HVAC Terms, Parts & Trade Language

HVAC Glossary & Parts Dictionary

An extensive plain-English reference for the equipment, parts, fittings, controls, tools, measurements and trade terms commonly used by HVAC mechanics, suppliers, contractors and homeowners.

Browse Aโ€“Z

265 HVAC terms and trade components

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.

A B C D E F G H I J K L M N O P Q R S T U V W Z
Quick Reference

HVAC Abbreviations

Common shorthand found on nameplates, proposals, wiring diagrams and service reports.

View abbreviations โ†’
Quick Reference

HVAC Measurements

Capacity, airflow, pressure, temperature and refrigeration measurements explained.

View measurements โ†’
Trade Reference

HVAC Parts & Supply-House Terms

A focused list of parts, fittings, fasteners, controls, tools and supplies mechanics order and install.

View parts reference โ†’
Glossary

A

Refrigeration

A2L Refrigerant

A 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.

Learn more: Refrigeration cycle โ†’

Electrical Part

AC Disconnect

A service disconnect located near outdoor HVAC equipment that provides a local means of disconnecting electrical power.

Cabinet Part

Access Panel

A removable equipment panel used to reach serviceable components inside a furnace, air handler, condenser or package unit.

Refrigeration Part

Accumulator

A vessel typically installed in the suction line to help prevent liquid refrigerant from reaching the compressor.

Controls Part

Actuator

An electric or electronic device that moves a damper, valve or other controlled component.

IAQ

Air Cleaner

A device or system used to remove airborne particles from recirculated indoor air.

Equipment

Air Handler

An indoor HVAC assembly that normally contains a blower and coil and may also contain electric heat, filters or controls.

Hydronic Part

Air Scoop

A hydronic fitting designed to help separate entrained air from circulating water.

Hydronic Part

Air Separator

A hydronic component that removes entrained or dissolved air from a hot-water heating system.

Hydronic Part

Air Vent

A manual or automatic device used to release trapped air from hydronic piping or terminal units.

IAQ

Air Washer

Equipment that passes air through water or wetted media for cleaning, humidification or process conditioning.

Controls Part

Airflow Switch

A switch used to prove that air is moving before or during operation of certain HVAC equipment.

Measurement

Ambient Temperature

The surrounding air temperature near equipment or a component.

Electrical Measurement

Amp Draw

The electrical current consumed by a motor, compressor, heater or other load during operation.

Service Instrument

Anemometer

An instrument used to measure air velocity and, with appropriate methods, estimate airflow.

Controls Part

Anti-Short-Cycle Timer

A time-delay control that helps prevent a compressor or other equipment from restarting too soon after shutdown.

Hydronic Control

Aquastat

A temperature-sensing control commonly used on boilers and hydronic systems to start, stop or limit equipment based on water temperature.

Glossary

B

Duct Part

Backdraft Damper

A damper designed to allow airflow in one direction while limiting reverse airflow.

Duct Part

Balancing Damper

A manual or automatic damper used to adjust airflow through a duct branch.

Piping Part

Ball Valve

A quarter-turn shutoff valve that uses a drilled ball to open or close fluid flow.

Venting Part

Barometric Damper

A draft-regulating device used on some combustion vent systems to help maintain proper draft.

Blower Part

Belt Drive

A motor-and-pulley drive arrangement that turns a blower wheel through a belt.

Air Distribution

Blower

The fan assembly that moves air through a furnace, air handler and duct system.

Safety Control

Blower Door Switch

A switch that interrupts equipment operation when a furnace or air-handler access panel is removed.

Blower Part

Blower Housing

The enclosure around a centrifugal blower wheel that directs air into the supply path.

Motor

Blower Motor

The motor that drives the indoor blower wheel.

Blower Part

Blower Wheel

A centrifugal fan wheel, often called a squirrel-cage wheel, that moves air through the indoor equipment.

Equipment

Boiler

Heating equipment that transfers heat into water for distribution through radiators, baseboard, radiant tubing or other hydronic terminals.

Hydronic Part

Boiler Drain

A drain valve used to drain water from boilers, piping or hydronic components.

Trade Process

Brazing

A metal-joining process using a filler metal with a melting temperature above typical soldering temperatures, commonly used for copper refrigerant piping.

