COP (coefficient of performance) is heat out divided by electricity in, at a stated outdoor temperature. A COP of 1.75 at 5°F means the unit delivers 1.75 units of heat for each unit of electricity at that test point — better than electric-resistance heat (COP 1), worse than a mild-weather COP of 3 or 4. ENERGY STAR requires at least 1.75 at 5°F, measured under Appendix M1, and at least 70% of the 47°F capacity, with a controls verification procedure so the lab result matches what the unit would do in a house.
That is why this site will not treat HSPF2 as a winter guarantee. HSPF2 is seasonal and Region IV. The 5°F COP is a single-point floor for cold-climate models (8.1 HSPF2 ducted / packaged, 8.5 non-ducted, in the ENERGY STAR criteria retrieved 2026-11-11).
The calculator can optionally illustrate the unit cost of heat at COP 1.75: kWh per MMBtu = 1,000,000 / (1.75 × 3,412), times your electricity price. At the U.S. 2025 average 17.23¢/kWh that illustration is about $28.86 per MMBtu — a cold-snap check, not an annual bill. Use the calculator and your own rate.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.