What size boiler do I need?

What does boiler size mean?

When it comes to boiler size, we’re not talking about the physical dimensions – most boilers are very similar in that regard. Instead, boiler size refers to how much energy a boiler can put into your heating and hot water system. This is expressed in kilowatts, or kW.

In larger homes that use lots of hot water, you might also need to think about the water flow rate. This is the amount of hot water the boiler can deliver, usually expressed as litres or gallons per minute (lpm or gpm).

Boiler sizing guide by house size

As a general rule, the bigger your home and the more bedrooms, radiators and baths/showers it has, the more powerful the boiler you’ll need. Of course, there are exceptions – if one person lives alone in a large house, they may not necessarily need a bigger boiler than a large family living in a smaller flat. And it’ll depend on how well insulated your home is too. A poorly insulated home may need a bigger boiler to keep it warm, as it’ll lose more heat than a well-insulated one.

And why is it so important to get the right size boiler? Well, not to get all Goldilocks, but one that’s too big could waste money and energy, while one that’s too small might not give you enough warmth and hot water.

Learn more about buying a boiler with British Gas

Try our boiler size calculator

To make it easy to work out what size boiler you need, we’ve put together a handy boiler calculator. All you need to do is answer a few quick questions about your home and we’ll give you personalised boiler recommendations tailored to you.

We’ll take you through it step-by-step but here’s what to expect:

• Tell us about your home
• Give us some details about your current boiler and heating system
• Choose whether you'd like to move or change to a different type of boiler
• Tell us where your flue is (don’t worry, it’s easy to find)
• Enter your details
• See your recommended boilers

Check the details so that you have the answers to hand when you use our boiler calculator, and we’ll work out which size boiler and type is the best one for your home.

Want to get started? Check out our boiler calculator now.

How to pick the best boiler for your home

With so many boilers out there to choose from, you need to decide a couple of things first to narrow down the range. Firstly, you need to know which type of boiler you’d like. There are three different types of boiler - combi, system and conventional.

Next, narrow down by the size in kW – this will be determined by the size of your home, how many baths and/or showers it has and the needs of your household. You might also want to consider boiler efficiency – so it’s good to know that all the boilers sold by British Gas are rated A-rated.

How to calculate what size boiler you need

There are a few different ways that you can work out what size boiler you need for your home. You can base it on the number of bedrooms, radiators and baths and showers you have, or you can do it by boiler type.

How to calculate what size boiler you need by boiler type

There are three main types of boiler – combi, system or conventional – and the type you have will make a difference to the size of boiler you need. The type of fuel it uses will have an impact as well.

Most boilers in the UK are powered by mains gas. You’ll know that this is the case with your boiler if you have a gas meter and get billed for your energy supply. Alternatively, some boilers run on oil or Liquefied Petroleum Gas (LPG). These are stored separately in a tank, and you’ll need to monitor your supply so you can re-order when you’re running low.