Electrical Part

Breaker

An overcurrent protective device that opens an electrical circuit when current exceeds its rating or a fault occurs.

Capacity

BTU

British thermal unit, a unit of heat energy. HVAC capacities are commonly expressed in Btu per hour.

Heating Part

Burner

A device that mixes fuel and air and supports controlled combustion in a furnace or boiler.

Heating Part

Burner Orifice

A precisely sized opening that meters gas flow into a burner.

Heating Part

Burner Rack

The assembly that supports and aligns multiple furnace burners.

Duct Part

Bypass Damper

A damper used in some zoning systems to relieve excess supply pressure by routing air around part of the distribution system.

IAQ Part

Bypass Humidifier

A humidifier that uses a duct bypass and furnace airflow to move air across a wetted evaporative pad.

Glossary

C

Electrical Part

Capacitor

An electrical component that stores energy and is commonly used with single-phase motors and compressors for starting or running.

Refrigeration Part

Capillary Tube

A fixed-bore refrigerant metering device made from small-diameter tubing.

Refrigeration Part

Catch-All Dryer

A trade term often used for a filter-drier installed in a refrigeration system to remove moisture, acid and debris.

Piping Part

Check Valve

A valve that allows flow in one direction and restricts reverse flow.

Controls Part

Circuit Board

An electronic control board that receives inputs and sends outputs to operate HVAC components.

Hydronic Part

Circulator Pump

A pump used to move heated water through a hydronic heating system.

Service Supply

Coil Cleaner

A chemical cleaning product formulated for evaporator or condenser coil surfaces. Product selection must match the coil and manufacturer guidance.

Heating

Combustion Air

Air supplied to a fuel-burning appliance for combustion.

Service Instrument

Combustion Analyzer

An instrument used to measure combustion gases and evaluate appliance combustion performance.

Accessory

Compressor Blanket

An acoustic or thermal wrap installed around some compressors to reduce sound or help manage temperature.

Electrical Part

Compressor Crankcase Heater

A heater used on some compressors to help prevent refrigerant migration and dilution of compressor oil during off cycles.

Cooling

Condensate

Water formed when moisture in indoor air condenses on a cold evaporator coil.

Drainage Part

Condensate Drain

Piping that carries condensate away from an evaporator coil, air handler, furnace or dehumidifier.

Drainage Part

Condensate Pan

A pan that collects water beneath an evaporator coil or other condensing component.

Drainage Part

Condensate Pump

A small pump used to lift condensate to a suitable drain point when gravity drainage is not practical.

Refrigeration

Condenser

The heat exchanger where refrigerant rejects heat and condenses from vapor toward liquid. In cooling mode, it is normally outdoors.

Learn more: Air conditioning โ†’

Refrigeration Part

Condenser Coil

The coil surface in the condenser where refrigerant rejects heat.

Motor/Fan Part

Condenser Fan

The outdoor fan that moves air across a condenser or outdoor heat-pump coil.

Motor

Condenser Fan Motor

The motor that drives the outdoor fan blade.

Electrical Part

Contactor

An electrically controlled switch used to apply line voltage to compressors, fan motors and other loads.

Electrical Part

Control Transformer

A transformer that commonly reduces line voltage to 24 VAC for HVAC control circuits.

Efficiency

COP

Coefficient of Performance, a ratio comparing useful heating or cooling output with energy input.

Trade Part

Copper Fitting

A fitting used with copper tubing, including elbows, couplings, reducers and tees.

Service Tool

Core Removal Tool

A tool used to remove or replace Schrader valve cores, often while maintaining system access.

Electrical Part

Crankcase Heater

A heater attached to or installed in a compressor sump to keep compressor oil warm during off periods.

Sheet Metal Part

Curb Adapter

A fabricated transition used to mount replacement rooftop equipment to an existing roof curb.

Controls

Cut-In Pressure

The pressure at which a pressure control closes or initiates operation.

Controls

Cut-Out Pressure

The pressure at which a pressure control opens or stops operation.

Efficiency

Cycling Loss

Efficiency loss associated with repeated equipment startup and shutdown rather than steady-state operation.

Glossary

D

Duct Part

Damper

A plate or blade installed in ductwork to regulate or shut off airflow.

