Case air flow is dependent on case design, motherboard layout in the case,
position of additional pci/apg cards, type of cooling on the cpu and video
card (fan, heatsink, water cooled), wire location, and wire configuration.
In general you want air to flow in at the bottom front of the case and out
the upper back of the case. Having said that, the blow hole in the top of
the case would move hot air out using natural convection forces (hot air
rises). Seeing that the fans in the back of the case are elevated in
comparison to the front of the case hot air would naturally exit the upper
back of the case, therefore the fans in the back of the case should exhaust
out hot air (blow air out of the case).

The issue of the side case fan blowing air into or out of the case depends
on the location of the fan. If the side case fan is located relatively
close to the cpu then the side case fan should blow air into the case. If
the side case fan is located above the cpu and relatively close to the power
supply it should blow air out of the case. In most of the cases I have seen
the side panel case fan is located relatively close to the cpu and therefore
should blow into the case providing cool fresh air to the cpu fan.

In relationship to a positive or negative pressure in the case, my
experience and testing lead me to believe that a positive case pressure is
better for two reasons. One, the positive pressure will prevent dust from
entering into the CD drives and covering the laser lens. Two, a positive
pressure keeps the heat build up around the power supply from entering into
the case around the cpu. A positive pressure means that you will have
higher cubic feet per minute fans blowing into the case than out of the
case.

The best way to setup case cooling is to use a fan contoller or manually
adjustable high speed variable fans (thermaltake smart fans, evermax fans)
especially at the front intake area of the case and buy a cheap
indoor/outdoor thermometer to monitor the temperature, adjust the fan speed
and watch the case temperature at various spots (esp around the cpu and hard
drives). Remember that more case fans does not lead to better cooling,
proper air flow though the case leads to better cooling. It also helps to
remove those stupid built in hole drilled case grills with a demel or tin
snips and use a wire grill in its place (if necessary).

If you think that this is long, you should see an engineering paper or
article discribing the effects of fan placement within a PC case. It is
very complicated and unpredictable. Try it, monitor it, and see if it works
for you.


"Travis King" wrote in message
news:72HBc.70875$Hg2.61444@attbi_s04...
I have three questions regarding case fans even though I know that this is
an Asus newsgroup. Should the back case fan blow in air or blow out air?
Should the case fan in the side panel blow in air or blow out air? Should
the case fan on the top blow in or blow out? Help would be appreciated.
Thanks.