I’m in SW Wisconsin and we bought one a number of years back. Unheated. I find it most useful from April through May for growing early spring things, and hardening off veggies that are eventually going into the garden.
Even on a sunny March day - that thing can hit 114 degrees if I don’t open it up!
There is a learning curve for sure, but if you can afford it, I highly recommend having an unheated greenhouse for getting the season started off early and extending the season in the fall. One winter I had cherry tomatoes into December!
There are plenty of books on unheated greenhouses. Elliot Coleman is my favorite author on the subject - he grows year-round in Maine! If he can do it, so can we! :)
In reality, I need to make much better use of what I’ve already got. It’s a 10’ x 8’ set-up with two roof vents and double doors across the front.
https://gardenerspath.com/how-to/greenhouses-and-coldframes/unheated-greenhouse/
Thanks Diana! Maybe I should get a thermometer. 😀