Heat Pump Control

Defrost Board

An electronic control used on heat pumps to manage outdoor-coil defrost operation.

Heat Pump

Defrost Cycle

A temporary heat-pump operating mode used to remove frost from the outdoor coil during heating operation.

Measurement

Delta T

Temperature difference between two points, such as return and supply air.

IAQ/Refrigeration

Desiccant

A moisture-absorbing material used in filter-driers, dehumidification equipment and other applications.

Air Distribution Part

Diffuser

A supply-air outlet designed to distribute air in a specific pattern.

Service Instrument

Digital Manifold

An electronic manifold instrument used to measure refrigerant pressures, temperatures and calculated refrigeration values.

Electrical Part

Disconnect

A local switching means used to isolate equipment from electrical power.

Heating Part

Draft Inducer

A motor-driven fan that establishes airflow through a furnace heat exchanger and vent system before ignition.

Drainage Part

Drain Trap

A shaped section of condensate piping used where required to allow proper drainage under positive or negative air pressure.

Psychrometrics

Dry Bulb Temperature

Ordinary air temperature measured without accounting for evaporative cooling effects.

Duct Material

Duct Board

Rigid fiberglass board used to fabricate certain duct systems or plenums.

Duct Part

Duct Collar

A round or rectangular fitting used to connect a branch duct to a trunk, plenum or air device.

Duct Material

Duct Liner

Insulation installed on the inside surface of metal ductwork for thermal or acoustic control.

Trade Supply

Duct Sealant

Mastic or approved sealant used to seal duct joints and leakage points.

Equipment

Ductless Mini-Split

A split-system heat pump or air conditioner using one or more indoor units without conventional central ductwork.

Glossary

E

Motor

ECM Motor

Electronically commutated motor used in many modern blowers and fans for efficient, electronically controlled operation.

Ventilation Part

Economizer

A control and damper arrangement that can use outdoor air for cooling when conditions are suitable.

Efficiency

EER2

Energy Efficiency Ratio 2, a standardized cooling-efficiency rating at specified operating conditions.

Refrigeration Part

Electronic Expansion Valve

An electronically controlled refrigerant metering device that adjusts flow through commands from a controller.

Heat Pump Control

Emergency Heat

A thermostat mode that disables normal heat-pump compressor heating and uses the configured backup heat source.

Controls Part

End Switch

An auxiliary switch that proves a damper, valve or actuator has reached a commanded position.

Ventilation Equipment

Energy Recovery Ventilator

A ventilation device that exchanges heat and some moisture between exhaust and incoming outdoor air streams.

Refrigeration Process

Evacuation

The process of removing air, moisture and non-condensable gases from a sealed refrigerant circuit using a vacuum pump.

Refrigeration Part

Evaporator Coil

The heat exchanger where refrigerant absorbs heat and evaporates. In standard cooling operation, this is normally the indoor coil.

Hydronic Part

Expansion Tank

A tank that accommodates thermal expansion of water in a closed hydronic heating system.

Airflow Measurement

External Static Pressure

Pressure resistance measured across defined external components of an air-moving system, often used with blower data to estimate airflow.

Glossary

F

Fan Part

Fan Blade

A propeller-style blade used on condenser fans, heat pumps, exhaust fans and other axial-airflow applications.

Controls Part

Fan Center

A packaged transformer and relay assembly commonly used in older or simple HVAC control systems.

Equipment

Fan Coil

An indoor unit containing a fan and coil used to heat or cool air.

Heating Control

Fan Limit Control

A control used on some furnaces to manage blower operation and high-temperature limit protection.

Airflow/IAQ

Filter

A media device used to capture airborne particles and protect HVAC equipment from debris.

Air Distribution Part

Filter Grille

A return-air grille designed to hold an air filter.

Refrigeration Part

Filter-Drier

A sealed refrigerant-line component containing desiccant and filtration media to remove moisture, acid and debris.

Heating Safety

Flame Rollout Switch

A safety switch designed to open if flame or excessive heat is detected outside the normal burner/heat-exchanger area.

Heating Part

Flame Sensor

A device used by many gas furnaces to prove that burner flame is present.

