Why Are My Windows Fogging Between the Glass?

Fog or condensation between the panes of a double-pane or triple-pane window is almost always a sign that the window’s insulated seal has failed. Once that seal breaks, the insulating gas (usually argon or krypton) can escape, and moisture from the outside air can get trapped between the panes. Because the space between the panes is no longer airtight, the window begins to fog, haze, or develop visible moisture.

What Causes Seal Failure in Insulated Windows?

1. Age and Natural Degradation

Most insulated glass units (IGUs) have a lifespan of 15–20 years. Over time, the perimeter seal breaks down due to temperature cycles, UV exposure, and the natural aging of sealants.

2. Thermal Expansion and Contraction

Windows constantly expand in heat and contract in cold. These cycles put stress on the seals. In climates with large temperature swings, seal failure is more common.

3. Poor Installation or Manufacturing Defects

If the IGU wasn’t properly manufactured or was installed without proper support, the seal may fail prematurely.

4. Excessive Exposure to Sunlight

South- and west-facing windows experience more heat load. This speeds up the breakdown of the seals and the escape of insulating gas.

5. Building Movement

Often overlooked, normal settling or shifting of a home can twist window frames slightly, causing stress on the insulated unit.

What Happens When the Seal Fails?

When the seal is compromised, three things occur:

1. Insulating gas escapes. The window loses energy performance.

2. Moisture enters. Water vapor gets trapped between the panes.

3. Fogging appears. Moisture condenses on the cooler inner surfaces, creating a cloudy or milky appearance that doesn’t wipe off.

Because the moisture is inside the sealed unit, cleaning the glass surfaces will not fix it.

Can Fogged Windows Be Repaired?

Defogging Services

Some companies drill tiny holes to remove moisture and apply a sealant. This may improve appearance temporarily, but it does not restore insulation performance and is not considered a long-term fix.

Glass Replacement

Sometimes the insulated glass unit can be replaced without replacing the entire window frame. This restores the clarity and insulation value, but is typically not a long-term solution.

Full Window Replacement (Most Common for Long-Term Investment)

While replacing only the glass can restore visibility, it does not address the bigger issues that come with aging windows. For most homeowners, full window replacement delivers far better long-term value. Here’s why:

1. Older frames often leak air and energy. A fogged IGU is usually a symptom of a broader problem: aging frames, deteriorated weatherstripping, and outdated insulation. Replacing the entire window improves the overall thermal performance of the home, not just the glass.

2. Modern windows offer dramatically better energy efficiency. Today's replacement windows include multi-chambered frames, advanced low-E coatings, warm-edge spacers, and superior gas fills. These upgrades can lower heating and cooling costs for decades — benefits that glass replacement alone cannot provide.

3. New windows solve operational and aesthetic issues.Homeowners often realize once the glass is replaced that the sash still sticks, the locks don’t feel secure, or the exterior finish is worn. Full replacement fixes all of those issues at once and immediately boosts curb appeal.

4. A new window comes with a full manufacturer warranty. Replacing only the glass usually provides a limited warranty on the insulated unit. A full window replacement includes warranties on the frame, hardware, seals, and glass, giving homeowners much more protection.

5. Increases home value more than glass-only repairs. Real estate data consistently shows that upgraded windows are one of the top ROI home improvements. Prospective buyers value energy efficiency, clean sightlines, and new hardware — all of which come only from full replacement.

6. Long-term durability prevents repeated service calls. Once a window seal has failed, others may not be far behind. A full replacement eliminates the cycle of fixing individual panes and ensures consistent performance across the entire home.

How to Prevent Future Window Fogging

• Choose windows with high-quality perimeter seals.

• Ensure proper installation to avoid undue stress on the frame.

• Install shade or UV film on high-exposure windows.

• Maintain exterior caulking and ensure proper drainage around frames.