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HVAC Glossery


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.

Air Flow 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.

ARI – Air Conditioning 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. 

BTUh – 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 ductwork, 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. 

Ductwork – 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.

HVAC – Heating, Ventilation and Air Conditioning.


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.


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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