Refrigeration/Piping Part

Flare Fitting

A mechanical tubing connection using a flared tube end and matching nut/fitting, common on mini-splits and some refrigeration systems.

Trade Part

Flex Connector

A flexible connection used to reduce vibration transmission in duct, gas or piping applications.

Duct Material

Flex Duct

Flexible insulated duct consisting of an inner liner, reinforcing helix, insulation and outer jacket.

Drainage Safety

Float Switch

A condensate safety control that opens a control circuit when water rises to an abnormal level.

Venting

Flue

A passage that carries combustion products from fuel-burning equipment toward the vent or chimney.

Trade Supply

Foam Tape

Adhesive-backed foam used for gasketing, vibration isolation, sealing and cabinet interfaces.

Equipment

Furnace

Heating equipment that warms air and distributes it through ductwork.

Electrical Part

Fuse

A sacrificial overcurrent protective device that opens a circuit when current exceeds its rating.

Safety Part

Fusible Link

A heat-sensitive link designed to release or open at a specified temperature in certain safety applications.

Glossary

G

Gas Piping Part

Gas Cock

A manual shutoff valve installed in a gas piping system.

Gas Piping Part

Gas Flex Connector

A listed flexible connector used between fixed gas piping and an appliance where permitted.

Heating Part

Gas Valve

An electrically controlled valve that regulates fuel gas flow to burners.

Service Instrument

Gauge Manifold

A service instrument used to connect to refrigeration systems and read high- and low-side pressures.

Refrigeration

Glide

The temperature range over which certain blended refrigerants evaporate or condense at a given pressure.

Air Distribution Part

Grille

An air inlet or outlet device with fixed openings and no adjustable damper.

Trade Part

Grommet

A protective insert used where wires, tubing or piping pass through sheet metal or other sharp openings.

Glossary

H

Electrical Accessory

Hard-Start Kit

A start-assist device, commonly using a start capacitor and relay, intended for specific compressor applications.

Refrigeration

Head Pressure

A trade term commonly referring to high-side refrigerant pressure during operation.

Thermostat Part

Heat Anticipator

An adjustable resistance element in older mechanical thermostats used to influence heating cycle timing.

Heating Part

Heat Exchanger

A furnace component that transfers heat from combustion gases to the circulating indoor air without mixing the two.

Equipment

Heat Pump

Refrigeration equipment that can provide both cooling and heating by reversing the direction of heat transfer.

Learn more: Heat pumps โ†’

Ventilation Equipment

Heat Recovery Ventilator

A ventilation device that transfers sensible heat between outgoing and incoming air streams.

Electric Heat Part

Heat Strip

An electric resistance heating element or assembly installed in an air handler or package unit.

Heating Safety

High-Limit Switch

A temperature safety control that interrupts burner operation if furnace temperature rises above its allowable range.

Refrigeration Safety

High-Pressure Switch

A pressure safety control that opens or signals a fault when high-side refrigerant pressure exceeds a set limit.

Heating Part

Hot-Surface Igniter

An electrically heated ignition element used to ignite gas burners.

Efficiency

HSPF2

Heating Seasonal Performance Factor 2, a standardized seasonal heating-efficiency rating for heat pumps.

IAQ Part

Humidifier Pad

A replaceable evaporative media panel used in many bypass and powered humidifiers.

IAQ Control

Humidistat

A control that senses humidity and operates humidification or dehumidification equipment.

General

HVAC

Heating, Ventilation and Air Conditioning.

Glossary

I

Heating Control

Ignition Control Module

An electronic control that manages ignition sequencing and flame proving on combustion equipment.

Heating Motor

Inducer Motor

The motor that drives a draft inducer fan.

Refrigeration Part

Inverter Compressor

A compressor driven by variable-frequency electronics so capacity can modulate over a range.

Controls Part

Isolation Relay

A relay used to electrically separate one control circuit or device from another.

Hydronic/Piping Part

Isolation Valve

A shutoff valve installed to isolate a component for service.

Glossary

J

Electrical Part

Junction Box

An enclosure used to contain electrical splices and wiring connections.

Glossary

K

Trade Term

Kickstart

A common trade reference to compressor start-assist products; actual component selection must match the compressor and application.

