Originally Posted by vladd
I'm of the exact opposite opinion. I prefer overpressure to underpressure. As you said, air will find it's way in but it will also find it's way out. By using an intake fan, you can control the air that goes into the case. When you have pets as I do (4 cats) or a dust rich environment, it is essential. by controlling where the air goes into the case, you can filter it better. If you have more than one case fan, use one (preferably the largest) or more for intake and use one for exhaust. Exact configuration will depend heavily on the layout of the case and the position of the fans.
Sorry for the late reply, been away and busy.
You haven't actually said anything that disagrees with my statement, you've just restated my argument but said that you use intake fans to achieve the same goal.
The most efficient thing that you can do is to create a wind tunnel. if you succeed in that, then the question of positive or negative pressure becomes immaterial because you are maximizing airflow over the components. However, most people don't or can't do this.
What I'm saying is that negative pressure is more efficient for cooling. And the guy who posted before me said that his only exhaust was his PSU fan. IMHO, that's just bad thermal planning, period. Sure, it can depend on the case, but a single exhaust fan means that as much warm air is going through that PSU.
Anyways, I've tried dozens of airflow configurations on nearly a dozen cases (both low grade and high end) and, in my findings, negative air pressure has always been easier to get right with fewer fans that positive air pressure.
At the risk of oversimplifying, air rushes to fill a negative pressure region so by carefully controlling where your air comes from and how it flows, you can guarantee airflow over components and you can guarantee that your case won't be holding alot of hot air that's going to get vented by your PSU.
@garydolson - a breeze is nothing but a movement of air. What causes the air to move, be it push or pull, is immaterial. The difference, however, between forced air and vacuum is that forced air creates quite a lot of turbulence in your air channels, creating eddies and dead spots. Negative pressure means that the airflow of the case will be relatively uniform throughout which can make life difficult for local hot spots which means you must be careful about how you let air into the case.
The only way that you would create a 'warm bubble of air around your PC' is if you were to fully enclose your case on three sides. But then you'd suffer similar issues with a positive airflow setup.
I do concede, though, that in dusty environments, it's much easier to keep the dust out with positive rather than negative pressure. I've got a pretty dusty place so I resign myself to hitting my cases with compressed air and cleaning the filters every quarter or so. A small price to pay for a quieter, cooler, case.