Energy Ratings For Double Glazing

Understanding Window & Door Energy Ratings

WER or Window Energy Ratings are covered by UK Building Regulations and new or replacement windows & doors need to be certified as compliant with these regulations. To identify the performance of any particular installation you should look for the Energy Rating Label attached to the product in question - this is the data that clearly shows whether the product you are buying is a net "loser or gainer' of energy.

  • The labeling system is overseen by the British Fenestration Rating Council and is the national system for the whole of the UK


Very similar to a 'traffic light’ the ratings are colour coded for quick identification with an added alphabetical code that runs from A+ to G (G being the lowest rating). So to get maximum energy efficiency you would need to install an A+ rated product.

When installing this type of home improvement, it is important to use a CERTASS or FENSA accredited company to do the work as they are approved to certify the installation as meeting building regulations (you can do this yourself but you will have to arrange inspection and pay fees for the inspection & approval).

Rating Label Information

  • The product overall rating (A+ to G)…
  • Rating for Energy – Example 3kWh/(m²•K) means this item will have a 3 kilowatt per-hour, per-square metre every year.
  • The ‘U’ value of the item
  • Air penetration effect
  • The amount of heat gain from solar (eg. g=0.43)

Basically, this information is saying how well or how badly the whole product works in terms of heat conservation, keeping wind out, condensation resistance and insulation from sound.

(Information courtesy of the British fenestration Rating Council)

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