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Guide to Window Energy Efficiency Ratings

10 February 2023

Window energy efficiency ratings have become increasingly important for homeowners, and therefore it is key for tradespeople and installers to understand as well. With energy efficiency ratings explained, you will be better able to get across the importance of these scores – and how windows perform in relation to them.

At Dempsey Dyer, energy efficiency is important for us as manufacturers. We know that everybody wants to save money on their energy bills, so they need profiles that are thermally efficient to keep the heat in and reduce the strain on central heating systems.

To help our installer customers and end-user homeowners understand window energy efficiency ratings, we’ve put together this complete guide with all the information you need. As an introduction to energy efficiency scores, this should give you a good starting point. If you have any questions about energy ratings or would like to talk about our expertly manufactured windows and doors, we welcome you to get in touch with our team today.

What is a Window Energy Rating?

A window energy rating (or WER) is the score relating to its thermal efficiency and heat transference. It’s a scale between E (at the lower end) and A+ at the top. This is generally the case, as different energy review bodies will have slightly different metrics, although some scoring systems may vary slightly.

You can find out more about the specific examples by visiting Certass, BSI and British Fenestration Rating Council respectively.

To place windows on the scale, a formula is used based on the total solar heat transmittance – that is, the amount of heat from the sun that can pass through the glass, also known as the g-value – plus the U-value of the whole window, frame and glass combined, which is how well the window keeps heat in your home without letting it escape.

While the formula itself may be complicated, you can see how these factors are massively important to homeowners and therefore installers and manufacturers, since they clearly assess how thermally efficient a window is – and as such, how much money customers can save on heating.

A formula is helpful since it makes the scoring system consistent with other products, so customers can easily see how energy efficient one type of window is compared to another, or how a window performs next to a door, for example, or even a washing machine or lightbulb!

How are Window Energy Ratings Given?

As you can tell from the formula above, the energy rating takes into account the glass and the frame combined. As such, energy efficiency ratings are not attributed to one instead of the other, like the frame or the glass individually – instead, it’s the whole unit.

That means that the manufacturing process is key here, which is why understanding energy efficiency ratings are so important to us as manufacturers. At the point when these window elements are combined, the energy rating can be given. If poor quality glass is installed into sub-par frames (or vice versa) the score will drop and the overall product will not score as well.

Window energy efficiency ratings keenly and intelligently are based on the whole product, so customers can be reassured that they are getting the full package that performs as well as it needs to once installed. This makes the WER system a trusted resource throughout the process.

Benefits of Energy Rated Windows

Here at Dempsey Dyer, we’re all about educating our customers on the benefits of our windows and how they will improve the end users’ lifestyle. As such, now you know how window are scored with the energy efficiency ratings systems, here are some of the key benefits of why homeowners should invest in them:

Trusted Scheme

Everybody can rely on numbers and formulae. With WER scored by a set system that’s easy to compare within the industry and across other sectors, it’s easy to rely on. Like results from other neutral, impartial accreditation bodies, window energy efficiency ratings will give you the facts.

Quality Manufacturing

With an impartial scoring system in place to go by, WER forces (quite rightly) manufacturers to create quality products on all fronts. They can’t compromise on any elements, such as the frame or the glass, since the score of calculated combined. As a result, energy rated windows are made to impress – both the efficiency score and customers.

Saving Money

Perhaps the most important benefit for homeowners (understandably) is how following the scores of the window energy efficiency rating system can save them money. With windows that score better on WER, customers will enjoy improved heat retention and reduced heat loss – meaning less reliance on energy bills and more disposable income!

Energy Efficient Windows from Dempsey Dyer

Here at Dempsey Dyer, we’re passionate about sustainability, and educating our customers on and abiding by the regulations of the window energy efficiency ratings system is a significant part of this. That’s why we wanted to put together this guide to explain not only why it’s so important to homeowners – but also why we work towards this.

Our windows and doors achieve excellent energy efficiency ratings, so end users can save money on energy bills in line with this trusted scheme.

For more information about how WER relate to our products, get in touch with our team. What’s more, you can use our online quoting tool to get a free quote for energy efficient windows and doors to start saving money – and the planet – today.


Installers and other businesses can only work effectively if they have a reliable trade supply service – offering the highest performing products. Luckily, here at Dempsey Dyer we only supply the latest options from market leaders. This guarantees quality, performance and durability – regardless of the product choice.


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