Comparing test units to the Air Conditioning and Refrigeration Institute
 
EFFICIENCY
A general term used to describe how effectively a heat pump, air conditioning system, or furnace converts incoming energy to outgoing energy. The higher the number, the more efficient the unit, and the lower the operating costs.

EVAPORATOR COIL/EVAPORATOR
An integral part of the indoor unit of a heat pump or air conditioning system. So called because when warm air passes over a coil filled with liquid refrigerant, the refrigerant itself evaporates and absorbs some of the heat. This gas refrigerant is then pumped to the outdoor coil, where it releases heat into the surrounding air and returns to its liquid state.

HEAT EXCHANGER
Responsible for transferring heat from furnace burners to the blower. Ruud uses some of the finest heat exchangers in the industry with limited lifetime warranties on some models.

HORIZONTAL FLOW
A term used to describe the direction of airflow through a furnace. A horizontal flow furnace takes return air from one side, heats it, and then delivers the warm air from the other side.

HSPF
Heating Seasonal Performance Factor. It measures the efficiency of the heating portion of your heat pump. The Department of Energy minimum is 6.8. (Similar to SEER.)

HUMIDIFIER
Usually available as an optional accessory, a humidifier is used to inject water vapor into the dry, heated air expelled from a furnace/air handler. The benefits can be improved efficiency and a more comfortable living environment.

HVAC
Heating, Ventilating and Air Conditioning. Used to refer to the industry at large, particularly dealers of heating and air conditioning equipment.

INDOOR COILS
Split-system home comfort systems use two main components to deliver air for a comfortable living environment. The indoor coil is the device responsible for transferring heat from indoors to the outdoors (or the reverse in the case of a heat pump in heating mode). Most modern systems are designed to achieve maximum efficiency when the indoor unit (coils and blower) is properly matched with the outdoor unit (air conditioner or heat pump). For best results, be sure to replace both the indoor and outdoor units at the same time.