I didn't realize you were talking about assembled windows. I don't think I have any that I would use for a greenhouse. I have some that are brand new and I eventually want to install them into my house...the two ends have no windows at all.

I must've misunderstood. I thought you had some old windows you were planning to take apart. Sorry.

Nope. I have a big pile of sash sans frames.

Gotcha. Not too hard to toss together a crude frame if you were so inclined. Guess it'd have to be compared against other venting techniques.

I went out and purchased a book on greenhouse construction to get ideas about that kind of thing. It took me years before I actually had the place, time, and money to build it. But, I had years to dream and plan.

I wound up using the fiberglass corrugated sheets on mine. There are a lot of the finer points that it doesn't have, but it certainly does the trick.

There are a number of things I'd do different were I to do it again, but I'm happy with it.

For my solar porch I went with 4'x12' Polygal double walled polycarbonate panels. When I had to redesign my house for sale after my ex left the realtor said that sort of thing didn't sell easily, so I ripped it off. I sold them on Craigslist easily enough, despite the screw holes. It was just a collector for hot air so was pretty narrow at 4' wide (vs 88' feet long), but was a good place to dry and store fire wood. I guess I could've put some planters in there.

Mr Incredible, it looks great. I bet that fiberglass was affordable, too.

The polygal ain't cheap. Unless you can find some sucker to sell them to you used, that is. :p