==original message==

<< We have an in-win q500 full-tower case.
 The power supply has a fan blowing out the back.
 We added an intake fan in the fan cage on the lower front.
 On the upper front we have a bay-cooler drive fan blowing in.
 There are two places in the case on the back where we could
 mount additional fans: one on the lower half (where the mother-
 board and the add-on cards are), and the other on the upper half
 (where the power supply and the drive bays are).
 If we were to add more fans, I suppose the upper fan should
 be an exhaust fan.
 If we were to add a fan on the lower back, should it be an
 exhaust fan (air blows front to back) or an intake fan (air
 blows bottom to top)?
 (We have a slot-A athlon with a dual-fan processor heat-sink
 on it, and an agp video card that came with a little fan on the
 video chip.  In addition, we have a scsi card, a cheap nic, and
 a legacy isa sound card.)
 Thanks for any explanation of the right way to do this.

      Frank R.Brown
      Frank.R.Brown@MailAndNews >>

Hi,
  The 3 general rules of thumb I follow for this are:

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
natrually 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.), 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.

Just my .02 worth,
Peter Hogan
[log in to unmask]

        The NOSPIN Group provides a monthly newsletter with great
       tips, information and ideas: NOSPIN-L, The NOSPIN Magazine
             Visit our web site to signup: http://nospin.com