the inline duct fans should be used for air intake only. The "can fans" are used to cool light and exhaust the room. I have my can fans "pulling" room air through the light and pushing out through the carbon filter. If I push air through my light, all the little seems and holes in my hood become heat LEAKS, THATS WHY YOU PULL THROUGH YOUR LIGHT. Now the seems and holes become little suckers pulling hot air from around the hood IN. I use a inline duct fan to boost the air coming into the room from the a/c vent just for a little added cooling in the summer but thats all its good for. I use a kitchen/bathroom fan mounted on the ceiling to exhuast the hot air thats trapped high, actually 2, 1 in each room, into a "Y" and out through a carbon filter and they work fine against the restriction. heres a couple pics, filters in window box,exhaust fans, ect.... the way i have it set up, im cooling 2 x 1000w with 1 x 4" growbright can fan. Im adding a 2nd light to my flower room this week. My setup will change a little. Now im adding a 6" to cool the 2 in the flower room and the 4 i have will cool the veg room light. these are all open to room air so they work as exhaust too.