Types of boiler explained: How to choose a boiler that’s right for you

05 November 2020 | Aimee Tweedale

Has your trusty old boiler packed in? We’ve all been there. With so many different types of boiler to choose from, starting the search for a new one can feel overwhelming.

It’s one of the biggest purchases you’ll ever make for your home, and something you’ll use almost every day – so naturally, you’ll want to get it right. 

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You might be asking yourself: what’s the difference between condensing and non-condensing? Do I need a combi or conventional boiler if I need enough hot water for a big family? You might not even be sure if you have to replace the old boiler at all.

You’ve come to the right place. Here’s everything you need to know about the different ways of heating your home.

What are the different types of boiler?

Let’s start with the basics: what is a boiler? Most homes have one, but perhaps you’ve never given it much thought – until it stopped working! A boiler is a central heating unit that pumps hot water through the pipes around your home. It supplies the hot water to your taps, and heats up your radiators. Usually, it’s powered by your mains gas supply.

Here are the four most common types of boiler that you’ll come across when looking for a new one. 

1. Combi boilers

A combi or combination boiler is a single unit that provides both your hot water and your space heating. This means it takes up less space in the airing cupboard than other types of boiler, which can come with bulky hot water cylinders and cold water storage tanks.

The added benefit of a combi boiler is that, because they don’t need to refill or heat up the water before you can use it, they can give you instant hot water as soon as you turn on the shower or tap. They’re also more energy-efficient, quick to install, and more cost-effective.

The downside? Combis are not great at providing hot water to multiple bathrooms, so it won’t be the best choice for you if you’ve got a big household. 

For more, read our guide to combi boilers and installation costs.

2. System boilers

Most houses in the UK now have combi boilers, but you might prefer to buck the trend by choosing a system or conventional boiler. 

Unlike combis, system boilers use a separate hot water storage cylinder. This takes up more space, but it means they can supply a lot of hot water on demand. This makes them ideal for households where more than one person might want to take showers at the same time. 

System boilers take water directly from the mains, and while they’re a bit bigger than combi boilers, they don’t need a hefty feed and expansion tank. If you’re replacing an old system boiler, it’ll be a cheaper and easier installation process if you choose to get the same again, rather than change to a combi.

However, they’re a little extra work. The cylinder has to be kept insulated, and they won’t give you instant hot water like a combi can. 

3. Conventional boilers

Also known as regular boilers or heat-only boilers, conventional boilers are also suited to bigger households. They have a feed and expansion tank (usually kept up in the attic) and a hot water cylinder, which means they take up a lot of space.

If you’re getting a new boiler to replace an old conventional boiler, then you should consider sticking to the same type. It’ll be more cost-effective, because you may not have to replace the pipes in your house (as you would if you decided to switch to, for example, a combi).

Bear in mind, though, that like system boilers, they need to be kept insulated or they can lose heat very quickly. 

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4. Condensing boilers

If you’re wondering whether to choose a condensing or non-condensing boiler: there’s no need! Current laws state that you have to install a condensing boiler, as they’re typically at least 25% more efficient than their non-condensing counterparts. All the types of boiler listed above (combi, system, and conventional) can also be condensing boilers.

In simple terms, a ‘condensing boiler’ is one that wastes less energy. While ‘non-condensing’ boilers allow heat to escape in the form of water vapour, ‘condensing’ boilers trap those escaping gases, and use the energy to heat up water.

Whichever boiler you choose, make sure it’s covered

When you’re installing a new boiler, the last thing you want to worry about is unexpected costs. Enjoy peace of mind with OVO boiler cover – complete with an annual boiler service.

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What type of boiler do you have?

Before choosing a new boiler, you need to establish what kind of heating system you already have in your house.

If you’ve just moved into a new place, you might not know the answer. Here’s how you can tell what type of boiler you have.

Do you have a combi boiler?

The answer is ‘yes!’ if:

  • The hot water fires up as soon as you turn on the hot tap
  • There’s no hot or cold water tank
  • There are copper pipes coming out the bottom of your boiler (usually five)
  • There’s also a pressure gauge

Do you have a system boiler?

Raise your hand if:

  • There’s a hot water cylinder or tank, but no feed and expansion tank
  • There are three copper pipes coming out of your boiler
  • It has a pressure gauge 

Do you have a conventional boiler?

Yes you do, if you can see:

  • Two copper pipes coming out the top of your boiler
  • One copper pipe from the bottom of the boiler
  • A hot water tank or cylinder
  • A cold water tank somewhere in the house (usually the attic)

Is your boiler connected to the UK gas network?

Before choosing a new boiler, you need to know how it will be powered. Most homes in the UK – about 85% of them, in fact – are connected to the gas grid, and use gas-fired boilers to heat their homes. But there are about 4 million that aren’t. You might be one of them if you don’t get a gas bill with your electricity bill. 

If you’re not connected, you might consider a system that’s powered by oil, or LPG (liquid petroleum gas). Both require a pretty big tank in your back garden, and need to be refilled when they run out. Mains gas is the best (and cheapest!) option if you can get it. 

You might also want to consider a low-carbon alternative, like a biomass boiler, or solar energy. Read more about those options down below.

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Should you stick with the same type of boiler you already have?

If you’re thinking of replacing your boiler, but you’re not sure which type to choose, consider the following questions.

How much hot water do you need?

If you’ve got a big house, or you’re extending, and you need a lot of hot water, your best bet may be a system boiler. The water won’t be ready to use instantly, like it is with a combi boiler – but once it’s heated up, you should have enough for everyone in the house to shower at once.

