How can I estimate my air source heat pump electricity costs?

The most reliable estimate is a range based on the heat your home needs, the heat pump’s seasonal performance and the electricity tariff available to you. A property survey makes the result more useful because it accounts for insulation, room sizes, radiators, hot water use and the design temperature for the system.

Start with the home’s annual heat requirement. Your past fuel bills can provide a useful starting point, especially if the house has been occupied in a typical way. They do not give a complete answer, though. An oil or LPG boiler loses some heat through the flue, and the amount of fuel used can change with boiler condition, thermostat settings and the weather.

We use the building’s heat-loss information to test that starting point. Wall construction, roof insulation, windows, draughts and room-by-room heat loss all affect the result. A solid-wall house, barn conversion or older rural property may need more heat than its floor area alone suggests. The survey also shows whether insulation work or larger radiators would improve the design before installation.

Allow separately for hot water. Heating and hot water do not place the same demand on the system. Your cylinder may need a higher water temperature than your radiators, and your household’s bathing and hot-water habits affect annual consumption. A home with frequent hot-water use will need a different allowance from a property occupied only part of the week.

Use seasonal performance rather than a headline efficiency figure. A heat pump’s coefficient of performance changes with the outdoor temperature and the water temperature it must produce. Its seasonal coefficient of performance gives a more realistic view across a full heating season. Colder weather, high flow temperatures, defrost cycles and hot-water heating all reduce performance compared with mild-weather operation.

Your radiators and pipework therefore matter to the electricity estimate. If they can heat the rooms with water at a lower temperature, the heat pump can usually operate more efficiently. We check their output as part of the design rather than assuming that existing heating components will perform in the same way.

Apply the tariff to the expected demand. Use the unit rate that matches the tariff you would actually use, not a generic electricity price. A single-rate tariff is straightforward. A day-and-night tariff needs the expected demand divided between its rates, while a variable tariff requires an assumption about future prices. Treat that result as a planning estimate rather than a fixed bill.

• Keep the electricity unit rate and the standing charge separate.
• Include the heat pump’s electricity use for space heating, hot water and its auxiliary components.
• Show different tariff assumptions if the household is considering a time-of-use tariff.
• Allow for colder and milder winters instead of relying on one precise annual figure.

The standing charge belongs to the electricity supply as a whole, so it should not automatically be counted as an extra heat pump cost. If the property already has an electricity connection, the more useful comparison is usually the additional consumption created by the new heating system.

Account for solar panels and battery storage separately. Solar generation can reduce the electricity bought from the grid when the heat pump is running during daylight. A battery may shift some stored electricity into the evening, depending on its capacity, controls and the household’s other demand. Do not subtract the full annual solar generation from heat pump consumption: generation and heating demand do not occur at the same time, particularly during winter.

For an off-gas-grid home, compare the estimated heat pump electricity with the cost of the fuel actually delivered to the property. Include oil or LPG standing charges, delivery arrangements and boiler servicing where they form part of the household’s present heating cost. Comparing fuel prices alone can make the existing system look cheaper or more expensive than it is.

Expect the estimate to improve after commissioning. Your first electricity bills reflect the weather, the temperatures you choose and how the controls are set. A system running at unnecessarily high flow temperatures can use more electricity than the design estimate. We explain the controls and check that the heating curve, room temperatures and hot-water schedule suit the property.

When we prepare an air source heat pump quotation, we can show the assumptions behind the estimate rather than presenting one unexplained annual figure. That gives you a clearer basis for comparing tariffs, insulation work, radiator changes, solar generation and the likely running pattern of your home before you decide.