• Window Energy Ratings
  • Window Energy Ratings
  • Window Energy Ratings

Window Energy Ratings

Window Energy Ratings are particular ratings which constructors of buildings must demonstrate they meet.

The minimum level for domestic windows is band E. For windows in new domestic extensions, the minimum requirement is band D. Window Energy Ratings were launched in 2004 by the British Fenestration Council (BFRC), an independent organisation committed to the improvement of the energy efficiency of fenestration products. Window Energy Ratings are devised using a formula which considers available solar heat gains (window g-value) and subtracts the thermal losses (window U-value and air leakage:

WERs = Solar Gains – (Thermal Losses + Air Leakage)

The resulting numerical value is usually negative and is placed into a band on an A-G scale consistent with other energy performance labels:

BFRC Rating Scale

BFRC Rating

A 0 or greater
B -10 to < 0
C -20 to < -10
D -30 to < -20
E -50 to < -30
F -70 to < -50
G Less than -70


This rating system allows homeowners to choose the most energy efficient windows for their homes. Windows with a C rating or higher are endorsed by the Energy Savings Trust ‘Energy efficiency recommended’ scheme and may carry the EER logo.

The advantages of choosing a window with a higher WER rating are that the room will be more comfortable and less drafty as the room will be better insulated. There will also be less condensation as the inner surface of the glass stays warmer. Perhaps most importantly of all to the homeowner, not only energy but money is saved. Village Glass offers a wide range of products designed to improve window ratings. These include the Thermobar Warm Edge Spacer Tube which virtually eliminates condensation on the inner edge of a unit and perforation holes for the effective passage of air.