Customer asks:

On cold mornings, the outer panes of some buildings’ windows are fogged up or even frozen. Why is this? I am planning to buy windows soon. What should I keep in mind when ordering so that the windows remain clear and transparent?

Aru Grupp answers:

Condensation on windows:
Condensation forms on the outer surface when the glass surface is much colder than the air and the dew point (the temperature at which water vapor in the air begins to condense) is higher than the temperature of the glass.

The temperature of the outer surface of the glass unit is affected by:

• Heat transfer through the glass – paradox: the better the thermal insulation of the glass unit (lower U-value), the greater the likelihood of condensation forming on cold mornings!
• Movement of outside air (convection).
• Heat radiation – solar radiation or surrounding heat sources.

What to consider when ordering new windows:
To keep your windows clear even on cold and damp mornings, choose Anti-Fog glass for the outer pane of your glass package, which reduces condensation and allows for a clear view outside.

See also: https://arugrupp.ee/en/aru-slimline-a-really-good-window/