In the newsgroup alt.comp.hardware.overclocking, where they daily deal
with heat on a very up close and personal basis, the advice is
unanimous: The ATX power supply fan should be set so that it blows OUT
of the case, rather than sucking in. The idea is that you don't
necessarily want the warm air from the power supply blowing directly on
your CPU, warming it up even further. Also, warm air naturally tends to
rise, and it seems more efficient to use this fact to our advantage than
to fight it by forcing warm air downward.

An ideal situation for a tower configuration, for example, might be to
have a case fan at the lower front, sucking relatively cool air into the
case and blowing it back and up across the motherboard and CPU. The CPU
fan, if any, will work in concert with this air flow, directing its warm
air upward and away from the CPU. Finally, the power supply fan will
take this warmed air in, add its own heat to it, and force this
super-heated air out of the case in the most direct manner - right out
the back.

In the newsgroup mentioned above, the regulars advise that anyone
experiencing heat problems should check their ATX PS fan and make sure
it's blowing OUT. Some ATX fans are installed to suck air in, and some
improvement in cooling will likely be realized if this is 'fixed.' My
brand new Enlight ATX mid-tower case arrived with a fan that blows out,
so I didn't have to accomplish it myself. Using Motherboard Monitor, a
temp sensing program that monitors motherboard temps on select machines,
my motherboard runs 5-9 degrees (F) higher than room temp. I consider
this entirely acceptable and haven't had a single problem. FWIW, I'm
running a Celeron 300A at 450 MHz.


Jeff Delzer



Dave Perry wrote:
>
> As a long shot I'm presuming that the case is ATX. If it is your problem
> could be the direction that the fan works in the power supply. Does the fan
> suck air in or blow it out? If it blows out then I found that to be an
> inadequate way of cooling the motherboard and cpu. I removed the power
> supply and turned the fan around the other way giving me 10 degrees extra
> cooling on the cpu and motherboard. I'm running a k6-2 300 and am cooling
> it with the power supply fan only. Hope this helps.

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