Planted Tank Enthusiast
Join Date: Jan 2008
Location: Cleveland, Ohio
You really got two options:
1st - Piped heating and cooling from your house to the green house. Add dampers to control the output. You'll probably need to add an exhaust fan for circulation.
2nd - If you want more controls, I would recommend adding individual heating and cooling unit in there. It might cost $$$ upfront but it will provide you great controls and stable environment.
I am not a heating and cooling guy but I know people if you need a recommendation of type.