http://boards.cannabis.com/indoor-gr...-progress.html

That goes through it pretty thoroughly...

Basically, best to always pull air through the fewest bends possible. I have mine like this: carbon filter at the top of my closet, tubing from the cf bends down and around to my cooltube (don't use duct tape around the cooltube because it can melt), tubing then from the cooltube goes out my closet and to my fan. I put some duct on the other end of the fan to dampen the noise a little.

There's a nice little formula in that thread concerning how many cfm's you need for your space and light.