Glossary

L

Service Instrument

Leak Detector

An instrument or solution used to detect refrigerant or gas leaks, depending on the detector type.

Safety Control

Limit Switch

A temperature, pressure or position switch that stops or permits operation based on a defined condition.

Refrigeration Part

Line Set

The pair of refrigerant tubes connecting indoor and outdoor sections of a split system.

Electrical

Line Voltage

The higher-voltage power circuit supplying HVAC equipment, motors, compressors or electric heaters.

Refrigeration Part

Liquid Line

The smaller refrigerant line that normally carries high-pressure liquid refrigerant toward the metering device during cooling.

Refrigeration Part

Liquid-Line Solenoid

An electrically operated valve installed in a liquid refrigerant line to control refrigerant flow.

System Sizing

Load Calculation

A structured estimate of the heating and cooling required by a building under design conditions.

Learn more: HVAC sizing โ†’

Electrical

Low Voltage

The control-voltage side of many residential HVAC systems, commonly 24 VAC.

Refrigeration Safety

Low-Pressure Switch

A pressure control that opens or signals a fault when low-side pressure falls outside a defined range.

Electrical Rating

LRA

Locked Rotor Amps, a motor or compressor rating associated with starting current under locked-rotor conditions.

Glossary

M

Heating Measurement

Manifold Pressure

Gas pressure measured downstream of the gas valve and upstream of the burners on applicable equipment.

Design Method

Manual D

An ACCA residential duct-design procedure used to size and lay out duct systems.

Design Method

Manual J

An ACCA residential load-calculation procedure used to estimate heating and cooling loads.

Design Method

Manual S

An ACCA equipment-selection procedure used with load information to select residential HVAC equipment.

Duct Supply

Mastic

A thick sealant commonly used to seal duct joints and seams.

Electrical Rating

MCA

Minimum Circuit Ampacity, an equipment nameplate value used in sizing supply conductors according to applicable requirements.

Filtration

MERV

Minimum Efficiency Reporting Value, a standardized filter rating related to particle capture performance.

Refrigeration Part

Metering Device

A device such as a TXV, piston or electronic expansion valve that controls refrigerant flow into the evaporator.

Vacuum Measurement

Micron

A unit used to describe deep vacuum during refrigeration-system evacuation.

Service Instrument

Micron Gauge

An instrument used to measure deep vacuum during refrigeration-system evacuation.

Equipment

Mini-Split

A ductless or limited-duct split system using one or more indoor units connected to outdoor equipment.

Electrical Rating

MOCP

Maximum Overcurrent Protection, an equipment nameplate value identifying the maximum permitted overcurrent protective device rating.

Motor Part

Motor Module

The electronic control portion of certain ECM motors.

Blower Part

Motor Pulley

A pulley mounted on a motor shaft in a belt-driven blower system.

Motor

Multi-Tap Motor

A motor with multiple speed taps used to select different operating speeds.

Equipment/Controls

Multi-Zone System

An HVAC system serving multiple independently controlled zones or indoor units.

Glossary

N

Service Part

Needle Valve

A fine-control valve used to regulate small fluid or gas flows in service equipment and specialty applications.

Service Tool

Nitrogen Regulator

A pressure regulator used with nitrogen cylinders for pressure testing, purging or brazing support.

Refrigeration

Non-Condensables

Air or other gases in a refrigerant system that do not condense as the refrigerant does and can impair performance.

Glossary

O

Refrigeration Part

Oil Separator

A device used in some refrigeration systems to separate compressor oil from discharge gas and return oil to the compressor.

Refrigeration Part

Orifice

A fixed refrigerant metering opening, often installed in a piston-style distributor assembly.

Electrical Safety

Overload

A protective device that opens when a motor or compressor experiences excessive current or temperature.

Materials

Oxidation

Chemical reaction with oxygen that can contribute to corrosion of metals and electrical contacts.

Glossary

P

Drainage Part

P-Trap

A U-shaped drain trap used in condensate piping where required by equipment pressure conditions.

Equipment

Package Unit

A self-contained HVAC unit that houses major heating and/or cooling components in one cabinet.

Drainage Part

Pancake Condensate Pump

A low-profile condensate pump used where space is limited.

Electrical/Cabinet Part

Panel

A removable cabinet section or electrical enclosure used to access or protect components.

