Originally Posted by SergeantSilent
Problem with doing the front fan intake, and back out, is that the front fan in-front of the HDD's is probably not getting very much air in.
Currently I have all fans blowing in.
Choose a fan with a high static pressure for the HDD in-take fan (in general for anywhere that is obstructed, either CPU heatsink, hard drive cage fan, or fan where there is a filter and door in front of it). A noctua NF-P12 is probably a good choice. Calculate the CFM of all your intake fans by adding together the CFM at the appropriate RPM. Subtract the CFM of your exhaust fans. Ideally you want a slightly positive result in order to create positive case pressure so that dust does not get sucked in but is instead prevented from entering by the higher than atmospheric pressure in the case.