Glossary Of Heating And Cooling Terms


Annual Fuel Utilization Efficiency. A measure of a furnace’s heating efficiency. The higher the AFUE percentage, the more efficient the product. The US government’s established minimum AFUE rating for furnaces is 78%.

Air conditioning

The treatment of air (temperature, humidity, cleanliness and circulation) to produce specific standards.

Air Diffuser

Outlet or grille designed to direct air flow in specific patterns.


The distribution or movement of air.

Air Handler

The indoor part of a central air conditioning or heat pump system that moves cooled or heated air throughout the ductwork of your home. An air handler is usually a furnace or blower coil.


Air Conditioning and Refrigeration Institute.


American Society of Heating Refrigeration and Air Conditioning Engineers.

Balance Point

An outdoor temperature, usually between 30 degrees F and 45 degrees F at which a heat pump’s output exactly equals the heating needs of the house. Below the balance point, supplementary heat is required to maintain indoor comfort.


Fan or air handling device for moving air.


British Thermal Units. The amount of heat required to raise one pound of water by one degree Fahrenheit. What that means is the higher the Btu rating, the more heating capacity of the equipment.


British Thermal Units per hour – The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit in one hour.

Carbon Monoxide

An odorless, poisonous, flammable gas produced when carbon burns with insufficient air. Deadly to humans.


Cubic feet per minute. A standard measurement of airflow.


Amount of refrigerant put in a refrigerating unit.


See Condensing Coil.


The part of the outdoor air conditioner or heat pump that compresses and pumps refrigerant throughout the system.


The product (usually water) that results from moisture laden air being exposed to a cooler temperature.

Condenser Coil

The outdoor portion of an air conditioning or heat pump system that serves as a heat transfer point for dispelling heat to the outside air, as in an air conditioner or heat pump in the summer; or for collecting heat from the outside air, as in a heat pump in the winter

Condenser Unit

The condenser unit, often called the outside unit, handles the refrigerant providing the cooling (and heating in a heat pump). It consists of a condensing coil, compressor, fan motor, and control valves.

Cooling Load

Amount of heat which must be removed from a specific area under specific design conditions.


Coefficient of Performance. A ratio calculated by dividing the total heating capacity provided by the heat pump by the total electrical input


Located in ductwork to regulate airflow. Effective in controlling airflow for zoning.

Decibel (db)

The measurement of the intensity of sound.

Defrost Cycle

During the heating cycle of a heat pump, frost may build up on the outside coil. To remove the frost and to maintain efficiency, the system will automatically defrost itself. It is normal to see steam rising from the outdoor unit when this happens.

Downflow furnace

A furnace that takes return air from the top and discharges the warm air from the bottom.


The method by which air is channeled from the furnace or the blower coil throughout your home.




Similar to miles per gallon of an automobile. The rated performance.


Energy Efficiency Ratio. A ratio calculated by dividing the cooling capacity in Btu’s per hour (Btuh) by the power input (in watts) at a given set of conditions, expressed in Btuh per watt.

Emergency Heat

The backup heat built into a heat pump.

Energy Star

A voluntary partnership between the U.S. Department of Energy, the U.S. Environmental Protection Agency, product manufacturers, local utilities and retailers. When properly installed, Energy Star-labeled products can save consumers 10-40% on heating and cooling bills each year.


The process of removing moisture and other gases from a refrigeration system.

Evaporator Coil

The part of a heat pump or air conditioner system that is located inside the house in the air handler. It is here that the refrigerant evaporates as it absorbs heat from the air that passes over the coil.


Frequently Asked Questions.

Fan Coil

A combination of a blower and a coil


A device for removing particles from air.

Forced Air     

A type of heating system that uses a blower to distribute heat.


A type of heating system that uses gas, oil, or electricity to heat air that is then distributed by ductwork.


Same as Air Diffuser. May also be called a register.

Heat Exchanger

Located in the furnace, the heat exchanger transfers heat to the surrounding air, which is then distributed throughout the home.

Heat Gain

Measured in BTU’s, the amount of heat that a structure gains using specific indoor and outdoor design temperatures for a specific geographical location.

Heat Loss

Measured in BTU’s, the amount of heat that a structure loses using specific indoor and outdoor design temperatures for a specific geographical location.

Heat Pump

A HVAC unit that heats or cools by extracting heat (via refrigeration or reverse refrigeration) using either air or water as a source. In summer it extracts heat from within the area to be conditioned and discharges it outside. In winter, the procedure is reversed.

Heating Capacity

The rate at which a device produces heat rated in BTUH.


Heating Seasonal Performance Factor. A measure of heat pump heating efficiency. The higher the rating, the more efficient the heat pump. The US government’s established minimum HSPF rating for furnaces is 6.8%.


Equipment that injects moisture into heated air as it passes from the furnace into the ductwork to be distributed throughout the home.


A control that measures and regulates moisture in the air similar to a the way a thermostat measures and regulates heat in the air.


Heating, Ventilation, and Air Conditioning.

Indoor Coil

Same as evaporator coil.

Kilowatt (KW)

A measurement of electricity. 1000 watts.

Kilowatt Hour

The amount of kilowatts consumed in one hour.

Matched System

A HVAC system with components designed to be used together to provide specified results.

Outdoor Unit

See Condenser Unit.


A sealed chamber, located at the inlet or outlet of an air handler, where conditioned air collects before being distributed (or returned) through ductwork.


A fluid (liquid or gas) used in HVAC systems.

Refrigerant Lines

Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.


Device, that when installed at the end of a ductwork, regulates amount of air and the pattern of the air entering or leaving a given area.

Relative Humidity

The ratio (expressed in %) of the amount of moisture actually in the air compared to the amount the air could hold.




The ductwork through which air is returned to the source for re-conditioning.

Return Air

The air being returned to the source for reconditioning.

Reversing Valve

A valve that reverses flow direction of refrigerant in a heat pump.

Roof Top Unit

A HVAC unit located on the roof.


Seasonal Energy Efficiency Ratio. A measure of cooling efficiency for air conditioners. The higher the SEER, the more energy efficient the unit. The government’s minimum SEER rating is 13.


Term used to define a HVAC unit that restarts immediately after shutting off.

Single Package

A heating and cooling system contained in one outdoor unit.

Split System

A combination heat pump or air conditioner with indoor components such as a furnace or blower coil. Split systems should be matched for optimum efficiency.


The auxiliary or emergency heat provided at temperatures below the heat pump’s balancing point.


The ductwork through which air leaves the source after being conditioned...

Supply Air

The air that has been conditioned.


The measurement of heat.


A device, usually found on an inside wall to regulate heating and cooling equipment.


Unit of measurement for determining cooling capacity. One ton equals 12,000 Btuh.


Underwriters Laboratories

Upflow furnace

A furnace that takes return air in from the bottom and discharges the warm air from the top.

Vapor Barrier

A moisture proof covering to prevent condensation.


A measurement of electricity.


The ability of partitioning a home into various zones, thereby providing the opportunity to control comfort levels in each zone.

Indoor Air Quality
Photos Recent Jobs
A/C & Heating Trivia
Protecting Home Owners
Learn About C0
American Standard B B B CSLB Green NATE Energy Safety Safety Safety