Conventional boilers also provide a lot of water, but system boilers are generally a better option because they won’t need as much pipework (and you won’t have to find the space for a great big tank in the loft). However, if you already have conventional boiler pipework in your house, you might find it’s a lot cheaper to install.

How much money do you have to spend on installation?

If you’re on a budget, the cheapest way to replace your boiler is usually to go with the same type you already have, and put it in the same location. This minimises the work that has to be done on the rest of the house.

Where are your radiators and pipes?

If your radiators and pipes are buried under a lot of concrete (or what’s called ‘screed’ in construction), then it will cost a lot more to change them. 

With this in mind, if your pipes are hard to access, you should consider sticking with the type of boiler you already have.

What’s your budget for monthly bills?

If you want low monthly costs, you want a boiler that is cheap to maintain. Combi boilers fit the bill: get one with a 10 year warranty or guarantee from the manufacturer for even better protection against surprise costs.

Time for a new boiler?

A new energy-efficient boiler could save you hundreds off your heating bill every year. Get a deal on your new boiler.

If your boiler is on the blink, check out first if this is something you can solve without needing to call an engineer. Read our guides to common boiler problems and how to fix themhow to reset your boiler when it locks out, how to defrost a frozen condesate pipe, how long it takes to fit a new boiler, and how to decide when to repair or replace your boiler.

How to choose the right boiler for you

what is the right boiler for you

There’s no one-fits-all answer to the question, ‘what type of boiler do I need’? What’s most cost-effective and useful for you will depend on your own circumstances. Try answering the following questions to see if a combi, system, or conventional boiler is the right fit for you.

What kind of home are you heating?

If you live in a flat, you probably want to get a combi heater, which takes up less space. You’ve probably not got room for cold water tanks in the loft (in fact, you might not have a loft) if you’re sharing a 1- or 2-bed in the city. 

System boilers work best for medium or large homes, like a house with 3 bedrooms or more. If you have more than one bathroom, you should consider getting a system boiler connected to an unvented cylinder, because it’s more powerful than a combi.

Conventional boilers also have enough power to keep radiators blazing and multiple showers running hot through the winter months. System boilers are usually a more efficient choice – but if you’re living in an old house, with pipework that’s hard to access, you might want to stick with a conventional boiler.

How many people live with you?

More people in the house means more showers at the same time. If you’ve got a house or flat with multiple bathrooms, then you likely need to consider getting a system or conventional boiler with an unvented cylinder, to cope with all that demand for hot water.

How much space do you have in your house?

Is there room in your airing cupboard for a hot water cylinder? Or in the loft for a cold water storage tank? These are questions you need to answer when considering your new boiler.

For bigger houses, system boilers will provide more heat and hot water, but without taking up as much space as a conventional one. If your home is on the small or medium side, a combi boiler is the one for you, as it will take up much less room. But remember, it won’t be able to handle running several hot taps at once.

When you’re thinking about what size boiler to get, remember to also consider how much energy you need to heat the space. If you want to work out how much energy you need to heat your home in kWh (kilowatt hours), use our handy guide to calculate how many kWh you use at home. You just need to know your floor area. 

This is important because it will help you get a boiler that’s the right size: too small, and your house won’t be heated properly. Too big, and you’ll be paying for wasted energy.

How many radiators do you have?

As well as floor space, you should consider the number of radiators you have at home. In a home with up to 10 radiators, you should be looking at smaller combi boilers, no bigger than 30kW. Larger houses with 10-15 radiators, and/or an en suite bathroom, might need something in the region of 35kW.

By the way, it's a good idea to bleed your radiators once a year, so they're working as efficiently as possible. Find out how to do it, and why a yearly radiator bleed can bring your heating costs down, with our handy guide.

It might be tempting to get a boiler that’s bigger than you really need. Beware – this can be a waste of money, and lead you to pay for excess energy that your house is not using. That’s bad for the environment, as well as your wallet. 

Having pressure problems with your boiler? Save yourself the hassle and cost of calling out a professional and solve the problem yourself with our easy-to-follow guides to low boiler pressure and high boiler pressure.

Eco-friendly ways to heat your home

If you want to keep warm without harming the planet, the most important thing to consider is the energy-efficiency of your home. A home that uses energy sparingly, and doesn’t waste it, is more eco-friendly.

Turning down your thermostat, insulating and draught-proofing your house, and making sure you have energy-efficient radiators are all things you can do to improve the efficiency of your home. You could also use smart heating technology to give you more control over when your heating’s on. If you have a conventional or system boiler, do make sure to check that it’s only heating up as much water as you need, when you need it.

Boiler technology is being updated and becoming more eco-friendly all the time. Condensing boilers – which are a legal requirement in the UK – are more eco-friendly than their older non-condensing counterparts. 

Another type of eco boiler is a biomass boiler, which takes energy from burning wood. These have a renewable source, but it’s not clear what their carbon footprint actually is. Learn more about biomass energy by reading our handy guide.

You might want to get rid of your boiler altogether, and heat your home in an even greener way. Perhaps you want to install solar water heating, or air source heat pumps, which make use of natural, renewable sources of energy. If you’d like to know more about alternative ways to heat your home, read our guide to low-carbon heating systems.

Where can I get a new boiler?

You can get an A- rated, award-winning boiler from CORGI HomeHeat (part of the OVO family). Want to know more? Visit our boilers page to check out the offers from CORGI HomeHeat. Don’t leave it to guesswork – get a new boiler installed safely by local engineers.