If you’re just getting started in the HVAC industry (or preparing for your first job interview), here’s a primer on some basic HVAC terms you will need to be familiar with as you begin working in the field.
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Commonly used HVAC terms for industry beginners
AFUE (Annual Fuel Utilization Efficiency)
AFUE measures how efficiently a heating appliance converts fossil fuel (such as oil or gas) into heat.
Air-cooled system
An air conditioning system that uses a chemical substance called refrigerant to remove heat from the air and cool the space. Ambient air is used in a air-cooled system’s condenser to cool the hot refrigerant.
Air flow volume
The amount of air circulated through the space by an HVAC system, measured in cubic feet per minute (CFM)
Air handler (blower)
An indoor HVAC unit that includes the evaporator coil, fan or blower, filter, and sometimes heating elements.
BTU (British Thermal Units)
A measurement of heat energy used to indicate the heating or cooling output of an HVAC system. One BTU is the amount of energy required to raise one pound of water one degree Fahrenheit.
Capacity
The amount of heating or cooling produced by an HVAC system, measured in BTUs or tons.
CFM (cubic feet per minute)
A measurement of the air flow volume within an HVAC system.
Charge (refrigerant charge)
The amount of refrigerant in an air conditioning or refrigeration system or unit.
Chiller
A component of an air conditioning system that uses a refrigeration loop to cool a fluid (typically water or a water/glycol mix). The system then expels the heat using either an air-cooled or water-cooled condenser.
Compressor
A component of an air conditioning or refrigeration system that increases refrigerant gas pressure and moves it through a closed loop system from the evaporator to the condenser and back.
Condenser coil (outside unit)
Air conditioner component that releases absorbed heat outside the building.
Cycling
An air conditioner’s process of turning on when the thermostat or controller detects air above set temperature, cooling air until set temperature is reached, then turning off.
Damper
A plate positioned at the junctions of ductwork that can be opened or closed to control air flow.
Diffuser
Grille covering the end of an air supply duct that controls the direction or pattern of air distribution.
Drain pan (condensate pan)
A pan under the evaporator coil that collects condensed water that drips from the air conditioning unit as humidity is removed from the air.
Duct work
A distribution system for supplied air, return air, and exhaust air processed by an HVAC system. Ducts can be made from sheet metal, fiberglass, aluminum, polyurethane, or plastic.
Ductless mini split
An air conditioning system without ductwork that consists of multiple small air handlers within each room that are connected to a single condensing unit.
Economizer
An HVAC component that reduces energy usage by using outside air to reduce the load on the HVAC system, when outdoor conditions permit.
EER (Energy Efficiency Ratio)
EER is a measurement of the cooling output of an air conditioner in BTUs divided by its electricity usage in kilowatts. Unlike the SEER rating that’s based on a seasonal average, the EER is calculated under specific test conditions that represent peak load during the highest temperatures of the season.
Evaporator coil
An HVAC system component, located in an air handler or furnace, that absorbs heat from the air flowing over it.
Filter
A device designed to capture dust and debris particles in the air and keep from from entering the system components, where a build up can decrease system efficiency and cause damage.
Flue
A vent that runs from a heat appliance to the outside of the building to remove the byproducts of combustion (such as carbon monoxide) and preserve indoor air quality.
Fresh air intake
A mechanism for drawing outside air into a space to replace vented air, or into a heating system for fuel combustion.
Heat transfer
The process by which heat moves from a warmer surface or space to a cooler one. This process is instrumental in the operation of HVAC systems.
Heat pump
A type of HVAC system that can provide both heating and cooling, by absorbing heat from a warm space (either indoors or outdoors) and moving it to a cooler space.
HSPF (Heating Seasonal Performance Factor)
HSPF measures the efficiency of a heat pump system that provides both heat and air conditioning. HSPF is the ratio of the total space heating required during the heating season in BTU divided by the total electricity used by the heat pump system, expressed in kilowatt-hours.
Load calculation
A measurement to determine the heating and cooling capacity needed for a specific space, taking into heat gain and loss within the space.
Makeup air unit
An air handler that draws in and conditions air from the outside to improve ventilation. Make up air units are commonly used in restaurant kitchens and industrial spaces to replace air removed from the space by ventilation equipment.
Packaged unit (rooftop unit or RTU)
A self-contained heating and cooling unit in a single box, often installed on the roof of a building.
Packaged Terminal Air Conditioner (PTAC)
Small AC and heating unit that’s similar to a window air conditioner, but installed through the wall. Commonly used in hotel rooms.
Plenum space
An enclosed area (such as underneath a raised floor or above a dropped ceiling) used to provide airflow and equalize air pressure within the space.
R22 (Freon)
Formerly the industry-standard refrigerant for many HVAC and refrigeration systems, this refrigerant is being phased out by the EPA due to environmental dangers. R22 can no longer be imported or manufactured in the US after January 1, 2020.
R410a
A newer, more environmentally-friendly refrigerant being used in new and retrofitted HVAC and refrigeration equipment.
Refrigerant
A chemical substance used in air conditioning and refrigeration equipment and systems to remove heat from the air. Refrigerant is converted from a gas to a liquid (and back again) with temperature and pressure. As refrigerant changes form it removes excess heat and moisture from the air and releases it outside the building.
Refrigerant line
Copper tubing containing refrigerant that connects the condenser to the evaporator coil in an air conditioning system.
Register
A grille and/or damper installed where the HVAC duct ends at a wall, ceiling, or floor.
Return air
Air from the space that is pulled back into the HVAC system to be heated or cooled.
SEER (Seasonal Energy Efficiency Ratio)
SEER measures the energy efficiency of cooling equipment, calculated based on a seasonal average as opposed to specific laboratory conditions. The SEER is the ratio of cooling output in British Thermal Units (BTU) divided by electricity usage in kilowatt-hours.
Split system
A two-unit air conditioning system (commonly used in suburban homes) that consists of an indoor air handler and an outdoor condensing unit and compressor.
Thermostat
Device (typically wall-mounted) that monitors temperature and controls HVAC output. Modern thermostats are programmable and provide remote access via mobile device apps.
Ton
A unit of measurement of air conditioning output capacity, equal to 12,000 BTUs per hour.
VAV (Variable Air Volume)
An energy-efficient commercial air conditioning system that distributes a stable air supply (sometimes from a base building system) by varying the air flow rate to control the temperature.
Variable Refrigerant Flow (VRF)
Air-cooled HVAC systems that use multiple air handlers and variable-speed compressors to provide both heat and AC simultaneously to different zones within a space. VRF systems are energy-efficient and offer quiet operation.
Ventilation
Moving air into and out of an interior building or space, and circulating air within the space (using structural and mechanical means), to maintain comfort and indoor air quality.
Water-cooled system
An air conditioning system (typically used in larger buildings due to a higher initial investment) that pumps water through a condenser to cool a refrigerant that has removed heat from the space.
Zones
Areas within a space that can be independently controlled to meet varying heating and cooling needs.
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