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Boiler energy efficiency

By Matthew Knight

Once you have discovered how boilers are rated for energy efficiency, find out which boilers are the most efficient by using our boiler reviews.

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The cost of heating your home, particularly during the colder winter months, makes up about 60% of energy bills.

You can keep heating costs down and still keep your home cosy by making smart heating choices. Installing an energy efficient boiler can save you hundreds of pounds a year. Read on to find out all you need to know about boiler efficiency, including how much you're likely to save by installing a new, efficient boiler.

Lower heating costs: heating products

The age and type of boiler you have affects how efficient it is. A modern condensing boiler is the most efficient boiler on the market – find out more in our guide to condensing boilers.

If everyone in the UK with gas or oil central heating installed a high-efficiency condensing boiler with full sets of heating controls, we would save enough energy to heat nearly 1.9 million homes for a whole year and save around 6.7 million tonnes of CO2, according to the Energy Saving Trust.

The efficiency of a boiler is normally expressed as a percentage. Since April 2018 only boilers that are 92% or more efficient can be installed in homes, roughly a third of boilers on the market fall below this standard, so make sure you check the efficiency rating of the boiler before you get one fitted.

More recently boiler efficiency is stated as a rating on a boilers ErP energy label from A-G. Nearly all modern gas condensing boilers get an A energy rating.

It's worth noting that you wouldn't expect to see a difference in your gas bills if you choose a boiler that is 92% efficient over a 94% efficient boiler, or between one A rated boiler and another. The biggest saving comes from making a leap from an old inefficient boiler to a new one.

Boiler efficiency rating - how it is calculated

ErP energy rating

All modern boilers are rated for efficiency under the new European energy label introduced in September 2015. Nearly all modern gas condensing boilers available in the UK get an A rating on this label, so it can be more useful to use the Sedbuk 2009 efficiency rating if you are interested in the minuti of how one boiler compares to another.

Sedbuk, which stands for Seasonal Efficiency of Domestic Boilers in the UK, is a system used to classify and compare boilers on how efficient they are at converting fuel into heat. 

Sedbuk efficiencies: how boilers compare

Traditionally, Sedbuk ratings were shown on labels as a letter  - these ranged from A-G. But these letter labels have been withdrawn to avoid confusion with the European energy labels, which use similar ratings but are based on different principles. 

There are currently two different types of Sebuk ratings, called SAP scores, that you should look out for when you are buying a boiler.

  • SAP winter efficiency - this is the measured by an independent laboratory and is the measured energy efficiency of the boiler including space heating and hot water; It's calculated to an industry standard called SAP 2009. There are only marginal differences between modern condensing boilers on this measure.
  • SAP hot water efficiency - the hot water efficiency figure is hot efficient the boiler is at producing hot water for your taps. There tends to be a much bigger difference between boilers on this measure, and so if you are keen to get the most efficient boiler possible, it should be this figure that you hone in on.

You can find each boilers precise efficiency ratings for winter efficiency and hot water efficiency in our boiler reviews. For more tips on how to ensure your heating system is operating as efficiently as possible, head to our guide on 5 tips for a healthy and efficient central heating system.

 

Will an efficient new boiler save you money?

If you replace an old G-rated boiler with a modern A-rated boiler with a full set of heating controls, the Energy Saving Trust estimates you'll save around £340 a year on your gas bill. This does not take into account the cost of installing a new boiler.

The table below shows how much different types of boilers will cost you in energy bills, depending on the size of your house. (A boiler that's 15 years old or more is classed as 'old' in these calculations. A lightweight boiler can be attached to a wall; a heavyweight boiler is floor standing.)

Annual fuel costs with different boiler types (source: Sedbuk)
Boiler type Flat Semi-detached Detached Efficiency
Old gas heavy weight 779 GBP 1204 GBP 1705 GBP 55%
Old gas light weight 659 GBP 1019 GBP 1442 GBP 65%
New non-condensing 549 GBP 849 GBP 1202 GBP 78%
New condensing 481 GBP 744 GBP 1053 GBP 89%
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