1. Central Air Conditioner efficiency is measured by the Seasonal Energy Efficiency Ratio (SEER). The higher the SEER the more efficient the unit. Units with a SEER of 12 or above are considered high-efficiency; 17 is the highest available.

2. Furnace efficiency is measured by the Annual Fuel Utilization Efficiency (AFUE) rating. The colder the climate and the higher the local utility rates, the higher the AFUE you should get. Furnaces with AFUE ratings of 90% percent and above are considered high-efficiency; 96.6% is the highest available.

3. Heat pump cooling efficiency is measured by a SEER rating; a heat pump’s heating efficiency is measured as the Heating Seasonal Performance Factor (HSPF). A heat pump with a SEER of 12 or higher and an HSPF of at least 8 is considered high-efficiency.

4. Room Air Conditioner efficiency is measured by the Energy Efficiency Ratio (EER), which is the BTU/hr output, divided by the watts of electricity the unit uses. It basically tells you how much heat you get out of the unit compared to how much electricity you put into it. The higher the EER, the less the electricity air conditioning will use.