What Are U-Values?

U-values measure how effective your doors and windows are at keeping in heat. The lower the U-value the better the performance in terms of how much energy is needed to maintain a comfortable temperature inside your home.

In other words, the lower the U-value of your doors and windows, the less heat is lost and the better they at insulating your home. Bear in mind that U-values indicate the installation’s insulation level but not necessarily its energy efficiency.

The unit for U-values is W/m²K. This describes how much thermal energy in Watts (W) travels through one square metre (m²) of building components on either side of 1 Kelvin. (K).

From October 2010, it is law that windows and doors in the UK must achieve a U-value of 1.8W/m²K or less.

What Are Window Energy Ratings (WER)?

The British Fenestration Rating Council (BFRC) Energy Ratings system is a guide to measuring the energy eficiency of a window or door.

The scale ranges from A++ to G, with A++ the maximum rating awarded to the most energy efficient windows. ‘C’ is the minimum to satisfy Building Regulations for windows and ‘E’ for doors with glass installed.

Energy ratings not only take into account the U-value but also the solar gain and air leakage of a product.

At SWR, we only supply and install improvements that meet (and often exceed) the building regulations for U-values and energy efficiency.