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Steamy windows in the winter? Solve this problem!

Sarah Tolle – Homify Canada Sarah Tolle – Homify Canada
Rustic style house by Giovanni Marra Architetto Counselor Rustic
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A sauna is supposed to be steamy, but your windows aren't! If you're among the homeowners who find a constant fog on their windows from November to March, we're here to tell you why it happens. There are negative consequences to steamy windows – heath problems, fatigue, allergies – but fortunately, there are also ways for you to fix it!

​What actually happened?

Misting is a common natural phenomenon associated with high humidity and high temperature difference between the inside and outside of the house. As outdoor temperatures and humidity lower in Autumn, the interior of a home is hot and humid by comparison. Steamy windows are evidence of the condensation of water droplets in the air of your home as it lingers next to the cool temperatures permeating your windows. This leads to condensation on the windows. Condensation on windows occurs when the relative humidity exceeds 60% of the temperature difference between the indoors and outdoors starting at 20° C. You'll notice that your windows will be steamier during household tasks that produce water vapor, such as cooking, baking, ironing, or taking a bath.

​Why do only some windows steam up?

The recommended humidity in your home's room is 40-50%. To avoid fogged windows, excess moisture must be systematically withdrawn from your home's environment. New homes built with fully functional ventilation systems are designed to  handle this, but older homes often lack the proper air flow and water drainage systems. Some home renovation projects like removing non-load-bearing walls in order to open up a space will solve your air flow problems naturally. A dehumidifier can also be an effective solution. Of course, you can have your home's air flow and heat loss assessed by a professional, who can help you to install a new ventilation system that keeps humidity in your home at 40-50%. Naturally, you can also just open a window in order to let in some drier, cooler air from outside, but this is not a long term solution, especially in places that experience very cold winters. Over the long run, working with a professional to re-configure your home's ventilation is best.

​What's the danger?

High humidity and inadequate ventilation are the causes of fungi. Mycotoxins are one of the most potent poisons of plant origin, and they are produced by molds and fungi that can multiply in buildings and homes. They can cause a variety of ailments, from allergies and respiratory diseases to headache, fatigue, liver, and kidney damage. Since molds have very low nutritional requirements and tremendous capabilities for adaptation, they can grow on virtually any surface – wood, paper, textiles, concrete, plaster, plastic. Remember, those steamy windows are not just obscuring your views – they might be sign that your household's lack of airflow is negatively affecting your health.

​Proper ventilation

Most often, steamy window problems arise when there are issues with the natural air flow of a home, and can also occur because of issues with a mechanical vent. However, you'll need to look beyond your bathroom ceiling vent fan for solving an air flow issue, addressing all of the points where air moves through your home, from the seals on the windows to heat ducts in the floor to the chimney. The best way to ensure efficient ventilation in modern housing systems is through the use of a supply-exhaust heated air supply – preferably with heat recovery or recuperation for saving energy. A system like this offers the benefits of air filtration, energy savings on recovered heat, and removal of odors, and with a good insulation method it will also prevent drafts and provide good sound insulation.


Temperature fluctuations in your home can result in the formation of excessive moisture and, consequently, mold and mildew. The trick is to keep all of your rooms at the same consistent level of heat, even if they aren't being occupied. You can determine if your interior walls are at a  sufficient temperature by making sure they stay at or above 17 degrees Celsius. Your furniture should also be several inches away from your walls in order to ensure airflow across their surfaces.

​Insulating your windows and walls

With many architects bringing out modern window designs with tight, energy efficient, insulated seals, many homes require a special window fan (a type of air conditioner) that draws in air and adjusts its humidity according to your interiors before moving the air into the room. If there's moisture on your windows only in certain spots, or if there are stains on your window sills, or if there's frost forming on the interior window panes, contact an insulation company. These issues are the result of poor insulation of windows and walls, or a damage or break in the insulating layer.

​What else can help?

Beyond changing your heating, ventilation, and insulation, you can also make small changes to your lifestyle in order to regulate humidity in your home. First of all, it's not advisable to dry clothes by placing them on radiators or heaters. Likewise, taking frequent baths or boiling large amounts of water will increase your humidity levels. Even frequent use of an electric kettle can have this effect. Also, remember to leave your heating elements (radiators, heat ducts) free from long curtains or large furniture that can block the heat distribution through a room.

Thinking of getting new windows? This ideabook is all about choosing the right materials for new windows and doors.

Think this steamy window advice is helpful? Comment below!
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