Heat Pump COP Calculator

COP (Coefficient of Performance) is the ratio of heat output to electrical input. A COP of 3.0 means the heat pump produces 3 kWh of heat for every 1 kWh of electricity. A good ASHP achieves COP 3.0-4.0 at moderate conditions, while GSHP can reach 4.0-5.0. COP varies with source and flow temperatures.

COP is measured at a single fixed set of conditions (e.g. 7°C air, 35°C flow). SCOP (Seasonal COP) is the weighted average across a whole heating season under the BS EN 14825 test points, accounting for varying outdoor temperatures and defrost cycles. A true SCOP is usually 10-20% LOWER than the rated fixed-condition COP. Note: the "Climate-adjusted COP" this tool reports is an indicative season-average estimate that scales the instant COP up or down by UK climate zone — it is not a certified BS EN 14825 SCOP. For a guaranteed figure, use the manufacturer’s tested SCOP or the MCS heat pump database.

Lower flow temperatures give higher COP. At 35°C flow (UFH), COP might be 4.0. At 45°C flow (oversized radiators), COP drops to about 3.0. At 55°C flow (standard radiators), COP might be only 2.5. This is why properly sized emitters are critical for heat pump efficiency.

At the Ofgem price cap for 1 July-30 September 2026 (gas 7.33p/kWh, electricity 26.11p/kWh, Direct Debit average incl. 5% VAT), a heat pump with COP 3.0 produces heat at 8.7p/kWh vs 8.1p/kWh for a 90% gas boiler. The heat pump breaks even at COP 3.21 (26.11 ÷ (7.33/0.90) = 3.21) — so a well-installed ASHP at COP 3.5-4.0 beats gas at cap rates. With a heat-pump or time-of-use electricity tariff, or solar PV, the saving is larger. The price cap changes every quarter, so confirm the current Ofgem rate.

The Carnot COP is the theoretical maximum COP based on thermodynamics: COP_carnot = T_hot / (T_hot - T_cold) in Kelvin. Real heat pumps achieve roughly 40-60% of Carnot COP (~50% is a common reference; field data from OpenEnergyMonitor shows many UK installs sit between 40-50%). For example, at 7°C source and 45°C flow, Carnot COP ≈ 8.4, so a real COP of 3.4-4.2 represents 40-50% Carnot efficiency. This tool uses 45% for ASHP and 50% for GSHP, applied to the raw flow/outside temperatures without heat-exchanger approach offsets, so treat the temperature-based estimate as indicative.