diagrams and service reports.
View abbreviations โCapacity, airflow, pressure, temperature and refrigeration measurements explained.
View measurements โA focused list of parts, fittings, fasteners, controls, tools and supplies mechanics order and install.
View parts reference โA refrigerant safety classification for refrigerants with lower flammability than traditional highly flammable refrigerants. Modern residential equipment may use A2L refrigerants and associated listed components and service practices.
A service disconnect located near outdoor HVAC equipment that provides a local means of disconnecting electrical power.
A removable equipment panel used to reach serviceable components inside a furnace, air handler, condenser or package unit.
A vessel typically installed in the suction line to help prevent liquid refrigerant from reaching the compressor.
An electric or electronic device that moves a damper, valve or other controlled component.
Annual Fuel Utilization Efficiency, a standardized rating used to compare the fuel-conversion efficiency of furnaces and boilers.
A device or system used to remove airborne particles from recirculated indoor air.
An indoor HVAC assembly that normally contains a blower and coil and may also contain electric heat, filters or controls.
A hydronic fitting designed to help separate entrained air from circulating water.
A hydronic component that removes entrained or dissolved air from a hot-water heating system.
A manual or automatic device used to release trapped air from hydronic piping or terminal units.
Equipment that passes air through water or wetted media for cleaning, humidification or process conditioning.
The movement of air through HVAC equipment and ductwork, commonly expressed in cubic feet per minute (CFM).
A switch used to prove that air is moving before or during operation of certain HVAC equipment.
The surrounding air temperature near equipment or a component.
The electrical current consumed by a motor, compressor, heater or other load during operation.
An instrument used to measure air velocity and, with appropriate methods, estimate airflow.
A time-delay control that helps prevent a compressor or other equipment from restarting too soon after shutdown.
A temperature-sensing control commonly used on boilers and hydronic systems to start, stop or limit equipment based on water temperature.
Supplemental heat used with a heat pump when additional heating capacity is required.
A damper designed to allow airflow in one direction while limiting reverse airflow.
A manual or automatic damper used to adjust airflow through a duct branch.
A quarter-turn shutoff valve that uses a drilled ball to open or close fluid flow.
A draft-regulating device used on some combustion vent systems to help maintain proper draft.
A motor-and-pulley drive arrangement that turns a blower wheel through a belt.
The fan assembly that moves air through a furnace, air handler and duct system.
A switch that interrupts equipment operation when a furnace or air-handler access panel is removed.
The enclosure around a centrifugal blower wheel that directs air into the supply path.
The motor that drives the indoor blower wheel.
A centrifugal fan wheel, often called a squirrel-cage wheel, that moves air through the indoor equipment.
Heating equipment that transfers heat into water for distribution through radiators, baseboard, radiant tubing or other hydronic terminals.
A drain valve used to drain water from boilers, piping or hydronic components.
A metal-joining process using a filler metal with a melting temperature above typical soldering temperatures, commonly used for copper refrigerant piping.
An overcurrent protective device that opens an electrical circuit when current exceeds its rating or a fault occurs.
British thermal unit, a unit of heat energy. HVAC capacities are commonly expressed in Btu per hour.
A device that mixes fuel and air and supports controlled combustion in a furnace or boiler.
A precisely sized opening that meters gas flow into a burner.
The assembly that supports and aligns multiple furnace burners.
A damper used in some zoning systems to relieve excess supply pressure by routing air around part of the distribution system.
A humidifier that uses a duct bypass and furnace airflow to move air across a wetted evaporative pad.
An electrical component that stores energy and is commonly used with single-phase motors and compressors for starting or running.
The rate at which equipment can add or remove heat, commonly stated in Btu/h or tons.
A fixed-bore refrigerant metering device made from small-diameter tubing.
A trade term often used for a filter-drier installed in a refrigeration system to remove moisture, acid and debris.
Cubic feet per minute, a measure of the volume of air moving through the HVAC system.
A valve that allows flow in one direction and restricts reverse flow.
An electronic control board that receives inputs and sends outputs to operate HVAC components.
A pump used to move heated water through a hydronic heating system.
A chemical cleaning product formulated for evaporator or condenser coil surfaces. Product selection must match the coil and manufacturer guidance.
