How much electricity does a heat pump use?

Start with useful heat, not the heat pump’s label

The kilowatt number in a model name normally describes heating output under stated test conditions. It does not tell you how many kilowatt-hours the home will buy from the grid. Annual electricity use depends first on the building’s annual space-heating and hot-water demand.

A room-by-room heat-loss calculation is used for design-day sizing. Historic fuel use can provide a separate annual sense check, provided boiler efficiency, weather and household changes are considered. Neither floor area nor the rating of the old boiler is a reliable electricity forecast by itself.

• Annual space-heating demand
• Domestic hot-water demand
• Seasonal system efficiency, not one laboratory COP
• Electricity used by pumps, backup heaters and controls
• Changes in occupancy, comfort or heated floor area

Use one transparent calculation

The basic relationship is useful heat demand ÷ seasonal performance factor = heat-pump electricity. If space heating needs 10,000kWh and hot water needs 2,000kWh, the combined 12,000kWh divided by an SPF of 3 gives 4,000kWh.

At Ofgem’s published average Direct Debit electricity rate of 26.11p/kWh for 1 July to 30 September 2026, 4,000kWh would cost about £1,044 before standing charges. At 2.5 SPF the same heat would cost about £1,253; at 3.5 SPF it would be about £895. Tariff rates change quarterly and Scottish regional rates differ, so replace the example rate with your own.

Keep in mind: Standing charges are normally left out of a heating comparison unless changing system lets the household remove another fuel supply and its standing charge.

Why the seasonal number matters

A headline COP is a snapshot at defined temperatures. Seasonal performance includes changing outdoor conditions and a wider period of operation. Energy Systems Catapult reported a median SPFH4 of 2.80 for 291 air-source systems in its interim analysis, with an interquartile range of 2.53 to 3.09. That spread is a reminder that design and operation matter.

The project also found that median cold-day performance fell, as expected, when outside temperatures were lower. A responsible estimate therefore tests more than a mild-weather catalogue point and explains the proposed flow temperature.

What pushes electricity use up or down

A home loses more heat when it is colder outside, when more rooms are heated or when the target temperature is raised. The system then has to deliver that heat. Poorly sized emitters can add a second penalty if the heat pump must produce hotter water than the design should require.

Hot-water settings, immersion-heater use, a high heating curve, aggressive on-off scheduling and unresolved faults can all add consumption. Sensible fabric work can reduce demand, while larger suitable radiators and good commissioning can help the heat pump deliver that demand efficiently.

• Check the proposed annual heat demand
• Ask what SPF or SCOP the estimate uses and what is included
• Ask what flow temperature supports that efficiency
• Use your actual tariff, not a national price-cap total
• Request a monitoring and handover plan

What a useful quote should show

The installer should be able to connect the heat-loss work, emitter schedule, chosen unit and estimated electricity use. A single low running-cost number without its heat-demand, efficiency and tariff assumptions cannot be checked.

Treat the estimate as a range. Compare it with historic consumption and ask what would change the upper and lower case. That makes the number useful for a household decision rather than a sales promise.

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