Demciflex dust filters

[Church]

Funkwagen: there can be another "gotcha" with TOO positive or too negative pressure - as in such configurations fans work extra hard to pressurise or vacuumise air in case, resulting in extra loss of airflow and cooling efficiency. Imho best is to have "slightly" positive pressure. It's not as simple as having one less fan blowing out then fans blowing in though, as one has to take into account that dust filters themselves (on fans blowing in) are resistive and hinder airflow. I'd say rather something like ammount of fans blowing out 1/3rd more then ammount of fans blowing in. One can check what resulting air pressure in case is by using something like lighter flame or smoke near some mesh/cutout/hole at case - if that flame/smoke gets pushed off case (positive) or sucked in (negative).
It's interesting to see how many case vendors wrongly implement dust protection. Eg. have dust filters on few fans, but clearly negative pressure fan direction balance overall + mirriads of meshes/cutouts in case back/walls where because of negative pressure dust unfiltered air gets sucked in instead of being sucked in just through dust filters.
EDIT
mingbogo: see above how resulting airpressure can be "tested" without calculating/tools