They can be adjusted by twisting them, and you can also remove the wax cylinder entirely to convert them into manual hatches, which is that I did for my roof hatch. You could twist them to the highest temperature in their range so they only open when the fan is already not doing a great job, but I do think you’d want to open the door or doors in that case, too.
There was some great input from other forum members on heating/coolinga greenhouse in the thread I started for my greenhouse awhile ago: