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Originally Posted by gingerbee  exhaust fans are nice but not needed at all it's basic thermal dynamics positive pressure will easily push hot air that is rising out anyway. just my 2 cents |
The goal of any good system builder is to be able to control the airflow through the case. i say "through" because you want to move it ALL in and ALL out quickly. Positive air pressure as your talking is generally a bad idea for anything but a basic low power computer.
The reason i say its a bad idea is because most computer fans are not designed to be high pressure fans, because they are not designed to be used this way, the actuall "pressure" in the case is not really that high.
Sure you will get positive pressure, and you will loose the hot air like you want to, but the volume of air going through the case will be alot smaller than if you were to present the fans in the conventional way.
Another issue you'll have is that you cannot control where the air is exhausted, most computer cases have vent holes, so typically you'll loose the air in those locations but unless the case is designed for that in mind, those locations will likely not be ideal.
Another issue you'll have is that you'll create alot of "dead air" pockets. What this means is that you'll have areas inside your computer case where air will not flow at all, these areas absorb heat and cause hotspots. Almost all cases, even properly designed will have dead air pockets, but with proper airflow you can eliminate the ones that will cause the biggest issues.
When your doing a computer build it is important to put it together in such a way that you can get a very large volume of air in, through with as few obstacle as possible, and out. The longer the air is in the case, the hotter it becomes, and the hotter everything else gets.