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Q. About 10 years ago we replaced our original windows with vinyl thermal pane windows. These windows had Low-E film, argon gas, and a 10 year warranty. At 8 years moisture entered one of the sashes between the panes of glass and fogged up. The manufacturer replaced the window but the dealer charged for the labor of installation. More windows on that side of the house have gone cloudy. What is the life expectancy of thermal pane windows? What happened to the argon gas? How did the moisture get in? Can a glass dealer replace a thermal pane in a vinyl sash? What are the facts about thermal pane windows?
A. Generally, you can't reseal dual-pane insulating glass that has lost its seal and has formed a condensation fog between the panes. I have seen people try to do it but it's a doomed effort. There is a company from the UK and Canada called Crystal Clear Windows (www.ccwwi.com) that claims they can do it but I’ve never seen their work around here. Normally the whole glass assembly has to be replaced as you had done under warranty two years ago. I frequently walk into houses as old as yours and see a number of windows on the sunny side of the house in some state of seal failure or another. It's a common problem.
The space between the panes uses air as an insulator. The less expensive insulating glass technology is not really sealed completely tight and that has to do with the thickness and the strength of the glass. Fancy, high priced insulated glass windows-- like the ones you bought-- now are completely sealed using a stronger grade of glass and inert gasses placed between the panes such as argon. They also anneal a micron or so of metal to the inside face of the inside pane as a reflector for those heat radiating infrared rays and the whole package is quite remarkable from an energy conservation perspective. Those are called low-E windows, for low-emissivity, and they are the minimal quality that I would specify for both room comfort and energy savings during heating and cooling seasons. The less tightly sealed spacers have a semi-permeable membrane to allow pressure equalization between the outside air and the air between the panes. It has a dryer in it called a desiccant and when that fails the windows fog. Those windows usually have a five year warranty and last just about that long if they get direct sunlight at sometime during the day. Insulated glass windows in the shade tend to last and last. It’s the cyclic temperature changes from the sun that do in the spaces between the glass. When the dryer fails over time, the air entering the space between the panes of glass will drag whatever moisture is in the outside air along with it. When temperatures change, the moisture in the air now trapped between the panes condenses and you get the "fog" that signals that the seal has failed. Once begun the fogging will worsen over time both from additional moisture getting in even creating drips and a photo-chemical reaction from sunlight sets up that etches the inside surfaces of the glass. Your seals, as air-tight as they were designed to be, are failing and the action of the sun has driven the argon out and allowed moist air in that condenses between the panes. They made it past warranty. That doesn’t do you much good. The longest seal warranty in the window business of which I am aware is from Andersen and is longer than 20 years. It's quite confusing when you see all that's available these days in the window market especially comparing quality against price. You can contact the National Fenestration Rating Council (NFRC) in Silver Spring at 1-301-589-1776 or visit their website @ www.nfrc.org/ for some info on how to compare one window to another. Local glass companies can and do replace insulated glass. They do it every day but I can’t vouch for their warranty periods. You’ll have to ask. Generally, you’d be better off replacing the entire window rather than just an upper or lower pane that’s fogged up. It's a safe bet that the adjacent pane will soon lose its seal. After all, it's 10 years old too and experiences the same environment. Why only fix the upper sash just to have to do the same for the lower sometime in the not too distant future? In the old days we had single pane glass windows and maybe storm windows over that. The windows were air leaky at the edges and taking the storms on and off was work. The R value of that arrangement was barely over R-1. Windows have gotten better and more sophisticated over the years and old windows are like classic cars compared to what we have now. I like looking at them but wouldn’t want to rely on one.