Case can hold 5 case fans

[jrglol]

I have a problem with my "case". My case has 2 front, 2 top, and 1 rear fan holder(s). Do I have to put negative or positive air pressure?

My case : Antec P6

 

[Dark Lord of Tech]

+ Positive pressure \ more intake power than exhaust
- Negative pressure \ more exhaust power than intake

 

[Paperdoc]

There have been long discussions about the choice of whether a case should have positive or negative air pressure. My own opinion is that positive is better. Any case has several places where there are small air leaks. If the air pressure inside is slightly lower than the outside room, air will flow INTO the case at those points and carry with it small amounts of dust that will accumulate. If the pressure inside is slightly higher than outside, air will flow out of those leaks, preventing dust from entering. Then you must ensure that there are dust filters in front of the intake fans so that all air flowing into the case is clean. This will greatly reduce dust accumulation side, although it will NOT eliminate it completely.

In practical terms, ensuring this is set up and working requires some care. First, you need to ensure that the capacity or ability of your fan system is arranged on the basis of AIR FLOW, and not just on fan count or size or speed. Get the specs on what is the maximum air flow the fans you buy can deliver. IF ALL of your case fans are identical, then the number of them can be a good guide to balancing. In that case, simply ensuring that there are more Intake than Exhaust fans can do most of the job. But you need to consider two additional factors. One is that the dust filters you must have on the intake fans will reduce the intake slightly, so an exactly even number of intake and exhaust identical fans actually should produce a slight NEGATIVE case pressure. Further, those filters will restrict the air intake even more as they get clogged, so you MUST check and clean them from time to time to maintain good air flow. If you have even numbers of intake and exhaust fans, to ensure positive case pressure you can buy DIFFERENT fans for the intake locations so that they produce MORE air flow (in) than the exhaust fans do. You can do that either by using different sizes or by different fan models with higher air flow specs for the intake fans.

On the other hand, if you use an odd number of fans, you can arrange to have more intake fans than exhaust, and that probably will produce positive pressure if they all are similar designs. OP, you have a combination of fan potential locations. As a rough guide, one usually arranges front fans for intake, rear for exhaust, and top often intake if those latter are only case ventilation fans. For your situation, if you were to place four fans (front and top) as intakes and one rear exhaust fan, I would consider that too unbalanced. I would be more inclined NOT to put intakes in the two top positions. That would do 2 front intakes with dust filters plus one rear exhaust, producing positive internal case pressure. It would not use all of your fan capacity potential, but that would be OK for many mid-line system designs. You do not need to feel compelled to fill up all the fan spots. BUT if you are building a high-performance system that needs a lot of cooling you will need more than three fans.

Many builders are using AIO liquid cooler systems for the CPU, with a radiator and fans mounted in the top. If that is done, the impact of the air flow by those radiator fans (and of course, which direction they blow) has to be considered and that makes the whole thing trickier. In part, that is because the actual air flow produced by fans mounted on a radiator is much less than their max spec, because the radiator itself is a major restriction on air flow. It is impossible to predict the magnitude of this effect, so you can not know what your air pressure will be before it is assembled and working. If you are NOT using one of these cooling systems on your CPU this will not be a problem for you, OP.

As a practical hint, here's a way to test your air flow balance after your system is assembled and working. You need a small source or smoke as a "tracer". For this a smouldering incense stick can do, or maybe a cigarette. With the system running, slowly move the smoke source around the outside of the case, especially where there are little cracks for air to leak. Observe carefully which way the smoke blows, and that will tell you whether the air leaks are IN or OUT.