Glossary
A
Absolute Humidity
The amount of water vapor present in a given volume of air, typically measured in grams per cubic meter.
TopAC
Abbreviation for air conditioning or alternating current, depending on the context.
TopAccumulator
A refrigeration component that prevents liquid refrigerant from entering the compressor.
TopACH (Air Changes Per Hour)
A measurement indicating how many times the air inside a building is completely replaced in one hour.
TopActivated Carbon Filter
A filter that removes odors, smoke, and volatile organic compounds from indoor air.
TopAdaptive Thermostat
A programmable thermostat that automatically adjusts temperature settings based on usage patterns.
TopAFUE
Annual Fuel Utilization Efficiency. A rating that measures how efficiently a furnace converts fuel into usable heat over a heating season.
TopAir Balancing
The process of adjusting airflow throughout an HVAC system to provide consistent comfort in every room.
TopAir Filter
A replaceable component that captures dust, pollen, and airborne particles before air circulates through the HVAC system.
TopAir Handler
An indoor HVAC unit containing the blower, evaporator coil, and other components responsible for circulating conditioned air.
TopAirflow
The movement of conditioned air through ductwork and into living spaces.
TopAmbient Temperature
The temperature of the surrounding environment where HVAC equipment operates.
TopASHRAE
The American Society of Heating, Refrigerating and Air-Conditioning Engineers, an organization that develops industry standards.
TopB
Backdraft
The reverse flow of combustion gases into a building instead of safely venting outdoors.
TopBalance Point
The outdoor temperature at which a home’s heat loss equals the heat produced by the HVAC system.
TopBlower
A fan assembly that moves conditioned air through ductwork and into occupied spaces.
TopBlower Door Test
An energy audit procedure used to measure how airtight a building is.
TopBoiler
A heating appliance that heats water or creates steam for distribution through radiators or hydronic systems.
TopBTU
British Thermal Unit, a standard measurement used to describe heating and cooling capacity.
TopBTUH
British Thermal Units per Hour, indicating how much heating or cooling equipment can produce in one hour.
TopBurner
The component within a furnace or boiler where fuel is ignited to produce heat.
TopBypass Damper
A damper that redirects excess airflow to help maintain proper system pressure in zoned HVAC systems.
TopC
Capacity
The amount of heating or cooling an HVAC system can provide, typically measured in BTUs per hour or tons.
TopCapacitor
An electrical component that stores and releases energy to help start and operate HVAC motors.
TopCarbon Monoxide (CO)
A colorless, odorless gas produced by incomplete combustion that can become dangerous if allowed to accumulate indoors.
TopCentral Air Conditioning
A whole-home cooling system that distributes conditioned air through a network of ducts.
TopCFM
Cubic Feet per Minute, a measurement used to describe airflow through an HVAC system.
TopCharge
The amount of refrigerant contained within an air conditioning or heat pump system.
TopCompressor
The heart of a refrigeration system that compresses refrigerant and circulates it through the cooling cycle.
TopCompressor Lockout
A safety feature that prevents compressor operation when potentially damaging conditions are detected.
TopCondensate
Water created when moisture is removed from indoor air during the cooling process.
TopCondensate Drain
A pipe or tubing that safely removes condensation produced by an air conditioner or furnace.
TopCondenser Coil
The outdoor coil where refrigerant releases heat absorbed from inside the home.
TopCondenser Fan
The fan located in the outdoor unit that moves air across the condenser coil.
TopConstant Air Volume (CAV)
An HVAC system that delivers a steady volume of air while varying the temperature as needed.
TopControl Board
The electronic circuit board that manages HVAC system operation and safety functions.
TopCooling Load
The amount of heat that must be removed from a building to maintain the desired indoor temperature.
TopD
Damper
A movable plate installed in ductwork to regulate or redirect airflow.
TopDefrost Cycle
A heat pump function that temporarily reverses operation to remove frost from the outdoor coil.
TopDehumidifier
A device designed to remove excess moisture from indoor air for improved comfort.
TopDiffuser
An air outlet that distributes conditioned air evenly throughout a room.
TopDigital Thermostat
An electronic thermostat that provides precise temperature control and programming features.
