Expert
blog
Monday 03 December 2018

Indoor condensation on windows and other surfaces: explanations, risks and solutions

“Why are my windows all fogged up?” This is a question we often get at this time of year, and it’s a sign of some concern. You’ll find a simple explanation below along with the risks you may be taking in not dealing with the situation, followed by some expert advice on air conditioning and heating.

Why is there condensation inside the house?

As soon as temperatures begin to drop outside, condensation can form on the inside of thermal insulation windows. Why do they fog up? Quite simply, this is due to the humid inside air condensing on the cold glass surfaces, which may mean interior humidity is too high. As warmer air contains more humidity, turning on seasonal heating can cause windows to fog up. And the colder it is outside, the more this condensation becomes visible.

How do you measure indoor humidity?

Humidity is measured with a device called a hygrometer, ideally an electronic one, that you can find in any good hardware store. Place it in the rooms where condensation occurs or in the main living area to determine if you have the ideal level of humidity.

What are the risks associated with improper humidity levels?

In addition to impacting materials and furniture inside your home, the wrong amount of humidity can harm your health.

  • Too humid (more than 60% relative humidity): With this much humidity in the air, mould and mildew can appear, and dust mites will proliferate. This can lead to allergic reactions and breathing problems like asthma.
  • Too dry (less than 30% relative humidity): Your breathing passages, nose and throat may become irritated, and you may experience difficulty breathing (especially if you suffer from asthma). Your skin may become dry (with accompanying irritation and red patches), and you may also develop dry eyes.

How do you lower indoor humidity?

Here are a few tips on how to lower the relative humidity inside your home:

  • Windows: Make sure your windows are in good condition. Recent thermal insulated windows are best. Fogged up windows are a sign insulation is inadequate.
  • Curtains: Don’t close your curtains during the day. Leave them open so the glass surfaces can warm up.
  • Shower: Spend less time in the shower. Turn on the bathroom fan or open a window to let humidity escape.
  • Kitchen: Put lids on your pots when cooking and always turn on your range hood fan.
  • Laundry: Avoid hanging your laundry indoors to dry. Make sure your dryer’s exhaust is pushing the moist air outside rather than inside your home.
  • Humidifier: If you have a working humidifier, make sure it isn’t set too high.

For more information on condensation problems, please don’t hesitate get in touch with us.
Our experts will be happy to answer all your questions and provide practical solutions.

Recommended Relative Humidity Levels

Source: Canada Mortgage and Housing Corporation
Outdoor temperature
(in °C)
Indoor relative humidity
(for a temperature
of 20°C)
-30° or less Maximum of 15%
-30° to -24°
Maximum of 20%
–24° to -18° Maximum of 25%
-18° to -12° Maximum of 30%
-12° to -6° Maximum of 35%
-6° to 0° Maximum of 40%