ᐅ Windows fog up, with high humidity causing mold growth on the window sills.

We have a problem with the windows in our single-family house. Since the cold season started, every morning our windows are completely fogged up. These are standard double-glazed uPVC windows. We ventilate and heat regularly, and a humidity measurement showed values between 45 and 55%. Room temperatures range from 19 to 22 degrees Celsius (66 to 72°F). In my opinion, these are normal values. What can I do to prevent the windows from fogging up? Sometimes the condensation is so severe that water drips from the panes and mold forms in the corners of the window sills.

Hello Konstantin,
there might be an error in the window construction, as the heat transfer seems too high.
However, warmer air condenses on cooler surfaces; at very low outside temperatures, this can also happen on the inside of insulated windows, but not at normal winter temperatures.

Have the window installer come and show them the fogged-up windows, and ask for their opinion.

I had similar problems in my old house. Did you perhaps have your walls newly insulated but kept the "old" windows? Humidity always condenses at the coldest spot in the room. You might need to replace your windows with triple-glazed units. How often have you measured the humidity? 45% to 55% is not very high, but it could be that the humidity rises significantly overnight. You should check that. I know it’s annoying to hear this repeatedly, but if the building structure is dry and in good condition, the only solution is more ventilation and heating.

Hello, I am a window installer.
The topic was window replacement. There are solutions that do not require full replacement. For double glazing, aluminum spacers were most likely used. It is possible to replace the panes while keeping the double glazing but using a TGI spacer instead. This spacer is made of plastic with a metal insert. Usually, upgrading to triple glazing is difficult because the narrow construction depth of old windows does not allow the glazing bead to accommodate triple glazing.

There are also soundproof ventilators.
Details:

Humidity-controlled supply air
Completely automatic without electrical wiring
Optional settings: off, on, or automatic operation
In automatic mode, the airflow is regulated according to room humidity using a humidity sensor (polyamide fiber tape).
30-year warranty on hygrostatic regulation. Supply air element rated at 41 dB
Suitable for all types of windows, as well as window frame extensions and roller shutter boxes

Attached photo

The solution described by the previous speaker is exactly right, as it can achieve very good results even without replacing the windows. However, it is still worth considering whether other damages might occur, because somehow the dew point has been shifted here.