I have never used my windows, I have four. I always use the door to the deck with its large screen door. It will also be so much easier to clean large panels down the road, rather than getting the green crud out of the crevices on the windows. Speaking from experience!
We have a good size fan built into the South facing glass wall, that is a necessity.
We have oil heat, which is part of the house, the warm air circulates through the whole house. Great on sunny Winter days, as the greenhouse warms up the whole house during the day. We also have AC, which is also part of the house. I would recommend having separate AC though. Especially if you keep it filled up with lots of plants during the Summer. So far, I have always emptied out my greenhouse for the Summer and scrub it out, and then take essentially the greenhouse off-line.
Also, if you have heating registers on the floor as I do, I would keep them raised, so when you water, you don't flood your heating ducts with water. Works well for me.
We have a sturdy steel bar along in the center of the greenhouse, to hang Vandas and large Cattleyas, I like it a lot.
