Condensation on windows is one of the most common complaints homeowners have — and it's often misunderstood. Internal condensation (on the room side of the glass) is caused by warm, moist air hitting a cold surface. It's most common in kitchens, bathrooms, and bedrooms, especially on cold mornings.
External condensation (on the outside of the glass) is actually a sign that your glazing is working well — it means the outer pane is staying cold because very little heat is escaping through the unit. This is normal with modern low-emissivity glass and usually clears by mid-morning.
Condensation between the panes, however, is a clear sign that the sealed unit has failed. The gas fill has escaped and moisture has entered the cavity. When this happens, no amount of ventilation or heating will fix it — the unit needs replacing.