Condensation on the outside of windows occurs mainly because the glass surface is colder than the dew point temperature of the outside air. This happens when warm, humid air comes into contact with a cooler window surface, causing moisture to condense on the outside. It is a natural phenomenon that usually happens in conditions of high outdoor humidity, little or no wind, and clear night skies, often early in the morning after a cool night. This type of condensation indicates that the windows are energy efficient, as modern well- insulated windows keep indoor heat inside, leaving the outer glass cooler than the outside air. It is not a sign of a window problem but rather shows effective heat retention inside the home. As the sun warms the glass, the condensation evaporates naturally. Factors contributing to outside condensation include high humidity, low wind speed, clear skies causing radiative cooling of the glass, and surrounding environmental conditions limiting air circulation. It can often be seen during seasons like spring and autumn when the dew point is higher than the surface temperature of the glass. In summary, outside window condensation is caused by the glass surface cooling below the dew point in warm, humid conditions, mainly due to heat retention features of modern windows and specific weather conditions. It is a normal occurrence and not usually a cause for concern.
