A condensing boiler is a modern, more energy-efficient type of boiler that uses condensing technology to make better use of the heat it generates. It collects the gas generated through burning fuels, then uses it to heat water. That way, the excess gas and energy aren’t wasted.
Condensing boilers are the most common type of boiler found in UK homes. As well as saving you money on your energy bills, they also cut down on your carbon emissions – meaning they’re better for the environment.
Condensing boilers and combi boilers often get mixed up with each other. Essentially, they’re the same – a combi boiler is simply a type of condensing boiler. It also uses condensing technology to make use of excess heat generated.
Combi boilers are popular due to their compact size. They don’t require any storage tanks or external equipment, as the entire system is contained and controlled within the appliance itself.
It’s easy to compare the cost of a new condensing boiler with MoneySuperMarket. Our boiler quotes include the price of the boiler, installation, and replacement of the old boiler, so you can see the total cost straight away.
If you’re getting a boiler replaced, you can expect the installation to go like this:
The installer will remove your old boiler
They’ll then fit your new boiler, along with any new pipework or equipment
Once the new boiler is installed, they’ll test it and complete any necessary paperwork
A simple combi replacement boiler should only take a day to fit. However, if it’s a more complex installation – for example, you’re switching boiler type, moving the boiler to a new room, or upgrading your radiators – it could take two or more days.
When a fuel like gas or oil is burned, excess gasses are produced via the flue. In older boilers, these flue gases would be released back into the atmosphere, which is both bad for the environment and a waste of potential heat.
Instead of releasing these gases, condensing boilers capture excess gas and recycle in back into your home’s heating system. Depending on the type of condensing boiler, how this works can vary. For example, combi boilers will use the gas to heat water through a secondary heat exchanger.
As condensing boilers use excess gases to heat your home, they’re much more energy efficient and cost-effective.
Since April 2005, all new gas boilers in the UK have been legally required to be condensing boilers (and April 2007 for oil boilers). So, the vast majority of boilers in UK homes are condensing boilers.
There are three main types of condensing boiler:
Combi boilers – one of the most popular types of boiler, combi boilers are compact in size and very cost-effective. They’re ideal for flats and smaller homes
System boilers – these require a hot water storage system, but not a water tank, so you won’t have to worry about leaks or frost damage. System boilers are a good choice for larger homes
Conventional boilers – also called traditional, heat-only, open vent or regular boilers, conventional boilers need both a cylinder and a water storage tank. They require some space, but they can supply a large amount of hot water to multiple bathrooms. They’re best suited to older homes which may already have a traditional heating system in place
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Yes, condensing boilers are much more energy efficient than older, non-condensing boilers. While non-condensing boilers reach between 70-80% efficiency, newer condensing ones can achieve over 90% efficiency.
Usually, a new condensing boiler should last between 10 to 15 years. The warranty might not last as long, however – boilers can come with one to 10 year warranties.
To make sure your boiler continues to run efficiently and last as long as possible, you should get it serviced by a registered Gas Safe engineer every year.
A new condensing boiler can cost anywhere between £500 to £1,700, depending on the brand and output in kW. Installation can cost between £600 and £1,800 – the price depends on whether you’re switching to a boiler of the same type, or to a different one.
You can expect the total cost of a combi boiler (including appliance and installation) to be anywhere between £1,500 to £3,000.
Not sure if your existing boiler is a condensing one? There are a couple of ways to check.
First, the easiest way to find out is to look at the boiler manual. If you don’t have this to hand, don’t worry – you can work it out in other ways.
If you know when your boiler was installed, you can deduce whether it’s a condensing one or not. If your gas boiler was installed from April 2005 onwards, it should almost certainly be a condensing boiler. You can contact the manufacturer for advice, too – by telling them the model of your boiler, they may be able to tell you if it’s a newer condensing boiler.
Finally, you can inspect your boiler flue and drainpipe (located outside your home). If you seem steam leaving the boiler flue, and a white plastic pipe leading to the drain, that means your boiler is condensing.
There are many advantages of having a condensing boiler:
Lower fuel consumption
Lower energy bills
Lower carbon emissions
In short, it’s better for the environment and your wallet.
Reviewed on 8 Dec 2025
