United Kingdom Laundry and water
How much does it cost to run an immersion heater?
An immersion heater is a 3 kW element inside a hot water cylinder. It draws the full 3 kW the whole time it is on, so two hours a day is 6 kWh, which is why it is one of the dearest ways to heat water unless you have cheap overnight electricity.
A 3 kW immersion heater costs about 79p an hour to run in Great Britain at 26.32 pence per kWh. Running it 2 hours a day comes to about £1.58 a day, £48.07 a month and £576.80 a year.
- Price: Ofgem cap, Oct to Dec 2026
- Wattage range with its source
- Checked 26 October 2026
Uses 6.0 kWh a day, 183 kWh a month, at 26.32 pence per kWh (Great Britain (price cap average)).
The dial places the daily cost between a 50 watt fan and a 4.5 kW water heater on 2.5 hours a day.
A 3 kW immersion heater costs about 79p an hour to run in Great Britain at 26.32 pence per kWh. Running it 2 hours a day comes to about £1.58 a day, £48.07 a month and £576.80 a year.
What this assumes
The default is a 3 kW immersion heater running 2 hours a day. Published typical ratings run from 3,000 to 3,000 watts. Your label or manual gives the exact figure, and the calculator takes it.
The price is the Ofgem price cap unit rate for 1 October to 31 December 2026, average for England, Scotland and Wales, paying by Direct Debit. The cap for 1 January to 31 March 2027 is announced in late November 2026. A fixed tariff, a time-of-use plan or a different payment method changes the rate, which is why the rate field is editable.
Cost by wattage and hours at the price cap rate
At 26.32p per kWh, running flat out. Multiply by the share of the time your thermostat keeps the element on.
| Power | 1 hour | 8 hours | 24 hours | A week at 2 hours a day |
|---|---|---|---|---|
| 3 kW | 79p | £6.32 | £18.95 | £11.05 |
How an immersion heater uses electricity
Heating a 120 litre cylinder from cold takes roughly 5 to 6 kWh and about two hours. Once hot, a well insulated cylinder loses about 1 to 2 kWh a day, so topping up is cheaper than heating from cold.
On an Economy 7 tariff the overnight rate can be a third of the day rate, which changes the sum completely. The calculator above lets you enter your own unit rate.
Ways to cut the cost
- Fit a timer so it heats once a day, ideally on the cheap overnight rate.
- Insulate the cylinder and the first metre of pipe.
- Set the thermostat to 60 degrees Celsius, no higher.
Questions people ask
How much does an immersion heater cost per hour?
3 kWh an hour, which is about 79p at 26.32p per kWh.
Is it cheaper to leave the immersion heater on all the time?
No. A cylinder on a thermostat still tops up heat losses all day. A timer that heats it once before the morning shower, on the overnight rate if you have one, costs less.
Other laundry and water costs
More in the UK
Sources
The electricity price on this page is read from the data file that also lists the release it came from. The wattage range is a published typical range, not a measurement of your appliance.