Home / Blog

What is a condensing boiler?

If you’ve purchased a boiler after 2005, chances are that it was a condensing, or high-efficiency, boiler. Rather than being a ‘type’ of boiler – such as combinationsystem, or conventional – the term ‘condensing’ refers to the way it functions. A development on traditional heaters, condensing boiler systems offer a compact, easily accessible unit that has become the industry standard for all newly fitted systems. Due to their design, condensing boilers are far more efficient, increasing output and saving you money!

How Does a Condensing Boiler Work?

As with traditional heating systems, a condensing boiler burns natural gas to heat the water throughout your home, producing a combination of carbon dioxide and water vapour. Unlike traditional systems, it features a larger heat exchanger, or in some cases a secondary heat exchanger, which recycles the waste gases back into the heating system. By doing this, the system maintains an energy efficiency of around 90%, far higher than the 70-80% produced by non-condensing boilers. From the off, the advantages of a condensing boiler are evident, offering cost-effective, 24-hour heating for your entire home.

What are the Advantages of a Condensing Boiler?

The one clear benefit of using a condensing boiler is energy efficiency and thus cost efficiency – saving money on your heating bill. While the exact saving will depend on the age and efficiency of your old unit, it’s estimated that you could save up to £350* annually by replacing a G-rated system with a newer energy efficient one. Other condensing boiler benefits include:

  • Being green. Due to their higher efficiency, condensing boilers produce fewer carbon emissions than traditional systems. A new condensing boiler could save as much as 1,220kg of carbon dioxide a year.**
  • New condensing gas boilers are fitted with a non-ferrous metal, preventing them from corroding over time.
  • Don’t require a timer to operate effectively, as they produce hot water automatically when it is needed.
  • Drawing air from the outside, directly through the flue, they are more effective than non-condensing boilers which take air from inside the home.

What are the Disadvantages of a Condensing Boiler?

There are, however, some condensing boilers problems you may run into. While these disadvantages don’t diminish the advantages of energy efficient systems, they can cause problems that may not make them the most effective solution in your home:

  • The process of condensation produces acidic waste that isn’t present in conventional boilers and requires the installation of a fluid draining system.
  • This extraction must be fitted to the waste pipe, either internally or externally. If it is external, the drainage point has to be insulated to prevent frost damage in colder months. If this is not adequately done, the unit could shut down.
  • Due to the steam produced by the waste pipe, the placement of the boiler has to be carefully planned, meaning less flexibility.
  • When fitting a new condensing boiler, a system power-flush may be required which has to be added to the existing costs of a replacement.
  • In order to ensure the convection flow of exhaust gases, a fan is required. This adds to the complexity of your boiler’s mechanism and installation.

Installing a Condensing Boiler

Installing a condensing boiler system is a relatively simple procedure, depending on your home’s layout and boiler position. Typically, the size of your unit will depend on the size of your home as well as the amount of hot water you will require. For example, if you have a small house but need water for five family members, a larger boiler will be required. However, there are some considerations you should bear in mind when considering installing these types of units:

  • Whether you want a wall hung boiler or a free standing one. Both options are equally viable and depend on preference and layout.
  • As previously mentioned, due to the waste that is produced by a condensing boiler, it is preferable to have the unit installed near a waste pipe.
  • Planning permission may be needed if your flue chute extends above the roof by more than a metre.

In all cases, it is vital to consult with a Gas Safe Registered installer to ensure a safe and effective installation for your home.
You can verify whether your engineer is on the gas safe register by asking to see his identity card – all registered engineers must carry one with them. You can also check online whether their registration number is valid. Make sure that your engineer’s qualifications are legitimate. Hiring an unqualified engineer to replace your boiler could have disastrous consequences, as well as invalidate your warranty.


** These are estimated figures based on installing a new A-rated condensing boiler and full set of heating controls in a gas-heated, semi-detached home with three bedrooms

We Beat or Match Any Quote

Call 0330 912 4843 and we’ll beat or match any quote.

Serious About Service

24/7 claims support & rated Excellent on Trustpilot

Cover Match Guarantee

Get a £50 gift card if you find something we don’t cover

All Gas Boilers Covered

All makes and models, regardless of age