The HVAC Glossary is a comprehensive collection of industry-specific terms designed to help homeowners, business owners, and HVAC professionals better understand heating, ventilation, and air conditioning systems. Whether you’re researching repairs, looking to upgrade your system, or simply want to know what your technician is talking about, this glossary provides clear, concise definitions of key HVAC terms. From efficiency ratings and refrigerants to ductwork components and safety certifications, this resource empowers users with the knowledge they need to make informed decisions about their indoor comfort and system maintenance.
Search on this page for commonly used HVAC terminology to help you better understand your Dor-Mar service technician or replacement estimate.
ACCA | ACH (Air Changes Per Hour) | Air Conditioner | Air flow | Air handler or air handling unit | Annual Fuel Utilization Efficiency (AFUE) | ASHRAE | Balance Point | Boot | British Thermal Unit (BTU) | Capacitor | Checking the charge | Coil | Compressor | Condenser | Controller | Delta T (ΔT) | EPA Certification | Evaporator | Furnace | Grille | Heat Exchanger | Heat pump | Heat Source | High Efficiency | Humidistat | HVAC | Latent heat | Line set | Load Calculation | Load calculation | Media air cleaner | MERV | NATE | Plenum | Refrigerant | Refrigeration cycle | Register | Return | SEER | Split system | Standard Efficiency | Static Pressure | Supplementary Heat | Supply | Thermostat | Tons of air conditioning | Trunk | Two-stage | Variable Speed | Zoning System |
ACCA: A major trade association for the HVAC industry, the Air Conditioning Contractors of America.
ACH (Air Changes Per Hour): The number of times per hour a room’s air is replaced through ventilation.
Air Conditioner: An appliance designed to dehumidify and extract heat from a home or office, leaving the remaining air cooler.
Air flow: The volume of air your duct system moves. In general, air conditioners are designed to move about 400 cubic feet per minute (cfm) for each ton of air conditioner capacity.
Air handler or air handling unit: A large metal box, part of the indoor unit for a furnace/AC system that contains the blower and heating or cooling elements.
Annual Fuel Utilization Efficiency (AFUE): The thermal efficiency measure of space-heating furnaces and boilers, expressed as a percentage.
ASHRAE: The American Society of Heating, Refrigerating, and Air-Conditioning Engineers.
Balance Point: The outdoor temperature at which a heat pump’s output matches heating needs.
Boot: The section of shaped sheet metal that transitions the duct on one end to the grille or register on the other end.
British Thermal Unit (BTU): One BTU is the energy required to raise one pound of water one degree Fahrenheit.
Capacitor: Also known as a ‘run capacitor’, it gives an air conditioning system the initial boost it needs to turn on and also provides continuous power.
Checking the charge: Measuring the pressure of the refrigerant of an AC system to determine if it contains the proper amount.
Coil: Part of the air conditioner that performs heat transfer to air, mounted inside an air handler or ductwork.
Compressor: A device that raises the temperature and pressure of the refrigerant in an air conditioning system.
Condenser: A heat exchanger that removes heat from the HVAC system. The condenser is the ‘hot’ side of an air conditioner or heat pump.
Controller: The part of an HVAC system that controls all or part of the system, usually based on input from a thermostat.
Delta T (ΔT): Measurement of the change (delta) of the temperature of air moving through the evaporator coil.
EPA Certification: A certification required by the Environmental Protection Agency (EPA) for HVAC technicians to be able to handle refrigerants.
Evaporator: Part of the basic refrigeration cycle that absorbs or adds heat to the system, usually to absorb heat from the air.
Furnace: Part of an HVAC system that adds heat to the air of a home.
Grille: Register used primarily in return air vents that doesn’t contain any moving parts.
Heat Exchanger: Part of an HVAC system that transfers heat from the hot parts of the system to the cold parts.
Heat pump: Moves heat from inside to outside in the summer months and from outside to inside in winter.
Heat Source: A source from which heat is collected, such as outdoor air for heat pumps.
High Efficiency: Based on the AFUE rating of a furnace, usually referring to a 90% or higher efficiency furnace.
Humidistat: A device that controls indoor humidity levels by adjusting moisture in the air.
HVAC: Abbreviation for Heating, Ventilation, and Air Conditioning.
Latent heat: Heat that must be removed from the air to remove moisture.
Line set: Tubing that connects the condensing unit to the evaporator coil of an air conditioner.
Load Calculation: Determining the correct HVAC system size for a home based on heat gain/loss.
Load calculation: The process of determining the proper size of an air conditioner and/or furnace for a home.
Media air cleaner: More efficient air filters for an HVAC system, constructed of materials that catch smaller particles.
MERV: A rating for filters used in HVAC systems. The higher the MERV rating, the more particles it catches.
NATE: North American Technician Excellence, a certification for HVAC professionals.
Plenum: The sheet metal box connected to either side of an HVAC system’s air handler.
Refrigerant: The coolant that enables modern air conditioning systems to remove heat from the home.
Refrigeration cycle: The cycle that allows an air conditioner to transfer heat from inside and send it outside.
Register: Cover for a heating or air conditioner grate inside a home, usually with movable louvers.
Return: The section of an HVAC ductwork system that returns air from the house back to the air handler.
SEER: Seasonal Energy Efficiency Ratio, measuring air conditioning and heat pump cooling efficiency.
Split system: An air conditioning system with an indoor unit and an outdoor condensing unit.
Standard Efficiency: Refers to an AFUE rating of a furnace, typically in the 80% range.
Static Pressure: The pressure inside a home’s ductwork system, affecting HVAC efficiency.
Supplementary Heat: Auxiliary or emergency heat used when temperatures drop below a heat pump’s balance point.
Supply: The part of a home’s duct system that moves conditioned air into the living space.
Thermostat: A device that monitors and regulates an HVAC system.
Tons of air conditioning: The capacity of an air conditioning system. One ton equals 12,000 BTU/hour.
Trunk: A large piece of ductwork that attaches directly to the plenum and distributes air.
Two-stage: An air conditioning system with high and low settings for efficiency.
Variable Speed: HVAC motors that adjust speeds for improved energy efficiency and comfort.
Zoning System: Divides a home into sections that can be controlled independently for comfort.