How to Fix a Window Seal

The symptoms of failed or broken window seals are easy to spot. The multi-pane thermal glass window can develop things like 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.

If you notice a window seal failure, you have a few options. Read on to see what you can do to fix it or if it can be left alone.

What Is an Insulated Window?

An insulated window features two or three panes of glass with open space between the panes. This window assembly is an IGU—an acronym for insulated glazing or insulated glass units. Insulated windows are sometimes called thermopanes or thermal windows.

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

When a seal that protects the window edges breaks, the inert gases can escape. Air and moisture can enter the space between the panes, and then the window loses its extra insulating value. The visible symptom of this failure is the tell-tale fogginess or condensation between the panes on the inside surface of the glass. The break in the seal can make it difficult to see through the window, and the window can lose its energy-saving capacity.

Understanding Window Seals

Some window seals have different qualities, particularly the edges of the glass panes in double- or triple-pane IGU windows, which are embedded with a sealing material. It appears to have one seal but has 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 functions as an adhesive, holding the glass unit together and keeping it tight during the service life.

Although 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 can also cause a seal to fail.

However, all seals will expire eventually. The International Association of Certified Home Inspectors estimates that the gas escapes at approximately 1 percent per year under ideal conditions. This loss of gas can be faster if an IGU is poorly manufactured.

Identifying a Damaged Window Seal

Tell-tale signs your window seal is damaged include the following:

• Foggy windows or condensation in the space between double-paned glass
• Drafty windows or temperature fluctuations may that can lead to higher energy bills
• Window frame damage around the caulking and edges can cause water damage or mildew issues; left unfixed, it can cause difficulty opening or closing windows

Options for Fixing (or Living With) a Broken Window Seal

Check the Warranty

• Look at the paperwork you received when you purchased the windows to determine if they are still under warranty. Premature window seal failure indicates a defective product, and window manufacturers may offer partial or complete replacement of the IGU or prorated compensation if the failure occurs within a specific time frame.
• If you acquired the windows through a home purchase, contact the manufacturer to ask about warranties and whether the warranty on those windows is transferable.

Fix the Condensation Problem

Remedy the fogging between the panes by hiring a defogging service or using a DIY defogging kit if it is past the warranty. Windows are not removed and replaced; all materials stay in place. Here’s how it is done by a window expert:

• A technician drills a tiny hole in the glass and expels the moisture between the glass panes. 
• An anti-fog solution is applied to the inside of the IGU.
• A liquid sealant is added to the bottom.
• A seal is installed in the drilled hole.

Replace the IGU or the Window

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

Leave the Window Alone

Ignore the failed seal if you can live with the aesthetics of a window that occasionally fogs up. In a mild to moderate climate, you may never reap the full benefits of thermal windows. 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.

Tips for Preventing Broken Window Seals

• Buy windows with extended warranties. While 10- and 20-year warranties are common, some companies offer lifetime warranties.
• Get 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. Keep the seam clean and well-painted.
• 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. Carefully scrape and sand frames when repainting windows with IGU panels.

When to Call a Professional

Professionals are usually the best bet for defogging between window panes and replacing the IGU within a frame. They have the experience and tools to get the job done right and quickly. However, a determined DIYer can get the job done and save the labor costs.

Before you consider defogging, know that the reviews of defogging are mixed. Inert gases are not replaced with this process, so the original insulating value of the window is not restored. The initial seal problem is not corrected unless the seal failure is at the bottom of the IGU (where the new sealant is applied), so fogginess may return. Although DIY kits are available that allow homeowners to try this repair themselves, they are hard to use successfully. The better option is to hire a window specialty company.

Professionals are also best poised to replace the IGU within a frame. Still, 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 complicated DIY project, but it can be considerably cheaper than replacing an entire window.