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Replacing your boiler

Boilers account for around 55% of what you spend in a year on energy bills, so an efficient boiler makes a big difference.

Replacing an old gas boiler with an A-rated high-efficiency condensing boiler and improving your heating controls will significantly cut your home's carbon dioxide emissions - and could save you as much as £310 a year.


How much could you save?

This will depend on how old and inefficient your existing boiler is.

Old boiler rating Annual saving Carbon dioxide saving per year
G ( < 70%) £310 1,200kg
F (70–74%) £205 810kg
E (74–78%) £155 610kg
D (78–82%) £105 430kg

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 gas heated home with three bedrooms.  

The costs for replacing a boiler will vary, but a straightforward gas boiler replacement will typically cost around £2,300.

Why are new boilers more efficient?

Modern boilers are more efficient for several reasons, but their main advantage is that they are all condensing boilers. 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 condensing boiler has a bigger 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). When this happens, even more energy is recovered from the condensing vapour, and the efficiency gets higher still.


Installing a new boiler

If it is time to change your boiler, then the first thing is to decide what type of boiler you need.


The right fuel

If you have mains gas, then a gas boiler is usually the cheapest heating system for you.

If you currently have an oil, LPG or coal boiler, then it might be worth looking into the cost of getting gas supplied to your home. If there is no gas pipe near your home then this is not an option, but if it's available just round the corner then it might be worth paying for a new connection to get cheaper fuel.

You could also consider a wood-fuelled or biomass boiler. These burn logs, pellets or chips, and are connected to your central heating and hot water system; some models can be automatically fed. Installation costs can be high, but if you replaced electric heating with a wood-burning system you could save as much as £630 a year. Find out more about wood-fuelled heating.

The right boiler

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

A regular boiler is actually 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. The best option for you will depend on a number of factors:

  • How much hot water do you use?A large family using lots of hot water could be better off with a regular boiler – a smaller household using less may be better off with a combi.
  • Are you short of space?A combi boiler doesn’t need a hot water cylinder, and so needs less space.
  • Are you thinking of installing solar water heating?Many combis are not compatible with solar water heating or cannot use it so effectively.

Once you've decided on the type of boiler, you then need to make sure that you choose the most efficient model and get it installed safely and legally. You can make sure your boiler is of the highest efficiency by choosing an Celtic Green Energy recommended boiler:

Hot water cylinders

Celtic Green Energy recommended hot water cylinders have been factory insulated to help keep your hot water at the right temperature for longer. They play an important role in supplying you with readily available hot water, so it’s important that they are fully insulated to prevent heat escaping.

Upgrading your hot water cylinder to a Celtic Green Energy recommended one can save you around £45 a year. They are already highly insulated and are ready to be installed, so make sure you look for the label and choose a Celtic Green Energy recommended product to help you save the most energy and money.