Refrigeration Part

Piston

A fixed-orifice refrigerant metering component used in some HVAC systems.

Duct Part

Plenum

A large supply or return air chamber attached to HVAC equipment.

Measurement

Pressure Drop

The difference in pressure measured across a component such as a filter, coil, duct section or fitting.

Controls Part

Pressure Switch

A switch that changes state when sensed pressure reaches a defined threshold.

Service Reference

Pressure-Temperature Chart

A reference showing saturation temperature corresponding to pressure for a specific refrigerant.

Drainage Part

Primary Drain

The normal condensate drain connection intended to carry water away from an evaporator pan.

Controls

Programmable Thermostat

A thermostat that changes temperature setpoints according to a programmed schedule.

Service Tool

Puller

A mechanical tool used to remove pulleys, wheels or other press-fit components from shafts.

Refrigeration Process

Pump-Down

A controlled refrigeration procedure that moves refrigerant into part of the system for service or operation where the equipment is designed for it.

Glossary

Q

Service Part

Quick Disconnect

A fitting or connector designed for rapid connection and disconnection in approved service applications.

Glossary

R

Refrigeration

R-410A

A high-pressure HFC refrigerant widely used in residential air-conditioning and heat-pump equipment manufactured in prior generations.

Refrigeration

R-454B

An A2L refrigerant used in many newer residential air-conditioning and heat-pump systems.

Service Equipment

Recovery Cylinder

A refillable cylinder specifically rated and identified for storing recovered refrigerant.

Service Equipment

Recovery Machine

Equipment used to remove refrigerant from a system and transfer it into an approved recovery cylinder.

Refrigeration

Refrigerant

The working fluid that changes pressure, temperature and often phase as it moves heat through a refrigeration cycle.

Refrigeration

Refrigerant Charge

The amount of refrigerant contained in a system.

Air Distribution Part

Register

A grille-like air outlet or inlet that includes an adjustable damper.

Electrical Part

Relay

An electrically operated switch used to control another circuit.

Air Distribution

Return Air

Air drawn from occupied spaces back toward the furnace or air handler.

Duct Part

Return Drop

A vertical or horizontal duct section that connects the return system to the equipment.

Heat Pump Part

Reversing Valve

A valve that changes refrigerant-flow direction so a heat pump can switch between heating and cooling.

Electrical Rating

RLA

Rated Load Amps, a compressor or motor nameplate rating used for equipment application and electrical reference.

Heating Safety

Rollout Switch

A safety device that opens if flame or excessive heat appears outside the intended combustion path.

Electrical Part

Run Capacitor

A capacitor designed to remain in a motor or compressor circuit during operation.

Glossary

S

Drainage Part

Safety Pan

A secondary pan installed beneath equipment or a coil to help contain water if the primary drainage system fails.

Service Part

Schrader Core

A spring-loaded valve core used in many refrigerant service ports.

Refrigeration Part

Scroll Compressor

A compressor design that uses orbiting and stationary scroll elements to compress refrigerant vapor.

Drainage Part

Secondary Drain

An auxiliary condensate drain or overflow connection intended to provide warning or backup drainage.

Refrigeration Part

Service Port

A connection point used by qualified technicians to access refrigerant-system pressure.

Refrigeration Part

Service Valve

A valve on outdoor equipment used to isolate or access refrigerant piping.

Trade Fastener

Sheet Metal Screw

A self-tapping or self-drilling screw commonly used to assemble HVAC sheet-metal components.

Troubleshooting

Short Cycling

A condition where equipment starts and stops more frequently than normal instead of completing stable operating cycles.

Learn more: AC short cycling โ†’

Refrigeration/Hydronic Part

Sight Glass

A viewing device used in some systems to observe fluid condition, flow or moisture indication.

Fan Part

Slinger Ring

A ring or feature on some fan assemblies that helps distribute condensate or water.

Trade Process

Soldering

A lower-temperature metal-joining process used in some plumbing and hydronic applications.

Controls/Piping Part

Solenoid Valve

An electrically operated valve used to start or stop fluid or refrigerant flow.

Electrical Part

Spade Connector

A flat-blade electrical terminal used for quick wire connections.

