Normally, an Insulated Glass Unit (IGU), commonly known as double-glazing, is sealed airtight. This sealed airspace (often filled with insulating gas like argon or krypton) is kept completely dry by a desiccant material within the spacer .
When the seals on the IGU fail, two things happen:
Humid air from the outside (or inside) enters the air gap.
The desiccant material inside the spacer becomes saturated and can no longer absorb moisture.
Once the seal is compromised, the basic principle of condensation takes over:
Warm, humid air within the glass unit's cavity comes into contact with the cold inner surface of the outer glass pane (especially when it's cold outside).
As the air cools down to its dew point, the moisture it holds is released as liquid water droplets, forming condensation or "fog" between the panes.
Since the unit is still mostly sealed, this trapped moisture has nowhere to escape, leading to the persistent, foggy, or milky appearance characteristic of a failed double-pane window.
The core problem is the failed seal and the saturated desiccant, not just the water.
When a seal fails, the window unit has lost its key function: insulation. The dry gas (like Argon) often leaks out and is replaced by regular air. This significantly reduces the window's energy efficiency and R-value.
While the text asks why not just fix it, replacing the entire glass unit is often the most cost-effective and long-lasting solution because it restores the full insulating properties of the window with a brand new, factory-sealed IGU.
The provided text mentions several steps to remove condensation, such as using a hair dryer or commercial products. However, these are generally temporary fixes for minor, superficial condensation or methods to de-fog the unit after the seal has already failed. True repair usually involves a professional resealing process and sometimes drilling small holes to remove moisture and inject a new desiccant/gas, which can be less reliable than a full replacement.
The lifespan of a double-pane window is typically 10 to 20 years. The seals can break down due to several factors:
Old Age: The components naturally degrade over time.
Thermal Expansion and Contraction: Direct exposure to sunlight causes significant heat build-up in the glass panes, leading to constant expansion and contraction that stresses and eventually weakens the seals.
Water Retention/Improper Drainage: If water sits in the window frame or drainage around the window is poor, it can accelerate the degradation of the seals.
The best way to prevent this type of seal failure and internal condensation is to ensure the seals are protected:
Maintain proper drainage around the window to prevent water pooling in the frame.
Address any cracks or damage to the exterior sealant or weatherstripping immediately (as mentioned in point 6 of the provided text).
Regularly inspect the windows for signs of seal deterioration.
If the seals are intact, you should only see condensation on the inside or outside surface of the window, not between the panes, which is a separate issue usually related to high indoor humidity.
5 steps to help clear the condensation trapped inside your double glazing windows
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