What Size Electric Boiler Do I Need?

If you are considering an electric boiler, you might be wondering what size boiler to go for.

Electric boilers are sized differently to gas boilers. In this guide, we will explain how to choose the right sized boiler for your property and also give you all the information you need to choose the right boiler for you.

What size electric boiler do I need

Electric boilers are sized differently to gas and oil boilers. When you research electric boilers, you will find manufacturers talk about kilowatts.

This is an indication of the power capacity of the boiler rather than the physical size or the amount of energy it will use.

In this guide, we will explain what these different sizing’s mean and show you how to choose the best boiler to suit your property. We will also discuss running costs and what happens if you end up with a boiler that is the wrong size.

How do electric boilers work?

In order to understand what sized electric boiler you need for your property, you first need to have a grasp of how they work.

An electric boiler performs all of the functions of a gas or oil boiler, but without the need to burn physical fuel in order to heat the water that runs through your radiators and hot water taps.

Instead, this is done using electricity, a little bit like the electric kettle in your kitchen.

There are three main types of electric boiler:

  • Direct: A direct electric boiler heats water on demand
  • Storage: This type of electric boiler requires = a hot water cylinder either within the unit or elsewhere in your property.
  • Dry Core Storage: This type is less common and heat bricks overnight This heat is then used to heat water for your central heating and domestic hot water during the day. The idea of this system is to save money on fuel costs by using electricity at night when it is cheaper.

Advantages and Disadvantages of an electric boiler

There are a number of big advantages to choosing an electric boiler, but unfortunately also one significant disadvantage. The advantages include:

  • Safety – An electric boiler doesn’t use gas or oil so there is no need to store dangerous fuels and no risk of carbon monoxide leaks.
  • Environmentally-friendly – Using electricity is generally viewed as being better for the planet than gas or oil.
  • Installation costs – Electric boilers are typically much cheaper to install than a gas or oil-powered boiler.
  • Noise – Electric boilers run almost silently so there none of the clanking and whirring you can sometimes get from a gas boiler.

However, the big disadvantage is running costs. Gas and oil are generally much cheaper to use than electricity. Over the lifespan of your boiler, this can make quite a significant difference and is the main reason why electric boilers are not much more popular.

When to choose an electric boiler?

Electric boilers are best suited to smaller properties because they have higher running costs than conventional gas and oil boilers. They are also ideal because the boiler units themselves tend to be smaller and can easily be hidden away in a cupboard or under the stairs.

Electric boilers are generally not recommended for properties that have more than one bathroom. This is because they can sometimes struggle to reach the capacity for hot water needed to service both bathrooms.

But if you live in a small property that isn’t connected to the mains gas network, an electric boiler is worth serious consideration.

What sized electric boiler to choose?

As we noted at the top of this article, the size of an electric boiler is measured in kilowatts (kW). The kW rating of an electric boiler is designed to show how powerful it is and therefore what demand for heating and hot water it can cope with.

Generally speaking, electric boilers are not hugely powerful and it is unusual to find one that has a kW output rating much higher than 15kW.

The best way to work out the size of electric boiler you will need for your property is to assume you will need 1.5kW for every radiator in your home. So, if your property has eight radiators, you will be needing an electric boiler with a 12kW output.

RadiatorsElectric Boiler kW output

If you have more than ten radiators, you are going to be best served by looking for an alternative type of boilers such as a gas or oil-powered boiler.

What if you install the wrong-sized electric boiler?

If you inadvertently choose an electric boiler that is the wrong size for your property, you will face similar problems to gas and oil-powered boiler users too.

An electric boiler that is too small will struggle to heat your radiators and provide you with sufficient hot water. If it is too large, it will provide you with sufficient heat and hot water but will use more electricity than it needs too and so result in your utility bills going up.

How energy-efficient are electric boilers?

Electric boilers might cost more to run, but they are also extremely energy-efficient. Most electric boilers will have an energy efficiency rate of 99% which is higher than just about any gas or oil-powered boiler.

But, boiler efficiency is usually rated on a scale from A+++ for the most efficient to G for the least efficient and electric boilers tend to get a rating of D. This is because although electricity is greener and will reduce the carbon footprint of your home, electricity is usually generated by burning fossil fuels in power stations and this is not environmentally friendly.

Where to get a cheap gas-powered boiler

If you do decide to go with a gas-powered boiler be sure to get a quote from HEATABLE. This online installation company offers some of the best prices available on a huge range of high-quality gas boilers from all the top manufacturers.

Worcester Bosch Greenstar i from Heatable

Just head over to the HEATABLE website and fill in their form — it will only take 90-seconds and you don’t have to give them any personal details. They will offer you a fixed-price quote on the right-sized gas boiler for your property. Keep an eye out for some great special deals, such as extended warranties too.


It is just as important to get the right-sized electric boiler as it is the right-sized gas or oil-powered boiler.

In this guide, we have explained why and also provided some advice on how to identify the right-sized electric boiler for you. Typically, you should get 1.5kW of output for each radiator in your house.

We have explained why and also provided some tips and guidance on energy efficiency. If you think a gas-powered boiler sounds like a better bet for you, we have also recommended HEATABLE as the best place to get one at a low price.

  • Have you ever had an electric boiler?
  • Was size an issue for you?
  • How did it perform?

Do you have any tips of question we haven’t covered in this guide? It is always helpful to hear the experience of readers, so please do share yours with us using the comment box below.



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