Foggy Window Repair is Better Than a Full Replacement

A fogged window pane
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Foggy window repair might be the solution you are seeking for hazy window glass—instead of costly full replacement. Still a fledgling niche industry, window defogging is capable of producing cosmetic results that help improve visibility. On the downside, defogging does nothing to improve your windows' functioning or boost its R-value.

What It Looks Like

You first notice it when your thermal insulated window is fogged up, and you cannot seem to unfog it, no matter what you try.

At first, naturally, you think the window is not clean enough. So you clean it with Windex until your hands are raw, and the result: nothing.

If that describes your situation, you may want to know what is going on. More importantly, can you do anything about it, short of replacing the entire window?

Yes--perhaps. Window defogging is a process aims to expel water vapor within your IGU and quickly seal it up before vapor enters again.

IGUs: Gas-Filled Window Units No Longer Filled with Gas

Nearly all windows today, whether new construction or replacement, have, at their heart, an insulated glass unit, or IGU. This means two or sometimes three panes of glass that are factory-sealed together to form a single unit; they cannot be separated. Nearly every window is constructed this way now. Single pane windows are difficult to find and are mainly confined to older homes (pre-1980s) or outbuildings (sheds, etc.) where energy saving does not matter.

Heat or cold move more readily in an atmosphere like air. If the space between those two panes of glass were filled with air, it would do a fairly good job of acting as a thermal break.

But an IGU does a somewhat better job when that space is filled with dense gas. Enter argon and krypton.

These gasses are dense, meaning that their molecules move slower.

This causes the cold outside of your house to move slower as it tries to enter your warm house. Window manufacturers fill sealed IGUs with argon or krypton gas.

Foggy Window Repair Summary

  • The hole is drilled into the glass, solution sprayed in the window, and fog dries up.
  • Professionally done, not DIY.
  • About half the cost of new window replacement.
  • It will: get rid of fog and make your window look better.
  • It will not: replace the argon or krypton gas or improve its thermal performance.

But Gas Likes To Escape

There is a problem, though. If you have ever had a child's helium balloon, you know how difficult it is to keep gas contained. No matter what you do, the balloon eventually escapes.

It is the same with windows. This sealed environment is not perfectly sealed. According to Dr. Andreas Wolf of glassmaker Dow Corning, a host of factors such as "temperature and atmospheric pressure fluctuations, wind loads, working loads, sunlight, water, and water vapor that negatively affect their life expectancy."

All of those factors mentioned above describe the working life of a normal window. In other words, given enough time, your window seals will fail.

When the window seals fail—your window has two seals—the desiccant within the window panes saturates with water (if it had not been saturated years ago).

Your last line of defense is gone. Now the insides of your window panes will fill with tiny amounts of water that we call: fog. 

Fogged Window Options: Summary

Replace Entire WindowTotal fixMost expensive option
Replace Sash PortionsTotal fixDifficult to find a repair person
Leave It AloneCheapest of allVisual degradation
Defog WindowFog is goneGas is not replaced

1. Replace Entire Window

The complete fix is to replace the entire window.  After the project is finished, you will be the owner of new, gas-filled windows that have no fog inside of them.

Cost is the main problem, especially when you are replacing only a couple of windows. On a per-window basis, companies tend to charge more for replacing only a few windows.

2. Replace Sash Portions

If your windows have removable sashes, you may be able to replace just the sashes— keeping all of the frameworks in place.

For example, if you have a double-hung window, you have removable sashes. A double-hung window is a kind where both the top and bottom portions move.

Repair is usually cheaper than total window replacement because less labor and fewer parts are required. However, it can be difficult to find a company that will replace your sash only. Window companies make their real money with whole-house or substantially partial-house window replacements, not by switching out the occasional sash.

Contact the company that installed your windows, as they should be the ultimate source of sashes.

3. Leave It Alone

Surrender to the fog?

In fact, leaving your failed seal windows in place is a far better option than you might initially think. Failed seals mean two things: impaired visuals due to the fog and lower energy value.

If you can live with the looks, you might be surprised to learn that windows with failed seals still have moderate energy value.

AkzoNobel, the manufacturer of IGU gasses, estimates that an air-filled unit has an R-value of 2. This is about half of the insulating value of a double-pane, low-E argon gas-filled unit whose R-value is 4.3.

4. Defog Window

Window defoggers bore tiny holes in the IGUs, spray cleaning solutions inside, let the solutions dry up, and then install vents in those holes.

Do not be alarmed by the holes in the IGUs. First, these are tiny holes (2mm). Second, your insulated glass units never were completely air-tight in the first place.

As mentioned, your sealed windows have always had venting properties. It is impossible for sealed glass units to stand up to the pressures of solar heating and subsequent cooling. Even without those exacerbating factors, major IGU manufacturer PPG estimates that all units naturally lose 1% of their gas per year.

Window defogging usually costs 1/2 to 1/3 of the cost of window replacement.