What is a U-Value?

The U-Value or Uw is a measure of conductivity of the whole window (glass and frame included). It is a number calculated to return an amount of energy flowing through the product at a given temperature difference per meter squared of window. The Uw is a number that indicates how well a window or door will retain heat in the winter and reject heat during summer. The lower the Uw the better the energy efficiency of the product.

The Uw can be affected by the frame material and the glazing type. For example Aluminium conducts energy more readily than Timber or uPVC and as a result aluminium products will have a higher Uw than Timber or uPVC with the same glass. High performance glass can also have an impact on the Uw of the product, when a frame is fitted with higher performance glass like double glazing or low emmisivity glass the Uw will fall making the product more energy efficient.

For more information please access the below links.

i. U-value Marketing the Real Performance - Windows Magazine Article