Here's my understanding of SEER ratings. Lets say you have a 16 SEER Air conditioner for example,that would mean for every Watt of electricity consumed, the equipment would produce 16 BTU's. So to speak if your AC is producing 36,000 Btus and drawing 2250 watts, then your AC must be in the range of a 16 SEER. SEER rating are also figured by testing the equipment in various load conditions (different temperatures inside and outside the house) and then the average of the results is figured in

However what I want to understand is, HSPF. What is HSPF exactly? Heating seasonal performance factor I know but how do they come up with their ratings? like for example, what is the difference in power consumption between a heat pump with a HSPF of 7 and one with a rating of 10. How many more Watts does the 7 HSPF consume and how well does one extract heat from the air better the other? I know at different temperatures this will vary. Someone chime in and help me understand. Give me some equations and explain in a easy to understand manner.