• 416-726-9977
  • info@greensaving.ca
  • 4438 Sheppard Ave East Unit #311, Scarborough, On M1S 1V2


This page is meant to answer your questions about condensation: why it occurs and how to prevent it. By understanding condensation you will be able to minimize it. Read on for more information.


Exterior condensation occurs on cool surfaces such as glass when moist air comes in contact with it. This happens most often during the fall and spring, when a warm day is followed by a cooler night. This type of condensation appears when the dew point in the air is higher than the temperature of the glass.

Low-E glass reduces heat conduction from the warmth inside the house to the exterior surface of the glass. An efficient Low-E coasted glass can reduce heat conduction by about 50 percent. The heat energy that has been reflected by the insulating glass reduces the temperature on the exterior surface of the glass. In this case, exterior condensation may form. This is actually an indication that the insulating glass in the window is doing its job.


Condensation occurs on the coldest area of the room, usually the window, when there is too much humidity in the house. The warmer the air inside the home, the more moisture it will hold. Once this air comes in contact with a cool surface such as glass, it is cooled as the resulted condensation forms on the glass.

The meeting rail and the interior of the glass at the bottom of the lower sash is where condensation most commonly forms. This results from warm air cooling and falling down the interior of the window. The water vapor escapes and forms on the meeting rails surface. The air continues down over the meeting rail and once again condensation forms under the lower handle of the sash.

The most important factor in reducing condensation is controlling humidity by creating air movement. Humidity levels need to decrease as exterior temperatures drop. To control condensation you must increase ventilation and control sources of moisture. To do this, you can:

1. Use exhaust fans in the bathrooms, kitchen and laundry.
2. Vent clothes dryers and gas burners etc. to the outdoors.
3. Keep humidifiers off.
4. Keep ventilating louvers in your basement, crawl spaces and attics amply sized and open.
5. Open fireplace dampers to give moisture-laden air a way of escape.
6. Air out your house as necessary.

© Copyright 2018 GreenSaving Windows and Doors