Coefficient of performance (COP) is a ratio that describes how much heating or cooling a system delivers for each unit of energy it consumes. A heat pump with a COP of 3.0 produces three units of heating or cooling energy for every one unit of electrical energy it draws. The higher the number, the less electricity the system needs to do the same work.
How COP Is Calculated
The formula is straightforward:
COP = Useful heating or cooling output (in watts or BTU) ÷ Electrical energy input (in watts or BTU)
For a cooling system removing 12,000 BTU/h of heat while consuming 4,000 BTU/h of electricity, the COP is 3.0. For a heating system delivering 15,000 BTU/h while drawing 5,000 BTU/h, the COP is also 3.0.
Because COP compares output to input in the same units, it is a dimensionless number.
Typical COP Ranges
System Type |
Typical COP Range |
Notes |
Air-source heat pump (heating) |
2.0–4.5 |
Drops as outdoor temperature falls |
Air-source heat pump (cooling) |
2.5–5.0 |
Drops as outdoor temperature rises |
Geothermal heat pump |
3.5–5.5 |
More stable because ground temperature fluctuates less |
Electric resistance heater |
1.0 |
Converts electricity to heat 1:1, no multiplier |
Gas furnace (for comparison) |
0.8–0.95 |
Below 1.0 because some energy escapes as exhaust |
Electric resistance heaters sit at exactly 1.0 because they convert electricity into heat with no multiplier effect. A heat pump exceeds 1.0 because it moves existing heat rather than generating it from scratch. A gas furnace falls below 1.0 because combustion losses send a portion of the fuel's energy up the flue.
COP vs. EER and SEER
COP measures performance at a single set of conditions (a fixed outdoor and indoor temperature). EER (Energy Efficiency Ratio) does the same but uses BTU/h per watt as its unit instead of a dimensionless ratio. SEER (Seasonal Energy Efficiency Ratio) averages performance across an entire cooling season, accounting for the temperature swings a system faces from spring through fall.
Converting between them: EER = COP × 3.412 (since 1 watt = 3.412 BTU/h).
COP is the metric used most often in engineering specs and international standards. SEER appears more frequently on consumer-facing equipment labels in North America. Both describe efficiency, but over different time horizons.
Why COP Changes With Temperature
COP is not fixed. It shifts with the temperature difference between the source (where heat is pulled from) and the destination (where heat is delivered). The smaller the gap, the less work the compressor does, and the higher the COP. On a mild 50°F day, an air-source heat pump heating a home to 70°F might hit a COP of 4.0 or higher. At 10°F outside, the same unit could drop to 2.0, because the compressor has to work much harder to extract heat from colder air.