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How Much Does It Cost to Run a Electric Tankless Water Heater in the UK? (2026)
Electric tankless heaters draw enormous power, 12 to 36 kW, but only while hot water is flowing. They avoid the standby losses of a tank, saving 10 to 30 percent for most households, but need heavy wiring.
A typical electric tankless water heater (18,000 W) costs £4.68 per hour, or about £105.30 per month at 0.75 hours a day in United Kingdom. Expensive to run
| Wattage | Per hour | Per day | Per month | Per year |
|---|---|---|---|---|
| Low (12,000 W) | £3.12 | £2.34 | £70.20 | £854.10 |
| Typical (18,000 W) | £4.68 | £3.51 | £105.30 | £1,281 |
| High (36,000 W) | £9.36 | £7.02 | £210.60 | £2,562 |
Formula: watts ÷ 1000 × hours × price per kWh. Typical use is 0.75 h/day ≈ 4,928 kWh per year.
In the UK, with electricity at £0.26 per kWh (source: Ofgem price cap 1 Jul–30 Sep 2026, 2026-07), a typical electric tankless water heater costs £4.68 per hour and about £1,281 per year at 0.75 hours a day. Each £1.00 of electricity buys roughly 0.2 hours of use.
How to lower the cost of running a electric tankless water heater
- Install low-flow showerheads. Flow rate directly drives power draw.
- Fix hot water drips. Each one fires the heater.
- Set the outlet temperature to 49 C and skip mixing cold water at the tap.
In standby it draws about 2 W, which adds roughly 18 kWh (£4.56) per year if it is never unplugged.
Frequently asked questions
How much does a tankless water heater cost per month?
About 400 kWh a month for a family of four, roughly 10 to 30 percent less than a tank.
Do tankless heaters use a lot of electricity?
A lot at once, but for short periods. Total use is typically lower than a tank.
Do I need a panel upgrade for an electric tankless heater?
Often yes. Whole-house units need 100 amps or more of dedicated capacity.
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