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Before
After
Before
After
Before
AfterFoggy or Condensation Between Panes
What’s Happening
Fog or condensation trapped between the panes of a double- or triple-pane window almost always means the hermetic seal that holds the insulating gas inside the unit has failed. Once that seal breaks, the inert gas escapes and humid outdoor air moves in, leaving moisture that has nowhere to go. The glass itself is not cracked and the frame may look perfectly fine, but the insulating unit is finished – it cannot be dried out or resealed from the outside.
What you’re seeing is the long-term consequence of a seal that gave way. It may have taken years to show up visually, but the moment fog appears between the panes, the window is no longer doing the job it was built to do. The glass is still blocking wind and rain, but the thermal barrier is gone. That means higher energy bills, a pane that feels cold to the touch in winter, and a view that looks like a dirty aquarium no matter how many times you wipe it. The fogging is inside the sealed unit, so no amount of cleaning on either the room-side or exterior surface will change it.
Why It Happens
1. Seal Failure from Age and Thermal Cycling
Every day a window heats up in sunlight and cools down at night, the sealed unit expands and contracts slightly. Over years, that constant flexing fatigues the edge seal – the thin ribbon of butyl and desiccant that holds the two panes together at the perimeter. When the seal finally cracks or separates, the insulating gas (usually argon or krypton) leaks out and air moves in. You’ll notice fogging that seems worse on cold mornings and better on warm afternoons, then gradually permanent as the desiccant inside the unit becomes saturated and can no longer absorb any more moisture.
2. Improper Original Installation
A window unit installed without proper shimming, without adequate weep hole clearance, or against a frame that was not perfectly plumb puts uneven stress on the sealed unit from day one. That stress accelerates seal failure by years, sometimes by a decade. If multiple windows in your home are fogging at roughly the same time and they’re all the same age, installation quality is worth asking about. If only one window is fogging and it’s in a wall that has had water intrusion or settling issues, installation is likely a contributing factor.
3. Frame or Sash Damage Letting Water Track to the Edge Seal
A cracked sash corner, a gap in the exterior glazing tape, or a clogged weep hole can direct water directly to the edge seal. Water sitting against the seal softens it over time. Check the exterior perimeter of the window frame for cracked caulk, bubbling paint, or any area where water visibly pools or tracks after rain. If the fogging is concentrated in one corner of the glass rather than spread across the whole pane, moisture intrusion at the edge is a strong candidate.
4. Impact or Stress Fracture to the Edge Seal
A hard impact – a stone from a lawnmower, a ball, a door slammed hard enough to flex the frame – can break the seal without visibly cracking the glass. If the fogging appeared suddenly rather than gradually, or if you can see a small chip or star fracture near the edge of the pane, impact damage is likely. Run your finger lightly along the interior perimeter of the glass where the edge meets the frame. You won’t be able to feel a seal failure directly, but any visible deformation or chip at the glass edge is a clue worth mentioning when you call.
What to Do Right Now
- Photograph the fogging in natural light. Take a photo from inside and one from outside, at the same time of day. Morning light often makes the condensation most visible. These photos help our technician understand the extent of the failure before arriving and give you a baseline record.
- Note which panes are affected and where the fog sits. Is it one window or several? Is the fogging concentrated in a corner or spread across the whole glass? Does it seem worse after a cold night? These details matter for diagnosis and for writing an accurate estimate.
- Do not attempt to drill, score, or inject anything into the glass. Some online guides suggest drilling a small hole in the pane to “dry it out.” This destroys the structural integrity of the unit, voids any remaining manufacturer warranty, and does not fix the underlying seal failure. The unit needs to be replaced, not patched.
- Check whether the fogging is on the glass surface or between the panes. Run a dry cloth across the interior glass surface. If the haze wipes away, it is surface condensation caused by indoor humidity – a different problem with a different solution. If the glass surface is clear but the cloudiness remains in the middle, the seal has failed and replacement is the path forward.
- If the frame around the affected window shows any signs of rot, soft wood, or visible water damage, do not try to probe or repair it yourself. Note the location and let our technician assess it on arrival. Frame damage can affect the scope of the replacement and needs to be seen in person.
How We Fix It
The fix for a failed sealed unit is window replacement – either replacing the insulated glass unit inside an otherwise sound frame, or replacing the full window when the frame or sash is also compromised. When your local Lightwell Windows & Doors technician arrives, they’ll confirm which situation you have by inspecting the frame, the sash, the weep holes, and the perimeter seal. They’ll look at the brands and configurations that make sense for your opening – PGT, CGI, CWS, ES Windows, ECO Window Systems, Mr-Glass, or ViewLux depending on what fits the home – and they’ll give you a written price before anything starts. That written price is not a ballpark. It is the number.
Once the work begins, the affected unit comes out, the frame is inspected and prepared, and the new glass unit is seated, shimmed, and sealed. Before the crew leaves, you’ll get a photo of the clean-up. The finished job is covered by the 365-Day Done Right Promise: if it’s not right, we make it right. Most single-window replacements are completed in a single visit. Our window replacement and window installation services both apply here depending on scope.
Frequently Asked Questions
In nearly every case, the sealed insulating glass unit needs to be replaced – not repaired. Once the hermetic seal breaks, the inert gas is gone and the desiccant inside the unit is saturated. There is no way to restore the original performance by resealing from the outside. Depending on the condition of your frame and sash, we may be able to replace only the glass unit rather than the entire window, which is worth exploring during the estimate.
A fogged seal is not an immediate safety hazard – the glass is still intact and the window still keeps wind and rain out. The concern is performance and, over time, secondary damage: a failed seal lets thermal transfer run unchecked, which raises heating and cooling costs, and moisture that gets into a failing frame can eventually soften the surrounding structure. It’s not an emergency the way a broken pane is, but it’s not something to leave indefinitely either. Call us at (562) 478-8017 and we can help you understand what you’re working with.
Contact your local Lightwell Windows & Doors team at (562) 478-8017 – a real person answers that line, not a recording – and they’ll tell you the earliest available appointment for a free written estimate. Window replacement is a planned job, not an emergency service call, so we want to give you a proper assessment and a written price rather than rush the process. The estimate itself is free, and nothing starts until you have that price in hand.
The honest answer is that the price depends on the window size, the glass configuration (double- vs. triple-pane), the brand and profile that matches your existing frame, and whether the frame itself needs any attention. We don’t quote prices without seeing the window because a number we invent here will almost never match the number on your job. What we can promise is a written price before any work starts – every time, with no exceptions. Call (562) 478-8017 to schedule your free estimate.
Get It Fixed
Your local Lightwell Windows & Doors team is ready to take a look. Call (562) 478-8017 – a real person answers, day or night – or book online. We’ll come out, assess the window, and give you a written price before anything starts. That’s how every job works.
Written by Keith Yamada, Owner at Lightwell Windows & Doors, part of the Cedarwell network since 2010.
What Our Customers Say
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