Window - what heat protection is required?

Through windows, a lot of energy is lost. Manufacturers advertise therefore with ever lower U-values ​​in windows. What actually makes sense and what savings can be achieved with new windows can be read in detail in this article.

Legally required U-values

The EnEV in Germany no longer permits uninsulated windows. Old windows may remain as they are, but new windows may have at most a U-value of 1.3 W / (m²K).

All old windows above this value should, if possible, be converted to new, energy-saving windows.

Passive house standards

Passive houses are based on U-values ​​for the windows, which should definitely be below 0.8 W / (m²K), better still around 0.6 W / (m²K).

For non-passive houses this usually does not make much sense, especially not, even if the wall insulation has no passive house standard (less than 0.15 W / (m²K) at the outer wall).

Windows with U-values ​​of 0.8 or even below are not necessarily useful in a normal house. The very high cost of such windows usually does not pay for an ordinary house then.

Useful U-values

Modern energy-saving windows today have consistently U-values ​​between 0.9 and 1.1 W / (m²K). This already provides an excellent thermal insulation, the usual exterior wall insulation is appropriate. Also, the price-performance ratio of such windows is appropriate - after all, the window exchange must pay off even once.

Default values ​​of older windows

Which U-value an old window has depends mainly on the date of manufacture. Basically, one can assume that windows with a built-in date before 1995 are no longer up-to-date today.

The worst U-values ​​are found in windows built between 1975 and around 1985. There, the U-value of the window can well be at 2.0 W / (m²K) or even higher.

In some cases, however, window replacement of old buildings is not so sensible. This applies, for example, to very old box windows made of wood, which can consistently have quite passable U-values ​​- depending on the design often even 1.4 or 1.6 W / (m²K).

When it pays, and what payback period you have to rate read in this post.

Saving potential through new windows

Numerous online computers on the Internet promise to calculate the cent the exact annual savings potential through a window exchange. Such calculations should always be treated with caution, as they can by no means be exact.

What savings are possible depends on many factors:

  • the total window area (which you can often specify)
  • the location of the windows (on the south side, the solar heat partially recovers the energy losses)
  • the exact U-value of the current windows (often not exactly determinable and not known)
  • the type of heating and its efficiency (for gas condensing boilers, the savings are usually minimal)
  • the cost of heating (who heats with biomass, saves by the window exchange often only a little)
  • total insulation in the house (heat transfer values ​​of walls and ceilings)
  • the condition of the doors (doors also lead to heat loss)

An exact calculation is practically impossible.

Video Board: Windows: A cheap way to keep the heat and cold at bay