What Is COP in a Heat Pump, and What Number Is Actually Good?

COP is the cleanest efficiency number in HVAC and the one manufacturers are least eager to put on the box. Here is how to read it.

Coefficient of performance is a ratio with no units: heat delivered divided by energy consumed. A COP of 3.5 means the unit delivers 3.5 kW of heat for every 1 kW of electricity it draws.

Why COP moves constantly

COP is not a fixed property of the machine. It changes with outdoor temperature, indoor temperature, fan speed and compressor speed. The same unit might show a COP of 4.5 at 47°F and 2.1 at 5°F. When a spec sheet gives you a single COP number without stating the test conditions, it is close to useless.

Benchmarks worth memorizing

• Above 4.0 at 47°F — excellent, typical of a high-end inverter unit.
• 3.0–3.5 at 47°F — solid mainstream performance.
• Above 2.0 at 5°F — genuine cold-climate capability.
• Below 1.5 at 5°F — you are approaching the point where resistance heat is nearly as cheap.

COP versus HSPF2 and SEER2

COP is an instantaneous measurement at one condition. HSPF2 and SEER2 are seasonal averages that bundle an entire heating or cooling season into one figure, including defrost cycles and part-load behavior. HSPF2 is more useful for comparing two units you might buy; COP is more useful for understanding how a unit will behave on the coldest night of the year.

The number the installer never mentions

System COP, as opposed to equipment COP, includes duct losses, blower power and any backup heat that runs. A unit with an equipment COP of 3.8 sitting on leaky attic ductwork can deliver a system COP closer to 2.4. Duct sealing is usually the cheapest efficiency upgrade available and almost never appears on a replacement quote unless you ask for it.

Last checked August 2026. Prices are US ranges and vary by region — always confirm against written quotes.