energy efficient windows

Energy Efficient Doors and Windows

energy efficient windows

Understanding energy efficiency in windows (WER)

In 2005 the British Fenestration Ratings Council (BFRC) and introduced a scheme for measuring energy efficiency in windows.

To measure the energy efficiency of a window the WER ‘Window Energy Rating’ is used.

This rating system grades a window’s energy efficiency performance. The WER system is based on letters and is shown in an easily identifiable rainbow label (much like the one used on white goods which consumers readily recognise).

The WER rating system grades a window’s performance from ‘A++’ to ‘E’. A++ as the best energy efficient performing window and E being the worst.

Energy efficiency guide for windows

The rating label also takes into consideration: energy index, u-value, g-value and l-value.


A window’s U-value is its thermal value (how much heat is transferred). The U-value calculates how much heat is transferred from the warm side of the window to the cold side. The lower the U-value the warmer the window will keep your home warm.


A window’s G-value is its solar gain (how much heat a window lets in). The G-value calculates how much heat is let in by the sun’s rays. The G-value is set on a scale between 1 and 0. The higher the indicated number in solar gain the better as it means your window is capturing the sun’s heat.


A window’s L-value is its air leakage (how much heat is lost). The L-value calculates how airtight a window is. Air can leaked through a window if it has poor rubber seals or a weak point. The lower the indicated air leakage factor (ideally zero) means your window is less draughty.

What are the benefits of WER?

WER benefit the consumer. When buying new windows and doors you can ensure you are getting the best product available and can make informed decisions on your purchase.

What does the BRFC Govern?

The British Fenestration Ratings Council (BFRC) periodically inspects businesses supplying windows and doors, ensure glazing companies are supplying the correctly rated products.

Understanding Energy Efficiency in Doors (DSER)

As with windows, doors also have energy ratings ‘Door Set Energy Ratings’ (DSER’s). The Door Set Energy ratings provide an effective way of assessing the energy efficiency of residential doors.

In October 2010 laws stated that all new doors sold and fitted in the UK must have a u-value. The u-value calculates how much heat is transferred from the warm side of the door to the cold side. The lower the u-value the warmer the door will keep your home warm.

The Glass and Glazing Federation (GGF) have produced a great replacement windows and doors environmental checklist for all consumers looking to replace their windows are doors.