Equipment

Split System

An HVAC system with major components located in separate indoor and outdoor cabinets.

Electrical Part

Start Capacitor

A capacitor used briefly during motor or compressor startup to provide additional starting torque.

Airflow

Static Pressure

Air-system pressure associated with resistance the blower must overcome in filters, coils, ducts, fittings and registers.

Learn more: Static pressure โ†’

Refrigeration Part

Suction Accumulator

An accumulator installed in the suction line to reduce the risk of liquid refrigerant reaching the compressor.

Refrigeration Part

Suction Line

The larger refrigerant line that normally carries low-pressure vapor from the evaporator toward the compressor in cooling mode.

Refrigeration

Suction Pressure

A trade term commonly referring to low-side refrigerant pressure during operation.

Air Distribution

Supply Air

Conditioned air delivered from HVAC equipment to occupied spaces.

Duct Part

Supply Boot

A sheet-metal fitting that connects a branch duct to a register or grille opening.

Duct Part

Supply Plenum

The main chamber attached to the discharge side of a furnace or air handler.

Electrical Accessory

Surge Protector

A protective device intended to reduce damage from transient electrical voltage spikes.

Glossary

T

Cooling Measurement

Temperature Split

The difference between return-air and supply-air temperatures across cooling equipment.

Sensor

Thermistor

A temperature-sensitive resistor used in electronic HVAC controls and sensors.

Heating Part

Thermocouple

A heat-responsive device used on older standing-pilot systems to prove pilot flame.

Refrigeration Part

Thermostatic Expansion Valve

A refrigerant metering device that modulates flow into the evaporator based on sensed operating conditions.

Capacity

Ton

A traditional unit of cooling capacity equal to 12,000 Btu/h nominally.

Electrical Part

Transformer

An electrical device used to change voltage, commonly reducing line voltage to 24 VAC for controls.

Drainage Part

Trap Primer

A device used to maintain water in a plumbing trap where evaporation could allow the trap to dry.

Refrigeration Part

TXV

Thermostatic expansion valve, a common modulating refrigerant metering device.

Glossary

U

Piping Part

Union

A fitting that allows a piping connection to be separated without cutting the pipe.

Heating Equipment

Unit Heater

A self-contained heating appliance that discharges heated air directly into a space.

IAQ Part

UV-C Lamp

An ultraviolet germicidal lamp used in some HVAC applications, commonly aimed at coil or drain-pan surfaces.

Glossary

V

Service Equipment

Vacuum Pump

A pump used to evacuate air and moisture from a sealed refrigeration system.

Service Tool

Vacuum-Rated Hose

A hose designed for low-restriction evacuation work and deep-vacuum service.

Equipment

Variable Capacity

HVAC equipment capable of modulating output over a range instead of operating only at fixed stages.

Motor/Controls

Variable-Speed Blower

A blower system that can adjust airflow for different modes, capacities or control strategies.

Airflow Measurement

Velocity

The speed of air moving through a duct or air device, commonly expressed in feet per minute.

Venting Part

Vent Connector

The portion of a venting system that connects an appliance to a chimney or common vent.

Venting Part

Vent Damper

A motorized or automatic damper used in some vent systems to reduce standby losses or control vent flow.

IAQ

Ventilation

Intentional movement of outdoor air into or indoor air out of a building.

Trade Part

Vibration Isolator

A rubber, spring or composite mount used to reduce transmission of equipment vibration.

Electrical

Volt-Ampere

A unit of apparent electrical power used with transformers and AC electrical loads.

Glossary

W

Psychrometrics

Wet Bulb Temperature

A temperature measurement influenced by evaporative cooling and therefore related to air moisture content.

Electrical Part

Whip

A flexible electrical conduit assembly commonly used between a disconnect and outdoor HVAC equipment.

Electrical Part

Wire Nut

A twist-on insulated connector used to join electrical conductors where appropriate.

Glossary

Z

Controls/Duct Part

Zone Damper

A motorized damper that opens or closes to control airflow to a zone.

Controls Part

Zone Panel

A control panel that coordinates multiple thermostats and zone dampers with HVAC equipment.

Controls

Zone System

An HVAC arrangement that independently controls different areas using dampers, multiple indoor units or other zoning methods.

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