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Why You Need a Condensing Boiler

Becky Mckay
By: Becky Mckay
Updated: 19th September 2023

If you’re hanging on to an old non-condensing boiler then it could be causing more harm than good.

In 2005 it became illegal for anything other than a condensing boiler to be installed in the UK (unless special permission has been granted under certain exemptions). Despite this, there are still homes in the UK being heated by non-condensing boilers.

The reality is that you shouldn't necessarily leave your decision to upgrade your boiler to fate. being proactive now could save you both money and hassle and make your home significantly more efficient.

What is a condensing boiler?

A condensing boiler is a reliable, efficient and safe way to heat your home.

They burn fuel (commonly gas or oil) like non-condensing boilers but do so far more efficiently.

Before condensing boilers came along, around 30% of the heat made by a boiler went straight out the flue pipe. Which meant the boiler was burning through more fuel.

Now, thanks to the Flue Gas Heat Recovery system in condensing boilers, that heat can be used to warm your home.

They also have larger heat exchangers which enable them to extract more heat from the fuel. And, unlike a non-condensing boiler, there’s no need for a pilot light to be burning all the time.

A condensing boiler can be either a combi, regular or system boiler and all of the leading brands have a range to suit homes of all sizes.

Do I have a non-condensing boiler?

If your boiler was installed in 2005 or later, chances are that you already have a condensing boiler. That’s because condensing boiler regulations were introduced in April 2005 for gas boilers and April 2007 for oil boilers. They state that all new boiler installations from these dates must be condensing by law.
Blink: Condensing or non-condensing boiler

If your boiler was installed before these dates then you may need to look a little closer.

The easiest way to tell if you have a non-condensing boiler is by checking for a pilot light. This is a little blue flame that remains lit at all times – even when you’re not heating your home. If you can see a blue flame through a window at the front of the boiler then it’s non-condensing.

Condensing boilers don’t have a pilot light and instead have electric ignition. So going from non-condensing to condensing can save you money right away.

You can also tell if your boiler is non-condensing by looking at the efficiency rating. You should be able to find your boiler's rating in the manual or any documents that it came with. Failing that, find your boiler in our Comparison Tool which will tell you if it’s condensing or not.

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Why condensing boilers are better

The key advantage of a condensing boiler, and why all new boilers must be condensing, is their improved energy efficiency. A high efficiency, condensing boiler is, on average, 25% more energy efficient than a non-condensing boiler. For example, a G-rated boiler could be as low as 60% efficient while an A rated is at least 90% efficient.


If a boiler is 60% efficient it means that for every £1 you spend on energy, 40p is wasted. With a condensing boiler only around 8p is wasted as they reach efficiences of over 90%.

Over a year this could equate to as much as £300 in savings on your energy bills*. And this is without using smart heating controls which can take your savings even further.

*According to latest figures given by the Energy Saving Trust.

A greener home

We're only too aware of the impact our lifestyles are having on our planet. As condensing boilers use less fuel, they emit fewer carbon emissions into the atmosphere. So you’ll be reducing your carbon footprint and impact on the environment.

A safer home

Modern condensing boilers are completely sealed systems. This means they take air in from the outside and release waste fumes back outdoors through the flue pipe. They are also fitted with safety devices like pressure relief valves and thermostats which will switch the system off if they detect a fault.

Older boilers are open flued which means they take air from the room they are in and aren't equipped with safety devices.

More space at home

Modern condensing boilers are far more compact than older models. Replacing your traditional boiler system with a condensing combi boiler means you can get rid of the water tank in the attic and storage cylinder in the airing cupboard. A Combi is a single, compact unit that heats water on demand for both your home's heating and hot water.

Are condensing boilers future-proof?

The UK government has set a target of reducing carbon emissions to net-zero by 2050. And home heating is responsible for around a fifth of all carbon emissions in the UK. Mainly because millions of homes are heated by boilers that burn natural gas or oil, which are both fossil fuels.

Replacing non-condensing boilers with condensing boilers has gone a long way towards reducing carbon emissions from home heating. But even despite high efficiency levels, they still emit carbon into the atmosphere.

While gas and oil boilers won’t be fitted into

What size condensing boiler do I need?

The size of a boiler is known as the output rating. It’s measured in kilowatts (kW) and shows the power of the boiler.

You need a boiler with an output rating to suit your home. Get it wrong and your new boiler will either struggle to meet demand for heating and hot water or cause your bills to shoot up. So don’t go for the most powerful boiler you can afford for the sake of it.

What you need to keep an eye out for are central heating (CH) outputs and domestic hot water (DHW) outputs.

Combi boilers have both a CH output and a DHW output. Regular and system boilers only have a CH output. This is because combi boilers deliver heating and hot water on demand while regular and system boilers store domestic hot water in a cylinder.

Bedrooms Bathrooms Radiators Boiler type Central heating output rating
1-2 1 Up to 10 Combi 24-27 kW
2-3 1 10-15 Combi 28-34 kW
4+ 2+ Up to 20 System 28-34 kW

Larger homes can also go for a regular boiler but they’re only recommended if you already have one installed. Even if you do have a regular boiler then replacing it with a system boiler would allow you to remove the tanks from the loft.

How much will a new boiler cost?

A condensing boiler can cost anything from £450 to over £2,000.

How much you end up paying for a condensing boiler all depends on the manufacturer, model and output rating (a measure of the boiler’s power). Then there are additional costs if a new flue, cylinder or pipework is needed too.

You’ll also need to add the installation costs onto the price of the boiler. These can vary a fair amount which makes it important to compare quotes from at least 3 companies.

Type of condensing boiler Average cost (excluding installation) Average installation costs Total costs
Combi £500 - £2,000 £500 - £1,000 £1,000 - £3,000
System £500 - £2,500 £500 - £1,000 £1,000 - £3,500
Regular £500 - £2,750 £500 - £1,000 £1,000 - £3,750

Get quotes for a new condensing boiler

If it's time to replace your old boiler you need to get quotes from at least 2 different suppliers. Send us an enquiry today and we will put you in touch with up to 3 installers working in your area.

Each will give you their most competitive quote for the job. Then you just need to choose which, if any, of the quotes suits you best.

Becky Mckay

About the author

Becky Mckay

Becky has been a writer at Boiler Guide since 2021. Her vast boiler knowledge means she’s ready to help with any home heating query, big or small!

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