Air supplied to a fuel-burning appliance for combustion.
An instrument used to measure combustion gases and evaluate appliance combustion performance.
The component that circulates refrigerant vapor and raises its pressure and temperature.
An acoustic or thermal wrap installed around some compressors to reduce sound or help manage temperature.
A heater used on some compressors to help prevent refrigerant migration and dilution of compressor oil during off cycles.
Water formed when moisture in indoor air condenses on a cold evaporator coil.
Piping that carries condensate away from an evaporator coil, air handler, furnace or dehumidifier.
A pan that collects water beneath an evaporator coil or other condensing component.
A small pump used to lift condensate to a suitable drain point when gravity drainage is not practical.
The heat exchanger where refrigerant rejects heat and condenses from vapor toward liquid. In cooling mode, it is normally outdoors.
The coil surface in the condenser where refrigerant rejects heat.
The outdoor fan that moves air across a condenser or outdoor heat-pump coil.
The motor that drives the outdoor fan blade.
An electrically controlled switch used to apply line voltage to compressors, fan motors and other loads.
A transformer that commonly reduces line voltage to 24 VAC for HVAC control circuits.
Coefficient of Performance, a ratio comparing useful heating or cooling output with energy input.
A fitting used with copper tubing, including elbows, couplings, reducers and tees.
A tool used to remove or replace Schrader valve cores, often while maintaining system access.
A heater attached to or installed in a compressor sump to keep compressor oil warm during off periods.
A fabricated transition used to mount replacement rooftop equipment to an existing roof curb.
The pressure at which a pressure control closes or initiates operation.
The pressure at which a pressure control opens or stops operation.
Efficiency loss associated with repeated equipment startup and shutdown rather than steady-state operation.
A plate or blade installed in ductwork to regulate or shut off airflow.
An electronic control used on heat pumps to manage outdoor-coil defrost operation.
A temporary heat-pump operating mode used to remove frost from the outdoor coil during heating operation.
Temperature difference between two points, such as return and supply air.
A moisture-absorbing material used in filter-driers, dehumidification equipment and other applications.
The temperature at which air becomes saturated and water vapor begins to condense.
A supply-air outlet designed to distribute air in a specific pattern.
An electronic manifold instrument used to measure refrigerant pressures, temperatures and calculated refrigeration values.
A local switching means used to isolate equipment from electrical power.
A motor-driven fan that establishes airflow through a furnace heat exchanger and vent system before ignition.
A shaped section of condensate piping used where required to allow proper drainage under positive or negative air pressure.
Ordinary air temperature measured without accounting for evaporative cooling effects.
Rigid fiberglass board used to fabricate certain duct systems or plenums.
A round or rectangular fitting used to connect a branch duct to a trunk, plenum or air device.
Insulation installed on the inside surface of metal ductwork for thermal or acoustic control.
Mastic or approved sealant used to seal duct joints and leakage points.
A split-system heat pump or air conditioner using one or more indoor units without conventional central ductwork.
Electronically commutated motor used in many modern blowers and fans for efficient, electronically controlled operation.
A control and damper arrangement that can use outdoor air for cooling when conditions are suitable.
Energy Efficiency Ratio 2, a standardized cooling-efficiency rating at specified operating conditions.
An electronically controlled refrigerant metering device that adjusts flow through commands from a controller.
A thermostat mode that disables normal heat-pump compressor heating and uses the configured backup heat source.
An auxiliary switch that proves a damper, valve or actuator has reached a commanded position.
A ventilation device that exchanges heat and some moisture between exhaust and incoming outdoor air streams.
The process of removing air, moisture and non-condensable gases from a sealed refrigerant circuit using a vacuum pump.
The heat exchanger where refrigerant absorbs heat and evaporates. In standard cooling operation, this is normally the indoor coil.
A tank that accommodates thermal expansion of water in a closed hydronic heating system.
Pressure resistance measured across defined external components of an air-moving system, often used with blower data to estimate airflow.
A propeller-style blade used on condenser fans, heat pumps, exhaust fans and other axial-airflow applications.
A packaged transformer and relay assembly commonly used in older or simple HVAC control systems.