TopDirect Vent Furnace
A furnace that draws combustion air from outside and vents exhaust directly outdoors.
TopDisconnect Switch
A safety switch used to disconnect electrical power before servicing HVAC equipment.
TopDraft Inducer
A fan that assists in moving combustion gases safely through the furnace vent system.
TopDuct
A passageway that carries heated or cooled air throughout a building.
TopDuct Insulation
Insulating material wrapped around ductwork to reduce heat gain or loss.
TopDuct Leakage
Air escaping from gaps or openings in ductwork, reducing system efficiency.
TopDuctless Mini-Split
An HVAC system that provides heating and cooling without traditional ductwork.
TopDuct Static Pressure
The resistance to airflow within an HVAC duct system.
TopDX Cooling
Direct Expansion cooling, where refrigerant absorbs heat directly from indoor air.
TopE
Economizer
A ventilation feature that uses cool outdoor air to help reduce mechanical cooling requirements when conditions permit.
TopElectronic Air Cleaner
An air filtration device that captures airborne particles using electrically charged collection plates.
TopEnergy Efficiency Ratio (EER)
A measurement of cooling efficiency calculated by dividing cooling output by electrical energy consumed under specific conditions.
TopEnergy Recovery Ventilator (ERV)
A ventilation system that transfers heat and moisture between incoming and outgoing air to improve energy efficiency.
TopEvaporator Coil
The indoor coil that absorbs heat from indoor air as refrigerant evaporates.
TopEvaporative Cooler
A cooling system that lowers air temperature by passing air through water-saturated media.
TopF
Fan Coil Unit
An indoor unit that uses a fan and coil to provide heating or cooling within a room or zone.
TopFilter Dryer
A refrigeration component that removes moisture and contaminants from the refrigerant.
TopFlame Sensor
A safety device that verifies burner ignition and shuts off the gas supply if no flame is detected.
TopForced-Air System
A heating or cooling system that distributes conditioned air using a blower and ductwork.
TopFresh Air Intake
An opening that allows outdoor air to enter an HVAC system for ventilation purposes.
TopFurnace
A heating appliance that warms air before distributing it throughout a building.
TopG
Gas Valve
A control component that regulates the flow of natural gas or propane to a furnace burner.
TopGeothermal Heat Pump
A heating and cooling system that transfers heat to and from the ground for high-efficiency operation.
TopGrille
A protective cover placed over supply or return air openings.
TopH
Heat Exchanger
A component that transfers heat from combustion gases to the air without allowing the two to mix.
TopHeat Gain
The increase in indoor heat caused by sunlight, occupants, appliances, or outdoor temperatures.
TopHeat Load
The amount of heating required to maintain a comfortable indoor temperature during cold weather.
TopHeat Pump
An HVAC system that provides both heating and cooling by transferring heat between indoor and outdoor environments.
TopHeating Degree Day (HDD)
A measurement used to estimate heating demand based on outdoor temperatures.
TopHEPA Filter
A high-efficiency particulate air filter capable of capturing very small airborne particles.
TopHermetic Compressor
A compressor enclosed within a sealed housing to prevent refrigerant leaks.
TopHigh-Limit Switch
A safety device that shuts down a furnace if it overheats.
TopHumidifier
A device that adds moisture to indoor air to improve comfort and reduce dryness.
TopHumidity
The amount of water vapor present in the air, often expressed as relative humidity.
TopI
Ignition Control Module
An electronic device that manages the furnace ignition sequence and monitors burner operation for safe performance.
TopIgnitor
A component that lights the burner in a gas furnace using either a hot surface element or spark ignition.
TopIndoor Air Quality (IAQ)
A measure of the cleanliness and health of indoor air, including the presence of dust, allergens, humidity, and airborne contaminants.
TopInverter Compressor
A variable-speed compressor that adjusts its output to match heating or cooling demand, improving efficiency and comfort.
TopIonizer
An air purification device that electrically charges airborne particles to help remove them from indoor air.
TopInsulation
A material that reduces heat transfer through walls, ceilings, floors, and ductwork to improve energy efficiency.
TopIntake Vent
An opening that supplies fresh outdoor air for combustion or ventilation purposes.
