THANKS

I am getting ready to set up my system in a green house. I am trying not to overthink the process. Ive seen some setups that left me scratching my head. Im still trying to decide on tubs or tubes.
Another question came to mind.I am in Georgia, for the most part we have mild winters. no snow etc.. I have a solar water heater to help with temp control in my stock fish tank. My question is:

during the winter say for lettuce, is it more important for temp control on the roots of the plants or overall temp of the greenhouse?

thanks jb