Accounting for over 90 per cent of the domestic heating market in the UK, gas boilers are by some distance the most popular form of central heating. However, with environmental concerns on the rise, a real desire to make energy consumption more efficient for the sake of the environment, and a greater emphasis on consumer rights when it comes to having all relevant data available before purchasing a new boiler, boiler efficiency ratings have become more important than ever.

Whether it’s a boiler you already have or a new model that you’re thinking of getting, every boiler in the UK should have it’s own efficiency rating. This grade will tell you how much of the fuel fed into your boiler is actually converted into useful energy used by your central heating system. However, with a number of different rating systems which can appear confusing to the untrained eye, understanding what your boiler’s efficiency rating actually means is not always easy. Here at Viessmann, to help cut through the noise, we have put together this handy guide that tells you everything you need to know about boiler ratings. 

How are boilers rated?

Knowing how to use a boiler efficiently is one thing, but there is only so much you can do - especially if you are dealing with an old or poorly maintained model. But how do you know if your boiler is just not up to the job when it comes to efficiency? Well, luckily that’s where boiler ratings can help.

When it comes to how boilers are rated, efficiency is everything. Every boiler in the UK should have a rating ranging from A to G that signifies how much of the fuel used to power the boiler is actually converted into usable heat energy, against how much fuel is wasted in the process. This useful/wasted fuel consumption ratio is simply calculated as an efficiency percentage, and this percentage is what equates to the letter rating a certain boiler achieves - from A+++ (or A depending on rating systems) down to G.

Boiler ratings were made mandatory in the UK during the 1990s, initially operating alongside very similar EU energy efficiency guidelines. As time has gone on, the UK has fully adopted the EUs rating system, gradually replacing its own original system, with the aim of reducing household emissions uniformly with the rest of Europe. However, as a result of two slightly different rating systems overlapping over the past few decades, there are still technically two boiler rating systems you may come across. The two rating systems are the SEDBUK rating and the ErP rating. But what is the difference and why did ErP replace the older SEDBUK system?

What is SEDBUK?

The SEDBUK - or Seasonal Efficiency of Domestic Boilers in the UK - rating was introduced in 1999 as an energy efficiency guideline that all new boilers installed in homes and businesses across the UK had to follow. The SEDBUK system saw each new boiler provided with a rating from A down to G. The rating itself was applied based on the results of the average efficiency achieved each year, factoring in common seasonal variables and other small variations. ‘A’ was awarded to highly energy efficient boilers, ‘B’ was awarded to boilers that were classed as efficient, while the bands ‘C’ to ‘G’ were reserved for boilers classed as only having standard efficiency, on a declining scale.

However, after 2009 and the introduction of the EU’s new boiler efficiency rating system, the Energy related Products Directive (ErP), a second version of the SEDBUK rating was introduced so as not to confuse the user. SEDBUK 2009, as it has become known, replaced it’s letter ranked rating system with a percentage-based one to show efficiency. Boilers with a 90 per cent + score achieve the highest rating, while a boiler that scores below 70 per cent efficiency achieve the lowest SEDBUK 2009 rating. The SEDBUK rating system was officially replaced in the UK by the ErP Directive rating system in 2015.

 What is ErP?

The ErP is the Energy related Products Directive - an eco-design directive, created and rolled out by the European Union in 2009, that applies to the majority of domestic and commercial appliances that consume energy in order to function. Launched with the intention of lowering Europe’s carbon emissions by 20 per cent by 2020 (compared to levels recorded in the 1990s), arguably the largest impact ErP has had is on the design of heating products such as boilers through a universally recognised efficiency rating system.

By standardising efficiency ratings across Europe, the ErP has forced manufacturers to be more transparent about the efficiency of their products, while ErP energy labelling has allowed consumers to choose the most energy efficient products for their homes and businesses as easily as possible. In turn, this has enabled consumers and businesses to reduce their carbon emissions and save money on their energy bills in the process. 

 What does ErP stand for on boilers?

When you see ‘ErP’ on a boiler, this stands for the Energy related Products Directive. The ErP provides the efficiency rating system that is universally recognised across Europe, including here in the UK. This means, when you see an ErP label on a boiler, you’ll find the boiler’s efficiency rating, displayed as a letter from A+++ to G and colour-coded green to red. Each rating equates to the specific efficiency percentage of the boiler (how much of the fuel used to power the boiler is actually converted into usable heat energy). These ratings are as follows:

ErP Letter Rating Efficiency Percentage
A+++ > 150%
A++ 125% – 150%
A+ 98% – 125%
A 90% – 98%
B 82% – 90%
C 75% – 82%
D 36% – 75%
E 34% – 36%
F 30% – 34%
G Below 30%

Why did ErP replace SEDBUK rating?

The ErP Directive was launched across EU member countries in 2009 in the form of universal eco-design and energy efficiency guidelines. The main aim of the scheme was to gradually phase out poorly performing appliances and make the efficiency of products more transparent for consumers.

Although the UK already had its own efficiency rating system when it came to heating systems and boilers in the form of SEDBUK, it agreed to adopt ErP. The government acknowledged that a standardised scheme across Europe - which was tied-in with the EU’s goal of lowering Europe’s carbon emissions by 20 per cent by 2020 and achieving a 20 per cent improvement in overall energy efficiency across the EU - would ultimately make it easier for British consumers and manufactures to also achieve the same goals nationally.

Initially the ErP efficiency rating system was used alongside SEDBUK, however, in 2015 the SEDBUK rating system was officially replaced in the UK by the ErP directive system. Interestingly, many manufacturers still include the SEDBUK efficiency rating as well as the mandatory ErP rating, as it provides a clear percentage efficiency rating, alongside the ErP’s letter grade.

What is a good ErP for a boiler?

All modern boilers should have a good efficiency rating. This is to say, they should have an ErP rating of ‘A’ or higher when first installed. This represents an energy efficiency score of at least 90 per cent. A good example of a best-selling boiler with a good ErP rating is Viessmann’s Vitodens 100-W combi boiler. It is between 92 and 94 per cent efficient, and has an ‘A’ ErP efficiency rating.  

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