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U-value and other terms

When looking at how energy-efficient your windows are, there are several things to look out for. Below you can read what the key terms are when it comes to energy-efficient windows and which terms are most important for your home.

Insulation value of the glass

When buying windows, one of the things you look at is the energy balance of the glass. The energy balance number indicates heat loss versus heat gain. I.e. the ratio between the energy lost during that through the window and the heat added by the sun. The energy balance depends on where in the house a window is located. If you place a window on the north side of the house, there will be no sun on it in winter and therefore no energy added. On the other hand, a window on the south side of the house can provide extra heat from solar heat to replace the heating itself.


The g-value, also known as ZTA, is the solar factor. This value indicates how much (heat) radiation the glass blocks. The lower the g-value, the more solar thermal radiation the glass blocks.


The insulation performance of a window is called the U-value, and a distinction is made between the U-value of the window and the U-value of the glass itself. The U-value indicates heat loss and describes how well a window insulates. In short, how much heat passes from the inside to the outside through the window. The lower the U-value, the better.

New windows and doors?

We make beautiful window frames in pine, alu-clad and uPVC according to your wishes and needs. In our configurator, you can design your new windows and doors exactly how you want them. Among other things, you can choose your own colours, both inside and outside, and we produce to size so that your new windows and doors fits perfectly.

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