HSPF and Altherma

Wayco Wayne_2

I'm trying to compare the COP (coeffiecience of performance) of the Altherma heat pump boiler to the HSPF of a traditional Heat Pump. I've always thought that the HSPF was basically the btuh output/wattsper hour, but under what conditions are these performance numbers taken and how can I compare them to the Altherma's claim of 3 to 5 COP. Typical residential heat pumps lose the ability to heat the building enveope when the outside temperatures fall below the balance point (35F around here) The Altherma can perform down to -4 F according to literature. How do I compare the two??? Thanks for any help clearing this up in my mind. WW