Yeah you were blowing too much in and not extracting enough.. lol. Dependng on the fan. You can piggy back them. So your air velocity is like 900cfm exhausting. And it will suck through nicley. I'm going to do that in a few weeks... I need to piggy back my 6in inline fan with my 8" booster fan to go to my filter through my hood and then out... right now I'm using my booster fan to extract. I need more power to use the carbon filter and stil have good negitive air pressure. But that's my setup I've used a 4in and 6in inline fans on a speed controller as intake. And they seem to work bout the same. But the 6in is 2x the power... right now I'm stricktly passive. I Need more negitive pressure. Lol