ᐅ Glass panes fogging up on the inside during cold outdoor temperatures – troubleshooting the causes

As soon as the outdoor temperature approaches 0°C (32°F), we notice the following situation in our living room (see attachment). The glass panels of the sliding door fog up heavily overnight from the inside, causing water to run down the glass and form puddles at the bottom.

It should be mentioned that the windows on the left side of the picture have already been replaced with triple-glazed units, while the mentioned door has not been renewed yet (age unknown). The water always forms behind the closed pleated blinds overnight, when the room temperature drops.

Now I’m wondering if this effect is due to the age of the sliding door, meaning that its surface is colder and condensation forms there, unlike on the newer windows. Or does the condensation appear only there instead of on the newer windows because there is a radiator below the latter, which prevents it?

Or could there be completely different issues causing this?

Thanks in advance for your opinions.

Regards
N

What are the temperature and humidity levels?

Nanopixel schrieb:

closed pleated blinds overnight,

here lies the problem... it’s always an issue in winter.

Daytime temperature is 21°C (70°F), nighttime 17°C (63°F). Humidity ranges between 50 and 60%.

However, the drawn pleated blinds cannot be the sole cause of the problem, as the newer windows also have them closed, yet no moisture forms there.

Older windows tend to be colder than newer ones, which causes moisture to settle here.

Increase the indoor temperature at night or take measures to reduce humidity.

Nanopixel schrieb:

Is this effect due to the age of the sliding door, making the surface colder so that water condenses there but not on the newer windows? Or does the condensation only appear there instead of on the newer windows because the radiator is located underneath the latter, preventing it?

I believe both factors contribute to this distribution. Triple glazing might reduce the problem but probably won’t eliminate it, especially as long as the pleated blinds prevent the air from reabsorbing the moisture back into the room.