Step 2: Decide the pressure Set-up
Negative pressure Set-up
This happens when more air is going out of the case than coming in i.e. in the following example (it applies to any kind of set up, in cases with more than 2 fans, you add the CFM of the fans oriented in a particular direction) more air is exhausted by the rear fan than what is pulled by the front fan. This builds up a negative pressure. To compensate for this, air is pulled in from all the openings in the case, thus bringing in cool air. Though this is the best set up for cooling but is more susceptible to dust since air is coming into the case from the fans as well as from small crevices and openings. If your PSU has a dual fan set up wherein air is pulled from the case and exhausted, also add the CFM of the PSU’s fan.
Positive Pressure Set-up
In this set up more air is pulled in the case than what is exhausted. Though not as efficient cooling wise as the negative set up, its not all that bad either. The point to note here is that in a positive pressure set up, the air pulled into the case would be only from the intake fans. This is an excellent mechanism for cutting the dust entering the case. To go a step further, you can add a filter to the fan, similar to the one in an air-conditioner. You can easily source it from any hardware store and screw it between your intake fan and the case.
Good try.
