What is COP and what is a good COP for a heat pump?

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.

What is the difference between COP and SCOP?

COP is measured at a specific set of conditions (e.g., 7C air, 35C flow). SCOP (Seasonal COP) is the weighted average across an entire heating season, accounting for varying outdoor temperatures. SCOP is more representative of real-world performance and is typically 10-20% lower than the rated COP.

How does flow temperature affect COP?

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

Is a heat pump cheaper than gas at current prices?

At standard UK tariffs (gas 6.5p, electricity 24.5p), a heat pump with SCOP 3.0 produces heat at 8.2p/kWh vs 7.2p/kWh for a 90% gas boiler. The heat pump breaks even at SCOP 3.4. With time-of-use tariffs or solar PV, heat pumps are significantly cheaper than gas.

What is the Carnot COP?

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 40-50% of Carnot COP. For example, at 7C source and 45C flow, Carnot COP = 8.4, so a real COP of 3.0-4.0 represents 36-48% Carnot efficiency.

TradeCalculator

Heat Pump COP Calculator

Calculate the Coefficient of Performance from heat output and electrical input, estimate seasonal COP by climate zone, and compare running costs with a gas boiler.

Heat Output (optional)

Measured heat output, or leave blank

Electrical Input (optional)

Measured compressor power

Heat Pump Source

Climate Zone

Affects seasonal COP estimate

Flow Temperature

35C UFH, 45C large rads, 55C std

Outside Temperature

Current or design temperature

How We Calculate This

This calculator determines the COP of a heat pump either from measured heat output and electrical input, or estimates it from flow and source temperatures using Carnot theory.

COP calculation

From measurement: COP = Heat output (kW) / Electrical input (kW)
From temperatures: COP = Carnot COP x efficiency fraction (0.45-0.50)
Seasonal COP: Adjusted for climate zone and source type
Cost comparison: Heat pump £/kWh-heat vs gas boiler £/kWh-heat

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.