An immersion heater is an electric element that heats a tank of water, usually rated around 3kW. Enter its power, how long it runs to heat the tank and your rate to see the cost.
Heating water with electricity is dearer than with gas, so an immersion is most economical as a backup, or run on a cheap night rate, or topped up rather than reheating a cold tank. A well-lagged cylinder holds its heat for hours and needs less reheating. See immersion heater cost and hot water savings.
Common questions
How much does an immersion heater cost to run?
A 3kW immersion running 1.5 hours uses 4.5 kWh, about £1.17 at 26.11p. Daily, that is roughly £8 a week, which is why timing and lagging matter.
Is it cheaper to leave the immersion on or switch it on when needed?
For most homes, heat on a timer for when you need hot water rather than leaving it on, and lag the cylinder well so the stored heat lasts. Constant reheating of a poorly insulated tank wastes the most.