What does an immersion heater cost to run?
About 80p an hour, and a full tank from cold is a genuinely expensive thing to do on a standard tariff.
Typical model is rated 3,000W
Price cap is 26.11p
78p per hour, 548 hours a year, 1,643 kWh in total — about £36 a month.
An immersion heater is a 3kW element in a hot water cylinder. Like every electric heater it is 100% efficient, and like every electric heater the problem is the price of electricity rather than the efficiency of the appliance. Heating the same tank with gas costs roughly a third as much.
Two things make the biggest difference. A tank jacket or good factory insulation halves how fast the heat leaks away, so the element restarts less often. And a timer that heats the tank once, shortly before you need it, beats leaving it on constantly by a wide margin.
If the house has solar panels or an off-peak tariff, this flips completely. A diverter that pushes surplus solar into the immersion instead of exporting it at 15p is one of the best-value additions to a solar system, and heating the tank overnight on a cheap rate turns the most expensive water in the house into some of the cheapest.
The short answer: The dearest way to heat water on a standard tariff. On solar or an off-peak rate, one of the cheapest.
What actually helps
As an Amazon Associate we earn from qualifying purchases. It costs you nothing extra and does not affect the figures above.
This is the small stuff
Every appliance on this site put together is usually less than a third of a typical energy bill. Heating the house is the rest of it. If the numbers here bothered you, the number that actually matters is what your heating costs — and whether a heat pump would make it better or worse in your particular house.
Work out your heating costOther appliances
Energy figures checked 2026-08-26. Electricity priced at the Ofgem cap for 1 July – 30 September 2026. Your own machine and tariff will differ — put your figures in above.