Cleaning a Foggy/Hazy Window Insulated Glass Unit (IGU)

This is how I cleaned up my hazy windows (the haze is on the inside surfaces). Many window companies will tell you that it can't be done without replacing the glass units. In practice, it's simply not cost-effective for a business to spend more than a few minutes at your house.

As a homeowner, it may very well make sense to do this if you are handy and have a little bit of time. This is especially true if you have large insulated glass units that are heavy and costly. The window pictured above, for example, would cost about $1000 in glass alone (likely twice that with labor to replace it). It only took a few hours including trial-and-error to completely clean it up.

Total cost for tools and chemicals (for several windows) is well under $100.

Goals

1. Clear up the interior surfaces (make the window transparent again)
2. Retain insulating properties (more on this in the next step)
3. Keep window from fogging up again (for as long as possible)
4. Do minimal work (I don't want to move a heavy window unit)

Basics

• Pump Sprayer (1 Gallon is plenty)
• Several vinyl hoses
  I used these (outer x inner) sizes: 3/8x1/4, 1/4x3/16, 3/16x3/32
• Some thicker or thinner blunt-tip needles
  (14 gauge or thinner, 4+ inch long).
• Vinegar (10% if you can find it).
  About 1/2 gallon per large window.
• Pure Alcohol (100%)
  About 1/4 gallon per large window.

Depending on your window, you may also need:

• Glass drill bits (if not tempered and seal is hard to access)
• Siphon tool of some sort (if gravity draining is not possible)

Optional:

• Aquarium air pump or an air compressor with a blower (for quick drying)

NOTE: Amazon pays me a tiny percentage from sales when someone buys products via these links. UPDATE: Amazon refused to pay me, so ignore that.

Before we start fixing, let's understand how windows become foggy and hazy in the first place.

When windows are new, the insulated glass units (IGUs) are airtight. With temperature cycling over the years, the seals weaken, allowing a tiny bit of air to get pushed in and out by the pressure. This breathing action will push humidity in and then push only some of it out. Over time, moisture will accumulate inside, overwhelming the desiccant and leading to fogging. If this goes on long enough, this water will deposit minerals and dirt onto the inside surfaces of the glass, leaving swirls.

The story doesn't end there. Eventually, the microscopic fissures in the seal will widen, allowing air to go in and out more freely. This may actually dry the inside of the window, but the deposits will remain. This is how you get a hazy, partially opaque window.

But What About Insulation and U-value?

You may think that with the failed window unit seals, your window insulates poorly, but this is not true. Air is an excellent insulator, it is largely the movement of air (convection) that leads to heat loss. Inside your glass unit, there is very little air exchange happening, and the thermal efficiency is barely affected by tiny cracks. Even argon gas has little effect on the U value, so if you lost it, no big deal (see chart). This is why it makes more sense to repair the existing window units than to listen to salesmen that want to sell you new ones.

Obviously, defogging and dehazing a window involves cleaning the inside surfaces. Therefore, there are only two problems we need to solve:

1. How to get inside
2. What to use once we're in.

How to Get Inside

How we get inside will depend on your window. I'll assume that you don't want to take the IGU apart any more than I do. Therefore, you can either make a hole in:

• The outer glass pane (if your glass is not tempered)
• The seal between the panes.

If you have tempered glass, you cannot drill through it, so you must go through the seal.

What kind of seals do you have?

If you have soft seals, you may be able to poke through them with a bent piece of wire without removing the glass unit. You may need to melt your way through any plastic layers.

If you have metal seals, you'll need to drill them. To do this, you'll probably need to remove the glass unit, or at least pop it out of the window slightly, so that you can drill from the side or bottom.

My windows are tempered, but they have soft seals, so I'm poking through the seal without removing them.

BTW: The reason why I recommend drilling the outer pane and not inner is that we want cold dry winter air to dry the interior, as opposed to having humid interior air condensing on the cold glass. For most people, winter has the largest temperature differential, so this works. See also "To Seal or not to Seal", later on.

What To Use Once We're In

The process is fairly simple:

1. Spray some vinegar (10% seems to work well) onto the inside glass surfaces
2. Spray some alcohol (100%) to rinse them and to accelerate drying.
3. Wait for it to dry, or blow some air inside to speed things up.

Sprayer Needle

Whether you're going through glass or the seal, a spray needle is your best bet. You can buy "blunt tip needles" like I did, or try to use a ball inflator needle. You may need to bend it to your needs (longer needles are easier to work with). I found it easiest to bend with a piece of tight-fitting vinyl hose over the needle to keep it from folding.

You could forego the needle and just use a vinyl hose to spray, but a needle is easier to control and may require a smaller hole.

Pump Sprayer

We'll use a regular garden chemical pump sprayer to deliver both vinegar and alcohol. The only modification is to adapt the wand to the needle. I did this by removing the original spray tip, then stepping down with three different vinyl hose sizes until I got down to something I could mate to the needle.

I used a heat gun to stretch the hose diameter as needed (heat it up, stretch with needle-nose plyers)

To prevent leaks, you can use zip-ties over the hose connections.

Air Blower (optional)

Because I'm impatient, I chose to accelerate final drying from weeks to hours. I did this by using an aquarium air pump and blowing air through one of the holes (and out the other). You can use the needle or the hose, if it fits.

