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HVAC Terms

Below are some of the most common HVAC industry terms for your reference.


ACCA: Air Conditioning Contractors of America – www.acca.org

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

Air Conditioner: Assembly of equipment 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: The number of BTU’s per hour

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

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

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 gas to liquid.

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

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.

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, or flexible material flowing throughout a space which delivers air from an HVAC unit to the respective areas 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 airflow.

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.

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.

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.

Insulation: Protective material that slows down the transfer of heat.

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 – Leading Certification in the HVAC industry.

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

PSI: Pounds per square inch,

PVC: Polyvinyl chloride; a type of plastic.

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.

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

Supercooled Liquid: Liquid refrigerant cooled below its saturation point.

Subcooling: Creating a drop in temperature by removing sensible heat from a refrigerant liquid.

Superheated vapor: Refrigerant vapor heated beyond its saturation point.

Superheating: Creating a rise in temperature by adding heat energy to a refrigeration vapor.

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

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

Ton: The unit of measurement for air conditioning system capacity. One ton of air conditioning removes 12,000 Btu’s of heat per hour from a home. Residential homes air conditioning systems usually range from 1 to 5 tons.

Upflow Furnace: A furnace that pulls in air from the bottom or side 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.

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.