i was wondering about that, and i watched way too many vids on youtube about "the right way" to set up an air cooled hood.. the one guy had a hole in one wall drawing fresh air inside his grow room with the vortex which then went thru the hood to cool the lamp as it exhausted out the other side.. that made the most sense to me, as the point of the air cooled hood is to cool the lamp, i guess its pretty much the same thing, but there was something also about creating negative pressure when the fan was on the other side, sucking air out, which i think was a bad thing.. but opinions/vids were pretty much 50/50 with the fan either being on one side or the other. Would definately like to know more about it..