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Condensation 101 – Is it time to change your windows?

With the warm weather upon us, you may only be thinking of condensation as something that appears on the outside of your glass of iced tea. But condensation on your windows is a whole other story. With many factors involved in these droplets of water appearing and fogging up your windows, you might be surprised to hear there are a lot of things you can do.  Here’s what you need to know.

What is condensation?

Condensation appears when warm moist air comes into contact with a colder surface. Water collects as droplets on a cold surface such as on a window on a cold winter day or on your cold glass of iced tea on a warm Summer day.

What causes condensation?

Everyday living creates a surprising amount of moisture. Cooking three meals a day adds 10 or 15 litres of water a day. Every shower generates another 1/4 litre. Every activity that uses water adds moisture. Regardless of its cause, the moisture source doesn’t have to be where the condensation appears. Vapour pressure can actually force moisture through brick, wood, plaster and cement.

Interior window condensation is caused by excessive moisture in the house, and it often occurs in the winter when the warm air inside the house condenses on the cold windows. Exterior window condensation is simply dew and occurs when the window is colder than the dew point.

Does condensation mean you have bad windows?

Condensation on your windows doesn’t mean there’s a problem with your windows.  In fact, the presence of condensation, can be a sign that your windows have a good tight seal.

Everything that makes homes more energy efficient such as windows and patio doors that reduce air leakage, weather stripping, modern insulation, vapour barrier and new construction techniques also lock moisture inside your house and increase the chances of condensation forming.  

With cooler nights and warmer days in the Spring and Fall, condensation can also appear on the outside of your windows. This is usually a good indicator of energy efficient windows. Low-E glass is designed to maintain comfortable conditions inside by reducing heat loss through the window, in some cases cutting heat transfer by 50 percent. As the glass reflects the heat energy back into the room, the temperature of the glass exterior falls, which can lead to condensation.

What can you do?

You can reduce condensation on your windows by promoting air flow and reducing humidity inside your home. As the temperature drops outside, your humidity levels may rise.

The amount of moisture in the air is often called “relative humidity” or “RH” for short. RH is important because it provides a way to assess moisture conditions and condensation risk in a home. RH run from 10-100%

Your first step should be to purchase a hygrometer, an instrument that measures the RH. Hygrometers can be purchased at a local hardware or building supply store. They are relatively inexpensive.

  • In very cold weather, a level of 30 percent or lower may be needed to prevent window condensation.
  • In the winter heating season, the relative humidity should not exceed 45 percent.

Here’s a helpful indoor humidity scale:

Now that you can measure the RH, here are some of the things you can do to control humidity levels inside your home:  

  1. Raise the temperature of the windows by raising the temperature of the home
  2. Use an exhaust fan in the kitchen every time you cook
  3. Run an exhaust in the bathroom when you shower until the mirror is clear
  4. Turn off or turn down humidifiers when they aren’t needed.
  5. Circulate the air by running a fan even in the winter (rotate in a clockwise direction to push warm air off the ceiling back down to the floor).
  6. Vent your attic and crawl space
  7. Ensure that all ventilation channels leading outside are unobstructed.
  8. Open your windows allowing air to circulate freely through your home for short periods every day.
  9. Don’t air dry wet clothes inside
  10. Move your plants away from your windows
  11. Don’t store fire wood inside
  12. Occasionally open the fireplace damper to allow moist air to escape

TIP: For condensation outside the windows, use RainX on the exterior of your windows. It makes the water gather together and run off the window. There is also Active glass that self cleans and will better resist exterior condensation.

What about condensation between your window panes?

  1. Try cleaning first, it may simply be build up and not condensation
  2. Replace the thermal unit; may or not be possible depending on the type, age and manufacturer of the original window.
  3. Replace the windows

If the condensation issues are not improving, it may be time to consider replacement windows or at the least, consulting with a professional window installer for more advice. Our Windows and Doors  experts will be happy to answer all of your window condensation questions and help with your window replacement needs.

Schedule your FREE In-Home Estimate

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