+ or - pressures in case, effect on cpu fan-------

[firebirdude]

Not sure what section this belongs in....there's no cooling section... but....
I'm looking to replace my case fans (80mm) with ones that move some serious air. Upwards of 70-80cfm a piece. All fans will be on a fan controller. I worried that I may still create a large negative or positive pressure in my case at some point. I have heard that this can effect the cpu fan's preformance. What do you guys think? If you must have one, is it better to have a positive or negative pressure in your case? Which brings me to my next question... what about having no fans at all for intake? Just a bunch of holes. Then have a couple of large fans of the exhaust. Or vice versa. The exhaust fans would obviously pull large amounts of air freely through the intake holes.... sounds like something to me... what do you guys think?

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[Mr5oh]

Ideally you want to have roughly the same amount of air as intake and exhaust. If there is more air going out, it will suck it in from somewhere. Honestly I did this in my last case. I had 5 80mm fans moving roughly 70-80 cfm each (Plus what ever the PSU moved). This really didn't make much a difference in my temps, yes it helped, but it tripled my noise level, and only dropped my temps a couple of degrees. I think I would have at least an intake in the front, just so you have some fresh air blowing over top the hard drive area.

Oh and when I got the sound meter out, my case with all those fans in it, measured 70db sitting next to it, 58 db in the next room.

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[Mr5oh]

Oh and in my case, I had two intakes on the side, blowing towards the video card, one intake in the front, and an exhaust on the back, and top.

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[jihiggs]

i dont know of any 12v fans strong enough to create the kind of negative presure in a case that would be needed for there to be much concern. not to mention all the little holes in a normal case.

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[Crashman]

Having equal intakes and exhaust makes the air move more easily and controlls direction of flow better, but in reality you really only need exhaust fans. 2 exhaust fans plus the power supply exhaust will pull out most of the heat of most systems provided the intake holes are of adequate size to allow a free flowing of air.

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[peteroy]

Put all your fans on exhaust and only 1 fan as intake.

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[Crashman]

I've had NO intakes and only 1 exhaust on a small tower with a P4 2.6C at 3.2GHz and passively cooled northbridge, and my northbridge temps never exceeded 35C. But my front panel was full of ventilation holes.

Front fans are handy because they move high speed air past the drives or direct it under the RAM so that the rising column of air cools the RAM better, but in reality they aren't needed for most people.

An additional exhaust fan would have been handy for me to reduce northbridge temps by up to 5C.

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[firebirdude]

So I take it my thoughts of no intakes isin't actually a bad idea? Provided intake holes are large enough. Cool. Might have to think about that. So what effect does a positive or negative pressure have on the CPU fan? I also have a side case fan. I wouldn't think I would want it blowing against the flow of the CPU fan either.... I'm sure the case fan moves more air then the CPU fan anyway...that might get ugly.

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[Mr5oh]

I think Jihiggs had the best point:

i dont know of any 12v fans strong enough to create the kind of negative presure in a case that would be needed for there to be much concern. not to mention all the little holes in a normal case.

I don't think you are going to get a fan powerful enough to cause your CPU cooler problems.

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[endyen]

The only fan (other than hsf) that is really important, is the one in the bottom of your psu. The second psu fan does more for system cooling than any other. Maybe that's why all AMD recommended psus have them.
They are also good for Intel systems, esp prescott.