I grow in a tent in a room that might as well be a greenhouse.
Daytime temps get as high as 28C, even with the window open.
Nighttime temps usually hit around 20c but I’ve messed up and had it go as low as 16.
Basic thinking-
If -10 outside open window a crack
If 0C open an inch
If 10C and raining you are screwed 
Humidity is a real problem too but it stays within acceptable (barely) limits.
Hope that helps