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Boiler replacement

Heating accounts for about 55 per cent of what you spend in a year on energy bills, so an efficient boiler makes a big difference.

All well-maintained boilers burn their fuel very efficiently, but they inevitably lose some heat in the hot gases that escape up the flue (a pipe for extracting fumes and supplying fresh air to the boiler). 

Modern boilers are more efficient for several reasons, but their main advantage is that they are all condensing boilers. A condensing boiler has a larger heat exchanger, so it recovers more heat, sends cooler gases up the flue and is more efficient.

Sometimes the flue gases get so cool that the water vapour in the gas condenses out, hence the name, and even more energy is recovered from the condensing vapour.

Things to consider

If it is time to change your boiler, you need to decide what type of boiler is right for you. Here are some things to consider: 

Fuel type

If you have mains gas, a gas boiler is likely to be the cheapest heating option. Our average fuel prices as of March 2019, show gas to be the cheapest heating fuel per kWh, compared to oil, economy 7, LPG and house coal.

If you don’t have a gas supply to your home, it might be worth considering a form of low carbon heating such as a heat pump or biomassWith the renewable heat incentive (RHI), these may be cheaper overall.

Alternatively you may want to get a gas connection to your home. The company that owns and operates the gas network in your area may be able to help with the cost of getting a new connection, and it may even be fully funded. Contact Energy Networks Association for further information.


Boiler type

Most old gas and oil boilers are regular boilers that have a separate hot water cylinder to store hot water, rather than providing it directly from the boiler. When you replace your boiler you can buy a new regular boiler, and keep your hot water cylinder, or buy a combi boiler that doesn't need a cylinder.

A regular boiler is more efficient than a combi at producing hot water in the first place, but then some heat is lost from the hot water cylinder, so a combi may be more efficient overall. Which is better for you will depend on different things:

  • Your hot water usage
    Large families using lots of hot water are likely to be better off with a regular boiler, whereas smaller households using less may be better off with a combi boiler.

  • Space in your home
    Combi boilers don’t need hot water cylinders, and therefore require less space in your home.

  • Compatibility with solar water heating
    If you’re thinking of installing solar water heating, it’s worth noting that many combi boilers are not compatible with this heating system or cannot use it so effectively. 


England, Scotland and Wales

Replacing a gas boiler

Northern Ireland

Replacing an oil boiler

Finding an installer

For a list of registered installers visit the Competent Persons RegisterSNIPEF, or Installers First.

For gas and LPG boilers, the installer must be Gas Safe registered. Registered installers: Gas Safe Register

For oil boilers we would recommend that you use an OFTEC registered installer. Registered installers: OFTEC.

It’s worth getting three quotes from different installers, and you may also want to check that installers:

  • have a local office
  • have been in business locally for several years
  • have customer references that you can review.

Your registered installer will ensure that your system complies with current building regulations, and will make sure you get all the documentation to prove this. Keep these documents safe; you will need them when you sell the property.

Improve your central heating system




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