Put a thermometer in that room and vent if over 80 ok, put right at the plants so you know what the temp is at them. With a 8x4x8 room and a (120v)one thousand watt hps, (or get a super ace bulb in that hps ballast for veg and bud and mount sideways with shade))you'll probally be good with only three plants. Just get a good multi speed smaller fan and put in there . Also a fan blowing around the plants will make them move and their stocks will grow stronger.

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).

If you do have to vent, get a length ya need of dryer vent hose and vent to your attac and put in a germicidal lamp on a timer. No smell no tell!

PS don't put that germicidal lamp in the room.