An indoor unit containing a fan and coil used to heat or cool air.
A control used on some furnaces to manage blower operation and high-temperature limit protection.
A media device used to capture airborne particles and protect HVAC equipment from debris.
A return-air grille designed to hold an air filter.
A sealed refrigerant-line component containing desiccant and filtration media to remove moisture, acid and debris.
A safety switch designed to open if flame or excessive heat is detected outside the normal burner/heat-exchanger area.
A device used by many gas furnaces to prove that burner flame is present.
A mechanical tubing connection using a flared tube end and matching nut/fitting, common on mini-splits and some refrigeration systems.
A flexible connection used to reduce vibration transmission in duct, gas or piping applications.
Flexible insulated duct consisting of an inner liner, reinforcing helix, insulation and outer jacket.
A condensate safety control that opens a control circuit when water rises to an abnormal level.
A passage that carries combustion products from fuel-burning equipment toward the vent or chimney.
Adhesive-backed foam used for gasketing, vibration isolation, sealing and cabinet interfaces.
Heating equipment that warms air and distributes it through ductwork.
A sacrificial overcurrent protective device that opens a circuit when current exceeds its rating.
A heat-sensitive link designed to release or open at a specified temperature in certain safety applications.
A manual shutoff valve installed in a gas piping system.
A listed flexible connector used between fixed gas piping and an appliance where permitted.
An electrically controlled valve that regulates fuel gas flow to burners.
A service instrument used to connect to refrigeration systems and read high- and low-side pressures.
The temperature range over which certain blended refrigerants evaporate or condense at a given pressure.
An air inlet or outlet device with fixed openings and no adjustable damper.
A protective insert used where wires, tubing or piping pass through sheet metal or other sharp openings.
A start-assist device, commonly using a start capacitor and relay, intended for specific compressor applications.
A trade term commonly referring to high-side refrigerant pressure during operation.
An adjustable resistance element in older mechanical thermostats used to influence heating cycle timing.
A furnace component that transfers heat from combustion gases to the circulating indoor air without mixing the two.
Refrigeration equipment that can provide both cooling and heating by reversing the direction of heat transfer.
A ventilation device that transfers sensible heat between outgoing and incoming air streams.
An electric resistance heating element or assembly installed in an air handler or package unit.
A temperature safety control that interrupts burner operation if furnace temperature rises above its allowable range.
A pressure safety control that opens or signals a fault when high-side refrigerant pressure exceeds a set limit.
An electrically heated ignition element used to ignite gas burners.
Heating Seasonal Performance Factor 2, a standardized seasonal heating-efficiency rating for heat pumps.
A replaceable evaporative media panel used in many bypass and powered humidifiers.
A control that senses humidity and operates humidification or dehumidification equipment.
Heating, Ventilation and Air Conditioning.
An electronic control that manages ignition sequencing and flame proving on combustion equipment.
The motor that drives a draft inducer fan.
A compressor driven by variable-frequency electronics so capacity can modulate over a range.
A relay used to electrically separate one control circuit or device from another.
A shutoff valve installed to isolate a component for service.
An enclosure used to contain electrical splices and wiring connections.
A common trade reference to compressor start-assist products; actual component selection must match the compressor and application.
Heat associated with moisture removal or phase change rather than a direct dry-bulb temperature change.
An instrument or solution used to detect refrigerant or gas leaks, depending on the detector type.
A temperature, pressure or position switch that stops or permits operation based on a defined condition.
The pair of refrigerant tubes connecting indoor and outdoor sections of a split system.
The higher-voltage power circuit supplying HVAC equipment, motors, compressors or electric heaters.
The smaller refrigerant line that normally carries high-pressure liquid refrigerant toward the metering device during cooling.
An electrically operated valve installed in a liquid refrigerant line to control refrigerant flow.
A structured estimate of the heating and cooling required by a building under design conditions.
The control-voltage side of many residential HVAC systems, commonly 24 VAC.
A pressure control that opens or signals a fault when low-side pressure falls outside a defined range.
Locked Rotor Amps, a motor or compressor rating associated with starting current under locked-rotor conditions.
