Calculate heat pump electricity consumption
A heat pump’s electricity use depends on the useful heat it must provide and its efficiency over the same period. The basic calculation is heat demand ÷ efficiency. Multiplying the electricity use by your unit rate gives the energy cost.
For example, a home needing 12,000 kWh of heat with a SCOP of 4 uses 3,000 kWh of electricity. At 0.30 per kWh, that is 900 a year. With the same demand and a SCOP of 3, consumption rises to 4,000 kWh and the cost to 1,200. These are illustrative scenarios in whichever currency you select.
Using your gas bill as a starting point
Select “Estimate from gas use” and enter annual fuel consumption for heating. The calculator multiplies this by your boiler’s efficiency to estimate the useful heat delivered. For 15,000 kWh of gas and a 90% boiler efficiency, that is 13,500 kWh of heat.
Subtract gas used for cooking, and exclude hot water unless the new heat pump will meet that demand too. A heat pump serving one room should not be compared against your entire home’s gas consumption. Changing the rooms heated or the indoor temperature also changes demand.
A 6 kW heat pump does not always consume 6 kW
Rated heating capacity is heat output, not automatically electrical input. At an output of 6 kW and a COP of 3, the corresponding electrical input is about 2 kW at that operating point. Both output and efficiency vary in use, so multiplying the nameplate heating capacity by every hour of the year gives a misleading electricity estimate.
Choose an efficiency that matches your installation
Use a seasonal estimate suited to the climate and heating-water temperature of your system. A measured whole-system seasonal performance factor can be useful when its measurement boundary includes the equipment you want to compare. Allow for backup heating and hot-water operation if those are outside the figure you enter.
For a cold-weather scenario, select COP and enter a relevant measured or manufacturer-specified value. Annual results then assume that fixed COP for the whole entered demand; they are a sensitivity scenario, not a weather forecast.
Background: Energy Saving Trust. You can also compare against a gas boiler.