How to Fix a Window Seal

Broken window seals often result in visible symptoms like condensation or fogginess on multi-pane thermal glass windows, a problem that can’t be simply wiped away. These issues occur when the edge seal, which holds the glass panes together, fails. When you see these signs of a failed window seal, you have several options to consider for repair or whether to simply tolerate the issue.

What Is an Insulated Window?

Insulated windows, also known as IGUs, consist of two or three glass panes with air removed from the space between them and replaced with a heat-resistant gas like argon or krypton.

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.

Window seals can last decades but can fail due to improper installation or damage from heat guns and pressure washers. With time, seals will naturally deteriorate, leading to gas loss at about 1% per year, faster if the IGU is poorly made.

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

When an IGU seal fails, consider hiring a professional or doing it yourself. Replacement IGUs can be installed in existing frames without needing to replace the whole window and frame.

Leave the Window Alone

If the aesthetics don’t bother you, you might choose to ignore the seal failure, especially in milder climates, as a few failed seals in a house with many windows may not significantly impact energy 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.