How to use this calculator
- Enter or choose heat output.
- Enter or choose electrical input.
- Enter or choose output (flow) temperature.
- Enter or choose source temperature (outdoor air or ground).
- Enter or choose heat needed per year.
- The coefficient of performance (COP) updates as you type. Use Copy result or Share to keep it.
Method
COP = Heat output ÷ Electrical input; COP(Carnot) = T_hot ÷ (T_hot − T_cold) in kelvin; Electricity per year = Heat needed ÷ COP
- T_hot
- output temperature + 273.15
- T_cold
- source temperature + 273.15
Worked example
- COP = 8 ÷ 2.5 = 3.2.
- Carnot COP = 308.15 ÷ (35 − 5) = 10.27, so the unit reaches 3.2 ÷ 10.27 = 31.15% of the ideal.
- Yearly electricity = 10,000 ÷ 3.2 = 3,125 kWh × 0.25 = 781.25.
Delivering 8 kW of heat from 2.5 kW of electricity is a COP of 3.2, so 10,000 kWh of heat costs about 781 a year.
What the result means
COP falls as the gap between source and output temperature grows, which is why low flow temperatures (larger radiators, underfloor heating) improve efficiency. A single COP measurement is a snapshot; the seasonal average (SCOP) is what sets yearly cost.
Assumptions and limits
- The COP entered applies to the whole year when estimating running cost.
- Defrost cycles, backup heaters and pump energy reduce real seasonal efficiency.
Questions
What is the difference between COP and SCOP?
COP is measured at one set of conditions; SCOP (seasonal COP) averages performance across a heating season and is the better guide to annual cost.
Can COP be higher than the Carnot COP?
No. If a measurement exceeds it, the heat or power readings are wrong.