A heat pump moves heat using work, usually supplied as electricity. Its heating coefficient of performance, COP, is heat delivered divided by energy input over a stated boundary and set of conditions. A COP above one is possible because the system transfers heat from the environment; it is not creating energy from nothing.
A worked energy example
Suppose an illustrative system delivers 12 kWh of heat while consuming 4 kWh of electricity during the same interval:
heating COP = heat delivered / electricity input
= 12 kWh / 4 kWh
= 3
If the same heat requirement were met at COP 2, the input would be 12/2 = 6 kWh. At COP 4 it would be 3 kWh. These values illustrate the arithmetic; they are not measurements of a named unit or a prediction for your home.
| Assumed COP | Heat delivered | Calculated electricity |
|---|---|---|
| 2 | 12 kWh | 6 kWh |
| 3 | 12 kWh | 4 kWh |
| 4 | 12 kWh | 3 kWh |
Define what the meter includes
Are fans, pumps, controls and backup resistance heating included in the electrical input? Where is delivered heat measured? A compressor-only result and a whole-system meter are different boundaries. Comparing them as though they were identical can exaggerate performance.
Electrical power in kW is a rate; electrical energy in kWh is accumulated over time. A 2 kW input sustained for three hours uses 6 kWh. Heat-output capacity is also expressed as a rate. The presence of “kW” on both sides of a specification does not mean every quantity is electrical consumption.
Why a seasonal rating differs from one COP value
Outdoor conditions, required supply temperature, part-load operation, defrost and auxiliary heat can change performance. A seasonal metric represents performance across an assessment procedure or operating season. Regional labels such as SCOP and HSPF2 have their own definitions, units and test assumptions; do not substitute one label's numerical value directly into a COP formula without the proper definition.
Compare equipment under the same relevant rating system and conditions. Ask which capacity and efficiency values apply at your design outdoor temperature and intended heating-system temperatures. A headline maximum cannot establish seasonal electricity use.
Build a transparent estimate
- Estimate or measure the useful heat requirement for the period.
- Choose a defensible system/seasonal performance assumption for those conditions.
- Divide heat energy by that performance factor, checking units and boundary.
- Add loads outside the chosen boundary once, rather than twice.
- Show a range for uncertain assumptions and compare it with actual metered performance later.
Installation design and local conditions matter. This explainer does not select equipment, calculate a building's heat loss or promise bill savings. For another boundary example, compare the server power and energy guide.