Have you seen the formula in here--> http://boards.cannabis.com/indoor-gr...-progress.html

That says 30% restriction for the carbon filter. You could have the duct run from outside the growroom to the cooltube, that way no stinky air gets blown out the exhaust. Or, I just put them all on the same line, with the cf being where the air goes in, the cooltube after it, and my fan was actually outside of my closet, pulling all the scrubbed air out the growroom. (I'd post attachments but they aren't working??)
You can see it here:
http://i363.photobucket.com/albums/o...w/Day36002.jpg
http://i363.photobucket.com/albums/o...w/Day36002.jpg

You might be able to see the earlier pics of how I set it up, fearing that the heat from the cooltube would be too much for the fan. In the end the fan could take the heat, and the closet was a few degrees cooler.