What to Do When Insulated Glass Windows Fail and Fog Up (2024)

The symptoms of failed or broken window seals are easy to spot. The multi-pane glass develops condensation or fogginess that can't be wiped off from either side of the window. The cause is a failure in the edge seal that secures the individual panes of glass. This common problem raises two equally common questions: Is there anything you can do about this issue, other than replacing the entire window? And is it really necessary to do anything?

Anatomy of a Thermal Window

A thermal window features two or three panes of glass with open space between the panes. This window assembly is known in the industry as an IGU—an acronym that stands for insulated glazing unit or insulated glass unit. Thermal windows are sometimes called thermopanes or insulated windows.

The space between the glass panes of an IGU is emptied of air by means of vacuum suction, and it is often filled with an inert (noble) gas, such as argon or krypton, to slow the passage of heat through the window unit. Inert gasses are less heat-conductive than air or a vacuum space.

However, if the seals that protect the edges of the IGU develop a break, then the inert gases can escape and ambient air and moisture can enter the space between the panes, resulting in the IGU losing its extra insulating value. The visible symptom of this failure is the tell-tale fogginess or condensation inside the IGU unit, on the inside surface of the glass. Not only do you lose the aesthetic value of a clear window, but the energy-saving value of the window will be cut dramatically.

Understanding IGU Seals

The different types of window seals each have an important purpose. The edges of the glass panes in double- or triple-pane IGU windows are embedded in a sealing material. While it appears to be one seal, it is actually two seals working together. The inner sealant is typically made of polyisobutylene (PIB). The outer sealant is an elastic rubber-like seal, or gasket, that, according toAkzoNobel (a maker of the gases used to fill thermal windows), "functions as an adhesive, holding the glass unit together and keeping it tight during the service life."

Although these window seals are meant to be long-lasting and may hold up for decades, they can and do fail. Seals can be damaged by house painters using heat guns to strip paint or by homeowners using pressure washers to clean the windows. Improper installation of an IGU window can also cause a seal to fail. But even when there is no such dramatic event, the seals are still destined to fail—eventually. The International Association of Certified Home Inspectors estimates that the gas escapes at a rate of approximately 1 percent per year under ideal conditions. This loss of gas can be faster if an IGU is poorly manufactured.

What You'll Need

Equipment / Tools

  • Warranty information (if available)


  • DIY defogging kit (optional)
  • Replacement insulated glass unit (optional)


How To Fix an Insulated Glass Window Seal

  1. Use the Warranty

    Premature window seal failure indicates a defective product, and window manufacturers may offer partial or complete replacement of the IGU if the failure occurs within a stated time frame. Other manufacturers may offer prorated compensation in the case of failure, scaled according to the age of the window.

    Look at the paperwork you received when you purchased the windows to determine if they are still under warranty. If you acquired the windows through a home purchase, get in touch with the manufacturer to ask about warranties and whether the warranty on those windows is transferable.

  2. Fix the Fog and Condensation Problem (But Not the Seal)

    If there is no warranty protection on the window, there may still be options for making the window look better. Specialty companies have captured this niche by offering defogging services that can make the window more aesthetically pleasing without actually restoring the sealed window spaces. Windows are not removed and replaced; all materials stay in place. Instead, the company drills a tiny hole in the glass and expels the moisture from between the glass panes.Then, an anti-fog solution is applied to the inside of the IGU, a liquid sealant is added to the bottom, and a seal is installed in the drilled hole. This is the only way to just replace the window seal without extracting the panes.

    Reviews of defogging are mixed. Inert gasses are not replaced with this process, so the original insulating value of the window is not restored. And the initial seal problem is not corrected unless the seal failure was at the very bottom of the IGU (where the new sealant is applied), so fogginess may well return.

    Although there are DIY kits available that allow homeowners to try this repair themselves, these are hard to use successfully—the better option is to hire a window specialty company.

  3. Replace the IGU Within the Frame

    When an IGU seal fails, you may be able to replace the glass unit itself without replacing the entire window and frame. Glass replacement companies make replacement IGUs that can be installed in existing window frames. Typically, this work is done by professionals, but it's possible to do it yourself if the window frames are constructed so they can be taken apart.

    Some windows have screws that join the frame pieces together; others have removable stop moldings that hold the IGU in place within the frame. This is a fairly complicated DIY project, but it can be considerably cheaper than having an entire window replaced.

  4. Leave the Window as It Is

    If you live in a mild to moderate climate, you may never reap the full benefits that thermal windows have to offer. In many areas, one or two failed window seals in a house with 20 windows will make little difference in the heating or cooling bills. You may decide to simply ignore the failed seal, provided you can live with the aesthetics of a window that fogs up occasionally.

Tips for Preventing Seal Failure

There are several ways you can help prevent problems with failed seals in thermal windows:

  • Buy windows with long warranties. While 10- and 20-year warranties are common, some companies offer lifetime warranties.
  • Have the windows installed by the manufacturer. With companies that manufacture direct-set IGUs, where the insulated panels are installed within the frames at the factory, the full warranty may be offered only if the manufacturer's technicians install the windows.
  • Examine the windows periodically for signs of separation between the IGUs and their frames. Caulk any gaps you find. Keeping the seam clean and well-painted can also help.
  • Don't use pressure washers to clean windows. The high-velocity water stream may cause gaps between the IGUs and frames.
  • Don't use heat guns to remove paint from window frames. Careful scraping and sanding is the preferred method when repainting windows with IGU panels.


  • Are weatherstripping and window seals the same things?

