Glossary of HVAC Terms

Below is a glossary of terms that are common to the HVAC industry. If you're hearing a word or phrase that doesn't sound familiar to you, check this page and you may find it.

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

Air Handler:
In a cooling only or heat pump system, an air handler (also called a fan coil depending on installation application) takes the place of an evaporator coil and the variable speed fan from a gas powered furnace. Air handlers extract heat from the air with refrigerant supplied by the air conditioner (or heat pump) in the summer, and move heated air from the heat pump through the home's ductwork during colder weather.

Balance Point:
An outdoor temperature, usually between 30° F and 45° F, at which a heat pump's output exactly equals the heating needs of the home. Below the balance point, supplementary electric resistance heat is needed to maintain indoor comfort.

BTU:
British thermal unit. The amount of heat required to raise the temperature of one pound of water (about one pint) by one degree F.

Condensing Unit:
Normally referred to as an air conditioner or heat pump, a condensing unit functions as a heat transfer point. The heated refrigerant returned from the evaporator coil (or air handler/fan coil) located inside the home is sent outside to the air conditioner/heat pump where it is pressurized and sent through the condensing coil. Under high pressure the refrigerant gives up the heat which is dispelled into the outside air, thus cooling the refrigerant to then be sent back inside to the evaporator coil or air handler to repeat the process.

Evaporator Coil:
The portion of a central air conditioning system that is located in the home and connected to the furnace. It functions as the heat transfer point for cooling indoor air. An evaporator coil is comprised of a series of coils filled with refrigerant. As the warm/hot air from the home is returned to the HVAC system it blows through the evaporator coil where the refrigerant filled tubes extract both heat and extra moisture, thus cooling the air. When heating with a heat pump, this processed is reversed to provide heat.

Fan Coil:
(See Air Handler)

Heat Pump:
A heat pump is an all electric unit that cools like an air conditioner using refrigerant. The primary difference is that a heat pump can also provide heat by reversing the cooling process. Heat pumps extract heat from the air as even in cold weather, heat exists in the outside air. They then send the heated refrigerant inside to the coil to heat the indoor air. Heat pumps operate efficiently typically at temperatures of 40° F and above while a gas furnace is more efficient below 40° F.

Heat Source:
A body of air or liquid from which heat is collected. With heat pumps, the air outside the home is used as the heat source during the heating cycle. For geothermal heat pumps (also referred to as ground or water source) heat is removed from the earth or body of water.

HSPF:
Heating Seasonal Performance Factor. A measure of a heat pump's heating efficiency. The higher the HSPF, the more efficient the product. There is no government established minimum HSPF rating for heat pumps.

MERV:
The Minimum Efficiency Reporting Value is the standard comparison of the efficiency of an air filter/air cleaner. The MERV scale ranges from 1 (least efficient) to 16 (most efficient), and measures a filter's ability remove particles from 3 to 10 microns in size.

Packaged System:
A year-round heating and air conditioning system that has all of the components of a normal split system completely encased in one unit. These are located outside the home either on the roof or concrete slab in the yard. Packaged systems can come as cooling only, cooling and gas furnace, heat pump (all electric) or hybrid (electric cooling with dual fuel source heating).

Refrigerant:
A chemical that produces a refrigerating effect while expanding and vaporizing. Most residential air conditioning systems contain R-410A or R22 refrigerant. R-410A is the new government mandate for air conditioners and heat pumps since R-22 has been proven to be dangerous to the environment.

SEER:
Seasonal Energy Efficiency Ratio. A measure of the amount of energy an air conditioner or heat pump requires to cool a certain space. The higher the SEER, the more efficient the product. The government's established minimum SEER rating for air conditioners manufactured after January 2006 is 13.

Split System:
An air conditioning and heating system with components located both inside and outside the home. This is the most common design for home use.

Supplementary Heat:
The auxiliary or emergency heat, usually electrical resistance heat, provided at temperatures below a heat pump's balance point.

Ventilator (Air Exchanger):
Part of a complete indoor air quality solution, a ventilator exchanges stale indoor air with fresh air from outside with minimal energy loss regardless of the temperature/humidity level outside.

UV Lamp (UVC):
Part of a complete indoor air quality solution, UV lamps are often mounted in the evaporator coil to kill mold for the purpose of purifying the air and maintaining efficient operation of the coils.

Zoning:
A method of dividing a home into different comfort zones, so each zone can be independently controlled, depending on use and need.