Optimal Fan Placement and Direction for Air-Cooling a Computer

This is a rather interesting article on the subject.

It was our assumption that the tests with ALL the fans in operation would produce the best results but it didn’t. Time to idle represents how effectively the configuration removes heat from the PC case. The shorter the time the better. CPU peak and idle as well as System peak and idle are easy to interpret. We would like to think that System temperature represents an average of how cool every component in a PC is.

• The top and rear exhaust produced the best CPU and System results but nearly placed last for time to idle. We tested three times for this result as we didn’t believe the first two.
• A single rear exhaust fan produces the best results overall. This flushes the theory of more is better right out the door.
• A top only or top and front combination places in the middle of the pack for CPU and System peak cooling BUT does whisk away the heat in a very short amount of time.
• Even with no cooling fans besides the heatink…heatsink size and type of fan can deliver good results.

So there you have it. A few theories dashed upon the rock perhaps. At least for this type of PC case and components. What should be taken away from this? Quite simply that more may not necessarily be better but, for us enthusiasts, more may be cool…for looks.

What you want to do is move air through the PC. You want the case to be a bit like a wind tunnel. The best tactic is to have one intake and one outtake. For low noise I recommend a slow moving 12cm fan at each point. Since warm air rises it's also best if your outtake is somewhere high and your intake somewhere low.

I happen to have an inexpensive (50 euro) case with an intake 12cm fan at the bottom front and an outtake 12cm fan at the top back with both fans running at half speed. The amount of cooling this simple setup provides to all the components is considerable.

A note about intake fans though; they suck in lots of dust, so you'd be well advised to have some sort of air filter (a piece of stocking could work, if you can't get an actual filter). Also you could run the intake fan just a bit faster than the outtake fan to create pressure inside the case that will keep dust from accumulating on all the little holes and cracks throughout the case.

Accepted answer is good. It could also be important to think about the graphics card when balancing positive or negative air pressure. Positive air pressure assures that the graphics card do not use recycled and often preheated air. Reference: http://www.silverstonetek.com/techtalk_cont.php?tid=wh_positive&area=usa