When the weather swings from below zero to muggy in a single week, your windows take a beating. You might not notice the problem right away, but when condensation sneaks between the panes or rooms start to feel drafty, it often traces back to one thing: your window seals are failing. And when that happens in a Wisconsin home, insulation takes a hit fast.
In this article, we’ll break down how long window seals realistically last, what causes them to fail sooner, and how to spot the signs before your heating bill tells the story. We’ve worked on thousands of homes across southern Wisconsin, and if there’s one thing we’ve learned, it’s that ignoring a bad seal always costs more in the long run.
Reality check: Most seals wear out long before the window frame does
When we inspect older homes, it’s common to find window frames that are still structurally solid, yet the seals between panes have broken down completely. This leads to trapped moisture, foggy views, and poor energy performance even if the window looks “fine” from the outside.
Reality check: A double-pane window with a broken seal isn’t double-pane anymore. Once the gas escapes and moisture enters, that window works more like a single pane, even if the glass hasn’t cracked.
Note: The visible fogging between panes is usually the last sign. Drafts, temperature imbalance, and higher heating costs show up much earlier.
Warning: Wisconsin’s freeze-thaw cycles are rough on seals. We’ve seen failures in as little as 6 years on budget vinyl windows exposed to full sun and snow buildup.
How Long Should a Window Seal Last?
Lifespan depends heavily on materials and exposure
On average, a well-installed window seal will last between 10 and 20 years. But not all seals are made equal. Units with aluminum spacers and no edge seal tend to fail sooner. Higher-end units using warm-edge spacers and double seals stretch closer to that 20-year mark, sometimes longer if protected by deep overhangs.
Exposure shortens lifespan more than age
Windows facing south and west in Wisconsin take the most UV and thermal expansion stress. Add winter winds and ice, and even mid-range vinyl units start breaking down faster.
Pro tip: If your home was built between 2000 and 2010 and still has the original windows, it’s smart to check those south-facing ones every fall.
Signs Your Seal Has Failed
Condensation between panes
This is the most obvious signal and usually means the insulating gas has fully leaked out. You’ll notice moisture trapped inside the glass, especially during shoulder seasons.
Drafts despite closed sashes
Even if the frame looks fine, seal failure can lower the window’s thermal resistance, causing the area near it to feel colder in winter, even without visible air movement.
Reality check: Condensation on the inside of the window (the part you can touch) can often be due to high indoor humidity. But moisture between the panes means the seal is broken, no exceptions.
What Causes Seals to Fail?
Sunlight and temperature extremes
Repeated expansion and contraction, especially on unshaded southern exposures, weakens sealant over time.
Water infiltration from poor flashing
If a window frame isn’t flashed or caulked properly, water seeps into the glazing area, loosening the seal bond during freezes.
Warning: Ice dams that form along uninsulated eaves often force meltwater down into window units, even if they’re a full story below. That hidden moisture speeds up seal failure.
Can You Repair a Failed Window Seal?
Some companies offer de-fogging
These services drill micro-holes, remove moisture, and attempt to re-seal the unit. Results vary.
Note: While this may clear the fog for a year or two, the insulating value isn’t fully restored. The window still behaves like a downgraded thermal unit.
Full IGU replacement is often smarter
Swapping just the insulated glass unit (IGU) within the frame typically costs between $250 and $500 depending on size. This restores energy performance and clarity without replacing the entire window.
Pro tip: If you’re replacing 3 or more IGUs at once, many glass shops will lower the per-unit rate. Always ask.
Wisconsin-Specific Considerations
Winter seals fail harder
When temperatures plummet, window materials shrink. A seal that held together in October can fail by February after weeks of pressure from snow and subzero nights.
Reality check: Once a seal fails in winter, the extra strain from thermal gaps worsens the problem, often warping the sash or frosting over the inside edge.
Summer fog can be misleading
In July and August, we see foggy glass that disappears midday. Often, this is early-stage seal failure triggered by overnight humidity combined with early morning sun. Don’t ignore it.
Expert Input: What Inspectors Look For
“I always run a thermal camera over windows on first walkthrough,” says Dana Schultz, energy auditor based in Madison. “If you see temperature bleed between panes, there’s almost always a failed seal behind it.”
Heins Contracting crews perform visual and infrared checks during every window inspection. In the past 3 years, we’ve replaced more than 1,800 failed IGUs across Dane, Green, and Rock Counties. That number goes up every year, especially after harsh winters.
FAQ: Window Seal Lifespan and Failure
How can I check if my window seal is bad?
Try fogging the window with your breath. If the mist stays outside the panes but moisture is already trapped inside, the seal has likely failed.
Is seal failure covered under warranty?
Most manufacturers offer 10–20 year warranties on IGUs. If you’re within that window, check your paperwork. Labor may not be included.
Can I replace the seal without changing the whole window?
Yes. Most modern windows allow for IGU replacement while keeping the original frame, especially wood and aluminum-clad types.
How much does it cost to replace a sealed unit?
Expect $250–$500 per IGU depending on size and accessibility. Labor costs vary by frame material and removal complexity.
Don’t Let a Small Seal Problem Lead to a Bigger Repair
If you’re seeing signs of window seal failure, especially in south- or west-facing rooms, it’s worth addressing before peak winter hits. The longer you wait, the more energy escapes, and the higher your risk of moisture damage inside the frame.
At Heins Contracting, we’ve seen firsthand how small thermal gaps lead to bigger repair costs. Our team’s trained to evaluate whether repair or full replacement makes the most sense for your setup, age of windows, and climate exposure.
Window seal failure isn’t always urgent, but it’s never harmless. Knowing what to look for, and when to act, helps you stay ahead of weather damage and rising energy bills.