Gas pressure measured downstream of the gas valve and upstream of the burners on applicable equipment.
An ACCA residential duct-design procedure used to size and lay out duct systems.
An ACCA residential load-calculation procedure used to estimate heating and cooling loads.
An ACCA equipment-selection procedure used with load information to select residential HVAC equipment.
A thick sealant commonly used to seal duct joints and seams.
Minimum Circuit Ampacity, an equipment nameplate value used in sizing supply conductors according to applicable requirements.
Minimum Efficiency Reporting Value, a standardized filter rating related to particle capture performance.
A device such as a TXV, piston or electronic expansion valve that controls refrigerant flow into the evaporator.
A unit used to describe deep vacuum during refrigeration-system evacuation.
An instrument used to measure deep vacuum during refrigeration-system evacuation.
A ductless or limited-duct split system using one or more indoor units connected to outdoor equipment.
Maximum Overcurrent Protection, an equipment nameplate value identifying the maximum permitted overcurrent protective device rating.
The electronic control portion of certain ECM motors.
A pulley mounted on a motor shaft in a belt-driven blower system.
A motor with multiple speed taps used to select different operating speeds.
An HVAC system serving multiple independently controlled zones or indoor units.
A fine-control valve used to regulate small fluid or gas flows in service equipment and specialty applications.
A pressure regulator used with nitrogen cylinders for pressure testing, purging or brazing support.
Air or other gases in a refrigerant system that do not condense as the refrigerant does and can impair performance.
A device used in some refrigeration systems to separate compressor oil from discharge gas and return oil to the compressor.
A fixed refrigerant metering opening, often installed in a piston-style distributor assembly.
A protective device that opens when a motor or compressor experiences excessive current or temperature.
Chemical reaction with oxygen that can contribute to corrosion of metals and electrical contacts.
A U-shaped drain trap used in condensate piping where required by equipment pressure conditions.
A self-contained HVAC unit that houses major heating and/or cooling components in one cabinet.
A low-profile condensate pump used where space is limited.
A removable cabinet section or electrical enclosure used to access or protect components.
A fixed-orifice refrigerant metering component used in some HVAC systems.
A large supply or return air chamber attached to HVAC equipment.
The difference in pressure measured across a component such as a filter, coil, duct section or fitting.
A switch that changes state when sensed pressure reaches a defined threshold.
A reference showing saturation temperature corresponding to pressure for a specific refrigerant.
The normal condensate drain connection intended to carry water away from an evaporator pan.
A thermostat that changes temperature setpoints according to a programmed schedule.
The study of the thermodynamic properties of moist air, including temperature, humidity and enthalpy.
A mechanical tool used to remove pulleys, wheels or other press-fit components from shafts.
A controlled refrigeration procedure that moves refrigerant into part of the system for service or operation where the equipment is designed for it.
A fitting or connector designed for rapid connection and disconnection in approved service applications.
A high-pressure HFC refrigerant widely used in residential air-conditioning and heat-pump equipment manufactured in prior generations.
An A2L refrigerant used in many newer residential air-conditioning and heat-pump systems.
A refillable cylinder specifically rated and identified for storing recovered refrigerant.
Equipment used to remove refrigerant from a system and transfer it into an approved recovery cylinder.
The working fluid that changes pressure, temperature and often phase as it moves heat through a refrigeration cycle.
The amount of refrigerant contained in a system.
A grille-like air outlet or inlet that includes an adjustable damper.
An electrically operated switch used to control another circuit.
Air drawn from occupied spaces back toward the furnace or air handler.
A vertical or horizontal duct section that connects the return system to the equipment.
A valve that changes refrigerant-flow direction so a heat pump can switch between heating and cooling.
Rated Load Amps, a compressor or motor nameplate rating used for equipment application and electrical reference.
A safety device that opens if flame or excessive heat appears outside the intended combustion path.
A capacitor designed to remain in a motor or compressor circuit during operation.
A secondary pan installed beneath equipment or a coil to help contain water if the primary drainage system fails.
The boiling or condensing temperature corresponding to refrigerant pressure.
A spring-loaded valve core used in many refrigerant service ports.
A compressor design that uses orbiting and stationary scroll elements to compress refrigerant vapor.
