Quote Originally Posted by Demoness View Post
Negative pressure is not quite as good as positive pressure, and I will list two reasons why.

1. The dust issue people have been talking about. If you create negative pressure inside the case, that is creating a vacuum inside the case that will suck air from any direction it can, and that is not limited to the fan ducts. You will be sucking dust in through all of the cracks and have a very dirty PC.

2. Air cooling works by the component conducting heat into the heatsink, and the heatsink conducts its heat into the air. If you can compress the air that passes over the heat sink, you are increasing the mass of the air in the same volume passing over it in the same amount of time. If you have negative pressure, that means the air is in vacuum and has less mass, and less ability to absorb heat.

The second reason is such a subtle effect that it will not change the temperature more than 1% at any given time, but the effect does occur nevertheless. There is literally no reason to use negative over positive. When I set up air flow in my clients builds, I use two rules.

1. If they choose a case with a top vent, that vent is always exhaust, because heat always rises. The idea goes the same for intakes. Cool air should enter the bottom, front, and the side of the case, and exit the back and top always. (in air cooled rigs)

2. CFM stands for Cubic Feet Per Minute. This tells you how much air your fan moves. Add up the CFM of all of the fans you are using in your build and make sure that the intake CFM is higher than exhaust. Generally, you can avoid math entirely if you only ever use the back fan by the processor, and the top fan as exhausts, and make all others intake.

I hope this helped explain with a little detail instead of "pos bettar herp derp"
Great thanks!