Windows should be as energy efficient as possible. Therefore, the U-value is one of the decisive criteria for choosing windows when purchasing new windows. In this article, you can read about what to be concerned about the U-value of plastic windows and the information provided by retailers.
Different U values
Resellers often provide different information about U-values. Therefore, you must always pay close attention to the values indicated.
Ug value indicates the heat transfer value of the glass
Uf value indicates the heat transfer value of the frame
Uw value indicates the heat transfer value of the whole window
The total U value of the window
The Ug value, known as the overall heat transfer value, is the standard to measure everything. Although a window can have well-insulated glass, if the frame is not structurally sound, the window will still have a high overall U-value.
The overall U-value of a window cannot be calculated simply by adding the Ug and Uf values together. The required calculation process is much more complex. Values such as the perimeter of the glass area and the ratio of the window area to the frame area also play a role in the overall U-value.
The weak point of the glass is the edge of the frame, which no doubt must also be taken into account. It represents a thermal bridge in every window, but usually the insulation value of the frame edge is not given.
Problems with the information given by the dealer
Resellers often give only the U-value of the glass and not the overall U-value. This is often misleading because the overall U-value cannot be calculated. However, according to national standards, the overall U-value of a window must be less than 1.4 W/(m²K).
Normally, resellers only give values for a specific window type. However, the actual U-value of a window also depends on its size and scale. Such type of information only can be used as a guideline for choosing a window model, but can not as a basis for calculations.
Other important values
The G value of a window also acts as an insulator. This particular heat transfer value indicates how much thermal radiation the glass allows from the outside to the inside (e.g. solar heat).
Tip: When choosing a window, it is important to know the standard of value you want. In the case of new buildings, you can also work with your builder to develop overall energy standards for your home.