Energy ratings – what do they mean?

We decipher the jargon about energy ratings to help you understand what it all really means

The benefits of uPVC windows over the timber-framed variety are numerous – toughness and durability, resistance to rot, low maintenance and wide choice of styles. But for many, the biggest selling point of uPVC is its energy efficiency – not surprising, given that 25% of a home’s heat can escape through the windows.

So before choosing new windows, it’s vital you know how effective they are and that’s why the British Fenestration Ratings Council (BFRC) created the WER (Window Energy Rating) scheme, which measures the thermal performance of windows and doors on a scale from A (the best) to G (the worst) and displays this on a traffic-light style label. This is a useful tool that helps you make a quick and informed decision when choosing the best windows for your home, but it’s also useful to know about the following three key elements that the WER is based on.

U-Value

This is the way thermal efficiency is measured and indicates the degree of heat loss through any building material, whether it be the glass in your windows, the bricks that form your walls or the tiles on your roof. Materials that allow out more heat have a higher U-Value than those that let out less heat.

G-Value

Modern glass is designed to allow in a specific amount of the sun’s rays, otherwise known as solar gain, and the higher the G-Value rating, the more efficient the windows are at absorbing infrared radiation. This has the benefit of heating your home naturally, with less reliance on fossil fuels to provide warmth in the winter months. However, rooms that are either south-facing or have particularly large windows can benefit from solar-reflective glass to prevent overheating in the summer.  

L-Value

The ‘L’ in this case, stands for leakage. Thanks to advances in technology, new uPVC windows are designed to be 100% airtight but where there is a weak point, such as around the seals, draughts can occur, hence the term L-Value. Often you’ll know it’s time for new windows when your windows have become draughty beyond repair.

To see how much money you could save on your energy bills and to find out how significantly you could reduce your carbon footprint, use the Glass and Glazing Federation’s Energy Savings Calculator. It can even tell you how much more you could save by installing windows with an ‘A’ rating compared to the ‘B’ to ‘G’ rated products.