Industry Terms

Active Cooling
HVAC term for compressor driven air conditioning.
Air Cleaning
In HVAC an IAQ control strategy to remove various airborne particulates and/or gases from the air. The three types of air cleaning most commonly used are particulate filtration, electrostatic precipitation, and gas sorption.
Air Conditioner
A device used to control temperature and humidity of the air.
Air Conditioning
In HVAC the control of the quality, quantity, and temperature-humidity of the air in an interior space.
Air Vent
HVAC term for a valve, either manual or automatic, that is used to remove unwanted air from the highest point of a piping system.
Ambient Air
The air external to a building or device.
Attic Fan
A fan mounted on an attic wall used to exhaust warm attic air to the outside.
Attic Vent
HVAC term for a passive or mechanical device used to ventilate an attic space, primarily to reduce heat buildup and moisture condensation.
In HVAC the device in an air conditioner that distributes the filtered air from the return duct over the coil/heat exchanger.
The device in an air conditioner or heat pump in which the refrigerant condenses from a gas to a liquid when it is depressurized or cooled.
Condenser Coil
The device in an air conditioner or heat pump through which the refrigerant is circulated and releases heat to the surroundings when a fan blows outside air over the coils. This will return the hot vapor that entered the coil into a hot liquid upon exiting the coil.
Condensing Unit
The component of a central air conditioner that is designed to remove heat absorbed by the refrigerant and transfer it outside the conditioned space.
Conditioned Air
Air that has been heated, cooled, humidified, or dehumidified to maintain an interior space within the "comfort zone." (Sometimes referred to as "tempered" air.)
HVAC term for controls that vary airflow through an air outlet, inlet, or duct. A damper position may be immovable, manually adjustable or part of an automated control system.
Dual Duct System
An air conditioning system that has two ducts, one is heated and the other is cooled, so that air of the correct temperature is provided by mixing varying amounts of air from each duct.
Duct Fan
HVAC term for an axial flow fan mounted in a section of duct to move conditioned air.
The round or rectangular tube(s), generally constructed of sheet metal, fiberglass board, or a flexible plastic-and-wire composite, located within a wall, floor, and ceiling that distributes heated or cooled air in buildings.
Exhaust Ventilation
HVAC term for mechanical removal of air from a portion of a building (e.g., piece of equipment, room, or general area).
Filter (air)
A device that removes contaminants, by mechanical filtration, from the fresh air stream before the air enters the living space. Filters can be installed as part of a heating/cooling system through which air flows for the purpose of removing particulates before or after the air enters the mechanical components.
Forced Air System or Furnace
HVAC term for a type of heating system in which heated air is blown by a fan through air channels or ducts to rooms.
Furnace (Residential)
In HVAC a combustion heating appliance in which heat is captured from the burning of a fuel for distribution, comprised mainly of a combustion chamber and heat exchanger.
Mechanically Ventilated Crawlspace System
In HVAC a system designed to increase ventilation within a crawlspace, achieve higher air pressure in the crawlspace relative to air pressure in the soil beneath the crawlspace, or achieve lower air pressure in the crawlspace relative to air pressure in the living spaces, by use of a fan.
Natural Ventilation
In HVAC the movement of outdoor air into a space through intentionally provided openings, such as windows and doors, or through non-powered ventilators or by infiltration.
Preventative Maintenance
Regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventive maintenance helps to prevent parts, material, and systems failure by ensuring that parts, materials and systems are in good working order.
Programmable Thermostat
A type of thermostat that allows the user to program into the devices' memory a pre-set schedule of times (when certain temperatures occur) to turn on HVAC equipment.
A measure of the capacity of a material to resist heat transfer. The R-Value is the reciprocal of the conductivity of a material (U-Value). The larger the R-Value of a material, the greater its insulating properties.
Radiant Barrier
In HVAC a thin, reflective foil sheet that exhibits low radiant energy transmission and under certain conditions can block radiant heat transfer; installed in attics to reduce heat flow through a roof assembly into the living space.
Radiant Ceiling Panels
Ceiling panels that contain electric resistance heating elements embedded within them to provide radiant heat to a room.
Radiant Energy
Energy that transmits away from its source in all directions.
Radiant Floor
A type of radiant heating system where the building floor contains channels or tubes through which hot fluids such as air or water are circulated. The whole floor is evenly heated. Thus, the room heats from the bottom up. Radiant floor heating eliminates the draft and dust problems associated with forced air heating systems.
Radiant Heat Transfer
Radiant heat transfer occurs when there is a large difference between the temperatures of two surfaces that are exposed to each other, but are not touching.
