I have been told that moisture between the panes of insulated glass windows can be eliminated by drilling small holes att he top and bottom of the pane to allow air circulation. Any ideas? And if the condition has existed for a long time... will an interior stain remain? Thanks

Double-pane windows are made by purging the volume between the windows with dry nitrogen. This is done so the insulating ability of the windows is maximized. If moisture condenses between the panes, you can be sure that the insulating ability is compromised. The condensation cycle actually pumps heat out of the house in the winter and into the house in the summer.

I would recommend that you replace the pane.

If you drill holes in the top and bottom of the pane, the water will drain out and air circulation may dry it out. Interior marks will surely remain. The insulating capability of the window will be seriously compromised.

We had this problem with windows installed by Home Depot. They were a real pain to deal with, first claiming that there was nothing wrong with the windows; it mjst be something else. We recognized the problem as faulty manufacture. They later claimed that it was a problem with the supplier and that all was better since they had changed to a different supplier. I said fine, replace the faulty windows with proper ones from the new supplier. They refused to do that saying that they had already paid the old supplier for our windows, and, as such, they would only replace them with windows from their old supplier. It took many phone calls. We had representatives of Home Depot and the window manufacturer here multiple times. It took almost 3 years from the initial installation, but we finally got the faulty windows replaced -- but, only the ones that we could prove were faulty.

If your windows are still under warranty, I recommend that you contact your supplier and demand replacement. If they are not under warranty you are on the hook for the cost, but Perito is right. They should be replaced.

There are companies that claim to do a great repair job but I know of no DIYer fixes. Gas is only used in higher end thermopanes now and they sometimes use argon, pricey. YouTube - Get the Fog Out - Thermopane Window Repair Rochester NY