HVAC Terminology
AC
AC stands for Air Conditioning, a system used to cool and dehumidify indoor air.
ACCA
Air Conditioning Contractors of America: a trade association representing HVAC professionals.
A-Coil
A type of evaporator coil shaped like the letter “A,” commonly used in air conditioning systems.
AC or DC
Refers to alternating current (AC) or direct current (DC) electrical power.
Acoustical
Relating to sound or the control of sound, especially in HVAC equipment design.
AFUE
Annual Fuel Utilization Efficiency: a measure of how efficiently a furnace converts fuel to heat.
AGA
American Gas Association: an organization that sets standards for gas appliances.
AHRI
Air-Conditioning, Heating, and Refrigeration Institute: certifies HVAC equipment performance.
Air cleaner (also Air Filtration System)
A device designed to remove contaminants from the air in your home or building.
Air Conditioner
A system or machine that cools and dehumidifies the air in an enclosed space.
Air Filtration System (also Air Cleaner)
Another term for air cleaner, used to filter out airborne particles.
Air flow volume
The amount of air moved by an HVAC system, typically measured in cubic feet per minute (CFM).
Air handler
The indoor unit of a split-system air conditioner or heat pump that circulates air through the home.
ASHRAE
American Society of Heating, Refrigerating and Air-Conditioning Engineers: sets HVAC industry standards.
BTU
British Thermal Unit: a measure of heat energy, used to rate HVAC system capacity.
BTUh
British Thermal Units per hour: a rate of heat energy transfer.
Burner
A device in a furnace that burns fuel to produce heat.
Burner Orifice
A small opening in a burner through which fuel is released for combustion.
Burner (sealed combustion)
A burner system that draws air for combustion from outside the building, improving safety and efficiency.
CADR Clean Air Delivery Rate (CADR)
A rating that measures how well an air cleaner removes dust, pollen, and smoke from the air.
Capacity
The cooling or heating ability of an HVAC system, usually measured in BTUs or tons.
Celsius
A temperature scale where water freezes at 0° and boils at 100°.
Certified Matched System
An HVAC system where all components are tested and certified to work together for optimal efficiency.
CFM
Cubic Feet per Minute: a unit of airflow volume.
Charge
The amount of refrigerant in an HVAC system.
Comfort™ coil (also evaporator coil or indoor coil)
The indoor coil in an air conditioner or heat pump that absorbs heat from the air.
Compressor
The heart of an air conditioning or heat pump system, which compresses refrigerant.
Condensate
Water produced when warm, humid air comes into contact with a cold surface.
Condenser coil (or outdoor coil)
The outdoor coil in an air conditioner or heat pump that releases heat to the outside air.
Condenser fan
The fan in the outdoor unit that helps dissipate heat from the condenser coil.
Contactor
An electrical relay used to control large current loads in HVAC equipment.
Crankcase heater
A heater that keeps the compressor oil warm to prevent refrigerant migration and liquid slugging.
CSA
Canadian Standards Association: certifies HVAC equipment for safety and performance in Canada.
Damper
A movable plate that regulates airflow in ducts.
DB (Decibels)
A unit that measures the intensity of sound.
DC
Direct Current: a type of electrical current used in some HVAC systems.
Defrost
The process of removing ice from the outdoor coil of a heat pump.
Degree-day
A measure used to estimate heating or cooling requirements based on outdoor temperature.
Dehumidifier
A device that removes excess moisture from the air.
Diffuser
A device that distributes air evenly in a room.
DOE
Department of Energy: regulates energy efficiency standards for HVAC equipment.
Downflow furnace
A furnace that discharges air downward.
Drain pan
A pan that collects condensate from the evaporator coil.
Dry bulb temperature
The temperature of air measured by a standard thermometer.
Dry bulb thermometer
A standard thermometer that measures air temperature.
Dual Compressors
A system with two compressors for improved efficiency and redundancy.
Ductwork
The system of ducts used to distribute air throughout a building.
DX
Direct Expansion: a type of air conditioning system where refrigerant cools air directly.
Ecologic
A term sometimes used for environmentally friendly HVAC systems.
EER
Energy Efficiency Ratio: a measure of cooling efficiency.
Electronic Air Cleaner (EAC)
A device that uses electricity to trap airborne particles.
EPA
Environmental Protection Agency: regulates environmental standards for HVAC systems.
Evaporator coil (also Comfort™ Coil or Indoor coil)
The coil in an air conditioner or heat pump that absorbs heat from indoor air.
Expansion valve
A device that controls the flow of refrigerant into the evaporator.
Fahrenheit
A temperature scale where water freezes at 32° and boils at 212°.
Fan
A device that moves air in an HVAC system.
Filter
A device that removes particles from the air.
Flue
A vent for exhaust gases from a furnace or boiler.
Furnace
A device that heats air for distribution throughout a building.
Fuse
A safety device that breaks the circuit if current exceeds a safe level.
GAMA
Gas Appliance Manufacturers Association: represents manufacturers of gas appliances.
