During the winter months, the ambient temperature outside drops significantly, while the warm air inside your home remains humid. When this warm, moist air comes into contact with the cold surface of a window, it cools and condenses into water droplets. If the temperature is low enough, these droplets can freeze, forming an icy layer. This phenomenon is particularly prevalent in older homes with single-pane windows, which lack the insulation properties of modern double or triple-pane windows.
The problem is exacerbated in rooms with poor ventilation, as the humidity levels tend to be higher. Activities like cooking, showering, and even breathing contribute to indoor humidity. For instance, a family of four can add up to 12 liters of moisture to the air each day just through daily activities. Without proper ventilation, this moisture-laden air continuously condenses on cold surfaces, creating those pesky icy windows.