no need for in or out ventilation. keep the room sealed and have the vent in/out go through the lights. that will keep the co2 in the room and not waste it. a/c is only needed if the temp in the room is too high, this is the end of the summer season for most of us, so most of us find using an a/c the cheapest method of cooling a room. during the winter months heat isn't nearly as much of an issue.