What is a Condensing Boiler?


All new boiler installations have to be condensing by law as they’re much more efficient than non-condensing units. But what is a condensing boiler and how do they operate differently to their non-condensing counterparts?

We’ve put this guide together so that you’ll know all the benefits of installing a condensing boiler, how they operate and where to start when looking to purchase one.

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Watch: What is a condensing boiler

How does a condensing boiler work?

Condensing boilers aren’t a type of boiler in the same way that Combi, System or Regular boilers are, instead it’s more of a feature. If a boiler of any type is fitted with a Flue Gas Recovery System it is condensing.

The purpose of a condensing boiler is to generate more heat from waste gases which would be lost with a non-condensing boiler. These waste gases are produced as the boiler operates and then emitted out into the atmosphere, so the heat they carry is normally lost. However, a condensing boiler has 2 internal heat exchangers which capture and reuse this heat so they can reach high efficiencies of over 90%.

How do I know if my boiler is condensing?

A boiler installed after April 2005 (when condensing boiler regulations took effect from) is most probably a condensing unit. You can find out by seeing if there’s a plastic pipe sticking out of an external wall close to where the boiler was installed that leads to a drain; this is a condensate pipe which all condensing boilers have.

Condensing boilers also achieve high efficiencies so if the unit has an ErP A rating then you’ll know that it’s condensing.

Benefits of a condensing boiler

From making your home more efficient to helping reduce your energy bills, there’s a long list of advantages to installing a condensing boiler:

Environmentally friendly

Condensing boilers have much lower CO2 emissions than other boilers and because of this are much more environmentally friendly. Every year a condensing boiler could save up to 1.7 tons of carbon dioxide that would otherwise escape into the atmosphere.

Energy efficient

Condensing boilers are around 15-30% more energy efficient than non-condensing boilers and, as we mentioned earlier, can reach efficiencies of over 90%. To help get your head around efficiency ratings, the best way to think about them is that 100% represents every £1 being spent on your energy bills, with every percentage under that being a penny lost.

Lower fuel bills

Higher efficiency means lower energy bills. This is because they need to burn much less fuel to extract the same amount of energy required to heat the home. Thanks to this, you could soon be making a return on your investment.


Condensing boilers are often compact units which means that they won’t take up too much space and in the case of Combi boilers can even fit into a kitchen cupboard so you don’t even have to look at it.

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Condensing boiler problems

Condensing boilers are fitted with a condensate pipe which leads waste acidic water, produced as the boiler operates, outside and into a drain. Being outdoors means that the pipe is susceptible to freezing during the cold winter months and you may need to thaw the frozen condensate pipe. You can do this yourself by pouring hot water over the pipe or applying a hot water bottle, warm cloth or microwaveable heating pack to the frozen area. If you don’t feel comfortable doing this yourself then you should contact a qualified engineer.

If you’re experiencing any other issues with your condensing boiler from low pressure to strange noises, take a look through the most common boiler problems to get your system back up and running.

Condensing boiler regulations

A series of condensing boiler regulations were introduced by the government in 2010 to help reduce the CO2 emissions produced by non-condensing boilers. In short, the regulations state the following:

Regulation Type of Boiler Installations Starting Date
All gas-fired boilers have to be condensing New and replacement 1st April 2005
All oil-fired boilers have to be condensing New and replacement 1st April 2007
All condensing boilers must have an efficiency rating of A or B New and replacement 1st April 2005

There are some exceptions to the condensing boiler regulations should it be considered too difficult or costly to replace an old non-condensing unit with a condensing boiler. An assessment must be carried out by a Gas Safe registered engineer who will provide a certificate as proof.

In addition to these regulations, Boiler Plus was introduced in April 2018 which states that new gas boilers must have an ErP efficiency rating of at least 92%.

Best condensing boilers

Whether you’re looking for a Combi, Regular or System boiler, you’ll have no problem finding a condensing unit as all manufacturers make them. Some of the leading manufacturers you might want to consider are Ideal, Vaillant and Worcester Bosch but it’s always worth checking condensing boiler reviews before making your final decision.

Once you’ve found the right condensing boiler for your home, you’ll need a qualified engineer to carry out the installation. This will add to the costs so to help you get the very best deal, we highly recommend comparing quotes from several engineers. By completing one of our simple online forms, you can get free quotes from up to 3 trusted engineers in your local area.

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If it’s time to replace your current boiler, use our free service to get quotes now