Argon Fills and Why Panes Fog Between the Glass

The gas between the panes is supposed to last as long as the window does. Often it escapes years early, and for a replacement window in Austin, TX that has gone cloudy, the notes at window replacement austin fish tommy cover the fogging in some detail.

What the gas does

An argon fill is heavier and slower to carry heat than ordinary air, so it lowers the u factor of an insulated glass unit. Krypton does the same job better in a thinner gap, and it costs more, so it appears mostly in thin triple pane units. The gas does not change the shgc, which belongs to the coating, so argon is a winter benefit more than a summer one.

How a seal fails

The edge of the unit holds the glass apart with a spacer and two layers of sealant. Austin summers heat the glass and the air in the gap, which expands and pushes at the seal. At night it contracts again. Thousands of those daily cycles wear the sealant, and seal failure lets in moist air that fogs the glass from the inside.

What fogging tells you

A cloudy film between panes means the seal has gone and the gas has leaked out. The unit now insulates like a thin sheet of glass with a damp air gap. The low e coating can also degrade once moisture reaches it, and the glass may show white mineral marks that do not wipe away because they sit inside the gap.

Spacers matter

A warm edge spacer made of foam or a composite material conducts less heat than an old aluminum spacer, and it flexes better as the unit heats and cools. Aluminum spacers are stiff, which stresses the sealant. Many failures that show up in the west-facing windows of houses in Zilker and Tarrytown start at a hard aluminum spacer on a sunny wall.

Repair or replace the unit

A fogged unit can sometimes be swapped alone if the frame is sound, a vinyl window or wood window in good shape with an unwarped sash. Where the frame is soft, cracked or out of square, new glass in an old frame only repeats the problem. The age of the frame decides, not the fog.

Checking the gas

A tech can test a unit with a handheld gas meter and tell whether argon remains. That test is useful before any claim of a leaking seal, since a fog line may be dirt on the outer face rather than failure between panes.