TopJ
Joule
A metric unit of energy occasionally referenced in HVAC engineering and equipment performance calculations.
TopJunction Box
An electrical enclosure that safely houses wiring connections within HVAC equipment.
TopJump Duct
A short duct connecting two rooms to improve air circulation and balance pressure throughout a home.
TopJ-Load Calculation
Another name for a Manual J calculation, used to determine the correct heating and cooling capacity for a building.
TopK
Kilowatt (kW)
A unit of electrical power equal to 1,000 watts, commonly used to describe electric heating equipment.
TopKilowatt-Hour (kWh)
A measurement of electrical energy consumption used by utility companies for billing.
TopKnockout
A removable section of metal in an electrical panel or HVAC cabinet used for routing conduit or wiring.
TopK-Factor
A value used in engineering calculations to evaluate heat transfer through building materials.
TopL
Latent Heat
Heat associated with changing the moisture content of air rather than changing its temperature.
TopLatent Load
The portion of a building’s cooling demand related to removing moisture from indoor air.
TopLine Set
The insulated copper tubing that carries refrigerant between the indoor and outdoor units of an HVAC system.
TopLoad Calculation
An evaluation of a home’s heating and cooling requirements based on size, insulation, windows, occupancy, and climate.
TopLockout Mode
A protective operating condition that temporarily disables HVAC equipment after repeated faults are detected.
TopLow Ambient Kit
A control package that allows an air conditioner to operate efficiently in cooler outdoor temperatures.
TopLow Voltage Wiring
The wiring that connects thermostats, control boards, and HVAC components using low-voltage electrical signals.
TopLouvers
Angled slats installed on vents or equipment cabinets that allow airflow while helping prevent debris or rain from entering.
TopM
Make-Up Air
Fresh outdoor air introduced into a building to replace air exhausted by ventilation systems, kitchen hoods, or bathroom fans.
TopManual D
An industry-standard method used to design residential duct systems for proper airflow and efficiency.
TopManual J
An HVAC calculation procedure used to determine the heating and cooling load requirements of a home.
TopManual S
An ACCA guideline used to select HVAC equipment after completing a Manual J load calculation.
TopMERV Rating
Minimum Efficiency Reporting Value, a rating that measures an air filter’s ability to capture airborne particles.
TopMini-Split System
A ductless heating and cooling system consisting of one outdoor unit connected to one or more indoor air handlers.
TopModulating Furnace
A furnace capable of adjusting its heating output incrementally to maintain consistent indoor temperatures.
TopMotor
An electric device that powers HVAC components such as blowers, fans, and compressors.
TopMulti-Zone System
An HVAC system that independently controls the temperature in multiple areas of a building.
TopN
Natural Gas Furnace
A heating system that burns natural gas to produce warm air for residential or commercial spaces.
TopNegative Pressure
A condition where indoor air pressure is lower than outdoor pressure, causing outside air to enter the building.
TopNominal Capacity
The approximate heating or cooling output assigned to HVAC equipment under standard operating conditions.
TopNon-Programmable Thermostat
A thermostat that maintains manually selected temperature settings without scheduling features.
TopO
Oil Furnace
A furnace that burns heating oil to generate warm air for distribution throughout a building.
TopOutdoor Condensing Unit
The exterior portion of an air conditioning or heat pump system containing the compressor and condenser coil.
TopOutdoor Reset Control
A control system that adjusts heating output based on outdoor temperatures to improve efficiency.
TopOverload Protector
A safety device that shuts down an HVAC motor or compressor when excessive heat or electrical current is detected.
TopP
Package Unit
An HVAC system that contains all heating and cooling components within a single outdoor cabinet.
TopPlenum
An air distribution chamber connected to HVAC equipment that directs conditioned air into ductwork.
TopPositive Pressure
A condition where indoor air pressure exceeds outdoor pressure, causing air to flow outward through openings.
TopProgrammable Thermostat
A thermostat that automatically adjusts temperature settings based on a user-defined schedule.
TopPropane Furnace
A heating system that burns propane gas to provide warm air for homes and businesses.
TopPsychrometrics
The science of measuring and analyzing the properties of air and water vapor in HVAC applications.
