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WHAT IS THE MEANING OF U-VALUE USED IN THE WINDOW INDUSTRY?

Low Energy glass

In simple words U-value shows how much interior heat is released via the window. Namely, three types of U-value markings that are used in the windows stand out. These are the following:

1. Uw = U-window. Shows heat transmittance of the entire window.

2. Ug = U-glass. Shows heat transmittance of the glass unit.

3. Uf = U-frame. Shows heat transmittance of the window frame.

The most important of above-mentioned factors is the U-value of the entire window – Uw, which is final (i.e. calculated based on the average U-values of a frame and glass). This is also expressed as a simple U, for instance U=1.2 W/m²k.

Sometimes the specification is shown as simply U=1.2 W/m²k, but this value is meant to be Ug and not Uw. In this case, the Uw value of the window is bigger than 1.2 and thus the price is more favourable. This means that offers that seem identical on paper, are not necessarily equal in reality. To be on a safe side, it is certainly worth asking the company with the respective offer whether the price offer includes the U-value of the glass unit or the entire window.

U value formula