How to Identify Condensation in an Insulated Glass Unit and Why Replacement Is Better Than Repair

Condensation inside your window pane is more than a cosmetic problem. it’s a sign of a failed seal in your unit. As a licensed glazing contractor in Sacramento, we frequently help homeowners identify failure and understand why full glass replacement is the safest and most cost-effective solution.

If you see foggy windows that won’t wipe clean, we can help explain what’s happening, how to spot the problem, and why replacing the panel is the right long-term fix.

What Is an Insulated Glass Unit?

An IGU consists of two or three panes of glass sealed together with a spacer and filled with insulating gas (such as argon). This design improves:

• Energy efficiency
• Indoor comfort
• Noise reduction
• Moisture resistance

When the seal fails, the unit can no longer perform as designed.

How to Identify Condensation Inside an IGU

Not all condensation means your window has failed. The location of the moisture is the key indicator.

1. Condensation Between the Panes

If moisture, fog, or water droplets appear between the glass layers, the IGU seal has failed. This moisture cannot be cleaned from either side and will usually worsen over time.

2. Persistent Fogging

A hazy or milky appearance that changes with temperature but never fully clears is a common sign of a compromised seal.

3. Visible Water Stains or Mineral Deposits

Over time, trapped moisture can leave permanent streaks or cloudy mineral buildup inside the glass unit.

4. Reduced Insulation Performance

Failed IGUs often cause:

• Drafty rooms
• Higher energy bills
• Hot or cold spots near windows

Why IGU Condensation Happens

Common causes of insulated glass failure include:

• Natural seal deterioration over time
• Excessive heat exposure (common in Sacramento climates)
• Poor original installation
• Frame movement or building settling
• Manufacturing defects

Once the seal is broken, the insulating gas escapes and moisture comes in, permanently compromising the unit.

Why Repairing a Foggy IGU Is Not Recommended

Some companies advertise “defogging” or drilling methods, but these are temporary cosmetic fixes that do not restore the IGU’s function.

Problems With IGU Repairs:

• ❌ The original seal is not restored
• ❌ Energy efficiency remains lost
• ❌ Moisture often returns
• ❌ No long-term warranty protection
• ❌ Potential safety risks if glass integrity is weakened

In California, where energy efficiency standards matter, these repairs often fail to meet homeowner expectations.

Why Replacing the IGU Is the Best Solution 

✅ Restores Energy Efficiency

A new IGU reestablishes proper insulation and helps lower heating and cooling costs.

✅ Eliminates Moisture Permanently

Replacement removes trapped moisture entirely instead of masking the problem like a band aid.

✅ Maintains Window Frame Integrity

In many cases, replacing the glass alone with fix your issue. Saving tons of money.

✅ Improves Home Value and Comfort

Clear, efficient windows enhance curb appeal and indoor comfort.

✅ Safer and Code-Compliant

Professional IGU replacement ensures the glass meets California safety and building standards.

Replacing an insulated glass unit requires proper tools, safety procedures, and experience. Handling broken or failed glass can be dangerous without professional training.

A licensed glazing contractor can:

• Accurately diagnose IGU failure
• Match glass thickness, coatings, and gas fills
• Ensure proper sealing and fit
• Provide warranty-backed workmanship

When Should You Replace a Foggy Window?

You should consider IGU replacement if:

• Condensation is between the panes- check out " Identifying condensation"  
• The window appears cloudy year-round
• Energy bills have increased
• The glass is more than 10–15 years old

Final Thoughts

Condensation inside an insulated glass unit is a clear sign of seal failure. While repair methods may seem cheaper upfront, they do not fix the root problem. Replacing the IGU is the only reliable way to restore clarity, efficiency, and safety.

If you’re a homeowner in Sacramento dealing with foggy windows, give M.J. Glass a call and we can help.!