What Are Electric Boilers?

For as long as we can remember, the majority of the houses in the UK have relied on gas boilers to heat their home and water.

This is set to change with the UK goal to become carbon neutral or net-zero by 2050, this is resulting in a growing pressure to phase out gas boilers over the coming years.

On top of that, around 2 million houses in the UK do not have access to the mains gas network and a large number of properties can't use gas due to flue restrictions.

This is why electric boilers/ heaters have grown in popularity within the last few years.

But how does an electric boiler work?

How do Electric Boilers work?

Just like a standard gas combi boiler, an electric boiler also is fed with cold water from the mains water supply.

Electricity from the mains electricity supply is also fed into the boiler, electric boilers essentially work like giant kettles - using electricity and a metal element to heat the water.

Cold water is passed over the metal heating element and heat is transferred, resulting in hot water that can be supplied to the radiators and taps on demand, you could also store the hot water in a hot water storage cylinder.

The exact way in which the boiler your interested in works in terms of heating and storage of the hot water depends on the type of electric boiler/ heater as there are different types...

Electric boilers are extremely efficient, many of them have an efficiency of 100%. Whereas gas boilers typically don't exceed the 90% efficiency. Also, unlike gas boilers, electric boilers do not produce any harmful emissions either, this makes them an environmentally friendly alternative to gas boilers.

There are a few different types of electric boilers, which vary in how they work and the one most suitable for your property depends on factors like; hot water demands, size of your property and pressure of your mains water supply.

Electric Combi Boilers

An electric combination or combi boiler is able to supply heating and hot water on demand from a single unit. They utilise a heating element and a design that maximises surface area so that as much cold water as possible can be heated as it passes over the element.

Combi boilers are typically wall hung and are ideal for small properties and or those with a low to average hot water demand. They are also the quickest and cheapest type of boiler to install.

The major disadvantage of an electric combi boiler is that they do not use a hot water storage tank and so you will be unable to take advantage of Economy 7 tariffs by heating your water overnight at a cheaper rate. In addition, they may not be able to meet the hot water demands of a larger property with multiple water outlets.

Electric Storage Boilers

An electric storage boiler utilises an electric flow boiler to heat the water and has a built-in hot water storage cylinder where hot water can be stored.

The major advantage of these storage boilers is that the water can be heated during off-peak periods so that you can easily set your thermostat timer to reap the rewards of certain energy tariffs. For example, customers on the Economy 7 tariff can set their timer to only switch the heater on during off-peak hours.

A storage boilers ability to take advantage of the Economy 7 tariff can help people take more control over their heating bills. However, a minor downside is that they are typically more expensive to buy and install and require more space to install.

Dry Core Storage Boilers

This type of electric boiler is similar to an electric storage boiler in that it utilises electricity during off-peak hours.



They differ in that they store the heat in a dry medium e.g. bricks. This heat can then be released at times when electricity prices are higher. The heat is released as needed into the water, which can then be used for central heating or hot water.

Dry core storage boilers are considered much more versatile than regular storage boilers since the heat is released into the water only as needed. For this reason, they are ideal for homeowners wanting to take advantage of the Economy 7 tariff.

Electric CSU Boilers

A Combined Primary Storage Unit or CPSU is a boiler that is able to store a large volume of hot water. This means it is able to release water to radiators and taps at a very fast rate, making it ideal for large buildings with high hot water demands.

They can be found in residential properties, but are much more commonly seen in commercial properties. They are also large boilers, requiring more space to house and are much more expensive than regular boilers.

Pair Electric Boilers with Solar

If you have a hot water storage cylinder with an immersion heater, also referred to as a megaflow boiler it’s possible to hook it up to a solar PV system so that you can power it during the daytime, practically for free.

What Size Boiler Do You Need?

The size of the boiler refers to the power output and for electric boilers and not the dimensions, this is measured in kilowatts per hour (kW). In general, the higher this is, the more water outlets it can provide hot water for.

Electric boilers are available in kW ranging from between 5 kW and 15 kW. The size of your property and heating demands will determine what size boiler (kW output) you require.

The general rule of thumb is that you need 1.5 kW for each radiator in your home. However, there are other factors that come into consideration, such as your mains water pressure, ceiling height and level of insulation in your home. For this reason, it’s always advised to have an engineer assess your properties heating needs.

It’s important to bear in mind that although it’s cheaper to buy and run a smaller electric boiler if it’s not the appropriate size for your property you will soon find yourself running out of hot water. While a boiler that is too big will result in an excessive heating bill, which is why correct boiler sizing is crucial.