Heat Pump Ratings
AFUE (annual fuel utilization efficiency) is one typical term used in rating residential gas furnaces. It measures how efficiently the funace is in converting energy in its fuel to heat over the course of a typical year. For example, an AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes thru the chimney or elsewhere.
However, measuring an air-source electric heat pump is a little more complicated, as they have several differenct ratings. The most common, SEER (seasonal energy efficiency ratio), measure cooling efficiency by calculating the total heat removed from the space during the annual cooling season.
A heat pump’s heating efficiency in indicated by the HSPF (heating season performance factor), which is the total space heating required during the heating season.
SEER and HSPF take into account the seasonal temperature and humidity under which HVAC systems operate. Unfortunately, they do not take into account for seasonal variations in temp and humidity.