For your room I see various options. Whatever time of the year you are going to need ventilation from the outside. Best set up would be to run your 2 400 through cool tubes, have an inline fan pulling air from outside over the lights (this will also enable you to grow closer to the lights with better light penetration) The inline fan sucking air over the lights would then need to be exhausted out of the room. I would either have a Y duct so that you can then pull fresh air into the room as well (and you can use the same fan that you use for the lights,) or better yet get a seperate inline fan for fresh air. With air being pulled in you could probably get away with a passive exhaust, although if you are going for a room like this, you'd be better to get a carbon filter and inline fan to exhaust out and clean exiting smells. So you need:2 X cool tubes,2 X inline fans (ideally) 1 X carbon filter. ducting.