When a substance changes its physical state from gaseous to liquid, this is known as condensation. In physical terms, condensation is the moist, misty film often seen on mirrors, tiles or window panes.
How does condensation form?
Condensation forms when warm, moist air reaches a cold surface. As soon as this warm air cools down, the excess water content turns into condensation. The window pane is a good example: even in winter it is warmed by the sun during the day to such an extent that no condensation can form. When the sun goes down, the pane starts to cool, so that at some point the water vapour in the air is deposited as condensation.
The higher the humidity, the greater the potential for condensation to form. Indoors, humidity is influenced by activities such as cooking, showering, breathing, sweating, steam ironing, washing up and so on. This explains why the air inside a room is always more humid than the air outside. The more people there are in a room and the more water is used, the more water enters the air and the higher the humidity. This is perfectly fine, because we humans feel uncomfortable when the air is too dry. However, the regular occurrence of condensation carries the risk of mould forming on the window. This can in turn be harmful to health.
Indoors, the necessary air circulation can be adversely affected by poorly positioned radiators, curtains or window sills. As a result, there can be insufficient heat circulation around the edges of the windows. The window cools down and condensation forms, despite regular ventilation and heating.
Tips to prevent condensation
One important measure to prevent condensation is to keep the room temperature as constant as possible. Ideal indoor climate values are:
- A steady room temperature of around 21°C
- Humidity of about 40-50%
The deviation from the room temperature should be no more than 6 °C at windows and no more than 2 °C at walls. Once these ideal conditions have been created, the likelihood of condensation forming on the window panes is rather low.
Optimal ventilation
As soon as condensation forms on the window panes, the room must be ventilated without fail. It is best to open the windows fully, depending on the season, and create a through-draught. So-called burst ventilation allows warm and cold air to be exchanged without cooling the room down as a side effect. With heating systems that have an automatic night-time setback, ventilation should take place before the heating temperature drops. This prevents condensation from forming as the air cools. In addition to ventilation, heating is also very important in order to create an ideal indoor climate. Windows that are constantly left tilted or ajar are not a solution here, as they cause the walls to cool down and, during the heating season, also lead to energy losses.
Reducing humidity
Here are some measures that help to reduce humidity:
- When cooking and showering, open the windows and keep the doors closed. This prevents moisture from spreading into adjacent rooms
- Avoid humidifiers or evaporators on radiators
- Do not dry laundry in living rooms, as this increases humidity
- Any condensation that has already formed must be removed regularly to prevent mould from forming
Condensation on roof windows
Very large temperature differences between inside and outside, as well as high humidity, encourage the formation of condensation. Windows are always the coldest surfaces in a room, which is why condensation settles there first. Roof windows are particularly susceptible to condensation. Because of their installation position, they are exposed to environmental influences even more intensely than upright windows. Any humidity already present is deposited here first.
