Double glazed sealed units are designed to trap a layer of dry air (or gas such as Argon) between the two panes of glass. This dry air acts as a thermal barrier, providing insulation for your home.
Solar Pumping
When the sun shines on a sealed unit, the air inside heats up and expands, creating positive pressure which pushes outward on the glass panes and the edge seal. When the sun moves away or sets, the unit cools down and the air contracts, creating negative pressure which pulls inward.
This daily cycle of expansion and contraction is known as "solar pumping". Over months and years, this constant flexing gradually weakens the edge seal of the unit.
How the Seal Fails
Eventually, the seal opens slightly under this pressure. When the unit cools and creates negative pressure, it draws in small amounts of cool, damp air from outside. Over time, the desiccant material in the spacer bar (designed to absorb small amounts of moisture) becomes saturated.
Once the desiccant is saturated, moisture begins to condense on the inside surfaces of the glass when the temperature drops. This is the mist, fog, or condensation you see between the panes.
Why It Gets Worse in Autumn & Winter
You may notice condensation appears or gets worse during the cooler months. This is because the temperature difference between inside and outside is greater, causing more moisture to condense on the cold inner surface of the outer pane.
The Good News
The good news is that this condensation can be removed and the unit restored using the Condensation2Clear repair kit. The repair process converts the sealed unit into a pressure-equalised unit, meaning it will no longer suffer from solar pumping and the condensation will not return.
The process is simple and can be completed by anyone with basic DIY skills. Learn how to remove condensation from your double glazing.