    It's easy to get the two confused. The seal that holds the gas sandwiched between panes of glass is permanent (unless it fails). Weatherstripping is another layer of temporary sealing that is used to fill the gaps between the window sash and frame during winter weather to keep warm air in and cold out. An additional type of seal, such as caulk, is used to seal the gap between the glass and frame, and it differs from the inner seal and weatherstripping.

  • Can you replace just the window seal?

    When the seal fails, the gas in the panes has likely leaked out, eliminating the window's extra insulating value. Fixing the seal is a bit more complicated than just adding a window's rubber seal replacement. However, if the window is not too old and the frame is in excellent shape, it's likely the window doesn't need to be replaced, and you may be able to swap out old and new IGU panes.

  • How much does it cost to reseal windows?

    A window specialist may charge between $70 and $245 or more to fix a window seal. The cost is based on many factors that go into repairing the seal, such as the window size, fixing damaged panes, replacing a sash, or defogging trapped moisture.

What to Do When Insulated Glass Windows Fail and Fog Up (2024)


What to Do When Insulated Glass Windows Fail and Fog Up? ›

When an IGU seal fails, you may be able to replace the glass unit itself without replacing the entire window and frame. Glass replacement companies make replacement IGUs that can be installed in existing window frames.

Is there a way to get moisture out of a double pane window? ›

Space heaters and hair dryers are products that are in almost any home and these can be used to help clear the condensation from your double pane windows. Place the space heater or hairdryer by the window and leave it on. This will absorb all the moisture in between the windows.

Can windows that fog up be repaired? ›

Some companies, and even some DIY kits, offer services that claim to get rid of the window fog without replacing the window or even restoring the sealed window spaces. They drill holes in the glass, vacuuming out debris, and install micro-vents to ensure air ventilation.

How do you remove the haze from a double pane window? ›

Drill a set of small holes at the top of the window and one small hole in a bottom window corner. After drilling, pour isopropyl alcohol into the holes. You could also insert a desiccate package or pellets in the space. This will help remove any fog or condensation.

Can fogged double pane windows be repaired? ›

Most experts agree that condensation or fogging inside of a double-pane window technically is not a fixable problem -- at least not in the sense that your window can be restored to its original level of performance.

How do you deal with poorly insulated windows? ›

  1. Use Weather Strips. Weather strips are an inexpensive way to seal doors and windows in your home. ...
  2. Install New Door Sweeps. Installing a door sweep along the bottom of an exterior door can block out cold air. ...
  3. Apply Foam Tape. ...
  4. Insulate with Window Film. ...
  5. Hang Insulated Curtains. ...
  6. Recaulk Windows and Doors. ...
  7. Use a Door Snake.

How do you fix condensation and moisture between double pane windows? ›

Fortunately, there are several ways you can reduce this condensation build-up such as using a heat gun, placing vinegar soaked towels between the panes, using dehumidifying products and replacing any sealant or weatherstripping around the window.

What clears moisture from inside windows? ›

Buy a dehumidifier: Dehumidifiers remove moisture from the air and keep it off of your windows. Place your dehumidifier near the windows where you tend to see the most condensation. Move your houseplants: Did you know that the more houseplants you have, the more moisture you'll find in the air?

Will a hair dryer remove condensation between glass panes? ›

Condensation will evaporate over time but if you want to get rid of it quicker, here are some tips: Hairdryer – Using a hairdryer on the affected area will clear up the condensation quicker but it's only a quick fix and won't actually solve the problem.

Should fogged windows be replaced? ›

Replacement is the Best Option for Fogged Windows

Whether the plan is to replace the sash, just the IGU, or the entire window, replacement is the smartest avenue when it comes to repairing fogged windows. Doing any of these things will do away with foggy glass and also restore energy efficiency.

How much does it cost to Defog windows? ›

Overall, the average price for a window defogging service is around $135 per window. Depending on the outside factors, you should expect a final price anywhere between $70 and $200 once the job gets completed.

Can you replace argon gas in windows? ›

Takeaway. Argon gas windows can be repaired, and gas can be re-added to the pane if the seals can be replaced. Otherwise, it can be a difficult process that is by no means a long-lasting fix. If your argon gas windows were poorly installed or damaged, gas will continue to seep out whether more is added or not.

How do you fix haze on glass? ›

Fill a container with a diluted vinegar solution: Plug up the sink drain or grab a bucket. Fill your vessel with equal parts vinegar and water. Soak your cloudy glassware in the vinegar solution: Put your cloudy glassware in the solution and let the pieces soak for about 30 minutes.

How do you remove cloudy haze from glass? ›

Soak a small rag or dish towel in vinegar, then rub a portion of the glass with the rag. A glass that's milky from hard water buildup should become clearer with each wipe.

Can condensation in double glazing be fixed? ›

There are now a number of specialist companies which can repair or recondition each faulty unit. In most cases, the process involves drilling a hole into the 'spacer' bar or glass pane unit. A special drying agent or desiccant is then pumped or injected in to dry out the air or expel the condensation within the unit.

Why do insulated windows fog up? ›

Moisture and condensation between panes of insulating glass can occur when the seal between the panes of glass fails and allows moisture to leak in.

Should insulated windows fog up? ›

If you see fog in your windows, you have a problem with your window's insulation. An insulated window's seal should prevent fogging, but if it doesn't, you need to replace your window. As you figure out the reason for your fogging windows, check your window seals, glass and sash.

Will a hair dryer get rid of condensation between glass panes? ›

Turning on a hairdryer and waving it over the window will dry the condensation and get rid of it, but this is very much a short term solution, and if you have regular and significant issues with condensation, it may be worth investing in a dehumidifier, which can extract the excess water in the air and keep your room ...


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