It is recommended to buy energy-efficient windows whenever possible. When buying new windows, U-value is one of the decisive criteria. In this article, you’ll learn what to look out for in the U-value of plastic windows, and what retailers have to offer.
Different U-Values
Dealers often provide different information about U-values. So it is necessary to know what values these refer to:
– Ug value only means the heat transfer value of glazing
– Uf value indicates the heat transfer value of the frame
– Uw value represents the heat transfer value of the whole window
– The total U-value of the window
The Ug value, the total heat transfer value, is the standard by which everything is measured. While a window may have good insulating glass, if the window frame is poorly constructed, the overall U-value of the window will still be high.
The overall U-value of a window cannot be calculated simply by adding the Ug value and the Uf value, because the required calculation is much more complicated. The perimeter of the glass area, the ratio of the window area to the frame area, etc. will also affect the overall U-value.
The weak point of the glass, the edge of the frame, must also be taken into account. It represents a so-called thermal bridge in each window, but usually no value is given for thermal insulation at the edges of the frame.
Problems With The Information Provided By The Dealer
Dealers tend to give only the U-value of the glass and not the overall U-value. Often this is misleading because the overall U-value cannot be calculated. But according to the energy saving concept, the total U-value of the window below 1.4 W/(m²K) is the best.
They usually only give values for a specific window type, especially in brochures. However, the actual U-value of a window also depends on its size and proportion. Such type information can at best be used as a general guideline for choosing a window model, but not as a basis for calculations.
Other Important Values
The G value of the window also acts as an insulation. This particular heat transfer value indicates how much thermal radiation the glass allows from the outside to the inside (such as solar heat from the outside).
Tips And Tricks
When choosing a window, be sure to know in advance what values you want. For example, with energy consulting, you can find out what makes sense. In the case of new building, you can also work with the architect to develop the overall energy standard for the house.