Terms used by HVAC professionals

The HVAC industry can be a maze of unfamiliar acronyms and industry terms. This dictionary will help you navigate the most common terms you’ll come across during your buying decision.



AC (Alternating Current): A type of current where the polarity is perpetually reversing, causing the directional flow in a circuit to reverse at regular intervals.

ACCA: Air Conditioning Contractors of America

Acoustical: Relating to sound, the science of sound, or a sense of hearing.

AFUE (Annual Fuel Utilization Efficiency): A measurement used to rate furnace efficiencies by dividing the ratio of heat output by heat input.

AGA: American Gas Association, Inc.

Air Conditioner: A device that changes humidity levels, temperature or quality of air.

Airflow Volume: Measured in cubic feet per minute (cfm), this is the amount of air circulated in a space.

Air Handler: Parts of a system including the fan-blower, filter and housing.

AHRI: Air Conditioning, Heating and Refrigeration Institute

ASHRAE: American Society of Heating, Refrigeration and Air Conditioning Engineers


BTU: British Thermal Unit. Measures the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit.

BTU/h: British Thermal Units per hour

Burner: The device that facilitates the combustion of air and gas.

Burner Orifice: The opening in the burner through which the gas or fuel passes prior to combustion.


Capacity: HVAC capacity is the output produced by the heating or cooling unit and is measured in BTUs per hour.

Celsius: A temperature scale that registers the freezing point of water as 0° and the boiling point as 100° under normal atmospheric pressure.

CFM (Cubic Feet per Minute): A measurement of airflow volume.

Charging a System: Adding coolant, or refrigerant, to an HVAC system.

Compressor: A pump that increases the pressure of gas.

Condensate: Vapor that is turned into a liquid as its temperature is lowered.

Condenser Coil: Also an outdoor coil. A device that removes heat from the refrigerant, allowing the refrigerant to be converted from vapor to liquid.

Condenser Fan: A fan that passes air over the condenser coil to facilitate the removal of heat from the refrigerant.

CSA: Canadian Standards Association


DC (Direct Current): A type of electrical current that only flows in one direction.

Damper: Found at the exit point of duct work, this plate usually contains grates that can be opened or closed to control the flow of air into a zone.

Degree-Day: Calculated by subtracting the average outdoor temperature for an area from 65º Fahrenheit. This measurement is used to estimate the amount of heating or cooling a home or building will need.

Dehumidifier: A device that removes humidity, or moisture, from the air.

Diffuser: A grille over an air supply duct with vanes that distribute the discharging air in a specific pattern or direction.

DOE: Department of Energy

Downflow Furnace: A furnace with an intake on the top and an air discharge at the bottom.

Drain Pan: Also a condensate pan. As the refrigerant vapor is liquefied, the drain pan collects the condensate and funnels it to the drain line.

Dry Bulb Temperature: The temperature as measured without the consideration of humidity.

Duct work: A network of metal, fiberboard or flexible material flowing throughout a space which delivers air from an HVAC unit to the respective zones of a home or office.


EER: Energy Efficiency Ratio

EPA: Environmental Protection Agency

Expansion Valve: A valve that meters the levels of refrigerant through a temperature or pressure control.

Evaporator Coil: Also an indoor coil. A device that is designed to absorb heat in the air in order to change the liquid refrigerant that flows through it into a vapor.


Fahrenheit: A temperature scale in which water freezes at 32 degrees and boils at 212 degrees at normal atmospheric pressure.

Fan: A device that creates air flow.

Filter: A device that acts like a strainer to remove dirt or undesired particles.

Flue: A vent that removes the byproducts of combustion from a furnace.

Furnace: The major component in heating a home. A device that facilitates the combustion of fuel and air to create heat.

Fuse: A delicate metal strip connecting two parts of an electrical circuit. This strip breaks, or melts, in the event of excess electrical charge, breaking the electrical circuit.


GAMA: Gas Appliance Manufacturers Association


Heat Exchanger: A device through which heat is transferred to a cold area or surface.

Heat Gain: The amount of heat added or created in a designated area.

Heating Coil: A coil that acts as a heat source for a heating system.

Heat Loss: The amount of heat subtracted from a designated area.

Heat Pump: A device used for either the heating or cooling of a space by transferring heat between two reservoirs.

Heat Transfer: Moving heat from one location to another.

HSPF (Heating Seasonal Performance Factor): This factor rates the efficiency of the heating portion of the heat pump.

Humidifier: A device that adds humidity, or moisture, to the air.

Humidistat: The device that measures humidity and turns the humidifier on and off.

Humidity: Dampness in the air caused by water vapor.


Ignition: Elevating the temperature of a substance to the point of causing a combustion reaction.


Kilowatt (kW): 1,000 watts.


Latent Heat: A type of heat that when added to an area produces an effect other than an increase in temperature.


Media: The fine material of a filter that traps dirt, dust, mildew or bacteria.


NATE: (North American Technician Excellence) is the only non-profit, independent, national certification and testing program for HVAC/R technicians accepted by the entire industry.

NEC: National Energy Council / National Electric Code

NEMA: National Electrical Manufacturing Association


Orifice: An opening or hole.


Package Unit: A heating and cooling system contained in one outdoor unit.

PSI: Pounds per square inch

PSIA: Pounds per square inch, absolute

PSIG: Pounds per square inch gauge

PVC: Polyvinyl chloride; a type of plastic.


Reciprocating Compressor: A type of compressor used in cooling systems to compress refrigerant by using a piston action.

Refrigerant: A chemical that condenses from a vapor to liquid and, in the process, decreases in temperature.

Refrigerant Charge: The amount of refrigerant in a system.


SEER (Seasonal Energy Efficiency Ratio): A rating system developed by the U.S. Government to indicate the efficiency level of cooling equipment.

Self-contained System: A package unit.

Sensible Heat: Heat added or subtracted that causes a change in temperature.

Sensor: A device that reacts to a change in conditions.

Split System: An outdoor unit combined with an indoor unit.


Thermostat: Sensors that monitor and control the output of an HVAC system.

Thermostatic Expansion Valve: A device that creates a constant evaporator temperature.

Ton: One ton is 12,000 BTUs per hour.


Upflow Furnace: A furnace that pulls in air from the bottom and releases it through the top.


Vacuum: A space where the pressure is significantly below that of standard atmospheric pressure.

Volt: A unit of electro-motive force.

Voltage: The force pushing electrical current along wires and cables.


Watt: The unit of electrical power equal to the flow of one amp at a potential difference of one volt.

Wet Bulb Thermometer: A thermometer that measures the relative humidity in the air.


Zoning: A system that divides a home, office or space into different regions in order to better control the temperature and effectiveness of a heating and cooling system.


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