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Immersion heaters heat water using electricity. This can be from the mains or renewable electricity you've generated from solar panels.

If you already have an immersion heater, find out how to use if most efficiently and cut costs.

If you're considering whether one is right for your home, read about the pros and cons and how you can get free hot water.

Use our independent switching site, Which? Switch, to compare electricity prices and check you're not overpaying. 

An immersion heater is an electric water heater that sits inside a hot-water cylinder. It's a bit like a kettle, using an electric resistance heater (which looks like a metal loop or coil) to heat the surrounding water. 

It's separate from your central heating boiler or radiators and connected its own power supply via a cable. You can switch an immersion heater on and off easily or connect it to a timer to heat at specific times.

An immersion heater can be your primary water heating, for example if your home has electric heating.

Many homes have them as a back-up water heater for a central heating system. This means that if your boiler fails, you still have a way to heat your water.

Immersion heaters are typically 3kW. It costs around 63p to run one for an hour at current electricity prices.

Over a year it could cost around £1,380 to heat enough water for a 2-3 bedroom house with a shower or bath.*

That's based on heating a 180 litre tank from 10C to 60C twice a day, taking around three hours each time.

How long you'll need to use your immersion heater each day - and therefore how much it costs - depends on:

Insulating your tank will help keep the water warmer for longer and mean you won't need to increase the temperature as much each time.

* Electricity price used is 21p/kWh (based on Ofgem's price cap for Oct21 - Mar22). Costs don't include keeping the tank at the same temperature between cycles and assume 100% efficiency.

Leaving the immersion heater on constantly will give you a steady supply of hot water - but is expensive and inefficient.

Follow these tips to ensure you have hot water when you need it and minimse the impact on your bills:

If you have a mainly south-facing roof, solar panels can be a good option for heating your water. Find out more about solar water heating .

Alternatively, if you have an immersion heater and solar panels or a wind turbine which generate electricity, you can divert any excess to your immersion heater. 

You'll need to buy a device that does this, such as Immersun or Solar iBoost, which cost about £200 to £400 plus the cost of installation. But it means that you'll be able to heat your water for free.

It's generally much cheaper to heat water using gas, rather than electricity. So if you have a gas boiler it's likely to be cheaper than using an immersion heater every day. 

If your boiler is quite old and inefficient, consider upgrading to a more efficient combi boiler.

See our reviews of the best boilers to make sure you buy a reliable brand that won't leave you in the cold.