Do windows cause condensation?

The Basics.

As winter approaches, or as cold weather sets in, you may notice condensation appear on your windows and doors. This is a result of high humidity and low temperatures. Fog or water droplets are all forms of condensation. They can either block your view to the outdoors, drip on the floor or freeze on the glass…a similar effect can be seen on your car windows during humid weather or bathroom mirrors after a hot shower.

In essence, condensation forms when warm and humid air reaches a cold surface. The better insulated the glass, the higher possibility to witness condensation on the exterior of the surface of the glass, especially in fall and spring. Environmental factors such as humidity and airflow can affect the duration and the extent of condensation.

Do windows cause condensation?

Windows do not cause condensation, but they are the first place that you’ll be able to see it. Regardless of the window type or material (wood, aluminum, PVC, etc.) excess humidity will condensate on any window.

During cold wintery months, air on the inside of the house will be much warmer compared to summer months and therefore hold a lot more moisture than outdoor air. As the warm humid air reaches the cooler window surfaces, this moisture in turn condensates on the glass.

Where is it?


If condensation occurs on the exterior, this is usually a good sign. Condensation on the exterior is common during the summer because of high humidity and little wind. Condensation appears on the exterior as it shows your home is keeping the hot air out while keeping the cool air in.


If condensation appear on the inside, it is because there is too much humidity in the house, which in turn increases the moisture in the air. Condensation on the inside usually appears during the winter, especially during the beginning of the cold wintery months because as the exterior temperature quickly drops, the inside surfaces become cooler. The cooler the exterior air, the more likely condensation will occur on the inside.

Between the glass

Very rarely will you witness condensation in between the glass. This is usually the sign of seal failure. Condensation in between the glass will likely appear at the bottom of windows. As the warm air rises, condensation will show near the bottom because humidity is attracted to cooler air.

Reducing indoor humidity.


Increased ventilation is a great way to reduce indoor humidity, especially over large surfaces of glass. Without air flow, condensation can be expected which does not mean something is wrong with the window but simply that not enough air is hitting the glass. This could be verified by just putting a portable fan to push air in front of condensating positions and you will notice all signs of condensation would go away.

As a temporary solution, you can also open a window. This would let all humid air escape and allow dry air back in.


Controlling indoor moisture is also recommended to mediate the extent and length of condensation. Humidity levels can be monitored with humidistats.

Frequently Asked Questions.

What is condensation?

Condensation can appear on windows in the forms of fog or water droplets.

What is humidity?

Humidity is water vapor (or moisture) that is found in the air. It is visible in forms of steam or fog but whether or not visible, all air contains some type of moisture.

Why are my windows and patio doors condensating?

As temperatures start to drop in winter months, warm air in the house comes into contact with cool glass surfaces.

Do windows or patio doors cause condensation?

Windows and doors do not cause condensation. Large glass surfaces provide a cool surface whereby water vapor can condensate. Condensation, however, does first appear on windows because they have low temperatures among other visible surfaces in the house.

Can windows lower moisture levels?

Aside from allowing for more ventilation in a given room, windows cannot prevent or reduce moisture. Windows, or any large surface of glass, can only act as indicators of moisture in the air in the form of visible condensation.

Do curtains or blinds cause condensation?

Although these do not cause condensation, curtains, blinds or any window covering application can restrict air flow over glass surfaces. Condensation is more likely to occur when curtains are closed and blinds are rolled down.