Condensation on Windows – How to Get rid?

Why do windows fog up from the inside?

Windows can fog up from the inside due to condensation, which occurs when warm, moist air comes into contact with a colder surface. The process is as follows: 

Warm, Moist Air Inside

When there is warm, humid air inside a room, and it comes in contact with a cooler surface, such as a window sash, the air near the window cools down. 

Cooling and Condensation

As the warm air cools down, its ability to hold moisture decreases. When the air reaches its saturation point, excess moisture begins to condense into tiny water droplets on the cold surface, which is often the glass of the window.

Condensation on the Glass

Condensation on Window

The water droplets on the glass create a foggy appearance. This is similar to how dew forms on grass in the early morning when the temperature drops.

Why do windows fog up from the outside?

Windows typically do not fog up from the outside. Condensation on windows generally occurs on the interior surface when warm, humid air inside the building comes into contact with a cooler window sash. This causes the air near the window to cool down, leading to the condensation of moisture on the glass.

However, if you are consistently seeing fog or condensation on the outside of your windows, it might be worth investigating further, as it could be a sign of other issues like problems with insulation or seals, or even an environmental factor specific to your location. In most cases, though, exterior window fogging is not a common occurrence. 

Several factors can contribute to the likelihood of window condensation: 

Temperature Differentials

The greater the difference in temperature between the inside and outside of the window, the more likely condensation is to occur.

Humidity Levels

Higher indoor humidity levels increase the chances of condensation. Activities like cooking, showering, or even the presence of many people in a confined space can contribute to higher humidity. 

Insulation and Ventilation

Poor insulation or inadequate ventilation can result in temperature differences that lead to condensation. 

Condensation on windows can cause several problems, including:

Moisture Damage

If condensation forms on the inside of the window, it can damage the surrounding wall or window frame. Over time, this can lead to mold and rot, which can compromise the structural integrity of the building.

Decreased Visibility

Condensation on windows can decrease visibility and make the windows appear foggy. This can be especially problematic for drivers, as it can impede their vision and make it difficult to drive safely. 

Reduced Energy Efficiency

Condensation on windows can indicate that the windows are not well-insulated, which can lead to energy loss and higher heating and cooling costs. 


If the condensation is not properly managed, it can lead to corrosion of the aluminum frame or other components of the window. This can compromise the integrity of the window and reduce its lifespan.

Poor Indoor Air Quality

Excessive moisture on the windows can increase indoor humidity levels, which can create an environment for mold growth and decrease indoor air quality.

To prevent condensation on aluminum windows, it is important to maintain proper ventilation and humidity levels in the home. Proper insulation and weather-stripping can also help to reduce energy loss and prevent condensation from forming on windows. If condensation is a persistent problem, it may be necessary to replace the windows with more energy-efficient models or to consider alternative solutions like dehumidifiers or improved ventilation systems. 

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