Window Energy Rating (WERs)

Window Energy Rating (WER) is a rating scheme that provides labels indicating how energy-efficient your windows are. The WER labelling scheme grades window energy performance using a scale A-G, with A being the best rating. The WER labelling scheme allows consumers to quickly and easily compare one window with another in terms of energy efficiency. If a window is rated between an A and a C, it will be approved to carry an Energy Saving Recommended label. 

Launched by British Fenestration Rating Council (BFRC) in March 2004, the WER system provides a scaling system specifically for windows and takes into account not just U-Values, but also solar heat gain (G Value) and the air leakage rate of all the components of windows.


Windows are scored on a scale of A – G, with an ‘A’ rated product being more energy efficient than one which is G rated.

the more we can do to prevent heat loss the more we’ll benefit all round.

BFRC makes the WER calculation based on the following three factors:

  • U-Value (Heat loss): It indicates the level of thermal transtittence or heat loss from the window. It measured in W/m2K. The lower U-value means the better insulation. 
  • L-Value (Air leakage): It measures how airtight a window is. A good quality window has low level air leakage. 
  • G-Value (Solar gain): The G-value measures how much heat the glass is able to gain from direct sunlight.

Building Regulation and WER 

Building Regulations require any replacement domestic window to achieve a minimum rating of ‘C’.


British Fenestration Rating Council (BFRC)

Glass and Glazing Federation (GGF)


Info Sources