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Do you know your WER from your G value? Energy efficiency ratings explained

Hardwood Timber Casement Windows with Georgian Bars and Monkey Tail Handles installed in Oxford by Paradise Windows

Up to a third of a home’s heating is lost through single glazing, and having windows which are energy efficient can save energy use by around 20%.

To be thermally efficient, windows should be double glazed as a minimum and have a low emissivity glass, with a non-toxic, inert and insulating gas such as Argon between the panes.

Replacement double-glazed windows can achieve a Window Energy Rating (WER) of A+12, while for triple glazing the figure can be A+32.

Given this efficiency, upgrading your windows could save you as much as £450 on your annual household energy bills.

What is WER rating?

The British Fenestration Council devised this system to make a window’s effectiveness simple. Grades go from A to A, with A being the best grade. Anything higher than that is followed by a number, and anything over an A10 becomes an A+.

A couple of years ago, the A++ rating was launched for windows with a score of over A+20. Britain’s highest currently available grade is A+32.

Three key elements make up the rating – U value (or low heat loss), air loss through ventilation and solar gain.

  • Solar gain

This is about capitalising on solar radiation and reducing dependency on carbon energy for heating a home during the winter.

The number of panes, they type of gas between them, and the kind of coatings added, all influence the solar factor.

  • U value

This is the technical way of measuring heat loss through a kind of building material. The lower the U value, the stronger the insulation the material provides. Modern double-glazed windows can achieve a U value as low as 1.4W /m²K, while triple glazing is even more energy efficient

  • Air leakage (L value)

This isn’t the same as ventilation, which is a controlled way of allowing in fresh air, and won’t affect energy efficiency.

Air leaks when the window frame has a weak point, such as at the seal, but for most modern units, they should be fully airtight, and have a zero L-value rating.

Sound insulation

There is another benefit to replacement windows – sound insulation so that you enjoy more peace and quiet. Clearly, that could be more important if you live in a built-up area, near heavy traffic, or under a flight path.

The same things that affect energy efficiency in windows also affect noise cancellation – gas to fill the cavities, airtight seals and having more glass panes.

At Paradise, offering double-glazed windows in Oxford and the surrounding areas, we’re well placed to advise you on the energy efficiency of your home improvements. Get in touch today.