At 20:09 09/17/00, [log in to unmask] wrote:
>1. Intake fans down low (blowing into the case)
>2. Exhaust fans up top (blowing out of the case)
>    This arrangement makes sense as the air in the case will rise
>    naturally as it gains heat from the components inside (cool air
>    in at the bottom, hot air out at the top).
>3. Balance the intake and exhaust airflows, in CFM (cubic feet
>    per minute)
>
>For #3, add up the individual CFM ratings of the fans, and try to
>get them approximately equal, so intake equals exhaust CFM. If you
>have to favor one over the other, I give it more intake CFM, to
>give the case a slightly "positive" pressure (more air going in
>than out). This causes any air "leaks" around drive doors (CD,
>floppy, etc.), to "leak" air from inside the case to the outside.
>   The inside case air, especially if you have filters on the
>intake fans, is generally cleaner (dust-wise) than the outside air,
>and the drive mechanisms will stay much cleaner with the air leaking
>out rather than in, at the gaps in the drive doors.


I completely agree with this. I'd just mention that if you have
filters on any of the intake fans, their effective CFM will be
considerably less than the ratings of the fans themselves.

I have filters that are similar to foam air conditioner filters on
the two 80mm intake fans at the bottom front of my cases. I suspect
that these filters cut my inward airflow practically in half.

Regards,
Bill

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