How to Prevent Foggy Windows and Doors


Homeowners love sparkling, clear glass in their windows and doors. But what happens when they’re not so perfect? The first signs of moisture on the glass can be concerning. But if panicking is your first reaction to seeing foggy windows and doors in your home’s glass, relax. Foggy windows and doors aren’t necessarily bad. While the fog can sometimes happen because of a damaged or broken seal, that’s not always the case. In fact, the problem might not be the window at all. Sometimes the case for foggy windows and doors is one that’s easily solved—and preventable. Condensation may be a sign that indoor humidity is too high and should be addressed before causing even bigger problems.

foggy windows

What Causes Foggy Windows and Doors?

If you have foggy windows and doors, you’ll want to understand the cause. It’s rarely bad glass. Take a close look at your windows and doors. Is the moisture on the glass surface or between two lites of glass? Depending on the location, the problem is likely due to one of two causes.

Moisture on the Glass Surface

The glass in windows and doors is usually where moisture, or condensation, first appears. Think about what happens after a hot shower; the bathroom mirror is probably fogged. The mirror in the bathroom isn’t at fault for the moisture and, in some cases, neither is the window.

Condensation is a result of warm air making contact with a cold surface, such as windows. As air cools, it contracts and its moisture condenses. When the temperature drops, you often see condensation on the windows, since this surface is usually the coldest inside. Depending on your climate, in winter months indoor air is warm and holds more moisture than outdoor air. As warm, humid indoor air cools and contracts, it comes into contact with the windows, creating condensation on the glass.

Eliminating Condensation on Windows

If your windows have single-pane glass, you may want to consider replacing them. Updating your home with high-performance windows can help create warmer interior glass surfaces, reducing frost and condensation. Windows with insulating glass (IG) can help reduce condensation significantly. Insulating glass is made to prevent significant heat transfer into or out of a building through glass. It consists of multiple pieces of glass separated by spacers made of either metal, such as aluminum, or structural foam. The space between the glass is sometimes filled with a noble gas, such as argon or krypton. IG is sometimes called double-glazed or double-pane glass. More recently, with additional lites of glass being added, it now can also be triple-paned or quadruple-paned glass. You can read more about insulating glass here.

In addition to the IG and gas-filling, adding a low-E coating to the glass can also increase the window’s performance.

While there’s no guarantee the upgraded windows will eliminate condensation, you should at least see a significant reduction.

If window replacement isn’t in your budget there are a few other steps you can take. To start, keep your fans turned on. This will help keep the warm indoor air from sticking to windows. You can also try using a dehumidifier, which helps remove moisture from the air. Applying window film is another option. Film can create a barrier to condensation, as it helps keep the warm indoor air off of the cold glass. Check any warranties on insulating glass units first, however, as the application of window film can void some warranties on certain brands of insulating glass units.

Moisture Between the Glass

Not all cases of foggy windows and doors are simple. Sometimes there is a real problem with the glazing. If the fog is between the pieces of glass in the IG unit, you may have a damaged or broken seal. This can be a major concern and can cause water damage, mold growth and floor stains. In these cases, don’t delay in getting the issues resolved.

Window seals can fail for a couple of different reasons. Sometimes, it’s simply because they are old. The breakage can also be due to water retention in the frame or improper drainage around the window. In addition, direct exposure to sunlight can also be a cause. This happens due to heat buildup, which can cause the panes to expand, contract and eventually weaken.

Most modern windows have two seals. The inner seal protects against moisture and corrosion and the outer seal protects the strength of the window. If one starts to break, the other may last for a little while. But, as the window ages, both seals will begin to wear out and lead to condensation. This is a good sign it’s time for a repair or replacement.

Repairing or Replacing a Broken Window Seal

If your window has a failed seal, you have several options. You can replace the window entirely, or replace just the glass or just the sash. Your decision will depend on whether or not the windows are still under warranty. Most high-quality windows come with a 20-year warranty for glass seal failure, while others are 10 years.

While there are do-it-yourself options, your best bet is to contact a window replacement professional. In many cases, experts can replace just the damaged glass, rather than replacing the sash or entire window.

Upgrading Your Homes Windows and Doors

Condensation on the interior surface or between the glass lites is certainly a reason to replace your home’s windows. But new windows can also help save you money. If you have older, single-pane windows, you’ll find that today’s high-performance windows are more energy efficient. That means they’ll help you save on heating and cooling costs, while also creating a more comfortable indoor environment.

Whatever the reason for your home’s foggy windows and doors, making the move toward new windows can be beneficial. You will find many resources on Glass.com that can guide you along the way. You can read more about choosing the right insulating window here and more about single- double- and triple-pane options here. Ready to take your search to the next level? Glass.com can also connect you to window repair and replacement experts right in your area. Our professionals are ready to work with you to find the right option for your unique needs. Whether you want a total window replacement, or simply want to discuss repair options, Glass.com can help.


Ellen Rogers

By Ellen Rogers

Ellen Rogers has been involved with the glass industry for nearly 20 years and is the editor of USGlass Magazine and Architects’ Guide to Glass magazine. Ellen received a degree from Peace College where she studied journalism.

Ellen enjoys running and competes regularly in races including half and full marathons. When not on the go, Ellen enjoys reading, wine tasting, true crime shows, and family game nights with her husband and son. Their favorite game is Clue. Ellen also bakes what is known locally as “World Famous Oatmeal Cookies.”


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