An auxiliary condensate drain or overflow connection intended to provide warning or backup drainage.
Seasonal Energy Efficiency Ratio 2, a standardized seasonal cooling-efficiency rating.
A connection point used by qualified technicians to access refrigerant-system pressure.
A valve on outdoor equipment used to isolate or access refrigerant piping.
A self-tapping or self-drilling screw commonly used to assemble HVAC sheet-metal components.
A condition where equipment starts and stops more frequently than normal instead of completing stable operating cycles.
A viewing device used in some systems to observe fluid condition, flow or moisture indication.
A ring or feature on some fan assemblies that helps distribute condensate or water.
A lower-temperature metal-joining process used in some plumbing and hydronic applications.
An electrically operated valve used to start or stop fluid or refrigerant flow.
A flat-blade electrical terminal used for quick wire connections.
An HVAC system with major components located in separate indoor and outdoor cabinets.
A capacitor used briefly during motor or compressor startup to provide additional starting torque.
Air-system pressure associated with resistance the blower must overcome in filters, coils, ducts, fittings and registers.
The amount by which liquid refrigerant temperature is below saturation temperature at the measured pressure.
An accumulator installed in the suction line to reduce the risk of liquid refrigerant reaching the compressor.
The larger refrigerant line that normally carries low-pressure vapor from the evaporator toward the compressor in cooling mode.
A trade term commonly referring to low-side refrigerant pressure during operation.
The amount by which refrigerant vapor temperature is above saturation temperature at the measured pressure.
Conditioned air delivered from HVAC equipment to occupied spaces.
A sheet-metal fitting that connects a branch duct to a register or grille opening.
The main chamber attached to the discharge side of a furnace or air handler.
A protective device intended to reduce damage from transient electrical voltage spikes.
The difference between supply-air and return-air temperatures across heating equipment.
The difference between return-air and supply-air temperatures across cooling equipment.
A temperature-sensitive resistor used in electronic HVAC controls and sensors.
A heat-responsive device used on older standing-pilot systems to prove pilot flame.
The device that senses indoor conditions and requests heating, cooling or fan operation.
A refrigerant metering device that modulates flow into the evaporator based on sensed operating conditions.
A traditional unit of cooling capacity equal to 12,000 Btu/h nominally.
An electrical device used to change voltage, commonly reducing line voltage to 24 VAC for controls.
A device used to maintain water in a plumbing trap where evaporation could allow the trap to dry.
Thermostatic expansion valve, a common modulating refrigerant metering device.
A fitting that allows a piping connection to be separated without cutting the pipe.
A self-contained heating appliance that discharges heated air directly into a space.
An ultraviolet germicidal lamp used in some HVAC applications, commonly aimed at coil or drain-pan surfaces.
A pump used to evacuate air and moisture from a sealed refrigeration system.
A hose designed for low-restriction evacuation work and deep-vacuum service.
HVAC equipment capable of modulating output over a range instead of operating only at fixed stages.
A blower system that can adjust airflow for different modes, capacities or control strategies.
The speed of air moving through a duct or air device, commonly expressed in feet per minute.
The portion of a venting system that connects an appliance to a chimney or common vent.
A motorized or automatic damper used in some vent systems to reduce standby losses or control vent flow.
Intentional movement of outdoor air into or indoor air out of a building.
A rubber, spring or composite mount used to reduce transmission of equipment vibration.
A unit of apparent electrical power used with transformers and AC electrical loads.
A temperature measurement influenced by evaporative cooling and therefore related to air moisture content.
A flexible electrical conduit assembly commonly used between a disconnect and outdoor HVAC equipment.
A twist-on insulated connector used to join electrical conductors where appropriate.
A motorized damper that opens or closes to control airflow to a zone.
A control panel that coordinates multiple thermostats and zone dampers with HVAC equipment.
An HVAC arrangement that independently controls different areas using dampers, multiple indoor units or other zoning methods.
Plain-English explanations of equipment and system operation.
Technical fundamentals for refrigeration, airflow, pressure, electrical and controls.
Start with the symptom when equipment is not operating normally.
Understand the terms contractors use in replacement proposals and equipment discussions.