However, negative pressure cases have a bad habit of sucking in dust through every opening, including optical drives, card reader slots, other front panel cracks and openings.
Here's a solution I've incorporated into my latest case project...a separate positive pressured chamber surrounding the rear of the 5.25" bays.
The chamber gets the positive pressure by means of the few rear vent holes on the rear of the Fortron PSU. A small amount of airflow normally escapes from the PSU at that location. And since my CPU is blowing all its' hot air out the case through a duct, the airflow out the PSU vent is relatively cool....usually around 30C.
The positive pressure that gets into this chamber is filtered at the intakes, and it escapes (a very small amount) through the front of the drive openings. The slightly positive pressure in this chamber prevents un-filtered air from entering here...and should keep my drives dust-free.
