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How efficient are my windows? The double glazing energy efficiency label explained

Water on Double Glazed Windows

We’re all familiar with the rainbow energy efficiency labels in the UK. We see them on everything from kettles and fridges to our TVs and double glazing. You may have stopped and wondered what these different categories mean and how energy efficiency is calculated. Does the energy efficiency rating apply to the panes of glass, the frame or both? Here at DG Solutions we understand windows – if you have any questions about how efficient your windows are, book yourself a free appointment with one of our glaziers today.

What is an energy efficiency rating?

Your windows are rated on a scale of A-G. Each of these bands represent a certain efficiency value, where the A rating applies to windows which are the most efficient at keeping the heat in and the G rating is akin to having an open hole in your wall. The rating itself applies to not just the glass, but the entire window unit, from the frame to the coating on the glass. The unit is examined and tested against a range of variables and the results are plugged into a formula which gives a set value. This value fits into one of the bands, A-G, giving you the rating you see on the rainbow sticker or label. Here at DG Solutions all of our window products are rated A for efficiency – the highest energy rating any double glazed window manufacturer can receive.

How is the energy efficiency rating calculated?

The rating is calculated looking at the results of three different tests. The first thing windows are tested for is the total solar heat which is transmitted through the window glass, known as the g-value. Next we have the U-value, which is a measure of how much heat is lost through the window; windows with a low U-value are also called Low-E, where E stands for emissivity. Finally we have a test to see how much air leaks through the seals around the window – the L-factor.

In the interest of standardising these tests, the values are carried out by a qualified technician from the British Fenestration Ratings Council (BFRC) where the windows tested are all set at a given size. This is what gives windows a uniform set of Window Energy Ratings (WERs).

What does the a rating mean?

Now that we know what’s being measured, what kind of values are we looking for? Windows rated A for energy efficiency have high g-value, a low U-value and low L-factor. This means that a lot of heat gets in, not a lot of heat gets out and there’s little-to-no air leakage through the seals. This in turn means a warmer, more comfortable home, lower energy bills and a greener household. With A rated windows, everybody wins.

Posted by: DG Blog

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