Window seal repair 101: How to identify and fix a broken window seal

Key points

• The best window seal repair is an insulated glass unit replacement or a full window replacement.

• Condensation between panes of glass is the clearest sign of a broken window seal.

• Broken window seals can mean drafts and decreased home energy efficiency.

You have several options to fix a broken window seal, including defogging or replacing the gas in a double-pane window. If your window is past its prime, though, it may be destined for full replacement.

“The most common and effective method of window seal repair is to replace the insulated glass unit (IGU) while keeping the existing window frame,” said Tim O’Shea, owner of The Build Pros, a home renovation and contracting company in San Diego. This allows you to recoup the window’s insulating properties without fully replacing it.

“In cases where the window frames are also damaged or outdated, a full window replacement might be the best option for improving energy efficiency and aesthetics,” O’Shea continued.

Most modern windows include double-pane glass with insulating gas between the two panes. This gas layer reduces solar heat transfer, helping to maintain a comfortable and consistent indoor temperature. If the window seal breaks, the window loses efficiency, and you might see increasing heating and cooling bills.

You can identify a broken window seal by condensation on the windows that you can’t wipe off from either side, but there are other signs, too. Understanding how to identify the need for window seal repair is crucial knowledge for any homeowner — finding and fixing the issue early can save you money on utility bills over time.

Why is a broken window seal an issue?

“Seals are designed to keep IGUs airtight, maintaining the separation between panes and preserving the insulating gas [such as argon or krypton] inside,” said O’Shea. A broken window seal doesn’t expose your living space to the elements, but it does present a few problems:

• Condensation on the windows: The most benign issue that can stem from a broken window seal is condensation between the panes of glass. This doesn’t present any structural problems or a risk of water damage, but it can be a nuisance since you can’t wipe away the fogginess from either side of the glass. “Fogging affects the windows aesthetically and can even make it difficult to see [through them],” said Richard Ala, founder of Six Brothers Contractors, a roof, window, siding and gutter replacement company in Lyndhurst, New Jersey.
• Decreased energy efficiency: Double-pane windows use insulating gas to prevent heat transfer between the panes, and when the seal is broken, you lose that benefit. That means decreased home efficiency.
• Increased heating and cooling bills: A key consequence of decreased efficiency is greater solar heat gain during summer and greater heat loss during winter. When you have windows with broken seals, you’ll spend more on heating and cooling to keep the temperature of your living space consistent, according to O’Shea.
• Added strain on HVAC equipment: Another issue related to increased heating and cooling bills is the added strain you’ll put on your equipment to maintain a comfortable temperature. HVAC equipment that works harder becomes more likely to break down over time.
• Uncomfortable indoor temperatures: “Broken window seals can allow drafts, making rooms uncomfortable,” said O’Shea. They allow greater heat exchange through the glass, especially if your heating and cooling equipment struggles to keep up with the demand.

How do you tell if a window seal is broken?

An overworked heating and cooling system, spikes and dips in indoor temperatures or fog between panes of glass are all telltale signs of a broken window seal. Here are the four primary ways to identify the issue.

Condensation between the panes

“Typically, the first sign of a broken window seal is condensation between the panes of glass,” Ala said.

Windows can fog if temperature differentials are large enough, but if you can’t wipe off the condensation from the inside or outside, it’s between the panes. This indicates a broken seal.

“Also, the view through the window may become hazy or distorted due to dirt trapped between the panes,” O’Shea said.

Warped glass

When the seal around a double-pane window breaks, the insulating gas escapes, and the glass can warp inward as the pressure between the panes changes. If the view through your window looks distorted, you might need window seal repair.

Uncomfortable indoor air temperature

A broken window seal means you effectively have a single-pane window, which allows greater heat transfer through the glass. If you notice that your living space is unusually hot in the summer or cold in the winter, a broken seal could be the culprit.

Spikes in your heating and cooling bills

“An increase in energy bills can also indicate your windows are not insulating as effectively as they should,” O’Shea said. Ultimately, the same reasons your indoor living space might feel less comfortable are to blame for higher utility bills.

What causes a broken window seal?

