My setup is: filter -> hood -> fan -> out. I also use a fan speed controller to give just a little more contact time with the carbon. Works just fine for me, and typically get about a year out of each filter. If interested in re-packing carbon to re-use the filter housing, a friend of mine has good luck running an orbital sander on top of it to settle the carbon and pack some extra in there. I personally just buy a new filter as it's pretty messy re-filling them.