Quote Originally Posted by Weedhound
250 should be plenty for you. I kept a 1kw hps plenty cool with a 170cfm and 4" in ducting and that worked just fine so you should be for you. (in fact that's what I use for my 400w hps these days.......4 inch ducting and my 170cfm fan, lol.)
With the single 400w hps, I assume you're working with a rather small grow space. How do you think the 170cfm w/4" ducting and carbon filter added in (minus any glass on your hood) would help towards odor control in your situation? You know, the take out some heat and kill off some odor at the same time approach. Are you currently venting out of your space?