TopPurge Cycle
A process that clears combustion gases or residual refrigerant from specific HVAC components before normal operation resumes.
TopPressure Switch
A safety device that monitors air or refrigerant pressure and allows equipment to operate only within safe limits.
TopQ
Quick Connect Fittings
Specialized fittings that simplify refrigerant line installation and servicing while helping minimize leaks.
TopQuiet Mode
An operating setting that reduces fan speed and compressor output to minimize system noise.
TopR
R-32 Refrigerant
A modern refrigerant with a lower global warming potential than many older refrigerants, commonly used in high-efficiency systems.
TopR-410A
A refrigerant widely used in residential air conditioners and heat pumps designed for higher efficiency than older refrigerants.
TopRadiant Heating
A heating system that warms floors, walls, or ceilings to provide comfortable and even heat throughout a space.
TopRefrigerant
A specialized fluid that absorbs and releases heat as it circulates through an HVAC system.
TopRefrigerant Leak
A condition in which refrigerant escapes from the sealed system, reducing cooling or heating performance.
TopRelative Humidity
The percentage of moisture in the air compared to the maximum amount the air can hold at a given temperature.
TopReturn Air
Air drawn back into the HVAC system to be filtered and conditioned again.
TopReturn Air Grille
A vent cover that allows indoor air to return to the HVAC system for conditioning.
TopReversing Valve
A valve used in heat pumps to switch between heating and cooling modes.
TopS
Sensible Heat
Heat that changes the temperature of air without changing its moisture content.
TopSEER2
Seasonal Energy Efficiency Ratio 2, the current standard used to measure residential cooling efficiency.
TopSmart Thermostat
A Wi-Fi-enabled thermostat that allows remote control, scheduling, and energy monitoring through a mobile device.
TopSplit System
An HVAC system with separate indoor and outdoor units connected by refrigerant lines.
TopStatic Pressure
The resistance to airflow inside an HVAC duct system.
TopSupply Air
Conditioned air delivered from the HVAC system into occupied spaces.
TopSupply Register
An adjustable vent that directs heated or cooled air into a room.
TopT
Temperature Differential
The difference between return air temperature and supply air temperature.
TopThermostat
A device that monitors indoor temperature and controls heating and cooling equipment.
TopThermostatic Expansion Valve (TXV)
A metering device that regulates refrigerant flow into the evaporator coil based on cooling demand.
TopTon
A unit of cooling capacity equal to 12,000 BTUs per hour.
TopTwo-Stage Compressor
A compressor capable of operating at two output levels for improved comfort and energy efficiency.
TopU
Ultraviolet (UV) Light
A germicidal light installed inside HVAC equipment to help reduce biological growth on coils and other components.
TopUpflow Furnace
A furnace designed to move heated air upward into the home’s duct system.
TopV
Variable-Speed Blower
A blower motor that automatically adjusts its speed to improve comfort, efficiency, and humidity control.
TopVariable Refrigerant Flow (VRF)
A high-efficiency HVAC system that precisely controls refrigerant flow to multiple indoor units.
TopVentilation
The process of exchanging indoor and outdoor air to improve indoor air quality.
TopVent Damper
A device that opens and closes venting pathways to improve heating efficiency.
TopW
Wall Thermostat
A thermostat mounted on an interior wall to monitor and control indoor temperature.
TopWhole-Home Humidifier
A humidifier connected to the HVAC system that adds moisture throughout the entire home.
TopWhole-Home Dehumidifier
A system designed to remove excess humidity from the entire home independently of the air conditioner.
TopWinterization
The process of preparing HVAC equipment for cold weather to prevent freezing and seasonal damage.
TopX
X-13 Motor
An energy-efficient electronically commutated blower motor commonly used in residential HVAC systems.
TopY
Year-Round Maintenance
Regular HVAC inspections and servicing performed throughout the year to improve efficiency and system reliability.
TopZ
Zoning System
An HVAC system that uses dampers and multiple thermostats to independently control temperatures in different areas of a building.
TopZone Damper
A motorized damper installed in ductwork that opens or closes to regulate airflow to a specific zone.
TopZone Control Panel
An electronic controller that coordinates thermostats, dampers, and HVAC equipment in a zoned comfort system.
Top