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Before
After
Before
After
Before
AfterFoggy or Condensation Between Panes
If you’re seeing a haze, fog, or moisture trapped between the panes of glass – not on the inside surface of the room, not on the outside – that window’s sealed unit has failed. The insulating gas that makes double- or triple-pane glass efficient has escaped, and outdoor air is now moving freely through that gap. It won’t clear on its own, and it won’t get better with a warmer day.
The glass itself is almost certainly undamaged. What failed is the hermetic seal around the perimeter of the insulated glass unit – the IGU, in glazing language. That seal is what keeps argon or krypton gas locked between the panes and outdoor humidity locked out. Once it breaks, the chemistry reverses: warm, humid air enters the cavity, hits the cooler inner surfaces, and leaves condensation you can’t reach to wipe. The frame, the hardware, and the opening itself may be perfectly fine. The repair is usually an IGU swap, not a full window replacement – though a technician needs to confirm which applies to your specific unit before anyone commits to a number.
Why It Happens
Seal failure from age and thermal cycling
Every time a window heats up in the sun and cools down at night, the frame and the spacer bar around the IGU expand and contract at slightly different rates. Over years, that mechanical fatigue works the sealant loose at the corners or along a straight run. You’ll typically see the fog start in one corner and gradually spread toward the center – that corner is usually where the first breach opened.
Water intrusion at the frame or sill
If the window frame itself isn’t properly flashed or the sill has a low spot where water pools after rain, moisture can wick into the gap between the frame and the IGU and accelerate seal degradation from the outside edge inward. Look at the sill after the next rain: standing water there, even briefly, is a reliable indicator that this is contributing to what you’re seeing.
Impact or pressure damage to the spacer
A hard impact – a ball, a door slamming the frame, a pressure washer run too close – can micro-crack the spacer bar or desiccant strip that runs around the inside edge of the IGU. The fog that follows tends to appear quickly, within days of the event, and is usually concentrated near the point of impact rather than spreading from a corner. If you remember something hitting the window recently, this is the likely cause.
Manufacturing defect or improper original installation
Some IGUs fail earlier than they should because the seal was thin at the factory, or because the unit was set into the frame without proper setting blocks and the glass rested directly on the sill, compressing the seal. If you’re seeing this problem on a window that’s only three to five years old, it’s worth pulling whatever documentation you have from the original install – a defect claim may still be an option, and a written photo record from the original job is the evidence that makes it actionable.
What to Do Right Now
- Photograph it with your phone before you do anything else. Get close enough that the fog pattern is visible, then step back for a full-frame shot. The pattern – corner, center, streak – tells a technician a lot before they arrive, and the timestamp proves when you first noticed it.
- Check whether the condensation is between the panes or on a surface. Run your finger across the interior glass. If the surface is dry, the moisture is definitely trapped inside the sealed unit. If the glass is wet to the touch on the room side, that’s a different problem – interior humidity or a ventilation issue – and worth noting separately.
- Look at the sill and the frame for standing water or soft spots. Press gently along the interior sill and the frame corners. Sponginess or paint bubbling can indicate water has been sitting there, which changes the repair scope.
- Don’t try to drill or introduce anything into the IGU cavity. DIY “defogging” kits exist, but they breach the unit permanently and void any remaining manufacturer coverage. The seal cannot be re-established once the cavity is opened without a full IGU replacement – so you’d be paying for the kit and then paying for the replacement anyway.
- Note whether the window is still operating normally. Can you open and close it without resistance? Does the lock engage cleanly? This tells a technician whether the frame has shifted – a relevant data point if the seal failure is linked to structural movement rather than material fatigue.
BeforeAfterHow We Fix It
When your local Sightline Windows and Doors team arrives, the first thing a technician does is measure the IGU – thickness, dimensions, glass type, and any existing Low-E or coating markings on the spacer bar. That measurement drives the replacement order, and it’s the same document that becomes your written price. Nothing moves between the survey and the invoice; that’s been the founding principle since 2012.
In most cases, the fix is an IGU replacement: the failed sealed unit comes out, the frame is inspected and cleaned, a new unit is set with proper setting blocks and glazing tape, and the sill is checked for drainage before the technician leaves. The service that covers this is our Window Replacement work, drawing from manufacturer lines including PGT, CGI, CWS, ES Windows, ECO Window Systems, and ViewLux depending on what your existing frame requires and what performance tier makes sense for your opening.
If the frame itself has water damage or the opening needs reworking, a full Window Installation may apply – the technician will tell you which, and why, before any work begins. Every completed job leaves a documented photo record and is covered by the 365-Day Done Right Promise under the Haven Standard: if it’s not done right, we make it right, in writing, not as a verbal assurance.
Most IGU replacements on a standard residential window are completed in a single visit. Custom sizes or specialty glass may require a short lead time for the unit to arrive. Your written estimate will include that timeline.
Frequently Asked Questions
A failed IGU seal is not a safety emergency in most cases – the glass isn’t at risk of falling and the window typically still closes and locks. What it does do is eliminate the insulating performance of that pane entirely, which raises your energy costs and can accelerate frame deterioration if moisture is involved. It won’t repair itself, and waiting longer usually just means the fog spreads and the frame takes more damage. If you want to know exactly what’s happening in your specific unit, call (509) 265-6387 and we’ll arrange a survey at no charge to you before any work is quoted.
In most cases, the IGU – the sealed glass unit – can be replaced without disturbing the frame, the trim, or the surrounding wall. The technician removes the glazing stops or stops bead, lifts the old unit out, and sets a new one in the same opening. A full window removal is only necessary when the frame itself is damaged, out of square, or the original unit was installed improperly. The survey tells us which applies; you’ll know before anything starts.
Your local Sightline Windows and Doors team handles scheduling directly, and calls are answered by a live person around the clock at (509) 265-6387. We’ll confirm what’s available in your area when you call. What we don’t do is make you wait for a callback window or a voicemail queue to find out.
The price depends on the glass size, the thickness of the unit, whether it carries a Low-E coating or specialty glazing, and what the frame condition looks like when a technician gets eyes on it. We don’t publish flat-rate numbers because a quote built without a measurement isn’t a quote – it’s a guess that tends to move later. What we can tell you is that every job starts with a free written estimate after the survey, the number in that document is the number you pay, and it won’t change once work begins. Call (509) 265-6387 to schedule yours.
Get It Fixed
If the fog is there, the seal is gone – and it won’t come back on its own. Call (509) 265-6387 any time – a live person will answer – or book online to schedule your free written estimate. Your local Sightline Windows and Doors team will survey the window, give you the price in writing, and get it documented from start to finish.
Written by Sonia Raman, Owner at Sightline Windows and Doors, serving communities nationwide since 2012.
What Our Customers Say
"They photographed the rotten sill they found under the old frame before replacing it, and the extra cost was agreed in writing before they carried on."
- Rosalind C."Front door install went smoothly. Written warranty, clear price, no pressure to upgrade anything."
- Nils H."Patio door had dropped and would not lock. They adjusted it rather than selling me a new one, and charged accordingly."
- Simone T.