I also tried using an air compressor at very low pressure. I used a blower (shown in picture), mated to the same vinyl hose arrangement. This works fine, but running a compressor for hours is annoying and much more dangerous.

Glass Drill Bits and Siphon

If you do need to drill glass (and it's not tempered!), drill with the smallest diamond coated bit that will fit both your needle and the smallest vinyl hose you are using. The ideal location is in the corners, about 1/3 inch away. You still need two holes (one to spray, one to drain). You will need to use a hose to siphon out the vinegar and alcohol*. I did not drill my glass, so you may want to research how to do that safely (for example, a plastic hole guide may be helpful to keep the bit from wandering and scratching the glass).

* ⚠ Do not use a vacuum cleaner! You will most likely start a fire if you suck up alcohol.

If you are going through the seal like I did, poke at least one hole through the bottom if you can. This will allow the solutions to drain out naturally. In my window, there is a frame drain plug that gives me access to the space below the IGU, and I just had to melt a hole in the window plastic frame (this is hidden inside the window) to gain access to the seal.

A Note On Hole Locations

A few commenters have pointed out that having one hole at the top would make spraying easier. I completely agree. The ideal arrangement for a rectangular window is two holes placed diagonally, whether in glass or seal. In my window, going through the bottom caused the least amount of exterior damage, so I had to work extra hard to spray upwards.

Shaping the Hole

If you poke through like I did, you'll bend the seal into the shape of a little crater, and it will keep the liquid you spray from draining completely. To fix this, I bent a needle into a hook so that I can grab the edges of the volcano and pull on them, bending the seal into a funnel instead. That shape is also less of an eyesore.

⚠ Remember to wear eye and hand protection. Disposable gloves do not hold up well enough, use thick rubber gloves. A face shield may be a good idea. ⚠

Vinegar

The first step is to coat the inner surfaces of the panes with the 10% vinegar solution. This will hopefully dissolve any mineral deposits left there over the years. The goal is to coat the entire interior surface of both panes. For this I need my spray to come out in a tight stream so that I can aim it precisely and so that it can reach all the way to the top of this rather tall window. I had to play with the shape of the needle and its tip quite a bit to get this right.

if you are drilling through the glass, you may need to suck the liquid out manually using a siphon type tool or a mity-vac. Do not use a vacuum cleaner on alcohol, it will catch fire!

Alcohol

Once the vinegar drains out, the next step is to rinse the vinegar out with alcohol. This is just like the vinegar application. Spray enough to reach all glass surfaces. Now you wait.

While you wait, you may want to use some water to rinse all the tools in case they have vinegar on them, and walls and any surfaces that could be damaged by acid.

⚠ Fire Hazard Warning! Remember that you now have a window full of flammable alcohol vapor! Do not use a vacuum cleaner (air will be exposed to spark) or any source of ignition! ⚠

Now, you can simply wait for the alcohol to evaporate through the holes you made. This can take many days. You'll also want to somehow keep bugs from crawling in there (screen material can work).

If you are impatient like me, you can use an aquarium air pump or a compressor* to blow air into one of the holes, replacing the air inside very quickly. This approach can clear up the vapor in minutes and dry droplets in a few hours.

⚠ Compressed air can easily blow up your window if it can't escape. Ensure that you have an unobstructed exit path (a second hole) and use very low pressure (slower is better, anyway).⚠

When the window is dry, it should be completely clear.

The window may still be drying for a while longer, although it is clear. You can test by plugging the holes and waiting a day (do you see any fogging?)

* I no longer recommend using an air compressor. It is unsafe and inefficient. A cheap aquarium air pump does a much better job.

Once your window is fully dry, you have a decision to make. You can fully seal up the holes you made, or you can leave tiny gaps to allow any moisture to escape. There are pros and cons.

If you seal it up and moisture gets inside, it will stay there, so you'll eventually be back to square one. If you leave it open, moisture will definitely enter, but it will also leave (albeit very slowly). The window will fog up when cold rain hits warm glass, causing moisture to condense, drawing more moisture in. It will clear up in a few days. This will also (eventually) cause the window to haze (although this may take years).

There may be some trial-and-error to this step. In very humid climates, sealing up the holes could yield better results.

Option 1: Seal It (this is what I did).

Just caulk the holes or use the sealing method of your choice, ideally when humidity is low.

Note: caulk may add moisture to the interior as it dries. I wound up doing the following after caulking:

1. Waiting a day, then poking through the caulk with two needles and blowing more air (with an aquarium air pump) through one to remove the moisture. The needle holes should self-close on exit (note: I bought some finer needles for this, 18 and 21 gauge). This was done in the summer, so humidity was still high, and the window started to fog up in winter. I let the pump blow for about 24 hours.
2. Waiting until winter, then repeating the above process on the driest, cold day (about 25F/35% in my case).

Now the window no longer fogs up even in winter.

Option 2: Let it breathe

You can loosely cover the holes to keep bugs out.

If you drilled through glass, one option is to insert plastic plugs with a pinhole poked in them. Good options are decorative screw covers, plastic anchors, hot glue, etc. The remaining hole should be too small for bugs to crawl inside but still allow a tiny bit of air exchange.

Good Luck!

Let me know how it goes and if you improve on this process.