What Causes Window Condensation and How Do I Get Rid of It?

January 4, 2022

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Like a cold glass of lemonade on a summer’s day, condensation occurs when the temperature on one side of the glass is drastically different from the temperature on the other side of the glass. While condensation on your windows can be frustrating, creating an unpleasant aesthetic and blurring the sights outside, it’s typically not concerning. And the good news is you can minimize or prevent condensation on windows with a few easy fixes.

Common Causes of Window Condensation

Although it might look like an issue, moisture on your windows doesn’t necessarily indicate a problem. In fact, window condensation can be a sign that your windows are forming an airtight seal, reducing air leakage and keeping the moisture inside your home.

Most of the time, moisture on your windows is a matter of temperature and humidity. When the air is hotter and more humid on one side of the glass, moisture collects on the window panes.

In winter, condensation can form on the interior of your windows because it’s cold and dry outside but warm and humid inside. In the summer, it’s the opposite. You may see condensation on the outside of your windows in the morning from dew — just as it forms on your lawn. If there’s moisture inside your home, it’s likely because it’s become too humid indoors. Now, if you can’t easily remove window condensation by wiping the glass, the moisture is between the panes. And that’s a sign of a bigger issue.

How to Prevent Condensation on Windows

Inside, outside and in between, each type of window condensation has a different set of solutions. So your first step is to figure out where the condensation is coming from. Once you identify where it’s at, try out these tips to stop condensation on your windows.

Interior Window Condensation

When you have condensation on the inside of a window, or roomside condensation, it’s a sign that the humidity inside your home is higher than it is outside. The humidity inside your house can be impacted by a number of things, including cooking, showering, houseplants and even laundry.

A comfortable humidity level inside a home varies depending on your climate and the time of year. Too low, and you may see warping of your woodwork or static electricity build-up causing you to get a small “zap” when you run your feet across the carpet before touching metal. Too high and you may risk dust mite infestation, air quality issues and condensation on walls, windows and other surfaces.

According to the Environmental Protection Agency (EPA), the relative humidity in your home should always be below 60 percent. Ideally, you want it somewhere between 30 and 50 percent. It’s normal to be on the lower end of the range (or slightly below) during winter months.

Preventing Window Condensation on the Inside

Stopping condensation on the inside of your windows starts with measuring the relative humidity. The EPA recommends picking up a hygrometer — a small, inexpensive humidity meter you can find at your local home improvement store or big-box retailers. Some home thermostats, like new smart thermostats, have a humidity meter built-in. Once you know how humid it is inside your house, you can take measures to bring the levels down:

  • Open window treatments. Condensation is more likely to occur when drapes are closed or shades are pulled down. Try drawing your treatments so the heat isn’t trapped on your window pane.
  • Circulate the air. The same way a gentle breeze can take the edge off the humidity outside, some air circulation can do wonders indoors. You can use ceiling fans in a clockwise direction — even during the winter — to move warm air from the top of your room down.
  • Turn down the humidifier. If you’re using a humidifier — in a nursery, to treat a cold or as part of your furnace — turn it down or off for a while until the relative humidity comes down.
  • Ensure proper ventilation in your home. Some areas are more prone to moisture, like your kitchen, bathroom and laundry area. Make sure to run exhaust fans when cooking and showering. Make sure exhaust fans and the clothes dryer vent outside your home are in good working order. If your home doesn’t have exhaust fans, try opening your window just a bit for a few minutes to dry the air out.
  • Keep firewood outside. Plants bring moisture into the air — even if that plant is now kindle for a fire. If you have a wood-burning fireplace, store firewood outside to help control the humidity.

Exterior Window Condensation

Condensation on the outside of your windows occurs when the exterior surface temperature of the glass falls below the dew point of the air. This type of condensation is more likely to occur when outside humidity levels are higher, like in the spring, summer and fall when cool nights follow warm days.

Exterior window condensation happens more in the summer months when the days are hotter and sunnier. It’s caused by three main conditions: high outdoor humidity, little or no wind and a clear night sky.

Getting Rid of Window Condensation on the Outside

Because it’s seasonal and climate-related, condensation on the outside of windows is quite common. It isn’t indicative of problems with your windows or the humidity inside your home. You can simply wait for the sun to come out and dry up all the moisture.

If the condensation on the glass is bothersome, try applying a water repellent to the exterior of your windows — you may have some in your garage already. Water repellent is commonly used on car windshields to help improve visibility in rainy weather. It can work in the same way to prevent condensation on house windows.

Condensation Between Window Panes

Moisture between window panes is not something you can control. If you see condensation in between pieces of insulated glass on dual-pane or triple-pane windows, it’s actually an indication of glass seal failure.

The performance of your windows has been compromised, so something will need to be replaced. Contact your local window professional about window condensation repairs. They will inspect the window and tell you whether they can simply replace the window panes or if you need a whole window replacement.

When to Worry About Moisture on Windows

If your windows are sweating, it’s no big deal. But if you don’t tackle the issues of indoor humidity, you may have problems later on. At a minimum, moisture can lead to musty odors.

In more serious cases, water on your windows can trickle down to the frames and cause blistering, cracking or peeling paint, warping and water damage. And if you have moisture on your windows, you may have it elsewhere in the home. Over time, that can cause damage to insulation, leave stains on the walls and ceiling or lead to structural damage in your home.

The important thing to remember is that your windows are trying to tell you something: Reduce the indoor humidity before it causes hidden, costly problems elsewhere.
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