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Energy Efficient Windows

Having energy efficient windows installed can help you make significant savings on your energy bills.

On the 1st October 2010, changes to L1B of the Building Regulations will come into force which state that all replacement windows must have a minimum Window Energy Rating (WER) of band c or a declared U value of 1.6 W/m2k.

Who determines Energy Ratings for Energy Efficient Windows?

The British Fenestration Ratings Council Ltd (BFRC) is an independent organisation dedicated to improving the efficiency of fenestration products.

What are Energy Ratings?

BFRC Energy Ratings are a method of informing customers of the relative energy efficiency of specific windows. The windows are rated on an A to G scale, which is consistent with other products such as light bulbs and white goods.

How are they calculated?

Ratings are determined by a formula that takes into account the following various factors that each have an effect on the overall energy performance of the window and how energy efficient windows are:

  • Thermal Transmittance (The U value)
  • Air Leakage (The L value)
  • Solar Factor (The G value)
  • UK Standard Domestic Occupancy
  • UK Climate Data

The U value explained

The thermal heat loss test calculates the amount of heat that is lost through the glass and frame. The lower the heat loss value, or U value, the better the window performance.

The L value explained

The air loss test indicates the amount of air that is lost through the frame. The lower the L-value the more energy efficient windows are.

The G value explained

The solar heat gain test demonstrates the amount of heat that is absorbed and trapped inside by the window. A high G-value indicates a more energy efficient window.
An energy efficient window is one that performs well across all of these tests and is achieved by marrying together high performance glass with a high performance frame.

What do BRFC labels mean?

The labels are similar to those currently used on other household appliances; An A-rated window is the most efficient and G rated windows the least efficient. From the 1st October 2010, all replacement windows must have a minimum rating of C.

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