Understanding a window or doors’ energy rating is highly important, as it’s estimated that up to 25% of the heat within most homes, escapes through the windows.

The energy performance of a window & door is either measured by their u-value or Window Energy Rating (WER). The U-Value is a scientific measure of how heat flows through an element. High U-Values mean more heat flows, so the lower the figure the better.

The Window Energy Rating scheme is a scale designed to tell you exactly how energy efficient your windows are so you can choose the most suitable for your home. The scale was developed to provide a rating system specifically for windows as it takes into account not just U-Values, but also solar heat gain (G Value) and the air leakage rate of all the components of the fitted window.

The scale runs from A++ to E, with A++ being awarded to the most energy efficient windows. ‘C’ is the minimum to satisfy building regulations for windows.

It is required by law that new build or replacement windows need to satisfy at least one of the following criteria:

• To have a whole window ‘U’ value of 1.6 W/m²K or lower.
• To have a minimum window energy rating (WER) of ‘C’.
• To use sealed units with a ‘U’ value of better than 1.2 W/m²K with argon gas fill and warm edge spacer bars.