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.

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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.