Gas furnace heat exchanger
The component in a gas furnace that transfers heat from combustion gases to air.
Heat exchanger
A device that transfers heat from one medium to another.
Heat gain
The increase in heat within a space, often from sunlight, equipment, or people.
Heating coil
A coil that heats air in an HVAC system.
Heat loss
The decrease in heat within a space, often through walls, windows, or ventilation.
Heat pump
A device that transfers heat from one place to another, providing both heating and cooling.
Heat transfer
The movement of heat from one place to another.
HEPA filter
High Efficiency Particulate Air filter: removes very small particles from the air.
Hertz
A unit of frequency, often used to describe electrical current (Hz).
Horizontal flow
A type of HVAC system where air moves horizontally.
HSPF
Heating Seasonal Performance Factor: a measure of heat pump heating efficiency.
Humidifier
A device that adds moisture to the air.
Humidistat
A device that controls humidity levels.
Humidity
The amount of water vapor in the air.
Humidity, absolute
The mass of water vapor per unit volume of air.
Humidity, relative
The ratio of the current amount of water vapor in the air to the maximum possible at that temperature.
HVAC
Heating, Ventilation, and Air Conditioning: systems that control indoor climate.
Hybrid heat (also Hybrid System)
A system that uses both a heat pump and a furnace for efficient heating.
Hybrid system (also Hybrid Heat)
See Hybrid heat.
Ignition
The process of starting combustion in a furnace.
Indoor coil (also Comfort™ Coil or evaporator coil)
The coil inside an air conditioner or heat pump that absorbs heat from indoor air.
Indoor/Outdoor system (also split system)
An HVAC system with separate indoor and outdoor units.
Inverter Compressor
A compressor that can vary its speed for improved efficiency and comfort.
Kilowatt (kW)
A unit of power equal to 1,000 watts.
Latent heat
Heat absorbed or released during a change of state (e.g., water to vapor).
Load calculation
A calculation to determine the heating or cooling needs of a building.
Media
The material in a filter that traps particles.
NATE
North American Technician Excellence: certifies HVAC technicians.
NEC
National Electrical Code: sets standards for electrical installations.
NEMA
National Electrical Manufacturers Association: sets standards for electrical equipment.
OEM
Original Equipment Manufacturer: the company that makes the original product.
Operating cost
The cost to run an HVAC system over time.
Orifice
A small opening that controls the flow of fluid or gas.
Outdoor coil (also Condenser coil)
The coil in the outdoor unit of an air conditioner or heat pump.
Packaged system (or Packaged unit)
An HVAC system where all components are housed in a single cabinet.
Packaged unit (or Packaged system)
See Packaged system.
Payback analysis
An analysis to determine how long it will take for energy savings to pay for equipment costs.
PSI
Pounds per Square Inch: a unit of pressure.
PSIA
Pounds per Square Inch Absolute: pressure relative to a vacuum.
PSIG
Pounds per Square Inch Gauge: pressure relative to atmospheric pressure.
PVC
Polyvinyl Chloride: a type of plastic used for pipes and fittings.
Reciprocating compressor
A type of compressor that uses pistons to compress refrigerant.
Reclaiming
The process of removing refrigerant from a system for reuse or disposal.
Recycling
The process of cleaning refrigerant for reuse in HVAC systems.
Refrigerant charge
The amount of refrigerant in an HVAC system.
Refrigerant lines
Pipes that carry refrigerant between indoor and outdoor units.
SEER
Seasonal Energy Efficiency Ratio: a measure of cooling efficiency.
Self-contained system
An HVAC system where all components are housed in a single unit.
Sensible heat
Heat that causes a change in temperature but not a change of state.
Sensor
A device that detects changes in temperature, humidity, or other conditions.
Setpoint
The desired temperature or humidity setting for an HVAC system.
Spine-Fin™ coil
A type of coil with unique fin design for improved heat transfer.
Split system (also indoor/outdoor system)
An HVAC system with separate indoor and outdoor units.
Thermostat
A device that controls the operation of an HVAC system.
Thermostatic expansion valve
A device that controls the flow of refrigerant into the evaporator based on temperature.
Ton
A unit of cooling capacity equal to 12,000 BTUs per hour.
Two-stage compressor
A compressor with two levels of operation for improved efficiency and comfort.
Two-stage heating/Two-stage cooling
An HVAC system with two levels of heating or cooling output.
U-Factor
A measure of how well a window or door insulates.
UL
Underwriters Laboratories: certifies electrical equipment for safety.
Upflow furnace
A furnace that discharges air upward.
Vacuum
A space entirely devoid of matter; in HVAC, often refers to low pressure.
Volt
A unit of electrical potential.
Voltage
The difference in electrical potential between two points.
Watt
A unit of power.
Wet Bulb Thermometer
A thermometer with a wet wick used to measure humidity.
Zoning
The division of a building into areas with separate temperature controls.
Zoning System
An HVAC system that allows different areas of a building to be controlled independently.
