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What Causes the Condensation on Your Home’s Windows?

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March 4, 2024

When temperatures decrease and small droplets of water or a thin layer of frost appear on your windows, it may lead you to question the quality or effectiveness of the windows. After all, windows are supposed to keep the elements out of your home. However, it is important to understand why fluctuations in temperature can cause water to accumulate on your window panes.

The presence of moisture or frost on windows is primarily a result of condensation. Condensation occurs when warm, humid air comes into contact with a cold surface, like a window pane. As the warm air cools down upon reaching the window, its ability to hold moisture decreases, causing the excess moisture to turn into liquid or solid form on the window.

This phenomenon is particularly common during colder months when the temperature difference between the inside and outside of your home is significant. When you use heating to keep your home warm, the indoor air becomes more humid. As this warm, moisture-laden air comes into contact with the colder window surface, condensation occurs.

Condensation on windows is actually a good thing, as it means your windows are effectively insulating your home and keeping the heat inside. High-performance windows are designed to maximize the sun’s heat during cold months and maintain a significant temperature difference between the indoor and outdoor panes of glass.

When this temperature difference increases and the humidity in your home reaches certain levels, condensation may form on the windows and doors. This is similar to how water droplets form on a cool glass of water on a hot summer day. It is important to note that condensation on windows does not indicate a leak but rather the collection of moisture from saturated warm air on a cooler glass surface.

There are several factors that can contribute to window condensation, and there are steps you can take to improve or prevent it. By addressing these factors, you can reduce condensation and maintain a comfortable and dry environment in your home.

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Window Condensation and Airflow

Do not underestimate the importance of airflow. To minimize window condensation, it is crucial to ensure proper air movement in your home. Utilize fans to encourage circulation and ensure that your bathrooms and kitchen have adequate ventilation with exhaust fans that release air outside. The same principles should be applied to laundry areas as well, as dryers can emit significant amounts of water vapour if not properly vented outside. Remember, maintaining good airflow is key to reducing window condensation.

Other Factors At Play

There are several unexpected items in your home that can contribute to an excessive amount of moisture in the air. For instance, if you store unseasoned firewood indoors or have numerous indoor plants, especially on window sills, these can create a more humid environment where condensation may occur.

Additionally, if you have a large family, this can further increase the moisture levels in your home. Surprisingly, normal breathing and perspiration from a family of four can introduce around half a pint of water into the air every hour, and cooking can contribute an additional four or five pints.

Pay Attention to Bigger Issues

A significant problem may occur if groundwater seeps through the foundation and causes excessive moisture in your home. To prevent this, it is important to ensure that your home has appropriate gutters, flashing, and downspouts, which will help channel water away from your foundation.

In some cases, dirt floor crawl spaces can contribute to moisture issues, so it is advisable to either vent these spaces or cover them with plastic to create a vapour barrier. Seeking the assistance of a professional in the field of building construction can help you identify and effectively address these potential causes of excess moisture in your home.

Take the Age of Your Home into Account

Excessive moisture is not only a problem typically found in older homes. It can also occur in new or recently renovated homes due to the moisture present in building materials like wood, plaster, and cement. When you turn on the heating system for the first time, this moisture can be released into the air and condense on your windows. However, you can expect this issue to resolve itself after the first cooling season in your home.

During the Coldest Months, Reduce Heavy Window Treatments and Raise Your Shades

While it may seem unexpected, using heavy window drapes and blinds can actually contribute to increased condensation on the glass. This occurs because these coverings can trap warm air against the cold surface, resulting in more moisture buildup compared to having the window exposed to the room. To minimize condensation, it is advisable to keep your window coverings open during the day when it is cold outside. Additionally, it is best to avoid using heavy drapery when dealing with window condensation.

Get to Know Your Humidity Levels

To determine the cause of moisture on your windows, it’s advisable to test the relative humidity in your home. Maintaining indoor humidity at 25 to 30 percent is recommended as a comfortable level. You can conveniently measure your home’s humidity levels using a hygrometer, which can be found at most hardware or home improvement stores. Additionally, certain smart home thermostats are equipped with the capability to monitor your home’s humidity levels.

The Cold Hard Truth: Old Windows and the Need for Energy-Conscious Choices

After replacing older or original windows with new ones, you might notice an increase in condensation. However, this doesn’t necessarily mean that your original windows were of better quality. In fact, the reason for this is that the insulation and weather-stripping in older windows allowed for more air circulation, allowing drier air to mix with more humid air.

Nowadays, windows and homes are designed to be more energy efficient, which means that humid air can get trapped inside the house more easily. So, the presence of more condensation simply indicates a change in the ventilation of your home rather than the quality of the windows.

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Understanding and Controlling Window Condensation

To better understand the source of moisture and methods to reduce it, it is essential to address condensation issues. Additional information and advice can be obtained from reliable sources such as Naural Resources Canada and These resources can provide valuable insights into controlling humidity and gaining a deeper understanding of the causes of window condensation overall.



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