SEER = Seasonal Energy Efficiency Ratio: The efficiency of air conditioners is often rated by the Seasonal Energy Efficiency Ratio (SEER) which is defined by the Air Conditioning, Heating & Refrigeration Institute. The higher the SEER rating of a unit, the more energy efficient it is.
EER = Energy Efficiency Rating: The higher the EER rating, the more energy efficient the equipment is. This can result in lower energy costs. This Web site can show how to calculate potential energy cost savings of a more efficient unit: http://www.hvacopcost.com/
HSPF = Heating Seasonal Performance Factor: HSPF is a measure of a heat pump’s energy efficiency over one heating season. It represents the total heating output of a heat pump (including supplementary electric heat strips) during the normal heating season (in Btu) as compared to the total electricity consumed (in watt-hours) during the same period.
Payback period: The amount of time it takes to achieve a full return on an investment. For instance, if a high efficiency air conditioner would cost you $300 more to purchase than a lower-efficiency model but would save you $100 a year in operating costs, your payback period on the extra $300 investment would be three years.
Return on investment (ROI): The annual rate at which an investment earns income. It is calculated by dividing the annual earnings by the investment. For instance, a bank savings account paying $3 per year per $100 investment has an ROI of 3% ($3 / $100). An efficiency investment's ROI comes not from money paid to you, but rather from money saved by you on your energy bills.
BTU = British Thermal Unit: A measurement of the energy in heat. It takes one Btu of heat to warm one pound of water by 1° Fahrenheit. BTU can be used either to define an air conditioner's cooling capacity (i.e., the number of Btu of heat that can be removed by the system) or a furnace's heating capacity (i.e., the number of Btu of heat that can be supplied by the system).
AFUE=Annual Fuel Utilization Efficiency: For instance, a gas furnace with an AFUE of 80% would provide 0.8 BTU of heat for every BTU of natural gas it burned.
