How to avoid condensation on windows during cold months

Moisture buildup on windows may be common in winter months, but that does not mean it should be shrugged off.

How does condensation form?

Condensation will often occur during colder weather when the moist air inside the home comes into contact with cooler surfaces, like a window. The risk of condensation increases as the weather gets colder and/or the inside humidity rises.

Air is only able to hold a specific amount of moisture before it reaches saturation and is then forced to condense and form dew. This could appear as fog or water droplets on your windows. You can reduce condensation on the windows by limiting the amount of moisture in the indoor air.

How to reduce the condensation on windows?

There are simple steps you can take to avoid or reduce condensation. Let us begin with some theory.

One of the most important things to understand when it comes to preventing condensation on the inside of windows is Relative Humidity.

In the simplest of terms, Relative Humidity refers to the level of moisture in the air at a given temperature in relation to the maximum level of moisture that air can hold at that same temperature.

There are tools, such a dehumidifiers and hygrometers, that can help you determine what the Relative Humidity level is in your home.

Next, you will want to determine what the ideal Relative Humidity should be. 
Based on outdoor temperature, your ideal home humidity levels will fluctuate:

Recommended Home Humidity levels based on outdoor temperature

Temperature Indoor Relative Humidity
0 °С 40%
-5 °С 35%
-10 °С 30%
-20 °С 25%
-25 °С 20%
-30 °С 15%

Once you have determined what the ideal humidity level should be in your home, then you can begin work on managing it.

Practical Guidance, Instructions & Tips

air circulation

1. Create better air circulation/increase ventilation in your home.

The movement of air helps moisture to evaporate. Increasing air circulation and establishing adequate ventilation is an essential step in reducing the formation 
of window condensation in your home.

air circulation near windows

2. Proper air circulation near windows is also necessary to minimize condensation.

Air flow across the glass surface helps to keep it warmer, and that 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, which can lead to condensation on the glass.


3. Make sure your HRV is on.

If your home is equipped with HRV (Heat Recovery Ventilation), make sure to turn it on and set it to run for about 20 minutes/hour. If the frost and ice build up on windows are particularly bad, try running the HRV continuously, until the issue is resolved.

ventilation switch

4. No HRV? Turn Ventilation switch on instead.

If you have a ventilation switch instead of an HRV, turn it on (day and night) during cold, winter months. This will help maintain air circulation in your home. (Having trouble finding the ventilation switch? It should be located next to your thermostat and will likely be labelled.)

ventilation in shower

5. Useful tips for new homes!

When moving into a new home, it is also suggested that the HRV or Ventilation Switch remain on for at least 2–4 hours per day for the entire first year. Additionally, you should run your ventilation systems for at least 
20 minutes after showering and 10 minutes after cooking.

window lock

6. Make sure all your windows are locked.

If you leave your window lock open, the frost and ice buildup that may appear on your windows will also appear inside the locking mechanism. You might remember from elementary science class — water expands when frozen. The additional pressure from the ice may damage and potentially ruin 
the locking mechanism for your windows.

air filter

7. Check and clean various filters.

Checking and cleaning furnace filters, air ducts and your HRV system is also good practice to ensure that your home’s winter performance is energy efficient and effective. You should also check and clean your humidifier’s filter if you have one.

exterior vent

8. Check and clean exterior vents.

It is also recommended that you check exterior vents on your home and be sure 
to remove and snow or ice buildup.

Some other routine or daily practices you may want to implement include:

  • Shortening the time spent in the hot shower.
  • Running your bathroom exhaust fan during and after showering for a minimum 
of 30 minutes.
  • Covering boiling pots of water.
  • Running the range hood fan while cooking and for an additional 10–20 minutes after.
  • Opting to use the dryer or hanging clothing outside (when weather allows) instead of hanging clothing to dry indoors.
  • Opening blinds or window coverings to allow airflow.
  • Moving furniture so it is not touching outside walls.
  • Removing items from window sills.
  • Leaving bedroom and other room doors open to allow better circulation.
  • Storing firewood outdoors.

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