From my Zone 7 perspective, I think you might well enjoy some very comfortable temps in your greenhouse on sunny days, even if they're quite cold. As pointed out above, as soon as the sun's rays are dimmed - whether by clouds or even bare tree branches, the cooling will be noticeable. Twin-wall polycarbonate glazing will have a slightly higher insulation value than glass, and you can (as I did for my greenhouse) insulate the north wall and install a draft barrier around the perimeter where the greenhouse meets the soil. Alas, I cannot find the log I kept our first winter with the greenhouse: inside/outside temperatures and weather conditions (sunny, cloudy, windy, calm, nighttime, etc.). Will keep looking as it might be helpful to you. January and February are the coldest months here, and can easily get down into the 20's in the daytime and teens and a few single digits at night. Even on a frigid day, with ice and snow, I'm comfortable in a tank top or t-shirt in my greenhouse. Although not diagnosed with SAD, winter was always a tough time for me, but being able to spend time out in the greenhouse, with the sights and scents of green, growing - even blooming - things, has made a big difference.

I am still potting up stuff for the garden club sale! lol Also sticking hydrangea cuttings into big plastic pots to root in the basement over winter. I make rounds every day to check on the garden and am happy to report that the Franklinia is blooming like crazy and the Grevillea victoriae is covered with blossoms. We are going to try to do cuttings of it this winter. The hardy fuchsias are all blooming and don't seem to mind the cold weather at all. Tomorrow we will start to make room in the basement to store some of the new hydrangea babies and a few tender things that we grow on the deck. I love this time of the year!

I'd do anything to get out of here for a vacation. Never been to Florida, much less the beach/ocean. I love seafood, the sun, and my birthstone is aquamarine, so it would seem like I would be a beach person, lol. I wish I had a greenhouse or a sun room. I'd practically live in it all winter long. A mostly rainy summer didn't help for the lack of sun (and when it was sunny, the humidity was unbearable). I hope your trip to the greenhouse yields in some new Hoyas and other plants. The Snow Queen is really kicking into gear. Freezing rain currently, which will change into plain rain later on once it gets warmer. Seeing the snow is pretty for a while, but one gets tired quickly of shoveling it, lol. Brad AKA Moonwolf

Good idea and you get fresher air to boot. When I used to work before retiring in 2008, my office was filled with many of my house plants as well. Men used to joke 'Welcome to the jungle' when they came in.