Quote Originally Posted by FourOneNine
Obviously, it would be better suited to have the carbon scrubber at the complete end.

(passive intake)-->Cooltube-->Fan-->Carbon Scrubber--> AIR

Construction should vary mostly on CFM of the fan.

I run a 400W MH, on A OPEN reflector. 6inch Duct connect to fan then scrubber, I get 82F.. But my fan is 400+ CFM so I dont need any take holes, air gets pulled from cracks around the cab. My friends seldom wonder why Smoke gets sucked into my closet.
I would like to know the reason why "obviously, it would be better to have the carbon scrubber at the complete end".

Most setups I have ever seen had the scrubber-->light-->ducting-->fan-->exhaust. Because fans suck better than blow, forcing a fan to blow against the filter will diminish the volume of air flowing.

I'm guessing you could find supporting info either way, but this page talks about it at the bottom.