Why do my windows have condensation?

Condensation appears when warm, humid air meets a colder surface. On the indoor face of the glass, it is often tied to household humidity (cooking, shower, dryer, too little ventilation).

New windows: sometimes more indoor fog

Yes, that can happen — and it is not necessarily a product defect. Better windows are tighter: they let far less air escape outdoors. Humidity therefore stays more in the house. Result: fog on the indoor face can be as frequent, or more so, than with old sashes that “breathed.” You then need to ventilate and control humidity (often around 30 to 50% in winter), not only change the glass.

Indoor vs between the panes

Fog on the room face: indoor humidity (and sometimes still-cold glass). Fog between the panes: sealed unit likely failed — then the window (or glass) needs to be fixed.

What to do

Reduce humidity (ventilation, heat-recovery ventilator, range hoods used properly), and have the sealed unit checked if fog is trapped between the panes. A new window improves comfort and airtightness; it does not fix an overly humid, poorly ventilated house.