AFUE Annual Fuel Utilization Efficiency — a rating that reflects the efficiency of a gas furnace in converting fuel to energy. A rating of 90 means that approximately 90% of the fuel is utilized to provide warth to your home, while the remaining 10% escapes as exhaust.

BTU: British Thermal Unit– In scientific terms, it represents the amount of energy required to raise one pound of water one degree Fahrenheit. One BTU is the equivalent of the heat given by a single wooden kitchen match. It represents the measure of heat given when fuel is burned for heating or the measure of heat extracted from your home for cooling.

CFM: A standard of airflow measurement. Cubic feet per minute. A typical system produces 400 CFM per ton of air conditioning.

Capacity: The output or producing ability of a piece of cooling or heating equipment. Cooling and heating capacity are normally referred to in BTUs.

Compressor: The heart of an air conditioning or heat pump system. It is part of the outdoor unit that pumps refrigerant. The compressor maintains adequate pressure to cause refrigerant to flow in sufficient quantities to meet the cooling requirements of the system.

Condenser Coil or Outdoor Coil: Located in the outdoor unit, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid.

Damper: Found in duct work, this movable plate opens and closes to control airflow. Dampers are used effectively in zoning to regulate airflow to certain rooms.

Downflow Furnace: A furnace that pulls return air from the top and expels warm air at the bottom.

Ductwork: Pipes or channels that carry air throughout your home.

Evaporator Coil: The coil that is inside your home. In the evaporator, refrigerant evaporates and absorbs heat from air passed over the coil.

Heat Exchanger: A device for the transfer of heat energy from the source to the conveying medium.

Horizontal Furnace: A furnace that lies on its side, pulling in return air from one side and expelling warm air from the other.

Humidifier: A device that injects water vapor into heated air as the air is expelled from the furnace.

Humidity: The amount of moisture in the air. Air conditioners remove moisture for added comfort.

HSPF: Heating Seasonal Performance Factor– Rating used in measuring the heating efficiency of a heat pump. The higher the number, the more efficient the unit.

HVAC: Heating, ventilation, and air conditioning.

Package System: A piece of air conditioning and heating equipment where all components are located in one cabinet. Used occasionally in residential applications, the package unit is installed either beside or on top of the home.

Refrigerant:  A substance that produces a refrigerating effect while expanding or vaporizing.

Split System: Refers to a comfort system configuration consisting of components in two locations. Common examples include an outside unit;   air conditioner and indoor unit; a furnace and coil.

Reversing Valve: A device in a heat pump that reverses the flow of refrigerant as the system is switched from cooling to heating. Also called a switch-over or four-way valve.

Thermostat: A temperature control device, typically found on a wall inside the home. It consist of a series of sensors and relays that monitor and control the functions of a heating and cooling system.

Ton: A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.

Upflow Furnace: A furnace that pulls return air from the bottom and expels warm air from the top.

Zoning: A method of dividing a home into zones and enabling you to control the amount of comfort provided to each.