Radiant Heating System
HVAC term for a heating system where heat is supplied (radiated) into a room by means of heated surfaces, such as electric resistance elements, hot water (hydronic) radiators, etc.
A room heat delivery (or exchanger) component of a hydronic (hot water or steam) heating system; hot water or steam is delivered to it by natural convection or by a pump from a boiler.
Radiator Vent
A device that releases pressure within a radiator when the pressure inside exceeds the operating limits of the vent.
Situation that occurs when the air being exhausted from a building is immediately brought back into the system through the air intake and other openings in the building envelope.
Recirculated Air
Air removed from the conditioned space and used for ventilation, heating, cooling, humidification, or dehumidification.
The compound (working fluid) used in air conditioners, heat pumps, and refrigerators to transfer heat into or out of an interior space. This fluid boils at a very low temperature enabling it to evaporate and absorb heat.
The process of the absorption of heat from one location and its transfer to another for rejection or recuperation.
Refrigeration Capacity
A measure of the effective cooling capacity of a refrigerator, expressed in Btu per hour or in tons, where one (1) ton of capacity is equal to the heat required to melt 2,000 pounds of ice in 24 hours or 12,000 Btu per hour.
Relative Humidity
A measure of the percent of moisture actually in the air compared with what would be in it if it were fully saturated at that temperature. When the air is fully saturated, its relative humidity is 100 percent.
Return Air
Air that is returned to a heating or cooling appliance from a heated or cooled space.
Return Duct
The central heating or cooling system contains a fan that gets its air supply through these ducts, which ideally should be installed in every room of the house. The air from a room will move towards the lower pressure of the return duct.
Seasonal Energy Efficiency Ratio (SEER)
A measure of seasonal or annual efficiency of a central air conditioner or air conditioning heat pump. It takes into account the variations in temperature that can occur within a season and is the average number of Btu of cooling delivered for every watt-hour of electricity used by the heat pump over a cooling season.
Setback Thermostat
A thermostat that can be set to automatically lower temperatures in an unoccupied house and raise them again before the occupant returns.
Specific Humidity
The weight of water vapor, per unit weight of dry air.
Split System Air Conditioner
HVAC term for an air conditioning system that comes in two to five pieces: one piece contains the compressor, condenser, and a fan; the others have an evaporator and a fan. The condenser, installed outside the house, connects to several evaporators, one in each room to be cooled, mounted inside the house. Each evaporator is individually controlled, allowing different rooms or zones to be cooled to varying degrees.
Supply Duct
HVAC term for the duct(s) of a forced air heating/cooling system through which heated or cooled air is supplied to rooms by the action of the fan of the central heating or cooling unit.
Temperature Zones
In HVAC individual rooms or zones in a building where temperature is controlled separately from other rooms or zones.
Ton (Air Conditioning)
A unit of air cooling capacity; 12,000 Btu per hour.
Unit Ventilator
HVAC term for a fan-coil unit package device for applications in which the use of outdoor- and return-air mixing is intended to satisfy tempering requirements and ventilation needs.
Variable Air Volume System (VAV)
Air handling system that conditions the air to constant temperature and varies the outside airflow to ensure thermal comfort.
A component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space.
Vent Damper
HVAC term for a device mounted in the vent connector that closes the vent when the heating unit is not firing. This traps heat inside the heating system and house rather than letting it draft up and out the vent system.
Vent Pipe
A tube in which combustion gases from a combustion appliance are vented out of the appliance to the outdoors.
Vented Heater
A type of combustion heating appliance in which the combustion gases are vented to the outside, either with a fan (forced) or by natural convection.
The process of moving air (changing) into and out of an interior space either by natural or mechanically induced (forced) means.
Ventilation Air
Defined as the total air, which is a combination of the air brought inside from outdoors and the air that is being re-circulated within the building. Sometimes, however, used in reference only to the air brought into the system from the outdoors; this document defines this air as "outdoor air ventilation."
Ventilation Rate
The rate at which indoor air enters and leaves a building. Expressed in one of two ways: the number of changes of outdoor air per unit of time (air changes per hour, or "ach") or the rate at which a volume of outdoor air enters per unit of time (cubic feet per minute, or "cfm").
In HVAC an area within the interior space of a building, such as an individual room(s), to be cooled, heated, or ventilated. A zone has its own thermostat to control the flow of conditioned air into the space.
The combining of rooms in a structure according to similar heating and cooling patterns. Zoning requires using more than one thermostat to control heating, cooling, and ventilation equipment.

*Courtesy of the HVAC source and the Renewable Resource Data Center