U value at the old window

Of course, anyone who has old windows in his house knows that they give away a lot of heat and are particularly negative in terms of energy efficiency. But how big the problem actually is expressed in numbers, the fewest can find out. Here we show which U value your windows probably reach and what value new windows offer.

Glazing and exchange

That a window with a single glazing should be replaced as soon as possible, is clear to everyone. Its U-value will probably be around 5.5 W / (m²K). According to the experts, these windows should reduce the heat loss by about 60 liters of heating oil per square meter of window area. But how urgent this replacement is with a double glazing, you should check.

double glazing

It has many names, the double glazing. Whether they are referred to as insulating glass panes or Thermopenfenster but does not matter, important is their age and the nature of the insulating layer of air between the panes. Depending on the age of this double glazing, a U-value between 2 and 3 W / (m²K) can be achieved with these windows. As a result, this window wastes only half of the above-mentioned single glazing.

Although the surface of the windows will no longer be decorated with frost flowers in winter, the temperature on the surface of the window can still drop to around six to seven degrees. This is a guarantee of moisture and mold around the frame and along the window fold.

  • Single glazing 5 to 6 W / (m²K) - about 60 liters of heating oil per square meter
  • Double glazing 2 to 3 W / (m²K) - about 30 liters of heating oil per square meter
  • Double glazing with gas filling in the space between the panes 1.2 to 1.7 W / (m²K) - about 10 liters of heating oil per square meter
  • Triple glazing with gas filling in the space between the panes 0.8 to 1.0 W / (m²K) - no more loss

Tips & Tricks

Just take a look at the surfaces of your windows. The loss of heating costs is finally always calculated on one square meter of window area. If you have very large windows with double glazing, there are several liters of fuel oil or gas that you have to pay. This will allow you to roughly calculate when new windows will pay off.

Video Board: Window U-value calculation