After we installed new plastic windows, they started sweating a lot when it gets cold. There's condensation on the glass, especially at night. The ventilation seems fine, but maybe the windows weren't installed properly?
Condensation on windows is more of a humidity problem in your home than an issue with the windows themselves, though installation can also be a factor. New plastic windows are very airtight, unlike old wooden ones, so moisture doesn't escape through gaps like it used to, but accumulates on the glass instead - this is completely normal. I noticed the same thing at my place after replacing the windows a few years ago.
First, check the following: do you cook a lot (boil water, make soups), do you often dry laundry at home, do you ventilate the rooms enough. For example, when I came back from school, I was boiling water several times a day - that's a huge source of moisture. If you turn on the kitchen hood and ventilate the rooms for at least 15 minutes a day, especially before bed, the condensation will decrease significantly.
If the sweating is really heavy even with normal humidity, the ventilation might be insufficient - ask the installers to check if the micro-ventilation system is installed correctly. Sometimes you need to adjust the window hardware. You can also put special water-repelling stickers on the glass or just wipe the windows with a cloth in the mornings - that helps me when during mushroom season I bring damp stuff into the house and don't have time to dry it.
They're right above about the airtightness. My friend ran into the same thing after getting new windows. The main thing is humidity in the apartment - new windows just don't let air through like old wooden ones do. Try ventilating more often, at least 10-15 minutes in the morning and evening, and make sure your radiators are heating well - the temperature contrast will reduce condensation. If it's really bad, it could be a poor installation job, call a specialist to check the foam and the sealing on the slopes, sometimes there are issues there.
I agree, airtightness is kind of a double-edged sword :) New windows don't let air through, so moisture builds up inside. Try ventilating more often, especially after cooking or showering, and check if your ventilation isn't clogged - sometimes when windows are installed, the vent channels accidentally get blocked. If it still fogs up after that, then yeah, it could be a faulty installation, but usually it's just about the humidity in the room.
It's actually usually not a problem with the windows themselves, but with humidity in your apartment. New plastic windows are super airtight, and if you used to have old wooden ones, they let air through literally everywhere - so moisture just escaped outside naturally. Now the moisture has nowhere to go, it condenses on the coldest surface, which is the windows. You especially notice it at night when the temperature on the glass drops below the dew point.
To fix this, you just need to get air circulation going in your apartment. Check if your ventilation is clogged - take off the grille and see if dust and debris have built up in there. Open your windows for ventilation, even if it's cold outside, for like 15-20 minutes a few times a day. And this is really important - make sure your heating radiators are working properly, because windows sweat way more when it's cold and humid at the same time in your place.
As for the window installation itself - if they're installed correctly, that shouldn't cause condensation, actually the opposite. Condensation appears precisely because the windows seal well, but the air in your apartment is humid. If you're still worried about it, call a technician to check it out, but in 99% of cases it's just about ventilating more often.
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