All window seals will eventually fail due to wear and tear over time. However, window seals can break due to other underlying factors, such as temperature fluctuations, shifting of your home’s framing or damage from other construction work. Here are four main factors that can lead to a broken window seal.

Temperature fluctuations

A common reason for a broken window seal is temperature fluctuation in the glass and sealants. “Repeated expansion and contraction from temperature changes can stress and eventually break the seal,” O’Shea said.

These components typically heat up during the day, especially if they’re in direct sunlight, and the sealants expand. At night, they cool off and shrink slightly. This constant cycle of expanding and shrinking weakens the seal over time and can cause it to crack or separate from the glass.

Shifting of the frame

Any uneven force on your window frames or the sashes holding the panes in place can cause the sealants on the panes to break, too.

“Incorrect installation can prevent the seal from seating properly, making it prone to breaking,” O’Shea said. Improperly trained window installation technicians and DIYers are more likely to make mistakes during the installation that can cause damage to the seals.

Similarly, installing a lower-quality window might mean a higher likelihood of damage to the seals during installation. “Spending more on a high-quality window typically extends their life as cheaper products tend to use lower grade materials,” Ala said.

If your home is older and the framing settles unevenly, you could see more broken window seals. “Building settling or shifting can put pressure on window frames, too,” O’Shea said. 

Old age

The sealants around your glass can dry out and crack over time, creating a broken seal. This is more likely to be your underlying problem once your window reaches the end of its useful life, which, according to the International Association of Certified Home Inspectors, is between eight and 20 years.

Work on the frames

Physical or chemical damage to the sealants around your panes of glass can also cause damage and break the seals. This can occur if you use heat, paint strippers or other solvents to remove paint from your window frames and inadvertently apply them too close to your seals.

How do you fix a broken window seal?

There are three ways to fix a broken window seal, but it’s important to note that not all of these will be possible for every window, and some are temporary fixes rather than long-term solutions.

Insulated glass unit replacement

Insulated glass unit (IGU) replacement is more affordable than a full window replacement. Modern windows often have individually removable units of glass that are sealed and contain the insulating gas, which allows you to replace just the glass rather than the entire window, including the frame. 

If you’re an avid DIYer and accurately measure the existing IGU, you could perform this repair yourself. However, hiring a professional is usually best to ensure your new glass unit is sealed properly and maintains good energy efficiency in your home.

IGU replacement is a permanent solution to a broken window seal.

Window defogging

Window defogging is a way to restore the seal between your panes of glass without removing them. This is an option for older windows that don’t have IGUs. A professional will first restore the seal around the glass and drill a small hole in the surface of one side. After using a chemical to dissolve the moisture between the panes, they insert insulating gas between them again and seal the hole.

Window defogging isn’t suitable for DIYers because it requires special equipment to fill the void with argon or krypton and seal the drilled hole without allowing the gas to escape.

This temporary fix is best for situations where you plan on a full replacement or IGU replacement but can’t get to the permanent repair right away.

“There are DIY repair kits available that claim to fix broken seals by removing moisture and adding a sealant,” O’Shea said. These provide a similar solution to professional window defogging but without inserting new insulating gas. “However, these are generally temporary fixes and don’t restore the insulating properties of the original IGU.”

Window replacement

Finally, you can replace the entire window, including the frame. This is costlier than just replacing the IGU, but it’s a permanent solution that might suit you best if your window is nearing the end of its life span anyway.

It’s possible to DIY this work, but hiring a professional is a good idea. Mistakes can lead to expensive water damage, drafts, pest infestation and damage to the new window.

What’s next?

If you suspect you might have a broken window seal, call in a professional to confirm and find the underlying problem. A pro should be able to determine what caused the window seal to fail, such as old age or shifting wall framing that’s putting undue pressure on the window.

Next, decide which type of window seal repair is best for your situation. Ask your local window repair technician which option they would recommend, and think about your budget and the age of your windows before deciding.

Consider a full window replacement if your window is near the end of its life anyway, and go with an IGU replacement if your tech believes there isn’t an underlying problem that will cause repeat window seal failure.

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