Heat Pump Electricity Consumption and Boiler Comparison

How much electricity does a heat pump use?

A heat pump does not make heat, it moves it: a compressor driven by electricity carries heat from outdoor air, the ground or water into the building. The ratio of heat delivered to electricity drawn is the COP:

P = Q / COP

A unit with a COP of 4 delivering 10 kW of heat draws 2.5 kW of electricity. The other 7.5 kW comes from the environment. For a resistance heater the ratio is 1, so the same heat takes four times the electricity.

Annual consumption

COP changes with outdoor temperature, so annual figures use the seasonal average, SCOP: E = Q_annual / SCOP. A house needing 12 000 kWh of heat a year uses 3000 kWh of electricity with a heat pump whose SCOP is 4.

If you do not know your annual heat demand, take it from your gas bills: annual gas use (kWh) times boiler efficiency.

Comparison with a boiler

For the same heat a boiler burns Q_annual / (η × H) of fuel, where η is the boiler efficiency and H the heating value per unit of fuel.

Example: for 12 000 kWh of heat a 90 percent efficient boiler burns 1253 m³ of gas at 10.64 kWh/m³. Which system is cheaper to run is shown by the break even SCOP: SCOP_b = f_electricity × η × H / f_fuel. If the real seasonal efficiency of your heat pump is above it, heating costs less.

What affects the result?

The biggest factor is flow temperature. Low temperature systems such as underfloor heating give high efficiency and old high temperature radiators give low efficiency. Efficiency falls as outdoor air gets colder, and air source units run defrost cycles. Read the SCOP on the label for your own climate zone and water temperature.

Limits

The tool compares running cost only. Purchase and installation, maintenance, standing charges and subsidies are not included. To see when the investment pays for itself use the energy payback calculator.