Why Do Dual Pane Windows Fog Between the Glass

Most people wipe at foggy glass from both sides for a week before admitting the moisture is sealed inside. A double pane unit in a window in San Bernardino, CA takes a daily beating from hard sun and cold nights, and new windows san bernardino comedy club williamsburg walks through the failure in the order it happens on the job. The cause is mechanical, and so is the repair.

How the unit is built

An insulated glass unit is two panes held apart by a spacer bar and sealed around the whole edge. Desiccant sits inside the spacer to pull stray moisture out of the trapped air. The unit stays clear only while that edge seal stays intact. The frame around it matters too, because a vinyl window, an aluminum window and a wood window all move at different rates as they heat up, and that movement works the glass edge.

Why the seal fails

Daily heating and cooling makes the gas between the panes expand and contract, and every cycle flexes the seal. Strong sun and big swings from day to night add stress. In Redlands and Muscoy, a west facing slider or picture window baking all afternoon often fails before a shaded one on the same house. Failure is not automatically an installation fault. Age and heat cycles can do it alone.

Fog versus condensation

Condensation on the inside surface wipes off. Fog between the panes cannot be wiped off from either side. Once the edge seal opens, humid air enters, the desiccant saturates and moisture condenses in the gap. Wipe both faces with a dry rag, and if the haze stays put, it is inside the unit. Fog often shows first on cool mornings and thins by afternoon, then returns thicker each season.

What stays behind

Argon fill can leak out after the seal fails, so the unit insulates worse even on a dry day. Repeated moisture can also leave a white mineral haze or etching that remains when the glass looks dry. Clearing the fog does not rebuild the seal, and the etching will not come off with cleaner because it is in the glass surface. A unit in this state is finished, even if it looks acceptable on a dry afternoon.

Replacing the glass, and the sprinkler problem

When the frame is sound, the sealed glass unit can often be replaced without replacing the whole window. Press the sill, check the corners for soft wood or cracked welds, and look at the weatherstripping on a casement or double hung sash before deciding. Measure the old unit's overall thickness and sight line and order the new one to match. A rotted sill or warped sash means full window replacement instead. Separately, lawn sprinklers hitting glass leave hard water spots, and those can etch outer surfaces over time. Aim the heads off the glass in Loma Linda and across San Bernardino County, and wipe spots off early before the sun bakes them on.