as a rule of thumb, never go over 80 degrees in your room at the plants or under 60. If you are introducing co.2 may be a consideration, my room is 8x4x8 and i got fifty plants in there and i dont vent either way and i run co2(Propane).

Who ever wrote this I hope you did not really mean PROPANE. Hey bro all this info sounds pretty solid, except for the propane thing. Co2 yes PROPANE NO!!! DANGER DANGER DANGER DANGER!! The best thing to do is take a little advice from everyone and then do what works best for you through trial and error.