Replace Windows – Yes, or No?
In general, tight windows make sense. Because windows are one of the major weak points of a house.
Here the cold air pushes inwards, while the laboriously generated heat can escape outside.
Thermal imaging cameras, which impressively display the loss in red, show that most of the heat is often lost through windows. The thermal image shows: Although the frames are closed, the warm air slips out.
The reason: the windows do not hold tight. Here you can find commercial window installation details.
The Number of Slices is Crucial
One, two, or three? For the heat loss, the number of panes in the windows is decisive – and whether they are filled with a noble gas or only contain a vacuum.
Whether a renovation makes sense can ultimately be seen from the so-called U-value. It defines heat loss or heat transfer. The fewer panes a window contains, the worse the U-value.
Since the current Energy Saving Ordinance of 2009, highly heat-insulating glazing has been mandatory. These windows are considered tight, the energy stays in the house. Windows with only one pane of glass have a U-value of up to 5.8, and an enormous amount of heat rushes outside.
Double insulating glass – mostly from the 70s and 80s – without gas filling has a heat transfer value of 2.7. Three glasses in a window without a noble gas are given as 1.9. Up to this U-value, energy consultants recommend having new windows installed. The savings potential is considerable.
The lowering of the U-value by 0.1 (W / m2K) alone saves one liter of heating oil per square meter of window area – TÜV Rheinland has calculated that 50 to 70 percent less heat is lost through new thermal insulation windows compared to the usual old building windows. “That saves money,” sums up Dr. Brickwedde. The heating bill can be reduced by around 240 to 260 euros.
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Free Energy Check
If the windows are installed after 1995, it is advisable to ask a specialist for advice and have the U-value determined.
The German Federal Environment Foundation is organizing a free energy check as part of its “House renovation benefit” campaign.
The initiative is carried out by trained craftsmen and energy consultants. It applies nationwide and is intended to give an initial overview of the energetic state of the house.
On the other hand, we do not recommend replacing double and triple heat protection glasses with a coating and gas filling.
They come to a U-value of at least 1.3, a replacement would not be amortized, according to the current study “Economic efficiency of energetic modernization in residential buildings used by the owner” by the German energy agency Dena.
Warning Mold!
New, heat-insulating windows make sense under the conditions described, but when renovating, replacing the windows is usually just one step among many. It is not without reason that many homeowners are afraid of moisture or even mold after they have bought their home new windows.
In fact, dense panes reduce the air exchange throughout the house. This increases the humidity in the rooms, which is particularly noticeable on cool walls – namely with mold. This effect is reinforced by poorly insulated exterior walls and ceilings, which are naturally cold in winter.
This is why energy consultants always recommend not only implementing one measure during the renovation, but also keeping an eye on the whole house.
The best insulating glass is of no use if thermal bridges lead the heated air outside. If there is not enough space, you would have to move the windows at the front edge of the masonry so that the insulation can later Can cover window frames and avoid thermal bridges, “advises Dr. Brickwedde.
In other words: It is always advisable to insulate the outer walls if the windows are to be replaced in an old building. If the renovation is not carried out immediately, it should be done after two years at the latest to prevent mold growth.
