Short answer
COP is heat output divided by electricity input at a defined operating point. SCOP or seasonal performance combines varying conditions over a season. A realistic seasonal value is more relevant for annual cost.
Important variables
- Outdoor and flow temperature
- Part load and defrosting
- Hot-water share
- Auxiliary energy and system boundary
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Worked example
COP 4 means four kWh heat per kWh electricity at the test point. If seasonal performance is 3, the same annual heat demand needs one third more electricity than at SCOP 4.
Break-even: What changes the result?
Milder source temperatures and lower flow temperatures help. Narrow system boundaries can make measurements look better than whole-system consumption.
Common mistakes
- Using datasheet COP as annual value
- Ignoring auxiliary power
- Comparing different system boundaries
Terms in this guide
Sources & assumptions
- IEA PVPS — Photovoltaic Power Systems Programme (2026-08-17)
- RATIOXA — Methodology and formulas (2026-08-17)
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