How efficient is my boiler?

Boilers might not seem like the most exciting subject but you could save a lot of money by making yours more efficient. Here we’ll explain how.

In a nutshell, your boiler powers your heating. With about 60% of your energy bill going into keeping your home warm, the better your boiler efficiency, the lower your energy bills. Simple as that.

Unfortunately, an old boiler will never be quite as efficient as a new model – but there are still some things you can do to make sure it’s running at peak performance. We’ll look at these in a moment but first, let’s get down to the basics…

How is boiler efficiency measured?

There are currently a few different systems in use – ErP, SEDBUK 2009, and SEDBUK 2005 – all based on slightly different calculations. While it's not ideal to have different rating systems, they're easy enough to understand.


Every new boiler carries an ErP energy label, which ranks its efficiency from A-G. Nearly all modern gas boilers get an A energy rating, which means they’re highly efficient.

Is your boiler efficient


Energy efficiency scale


SEDBUK stands for ‘Seasonal Efficiency of a Domestic Boiler in the UK’, and the 2009 system gives each boiler an exact percentage score. This score is the one to look for if you really want to get into the detail, but it’s worth noting that a difference of just a few percentage points won’t have a massive impact on your bill. The big savings come from swapping an old boiler for a new, high-efficiency one.


The previous SEDBUK system is featured on older boilers and is still used by lots of manufacturers. Like the ErP system, it rates boilers from A-G. A-rated boilers score over 90% for efficiency, while G-rated boilers come in under 70%.

How much could I save?

This table shows how much you could save in an average year if you swapped a standard older boiler for a new, high-efficiency model.  As you can see, the type of home you live in also makes a difference.

Estimated figures based on installing a new A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator controls (TRVs) in a gas-heated home from an older boiler with a programmer and room thermostat. Savings vary depending on the size and thermal performance of your home. Figures are based on fuel prices as of April 2018.

Which are the most efficient modern boilers?

Which are the most efficient modern boilers

Condensing boilers are the most efficient on the market, because they have modern heat exchangers that can recover more energy from condensing vapour – hence the name. Lots of old boilers use big cast iron heat exchangers that lose energy in the process.

Nearly all modern boilers are A-rated condensing boilers, so if you’re buying a new one, you can be confident it will be efficient. And in terms of saving money, there’s not a lot of difference between one A-rated, high-efficiency boiler and another.

Choosing the right boiler for you will depend on your particular circumstances – the size of your home, the amount of hot water you use, and the type of fuel you’ve got access to. See our information on choosing the right boiler.

Here at British Gas, we only install the latest A-rated energy efficient boilers and controls. You can learn more about these highly efficient boilers when you book a free, no-obligation appointment with an expert adviser.

If you’d rather do your own research, you can also find reviews and ratings in places such as Which? Magazine or website.

What else can I do to make my boiler more efficient?

Regular check-ups

An annual service will help your boiler run more efficiently as during the service the engineer will remove dirt and prevent corrosion. Your engineer can also check you have your boiler set up in the most efficient way (more on that below).

If you’re a HomeCare One, Two, Three or Four customer, regular servicing is included. If you’re not this type of customer, you can still book a one-off check-up at any time.

Is my boiler a high efficiency boiler

Central heating products and services

How to lower your energy bills

Modern heating controls and thermostats, new radiators and even a deep clean of your pipework and radiators can all help your boiler run more efficiently and last for longer.

Learn more about our central heating products and services.

Efficient settings

The way your boiler is set up can also make a difference. It all depends on the type of boiler you have and how you’ve set it up – its settings need to be changed as the seasons change.

As a watch-out, whatever the season, if you’ve got young kids or vulnerable people at home, be careful not to set your boiler temperature too high as your pipes, radiators, and water can get very hot. If you’re unsure about adjusting the controls, it’s always best to speak to a qualified engineer.

What is the cost of improving my boiler efficiency

Conventional boilers

What is my boiler energy efficiency

If your hot water tank has a thermostat, set it between 55°C and 60°C. Then you can adjust your boiler temperature to maximise energy efficiency:

  • In winter, set the boiler temperature control to max (80°C).
  • In summer, when you don’t need the heating, set it somewhere in the middle (55°C-60°C).

Combination boilers

If your boiler has two dials, set the heating control at a high setting (80°C). Set the water control as low as you can to produce the hot water you need. That’s usually somewhere between 55°C and 60°C.

If your boiler has a single dial, set it at maximum (80°C).

Is my boiler efficient

Back boilers

Will improving my boiler efficiency lower my bills

A back boiler sits behind a gas fire. The higher it’s set, the hotter your radiators will be, which means the room will be heated more quickly and more efficiently.

You’ll usually find the temperature control for a back boiler either directly under the fire, or to the side of the boiler. Most have an adjustable temperature setting of between 40°C and 80°C.

And that’s it. For more help and guidance, get in touch with our expert advisers. Our engineers can check your current set-up, help you choose a new boiler or recommend another kind of upgrade to maximise your boiler efficiency.

If the thought of your winter heating bills makes you dread the chilly season, consider having your boiler replaced beforehand to help to reduce them. Book a free appointment and one of our expert engineers will come and look at your boiler and central heating system. They’ll talk you through the best options for your home and give you a fixed price quote.