I have received two proposals for four different models of Carrier and Trane air source heat pumps. Since I live in Ohio, the HSPF numbers are of primary importance. The HSPF numbers on the units are 7.8, 9.0, 9.5 and 10.5. The highest number is with the Carrier Infinity 25VNA unit, and the lowest is the Carrier Performance 25HPA. All the units utilize Air Handlers that are "matched" with the compressor unit. My question relates to this question of how much "difference" in the amount of heat generated by the 7.8 verses the 10.5. I do know that my brother-in-law has the 7.8 unit in his 2000 square foot, two story home, and he has his thermostat at 72 degrees year round and has no problem, In fact, since his home is almost 25 years old, this is his second Carrier Performance 25HPA unit. I think that it would be fair to assume that the Carrier 25HPA could possibly generate more heat at a lower cost, but would the difference justify the cost difference.