Argon is invisible and has no smell, so you will never see or sniff it leaving a window. What you can see is the evidence it leaves behind once the seal that held it in has failed. Knowing how to read that evidence saves you from replacing windows that are fine and from living with ones that have quietly stopped insulating.
Why argon is in your windows at all
Most modern double-pane windows are built as sealed insulated glass units. Two sheets of glass are bonded to a spacer that runs around the edge, and the space between them is filled with argon instead of ordinary air. Argon is a dense, inert gas that occurs naturally in the air we breathe. Because it is heavier and moves more sluggishly than air, it slows the transfer of heat from the outer pane to the inner pane.
The seal around that spacer does two jobs. It keeps the argon in, and it keeps humid outside air out. The spacer also holds a desiccant, a drying material that absorbs whatever trace moisture is sealed inside during manufacturing.
The main sign: fog between the panes
When the edge seal fails, the gas slowly escapes and moist air takes its place. The desiccant soaks up moisture for a while, then becomes saturated. From that point, you start seeing condensation on the inside surfaces of the glass, in the sealed space you cannot reach.
It often shows up first on cool mornings, when the outer pane is colder than the air trapped inside the unit. You may see it come and go with the weather for weeks or months before it becomes permanent. Over time, the moisture leaves mineral deposits behind, and the glass takes on a cloudy, streaky look that never clears.
Other clues
- A milky or hazy film between the panes that is still there on a dry afternoon.
- Rainbow-like streaks or discoloration on the inner surfaces of the glass.
- Panes that appear to bow slightly inward or outward, which can mean the pressure inside the unit has changed.
- One window in a room that feels noticeably warmer near the glass than its neighbors on the same wall.
Make sure it is actually between the panes
Plenty of condensation has nothing to do with a failed seal. Before you assume the worst, find out which surface the moisture is on.
Wipe the inside surface with a dry cloth. If it comes off, the moisture was on the room side of the glass. That usually means indoor humidity is high and the glass is cool, which happens on the occasional cold Austin morning in a kitchen or bathroom, or in a house full of people and cooking.
Step outside and wipe the exterior surface. Dew on the outside of the glass on a humid morning is common with efficient windows. It means the outer pane is cool because the window is keeping your indoor heat inside, which is a sign the window is working.
If neither wipe clears it, the moisture is sealed inside the unit, and the seal has failed.
Why seals fail
Every insulated glass unit flexes. The glass and the spacer expand on a hot day and contract when it cools, and that cycle repeats every day for the life of the window. In Austin, a window on a west wall can go from baking in late-afternoon sun to cooling off after dark every day for months. Strong sun is hard on seals.
Other causes include installation that puts the unit under stress, a frame twisted by a house settling on shifting clay soil, water sitting in a sill track that does not drain, and simple age and manufacturing quality. Cheaper units with thinner seals and basic spacers tend to give up sooner.
Does a slow argon loss matter?
All sealed units lose a little gas over many years, even when nothing is wrong. That gradual loss is expected and does not erase the window’s value. A failed seal is different, because once moisture gets in, the gas is gone and the fog, staining and heat transfer follow.
There is no reliable way for a homeowner to measure argon levels in an intact window. Specialists can test with dedicated equipment, but for most people the practical test is visual. If the glass is clear and the room near it is comfortable, the unit is doing its job.
What you can do about a failed seal
You have three realistic options.
Replace the glass unit. If the frame and sash are in good shape, a new insulated glass unit can sometimes be fitted into the existing window. This works best on newer windows where only one or two units have failed.
Replace the window. If the frame is aluminum, warped, leaking air or failing in other ways, putting new glass in an old frame does not solve much. A complete replacement brings a new frame, new weatherstripping and new hardware along with the glass.
Check your warranty first. Many window manufacturers cover seal failure for some period. Find your paperwork, or look for a manufacturer name etched in a corner of the glass or printed on the spacer, and contact them before paying for anything.
You will see services that drill a small hole in the glass, dry out the space and reseal it. That can improve how the window looks, but it does not restore the original seal or put the argon back the way a factory unit is built. Weigh it as a cosmetic fix.
How long you can live with a fogged window
A failed seal is not an emergency. The window still keeps rain out and still locks. The costs build slowly. The room near that glass runs warmer in summer, the view gets harder to see through, and if the fogging comes with a draft or a leak at the sill, moisture can start damaging the wall or trim below it.
If only one or two windows have fogged and the rest of the house is in good shape, it is reasonable to wait and plan. If fog is showing up on several windows of the same age, expect more to follow, since units built and installed at the same time tend to fail around the same time. That is often the moment to price out a whole-house replacement and stop chasing individual units.
Choosing windows that keep their gas
When you replace, ask about the spacer system, the sealant and how the unit is filled. Look for low-E coated, argon-filled double-pane glass in a solid vinyl frame, and ask us about warranty coverage on the glass seal, since terms vary by product. Proper installation, with the frame set square and the sill draining correctly, keeps stress off the unit from the first day.
If you have fog that will not wipe away, we can look at it and tell you whether the glass, the window or neither needs replacing. Call The Window Source of Austin at (512) 524-9455 or book a free in-home estimate. You can also browse our replacement windows before we visit.