- An immersion heater rated 3 kW at 240 V uses 2.8 kW on a 230 V supply, so it costs 73.7p an hour at full power (79p at the full 3 kW). An hour and a half is £1.11.
- Prices from the Ofgem price cap, 1 October to 31 December 2026: the average for England, Scotland and Wales is 26.32p per kWh by Direct Debit. Your region and tariff change it, so use the calculator below.1
- Last checked: 28 October 2026.
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How much does an immersion heater cost per hour?
Costs at 2.8 kW and 3 kW for 30 minutes, 1 hour and 2 hours at full power.
| Power | 30 minutes | 1 hour | 2 hours |
|---|---|---|---|
| 2.8 kW | 36.8p | 73.7p | £1.47 |
| 3 kW | 39.5p | 79p | £1.58 |
How to work out the cost
Multiply the power in kilowatts by the hours it runs, then by your electricity unit rate. If the power is in watts, divide by 1,000 first.
For example: 2.8 kW x 1 hours x 26.32p per kWh = 73.7p.1
That is the cost at full rated power. If a thermostat switches the appliance off once the room is warm, it uses less. Standing charges are paid whatever you use, so they are not part of the cost of switching it on.
Typical immersion heater power
Heatrae Sadia's immersion heater manual gives the rating as “3.0kW @ 240V~/2.8kW @ 230V~”.2 Models are named only as examples of published ratings, not recommendations.
Its thermostat is “factory set to 60°C” with a range of 10 °C to 60 °C, so the element switches off once the water is hot. The cost depends on how long the element is actually on.2
The manual says: “The immersion heater must be installed, and commissioned by a competent person.”2
On an off-peak tariff
If your hot water heats on a cheaper off-peak rate, use that rate from your bill in the calculator instead of the single-rate average.
Next steps
1. Check your immersion heater's rating.
2. Use a timer so it only heats when you need hot water.
3. Work out your own cost with the calculator above.
Help with energy bills
If you are struggling with energy bills, check the help you may be able to get. These checkers are free and need no account.
Who these figures cover
The prices are from Ofgem's price cap for England, Scotland and Wales, 1 October to 31 December 2026.1 In Northern Ireland, use the unit rate on your bill in the calculator.
There is no VAT on household electricity in England, Scotland and Wales, and the rates above already reflect this.1 HMRC: “The temporary zero rate applies from 1 October 2026 to 30 June 2027.” The Budget on 28 October 2026 extended it from 31 March (announced; the legislation is due in early 2027). Gas stays at 5% VAT.4