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It’s winter, you’re cooking up a storm, something warm and hearty like a stew, as you’re cooking you want to enjoy the winter scenery, but you can’t, because your window is fogged up and water is carelessly dripping down its pane.  Irritating? Maybe a little.  Destructive? Oh yah.

The occasional light condensation is not where the problem at hand lies, but excessive, persistent amounts can, over long periods of time, cause damage to your window frame and the wall below it, which may eventually lead to mold.

Condensation occurs when moist air comes into contact with a cool surface, such as a window or door.  Warm air contains more moisture, so when that air comes in contact with a cold glass surface it is then cooled and moisture is released in the form of condensation.

It’s a common assumption that condensation is caused by the window, which in fact isn’t true.  The ‘water’ is produced from our normal daily activities such as showering, cooking etc.  In order to reduce this condensation, humidity must be controlled and airflow generated.

To decrease or control excess humidity and condensation you can:

  • Install replacement windows with triple glazing.
  • Run exhaust fans in your kitchen, laundry and bathrooms longer and more frequently.
  • Vent gas burners, clothes dryers, etc. to the outdoors.
  • Shut off furnace humidifiers and other humidifying devices in your home.
  • Be sure that the ventilating louvers in your attic, basement or crawl spaces are open and adequately sized.
  • Open fireplace dampers to allow an escape for moist air.
  • Air out your house a few minutes each day by opening windows and doors.
  • Make sure your furnace is in proper working order and is serviced regularly.
  • Open window coverings – such as blinds or drapes – during the day to increase airflow over the glass.

Something to consider if you’re thinking about installing new windows.

A thermally efficient window with Low-E (E = Emissivity) glass will reduce the transfer of heat leaving your window warmer, minimizing the hot and cold differences that turns moisture vapor into condensation.  Low-E glass works by reflecting heat back to its source, it allows sunlight to pass through but blocks the damaging ultraviolet light.  In the winter when you’re heating your home, the radiant heat bounces off your windows and back into your home.  Conversely, in the summer radiant heat from the sun bounces off the window and back into the great unknown.


Thanks to Larry Jacobsen for the great image of condensation on a window.