Window replacement in the old building - what about the amortization?

Especially in older buildings is often the question of whether a replacement of the windows is even worthwhile, and when he will pay for itself by saving on heating costs. Which factors are decisive, read in this article, you will find some example calculations.

Factors for the amortization

Costs for window replacement

First, of course, the window price is an important criterion. Depending on whether you opt for plastic windows or for high-quality aluminum windows or windows, different prices result.

For some buildings, standard dimensions can not be used - windows made to measure must be used, resulting in significantly higher costs.

Additional costs for the window replacement

In addition to the window prices, of course, the costs for the installation and disposal of the old windows still have to be included. Various subsidies, which you get for the window exchange, you can then deduct from the total amount.

heating costs

In order to be able to calculate when which windows pay for themselves with which U-value, you also have to know your heating well.

Depending on the total heating costs, the type of heating used and the efficiency of the heating, the savings are different. Summarized again, so you have to expect the following values:

  • with the efficiency of the heating (gas fired condensing boilers have an efficiency of almost 110%, old oil heaters are around 85% or even less)
  • with the type of heating
  • with the costs of the heating medium (biomass causes significantly less costs than oil and gas)

Texture of the windows

For a calculation one should know the U-value of its previous windows. In the case of windows between 1975 and 1995, it is possible to assume values ​​of more than 2.0 W / (m²K) in some cases, and from 1995 onwards most windows were around 1.4 to 1.6 W / (m²K).

Due to the air cushion, some very old wooden windows (box windows) often have values ​​of 1.6 to 1.8 W / (m²K) despite single glazing. In contrast, other single-pane glazings are again 2.5 W / (m²K) or even higher, especially if they are leaking. If in doubt, you can also test your window glass yourself to have an approximate idea of ​​the U-value.

Example calculations: Renew old building window

example 1

Old building from 1980, U-value of 2.2 W / (m²K) oil heating with 85% efficiency, replacement on a plastic window with a U-value of 1.1 W / (m²K), 40 m² window area

The annual saving here is about 300 euros in heating costs. If converted to gas condensing heating, total savings are already more than a third lower, at just under € 200 per year. The amortization period is correspondingly longer.

For biomass heating systems, the savings would once again be reduced to about half. An amortization of the windows is then only after decades, a window renovation is therefore a rather bad business.

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