Why do the windows fog up?

Fogging of windows is a common phenomenon that we often observe, especially during transitional periods, such as autumn and winter. The main cause of window fogging is the temperature difference inside and outside the room and air humidity. When warm, moist air from inside the room comes into contact with the cold surface of the glass, water vapor condenses, forming visible water drops.

Water in windows comes from condensation of water vapor in the air. Indoor air contains a certain amount of moisture, which comes from various sources, including: washing and drying clothes or cooking. When air rich in moisture comes into contact with cold glass, water vapor condenses to form water droplets on the glass surface.

What affects window fogging?

Several factors influence the intensity of window fogging:

1. Temperature – The greater the temperature difference between inside and outside, the greater the likelihood of condensation.
2. Humidity – Higher indoor humidity increases the risk of evaporation.
3. Ventilation – Improper ventilation leads to the accumulation of moisture inside rooms.
4. Window quality – Poorly insulated windows are more susceptible to condensation.

Choosing the right windows is key to minimizing evaporation and the overall energy efficiency of your home. Here are some factors worth paying attention to:

1. Type of glass
   • Insulating glass – Double (or triple) glazing with a space filled with gas (usually argon) between them, which improves thermal insulation.
   • Low-emission coatings (Low-E) – These coatings reflect heat back into the room, which helps maintain a constant temperature and reduces condensation.
2. Window frame
   • Material – Frames made of PVC, wood or aluminum with a thermal break provide better insulation.
   • Seals – Good seals around the window frame prevent moisture and cold air from entering.
3. Heat transfer coefficient (U)
   • U value – A low U-value (measuring the window's thermal transmittance) means better thermal insulation. For modern windows, this value should be less than 1.3 W/m²K.
4. Acoustic and thermal insulation
   • Additional layers of glass and special fillings – They improve acoustic and thermal insulation, which is especially important in noisy or cold regions.

How to prevent windows from fogging up?

There are several effective methods to prevent windows from fogging:

1. Improved ventilation – Regular airing of rooms helps remove excess moisture. Ventilation systems can be installed to ensure adequate air circulation.
2. Maintaining the right temperature – Maintaining a constant, moderate temperature in rooms reduces temperature differences between the inside and outside.
3. Using air dehumidifiers – These devices help maintain the appropriate level of humidity in rooms.
4. Using curtains and blinds – They can create an insulating barrier between the interior and the glass, reducing the risk of condensation.
5. Installing better quality windows – Windows with better insulating properties (e.g. double or triple glazing) are less susceptible to fogging.

Fogging of windows is a natural phenomenon resulting from differences in temperature and air humidity. To minimize this problem, it is important to ensure adequate ventilation, control humidity levels and invest in high-quality windows. Thanks to these steps, we can effectively prevent moisture from forming on the windows and enjoy clean windows all year round. Choosing the right windows, with the right technical parameters, is crucial for the comfort and energy efficiency of our homes.