How to Fix a Window That Has a Broken Seal

A broken window seal causes fogging between panes, reduced insulation, and higher energy bills. Here's how to confirm the seal has failed, what your repair options are, and how to protect your other windows.

What Is a Window Seal?

Double and triple-pane windows have an insulated glass unit (IGU) — two or three panes of glass bonded together with a hermetic seal around the edges. The space between the panes is filled with air or insulating gas (argon or krypton). The seal keeps this gas in and outside air out.

Signs of a Broken Seal

• Fog, haze, or condensation between the panes that doesn't wipe off
• Streaks or mineral deposits on the inner glass surfaces
• Visible gap or deterioration at the edge of the glass unit
• Window feels less insulating — noticeably colder or warmer near the glass
• Increased energy bills without other explanation

Confirming the Seal Has Failed

Try to wipe the condensation or fog with a cloth. If it doesn't wipe off, it's between the panes and the seal has failed. You can also look at the edge of the glass unit — a failed seal sometimes shows visible deterioration or a dark stain at the spacer bar.

Fix Option 1: Replace the IGU (Best Value)

A glazier can remove the failed glass unit from the existing frame and install a new sealed unit. This costs $100–$300 per window depending on size and glass type — much less than full window replacement. The frame is reused, so only the glass unit is replaced.

Fix Option 2: Defogging (Temporary)

Defogging services drill small holes, clean the interior, and install vents. This clears the fog temporarily but doesn't restore the seal or insulating gas. Results last 1–3 years typically.

Fix Option 3: Full Window Replacement

If the frame is damaged, rotted, or the window is very old, replacing the entire window is more economical long-term. Modern windows have improved seal technology and longer warranties.

Seal the Exterior Frame Immediately

While arranging for glass replacement, seal the exterior frame joint to prevent water from reaching the wall cavity and causing further damage.

• GE Advanced Silicone Caulk Window & Door Clear — waterproof, freeze-proof; seal the exterior frame joint around the failed IGU
• Bates Caulking Gun 10:1 No Drip — smooth, controlled application for exterior caulking

How Long Do Window Seals Last?

Most IGU seals are warranted for 10–20 years. Actual lifespan depends on: quality of the original seal, climate (extreme temperature swings accelerate failure), sun exposure (UV degrades sealants), and frame condition (water infiltration at the frame reaches the seal).

Preventing Seal Failure on Other Windows

• Keep frames painted and sealed to protect the IGU edge from UV and moisture
• Ensure window sills drain properly — standing water accelerates seal failure
• Recaulk exterior frame joints every 5–7 years
• Avoid pressure washing directly at window seals