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What size of boiler do I need?

Posted on 8/5/2019

Your boiler goes through a lot of stress and strain to keep your house warm and your water piping hot. So if yours is getting on a bit (they usually last 10 to 15 years) it might be time to think about getting a new one. When you take a look around, you’ll find that things have moved on since you last bought a boiler.

So how do you know which one is right for you? Here are a few things to look out for, to make sure you get the right size for your home.

Talk to an expert

When you’re getting a new boiler, you’ll need a qualified engineer to install it for you. If it’s a gas boiler, they must be Gas Safe registered. This is a legal requirement to make sure your new boiler is fitted correctly and safely. So why not ask their advice about which boiler would work best for your home?

They’ll look at your heating system and ask you some simple questions to get an idea of how much heat and hot water you use. Things like whether you like a quick shower in the morning, or prefer a long, luxurious soak in the bath.

Combi, conventional or system boiler?

There are many different types of boilers, but these three are the most common in domestic homes. To help you choose which one is right for you, here’s a quick overview.

Combi boilers are generally designed for smaller houses and flats where the heating demands aren’t too large. They’re usually recommended if there’s only one bathroom because they don’t cope well with two people showering at the same time.

Conventional boilers work better for larger homes and families, where there are more rooms to heat and more hot water needed for washing (both clothes and people). If you have two or more bathrooms, this might work best for you.

System boilers are designed for larger families with high heating and hot water needs, but where space is limited. They still need room for a hot water tank though, so make sure you take this into account.

How to choose the right size boiler for your home

If your boiler is too small, it may not be able to keep your home warm and cosy in the winter or produce enough hot water for washing. Too big and your energy bills could go through the roof (not to mention your carbon emissions).

So how big should your boiler be? There’s a simple rule – the bigger the house, the bigger the boiler. But that doesn’t mean the actual size of the boiler, it relates to the power output they produce.

Boiler output is measured in kW (or kilowatts) and for domestic homes it generally ranges from 24kW to 42kW. A heating engineer will calculate what you need based on three things:

  • How many radiators you have
  • How many bathrooms you have
  • How many people live in your home

We’d always recommend getting expert advice before choosing a new boiler, but here are some guidelines so you know what to look for.

  • Small terraced house, flat or bungalow
    If you have one or two bedrooms, one bathroom and up to 10 radiators – 24 to 27kW output boiler
  • Medium semi-detached or terraced house, or a larger bungalow
    If you have three to four bedrooms, one or two bathrooms and up to 15 radiators – 28 to 34kW output boiler
  • Large semi-detached or detached house
    If you have four or more bedrooms, two or more bathrooms and up to 20 radiators – 35 to 42kW output boiler

More help and advice

It’s a big decision buying a new boiler, so we’ve put together some helpful guides to help you choose the right make and model. Take a look at our 5 Things To Think About Before Buying a Boiler article, and 6 Reasons Why Most People Overpay for a New Boiler.

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