Why is my window covered with condensation?

Condensation of moisture on interior windows occurs naturally when interior air with sufficient moisture comes into contact with a cold window surface. 

Air can only hold a limited amount of water vapour at any given temperature. As warm room air comes in contact with a cool window surface, the air cools and loses the ability to hold water. If the moisture in the air is high enough or if the surface of the glass is cool enough, the water in the air will deposit on the glass surface. This is called condensation. 

Condensation typically appears on windows before any other surface because windows usually have the least insulation value of anything on an exterior wall and react the quickest to changes in outdoor temperature. 

When outdoor temperatures drop, you can reduce condensation in your home by limiting the amount of moisture in the indoor air. Routine activities such as cooking, showering and laundry add moisture to indoor air. Plants, fish tanks and humidifiers are also examples of common household items that contribute to indoor moisture.

You can reduce moisture by venting moisture-laden air to the outside and by bringing fresh, dry air from the outside into the home. Ventilation is accomplished in many ways. 

Exhaust fans placed near high sources of humidity, such as bathrooms and kitchens, are used to reduce localized humidity. Some new homes may also have a whole-home ventilation system. In its simplest form, this system consists of a central exhaust fan and a fresh air intake connected to the heating system. The system may be operated by a timer or by a switch located in a central position in the home. 

A more advanced ventilation system will recapture heat lost in the ventilated air and will have dedicated ventilation ducts in various locations throughout the home. Opening window coverings, even partially, during cold weather is an easy way to reduce condensation. Drapes can restrict air movement near the window which will cause the glass surface to cool, creating the perfect environment for condensation.

Heat outlets placed near windows wash the window surface with warm air. This increases the temperature of the window surface and reduces the potential for condensation. Do not deflect the movement of air away from windows or cover outlets with rugs or furniture. Finally, during periods of extreme cold, keep the furnace fan running to maintain a more even heat in the home.

If you have any further questions please don’t hesitate to contact a member of our team, we are always happy to help.

The video below is also a pretty good resource, it is American but does contain some helpful information.