Explaining the Windows Energy Rating (WER)

Window Energy Rating

Window Energy Ratings (WER), as the name suggests, indicate the energy efficiency of your windows. The system is based on an A-G scale, with A-rated windows being the most efficient, and G the least efficient. New and replacement windows must now be at least C-rated to comply with Building Regulations, it can be quite pricey to get windows that are efficient yet cheap especially for charities. Earlier this year we saw that Help to Buy Windows provided a grant of free windows & doors for a hospital caring for parents. so it is these three ratings that you will need to distinguish between in the buying process. WERs are easy to understand, with a rainbow label being used to indicate a window’s Rating. The scheme is much like that used on white goods, household appliances and light bulbs.

If you are looking to buy a double glazed window, you should certainly ensure that the manufacturer/supplier that you are considering uses this rating system, and offers windows of a suitably high rating. Originally launched in March 2004 by the British Fenestration Rating Council (BFRC), with other schemes since established by CERTASS and BSI, WERs have only increased in importance over the years, being recognised in various government-supported initiatives.

How is a Window Energy Rating determined?

A-Rated Windows

Window Energy Rating

The formula that is used for determining a window’s Rating takes into account the glass’s total solar heat transmittance – better known as the g value – as well as the window’s U-value (the window frame and glass combined) and air filtration through the window seals. A standard window size and configuration is used to ensure the standardisation of the Rating across all products. Finally, the resultant value is placed onto the A-G scale.

A Window Energy Rating and label are applicable to a whole window, including both the frame and glass. It does not refer to either the frame or glass individually. It is therefore the point at which a window’s various components come together in the production of a whole window that the Rating and label are obtained. This means that it is the window installer’s product that is usually rated and labelled, although if the window is a factory-glazed one, it could be the window manufacturer’s product.

What makes A-rated windows the best option?

In the determination of a window’s Rating, both the positive (solar gain) and negative (heat loss) aspects of the glass are considered. There are various other factors beyond these that can influence a WER, such as frame U-value, frame area and air-tightness. In general, though, in order to significantly improve a window’s Rating, the g-value needs to be improved without any compromise to the U-value, and the U-value needs to be improved without the g-value being reduced.

There are various means by which greater energy efficiency may be achieved – such as by incorporating an advanced five-chamber outer frame and PVCu thermal inserts. Ask the manufacturer/supplier that interests you, how they achieve the best possible WERs for their windows.

Why you should choose A-rated windows

More energy-efficient windows can obviously bring you some substantial savings on your energy bills – around £130 per year and about £650 over a five year period if you have a full house of new windows, each unit costing around £0.16, with energy savings of around 680KWH per year being achieved.