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Window Energy Ratings

The type of windows you select can make a big difference to the warmth of your home. Energy ratings allow you to compare the efficiency of your windows, allowing you to make an informed decision that is best for your home.

There are several rating scales for windows, but the three most widespread schemes are that of CERTASS, the British Fenestration Rating Council and the British Standards Institute. Helpfully, these scales all have colourful charts that rate windows from an A++ or an A+ to an E or G, respectively.

The letter ratings on windows are given depending on the energy efficiency on the entire window, including the frame material, frame design, the type of glass used and other components. The rating given will take into account the windows overall thermal efficiency, air leakage and any solar gain.

Understanding Your Rating

The windows rating will be listed at the top at the top of the rating chart, using the corresponding colour band. Further down the scale, you will notice your window’s Energy Index, which calculates solar heat gains (window g-value) and subtracts the thermal losses.

Will I Save Money?

The energy rating of your windows is a guide to how efficient they will be. The exact savings you will make will depend on other insulation you have in your home, as well as the location in the window. The GGF energy savings calculator can you an estimate on how much energy, carbon and money you could save by replacing your windows with a better energy rating.

Here at Williams Windows DG Limited, we only use products that are A rated on the CERTASS scale, keeping your home safe and warm. If you are considering in investing in new windows and doors, we welcome you to contact us. Please call 0208 428 5433 or fill out our online enquiry form and we’ll get back to you shortly.


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All Products are A Rated Efficiency