Which is more important. I am looking at two heat pumps:
1- HSPF 12.5 / COP 17F 2.46
2- HSPF 8.9 / COP 17F 2.7
I was very surprised that the lower HSPF HP actually had a better cold weather COP, which I believe would mean it will be cheaper to operate at that temp. Is HSPF just the ability for the heat pump to extract heat at lower temps then. In my case my utility supplier switches my HP over to my furnace at 10F and below.