I put some used (cheap) windows in my pallet greenhouse and three of them were fogged. I searched online for how to remedy this and most of the advice I saw said to take it to a professional, and never try to drill into the glass. In lieu of that, I took apart one window frame and proceeded to poke holes into the sealant between the two panes of glass. A nail being to difficult I used a tiny drill bit, which gummed up quickly but made 1/8" holes in the sealant. I made two holes in the bottom where the rubber gasket ends meet and two in the top corners, where the rubber gasket is cut to make the corner. Yesterday was sunny so I just put up some backing boards, with a towel and let the sun do its work. Sure enough, the fog was lifted and the window cleared! It remains to be seen whether it will refog or not, but I'm stoked and will try the same to the other two foggy windows. Hope this helps!