Windows, Doors, & Conservatories - 01435 866456

Quality & Accreditations

Heathfield Windows are proud to be a member of the guild of Master Craftsmen.

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Window Energy Ratings Certification


Conventional approaches (such as setting a glass or window U-value) simply assess how much energy a window loses. They do not take into account how much energy a window can gain.

The total energy flow in a window consists of three major components:

  • Thermal transmittance (U-value)
  • Solar factor (g-value)
  • Air Leakage (L50)

The British Fenestration Ratings Council (BFRC) has devised a Window Ratings equation based on values for these components. The rating is expressed as a number. The rating is converted into a grade between A and G (with A being the most energy efficient).