For homeowners

Condensation often occurs during colder weather when the moist air inside the home comes into contact with cooler surfaces. The moisture in the air can condense to form water droplets or even frost. The risk of condensation increases as the weather gets colder and/or the inside humidity rises. Condensation can form:

• on the glass
• on the frames and sashes
• near the weather seals
• between the glass panes if the seal is broken

Insulating units that use high-performance low-e glass are designed to reduce the heat that flows from inside the building through the glass to the outside during cold weather. Since the insulating unit keeps more heat inside, the outside glass surface stays colder.

Exterior condensation occurs when moist air comes into contact with cool surfaces, such as glass. This type of condensation appears when the dew point in the air is higher than the temperature of the glass. This occurs when a cool night follows a warmer day, typically during spring and fall.

Condensation is a result of temperature differences between the outside and inside. In the summertime, if condensation occurs, it will be on the outermost pane of your window as now your home is likely cooler than the warm air outside. This is also a result of the temperature difference.

Condensation in a home can be stopped by reducing humidity and increasing ventilation. Less humidity in the air means less water vapour to turn into condensation. Increased ventilation provides a way for water in the air to escape.

There are simple steps you can take to avoid or reduce condensation, for example, early morning exterior condensation.

1. Buy high-performance ENERGY STAR® certified windows, doors and skylights. They are more energy efficient and have less condensation compared to ordinary models. They are more energy efficient and have less condensation compared to ordinary models. Features that contribute to better energy efficiency are:

• Triple glazing.
• low-emissivity (low-e) coatings on the glass
• inert gas between the glass panes
• insulated frames, sashes and doors
• greater air tightness

Note: Low-e coatings on high-performance windows make the glass more energy efficient by reducing heat loss. However, if the night has been cool and calm and the air is humid, condensation may form on the outside surface of the glass around sunrise. Also, there is a higher risk of condensation if the low-e coating has been applied to the room-side surface of the glass.

2. Proper air circulation near windows is also necessary to minimize condensation. Airflow across the glass surface helps keep it warmer, which is one reason heat sources such as central heating vents and electric baseboards are located beneath windows in many homes. Deep window sills, closed drapes and blinds, and even nearby furniture can block air movement and allow cool air to pool near a window, leading to condensation on the glass.

3. Make sure your Heat Recovery Ventilator (HRV) is on if you have one.