condensation on windows

hello,
my new pvc windows sweat on the inside, and this is in a 25-year-old house without any residual construction moisture. I have 22C indoor temperature in the living area and 19C-20C in the sleeping area (currently it is 0C outside). My indoor humidity level is 53. I ventilate twice a day for a minimum of 5 minutes with the windows fully open. The doors in the rooms are only closed at night.
Question: how do I get rid of the condensation? Increase the floor heating or rather heat less?
Best regards hsgl

Hello hsgl,

This "sweating" is caused by condensation of warm room air on the cold glass; cold air or building surfaces absorb less water vapor than warm air, warm air condenses into water on cold surfaces.
You should not need to set the heating any higher, that could indeed lead to a sufficient temperature of the inner pane – but it would be uneconomical.

Has it always been like this, or is the fogging of the panes rather new?
The measured values for temperature and room humidity in any case should not lead to condensation on the inner pane with flawless windows.
If the windows are as old as the house itself, the seals between glazing and frame may be defective, so that the inner pane cools down more than planned.

Hello and thank you for answering me, the windows are made of pvc and are only 1 year old. With the old windows, we never had that. Best regards hsgl

Hello again,
With new/modern ISO windows, this should not happen; have you already contacted the window manufacturer? You have a 2-year warranty; in a SIA contract, the contractor bears the burden of proof within the first two years – in a contract according to OR, the burden of proof is always with the client.

You can measure the surface temperature of the inner pane.
That would be a start to get to the bottom of the problem.

Hello hsgl,

I agree with the colleague. To add, possible causes could also be:
- the installation position within the wall, as this influences the temperature distribution in the window
- whether the glass surface is accessible for air circulation (convection) or obstructed by curtains, drapes, or plants

Where does the condensation occur? On the surface or in the lower part around the edge seal?

Regards BAUfindus

hello and good day,
the condensation only occurs in the lower window area.
the windows are not obstructed by curtains or drapes.
the air circulation is ideal as the doors are usually open throughout the entire living floor except at night.
the facade is insulated with 15cm.
the windows were installed on the inside of the insulation.
the only cold bridge present is the shutter box mounted on the outside of the window.
i rather believe in an overly sealed house due to the new tighter windows.
fmg hsgl