If you are speaking of the Four Seasons brand and not using the term generically like some people do, I don't but a couple from my orchid society did and another member still does. The couple summered their plants outside. It still gets hot inside during the summer. They chose it because they liked it the best over the glass greenhouses they looked at. The other member bought one from a demolition sale and two blown knees later, had it up on her property. It does provide cooling challenges for her and her husband built some sort of venting system for it but it still gets hot inside. I looked into Four Seasons sunrooms and they didn't provide venting - only a fan in the roof. A couple in my sub have a home with one attached to it on a south facing wall and they say it gets hot in there. Their windows on that room are open all summer. The insulated high-e glass greenhouse I purchased still gets hot in the summer. I make sure my windows and sliding glass door on the greenhouse are open in the summer to draw air in when the ridge vent opens. If you decide to go with Four Seasons, I would find out if they still offer the fan option and how much air it moves. Another option is to purchase one that has as high a ceiling as possible since heat rises to the top. The only glass sunroom I've know to stay cool in the summer was attached to a house built on a wooded lot.

I think the owner meant you can use the boiler with a central AC unit if that central indoor unit had a hot water coil ontop/infront of it or built in. Find a local contractor to find out how much it would be to have a split cooling unit with HW coil. Then weather if it's necessary to close off the existing baseboard radiators so all the HW will go towards the new coil. Then you will need new ductwork also. Expect to spend over $10K for sure.

Chrisny, thank you for your opinions. I was hoping beyond hope that I would be able to get under the floor to install radiant heat, but no such luck. And I really don't want to rip up the beautiful tile floor. I only have about 6 feet of exterior wall space in which to put baseboard, so that wouldn't be an option. All other exterior wall space has either doors or sliders. Any thoughts about a 20000-30000 BTU cabinet heater? Do you think it'll cover the room enough to keep all areas fairly warm?

Where I grew up we had Hurricane season and recovering from Hurricane season. Here on Colorado's Front Range the seasons are perfect. We have 4 seasons. Just about the time you are getting tired of the activities associated with the current season, the weather changes and you have a new season. Our winters are not unbearable. Except for this year, when it snows it's usually 4-10 inches in one day and the sun is shining braightly the next day and melts it all. We only get snow every 3 weeks or so. The fall is wonderful with color and dry, cool days. Spring is when everything turns into amazing, bright colors. The days are still cool and everyone is out riding bikes and beginning to do lots of outdoor activities. And our summers never get really hot. We have several days in the upper 90's, but our humidity is usually in the single digits and very little rain. And, if you want a REAL winter, you can just drive a short distance (less than 60 minutes) into the mountains and have more snow than you'll ever need. In the summer if the heat is too bad, just drive right back into the mountains where the heat rarely reaches 90.