How to Clean Foggy Double Pane Windows

Double pane windows, commonly known simply as double glazing, has long been the go-to window solution for increased thermal insulation in homes and buildings. They are a big improvement in terms of ease-of-use from older style sash windows, which required a storm window to be installed in winter in order provide the necessary insulation.

For all the positive things that double pane windows have brought, such as decreased energy usage, homeowners have long been plagued by another problem that creeps up after a few years. The bane of double pane windows is the dreaded F-word: fog!

Foggy double pane windows are a nuisance for several reasons, not least because the fog makes it hard to see out of them. There are things that one can do about it, ranging from cheap and temporary, to expensive and permanent. But before we look at how to make your foggy windows sparkle again, we need to look at how they are constructed, in order to understand the nature of the problem of fogginess.

Construction of Double Pane Windows

Double pane windows consist of a window frame and an Insulated Glass Unit (IGU). IGU’s are sold as sealed units. They consist of two panes of glass separated by spacers, and sealed around the edges. The spacers are often filled with a desiccant that absorbs condensation. The gap in between the panes of glass is usually filled with an inert gas, such as krypton or argon, which is a poor conductor of heat. The size of this gap is the biggest factor that determines the degree of insulation that the panel would provide.

Reasons for Fogginess

IGUs usually have a lifespan of 10-25 years before they start fogging up. IGUs with longer warranties, in the 20 year range, will be less likely to fail early than those with shorter warranties. Obviously the cost would be higher for longer warranties, but the higher cost will be entirely justified in areas with huge temperature differences between summer and winter.

There is very little you can do to prevent foggy windows. By the time they start showing signs of fogging up, their seals are probably already ruptured. A bit of condensation in between the panes of glass is usually an indication that the desiccant is saturated. This saturation, in turn, happens when the seals that are supposed to keep moisture out and the inert gas in, is no longer doing its job.

At first there may be only a bit of condensation, which may or may not disappear after a while. Later, when the problem becomes more severe, you may notice an opaque layer of sediment, not unlike what you would encounter on a glass shower door.

The thermal insulation of severely foggy windows will also be somewhat less than it should be.

Remedies for Foggy Double Pane Windows

There are a few things you can do about your foggy windows, ranging from very cheap to very expensive. Ultimately, replacement would be inevitable, but having a few more options will at least buy you some time. Let’s have a look at the most and least expensive options:

  • Least expensive option: Just leave it!If you can live with the foggy window, you can just leave it. It will still have about half of the insulation value of a new IGU, which is still better than for single pane windows.
  • Most expensive option: Replace the IGUThe most common way to fix foggy double pain windows is not to clean it, but to replace it. This can be fairly costly, unless the failed IGU is still under warranty. This is also the best option, since you will have a brand new, crystal clear IGU, and better thermal insulation to boot.

Window Cleaning for DIY Enthusiasts

If you don’t want to replace the IGU yet, for whatever reason, there are some things you can do to try and clean it yourself. Going this route is a compromise between the other two options, since you will have clear windows, but lower thermal insulation. You can fix the problem with a few simple tools and household cleaners, but there are also several commercially available cleaning kits. The method is the same in either case.

Here’s what to do:

  • Drill two holes on the inside corners of the window, one on the top, and the other one diagonally opposite at the bottom. Cool the drill bit in a cup of water when it gets hot. If you don’t have a drill, read our cordless drill reviews to find the best one for your home.
  • Insert a piece of plastic tube into each of the holes. The top tube should be able to reach the middle of the IGU.
  • Attach a funnel to the top tube, and pour window cleaner into it. Move the direction of the tube around to reach the entire inner surface of the glass. Collect the drained window cleaner from the bottom tube in a bucket or bottle.
  • Once all the dirt on the inside has been removed, allow the window to dry.
  • When it has dried completely, cover the holes with clear industrial packaging tape, or use a waterproof sealant.

There is also a more difficult method that is definitely only for the handiest of handymen, but that might give a longer-lasting result.

  • Remove the IGU from the frame, and lay it down on a workbench.
  • Cut the seal against one of the panes of glass, using a utility knife. Optionally, you can also cut the seal against the other pane of glass to remove the spacers entirely.
  • Clean and dry the inside of both panes of glass thoroughly.
  • Optional: Open the spacer channels, and replace the old desiccant with new molecular sieve beads.
  • Lay the spacer channels on a pane of glass, and the other pane on top.
  • Reseal the unit along the edges using a silicon sealer suitable for use on glass.
  • Leave it to dry thoroughly overnight before reinstalling the unit.

This solution should last fairly long if it’s done with the right materials, and with an appropriate level of skill. It still won’t provide the degree of thermal insulation of a new IGU, but as far as DIY fixes go, it could last for years.

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