Window Energy Rating – how energy efficient is my integral double glazing?

The Window Energy Rating (WER) is a system that allows you to know just how energy-efficient your double glazed windows are. The rating system is based on a an eight point scale, The scale is labelled from A+ at the top end down to G for the most energy inefficient windows. You will no doubt be familiar with the energy rating system used on white goods, like washing machines, fridges or freezers. The principle is very similar.


Regularly touted figures show that up to 25% of the heat lost from a house is through the windows. This is one area that is worth looking at to lower this heat loss. If you are having double glazing fitted for the first time then the benefits of fitting and A or A+ rated window will be well worth it. However, the difference between C and A+ is much less noticeable. Sunshade Blinds use Planitherm™ energy saving glass that is manufactured by Saint-Gobain Glass because we have found it to be a market leader in energy efficient glass for double glazing.


It is worth noting that the WERS rating refers to the whole window – the frame and the glass. If you sell these components separately, then that WERS rating will not be relevant; it is the total system.


So how does Window Energy Rating work?


WERs are calculated using a formula. This takes into account the total amount of the sun’s heat that can pass through the glass. This is known as the g-value. The U-value is the rating attributed to the whole Unit, that is the whole window of the frame and glass combined. Other factors used in the calculation include:


  • Just how effectively the window unit keeps the heat inside your home.
  • Is there any air infiltration through the window seals?


The idea of the WERs is to have a standard that is consistent across all products. It is also judged against a standard window size and layout. After the calculation of the formula, a result is produced that will give a value that will be placed in the scale A to G. Obviously, the A-rated windows are the most energy-efficient.


The WERs are supported by various registered bodies who audit window installers. Examples of typical labels are shown below.

Window Energy Rating CERTASS

Certass Thermal Rating Register Scheme Website: www.certass.co.uk Tel. No. 0845 838 8580

Window Energy Rating BSI

BSI Kitemark Scheme for WER Website: www.bsigroup.com Tel. No. 0845 076 5602

Window Energy Rating BFRC

British Fenestration Rating Council WER Scheme Website: www.bfrc.org Tel. No. 020 7403 9200


Published Date: 5th November 2015
Category: Integral Blinds
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