The coefficient of performance (COP) is the amount of heat a heat pump delivers divided by the amount of electricity it uses to do so. A COP of 3 means the pump supplies 3 kilowatt-hours (kWh) of heat for every 1 kWh of electricity, which is sometimes written as 300% efficiency. The seasonal coefficient of performance (SCOP) is the same ratio averaged over a typical heating season.
COP, SCOP and SPF
| Measure | What it describes |
|---|---|
| COP | Efficiency at one moment, under fixed test conditions (a set outdoor and water temperature) |
| SCOP | Expected average over a heating season, calculated from lab tests and standard climate data |
| SPF (seasonal performance factor) | Efficiency actually measured over time in a real building |
A single COP figure can flatter a heat pump because it is often quoted at mild outdoor temperatures. SCOP is a better guide to yearly running costs, and a measured SPF is the most realistic of all because it reflects the real house, the installation and how the system is used.
What changes the figure
- Outdoor temperature. The colder the air or ground, the harder the pump works, so COP drops in a cold snap.
- Flow temperature. The hotter the water sent to radiators, the lower the COP. Larger radiators or underfloor heating let the system run cooler and more efficiently.
- Design and set-up. Correct sizing and controls matter as much as the unit itself.
UK rules
To be eligible for the Boiler Upgrade Scheme in England and Wales, an air-to-water or ground source heat pump must have a SCOP of at least 2.8, under the scheme’s regulations. The rules can change, so check GOV.UK for the current requirements; this is general information, not advice.
Read more: Renewable energy at home: what works in a UK house.