What Is the Seasonal COP and Why Is It So Important?
The seasonal COP (Coefficient of Performance) is the most important metric when it comes to heat pump efficiency. It indicates the ratio of generated heat energy to consumed electricity over an entire heating season. A seasonal COP of 4.0 means: from 1 kilowatt-hour of electricity, 4 kilowatt-hours of heat are extracted. The remaining 3 kilowatt-hours come from environmental heat and are essentially free.
The seasonal COP should not be confused with the COP measured under standardized laboratory conditions at specific temperature pairs. The seasonal COP reflects actual performance over the entire year, including cold winter days, defrost cycles (for air-source heat pumps), and domestic hot water production. Therefore, the seasonal COP in practice is always lower than the manufacturer's stated COP.
Typical Seasonal COP Values by Heat Pump Type
Air-to-water heat pumps achieve an average annual seasonal COP of 2.8 to 3.5. The variation is large because performance depends heavily on outdoor temperature. On a mild spring day at 15 degrees, the COP can be 5.0, but on a frost day at minus 10 degrees, it drops to 2.0 to 2.5. Modern models with inverter technology and R290 refrigerant achieve better values even at low temperatures.
Ground-source heat pumps benefit from constant ground temperature (8 to 12 degrees year-round) and achieve seasonal COP values of 3.5 to 4.5. Since there are no defrost cycles and the source temperature remains stable, they operate more consistently and efficiently. The higher purchase price is often recouped through lower operating costs within 8 to 12 years.
Water-to-water heat pumps use groundwater at a constant temperature of 8 to 12 degrees and achieve the highest seasonal COP values of 4.0 to 5.0. They are the most efficient variant but also the most complex to install, requiring water rights permits and adequate groundwater quality.
What Affects Your Building's Seasonal COP?
The most important factor influencing the seasonal COP is the flow temperature of the heating system. The lower the required flow temperature, the higher the COP. Underfloor heating typically operates at 30 to 35 degrees flow temperature, low-temperature radiators at 45 to 50 degrees, and conventional radiators in old buildings at 55 to 70 degrees. Each degree less flow temperature improves the COP by approximately 2 to 3 percent.
The insulation condition of the building indirectly affects the COP: A well-insulated house requires less heating power, allowing the heat pump to operate at lower capacity and flow temperature. A poorly insulated old building requires high heating power and flow temperature, significantly degrading the COP. In our calculator, the COP is adjusted based on insulation status: poor insulation reduces the COP by 0.5 points, while good insulation increases it by 0.2 points.
Additional factors include the sizing of the heat pump (an oversized or undersized system operates less efficiently), the quality of installation (proper hydraulic balancing, optimal heating curve settings), and user behavior (frequent window opening, strongly fluctuating room temperatures).
How Can I Improve My Heat Pump's Seasonal COP?
There are several measures to increase the seasonal COP. The most effective measure is reducing the flow temperature by enlarging heating surfaces (larger radiators or additional underfloor heating), improving building insulation (facade, roof, windows), and having a specialist company optimally set the heating curve.
Hydraulic balancing ensures that each radiator receives exactly the right amount of water flow. Without balancing, the pumps oversupply nearby radiators and undersupply distant ones. Balancing costs 500 to 1,500 euros and has been a prerequisite for BAFA funding since 2024.
Finally, a PV system can reduce effective electricity costs and thus improve the heat pump's economics, even though the COP itself does not increase. In combination with an intelligent energy management system, the PV self-consumption share for the heat pump can be increased to 30 to 50 percent.
Minimum COP Requirement for BAFA Funding
To receive BAFA funding, the installed heat pump must achieve a calculated seasonal COP of at least 2.7. This is calculated in advance based on building data and manufacturer specifications (the so-called COP calculation according to VDI 4650). The actual COP during operation may differ. It is worthwhile to verify the COP after the first year of operation and have settings optimized if necessary.