New fan: blow air in or out?

[Duh]

Adding a new fan to the back of the case. theres one in the front sort of sucking air in (not much), then the one on the CPU. and i was going to add one to the back of the case. im thinking if it blew air out of the case that would be a little better, since it would help the other fan suck more in. if that makes sense....

[Okie]

i agree completely on having the new fan pulling air out of the case, that is how i set my extra fan up, and as it pulls air out of the case it will draw cool air in from the outside, since i added a fan to do just that i have noticed a great increaze in coolness overall, COOL!!!

[Mulchman MM]

Generally fans on the back blow air out, fans on the front blow air in, fans on the side blow air in, and fans on the top blow air out.

[Dumb_terminal]

Bottom of case: Fan Blows Air in [ From outside]

On GPU: Nvidia GeForce2 [GTS] Fan/heatsink combo there...

On CPU: Air is Sucked into the Heatsink, than is passed out to a "Chimmney Designed tube, by the Thermal take Volcano 2 fan.
i Reversed the Fan on the Heatsink, so that air is pulled in.Why: [ i want Hot air out of my case] by a Chimmney design

On PSU: air is pulled out from case.
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this was my setup on an AMD 1.2 GIG T-bird

[MGP]

Also, make sure the fan blowing air into your case is the more (or equally) powerful one. That will create a slight positive air pressure in your case.

This is a desired thing -- if you have a vacuum in the case, dust will get sucked into the cracks of the CDROM drawer, floppy drive, or any other removeable media drive you have. More dust on the optical components and heads make them fail sooner.

[Choozo]

Have I been wrong all this time keeping my front/lower fan blowing air *out* to keep those pesky little dustbunnies from entering my case there? :D

Cheers :)

[Strike]

Originally posted by MGP:
<STRONG>Also, make sure the fan blowing air into your case is the more (or equally) powerful one. That will create a slight positive air pressure in your case.

This is a desired thing -- if you have a vacuum in the case, dust will get sucked into the cracks of the CDROM drawer, floppy drive, or any other removeable media drive you have. More dust on the optical components and heads make them fail sooner.</STRONG>
Wouldn't a higher pressure cause things to be FORCED into the tiny cracks? Anything, that is, that is at a stagnation point within the case. Of course you can't have a "vacuum" in your case, since it isn't completely sealed (Le Chatelier's principle dictates this). You don't really need fans blowing any air in at all, though it may help. All you need is some convenient entry point for air, and the low pressure area created by blowing air out of the case will be equalized by outside air moving into the temporarily lower pressure area (inside the case, via the entry point).

Actually, now that I think about it, fans blowing air in is probably best because you want turbulent air flow within the case to maximize the convective cooling. If you just depended on the pressure gradient to force air in, it might form streamlines of laminar flow that wouldn't cool as well. Also, the higher the velocity of the air, the better the cooling capacity.

[slacker_x]

If all the fans are blowing in, you are just going to be moving hot air around the inside of your case. You want cold air coming from the bottom of the case blowing hot air out the top.

[MGP]

Strike,

That's correct about not needing an intake fan at all. But a slight positive pressure in the case (overall airflow is still in the bottom front and out the top rear) will keep dust from being sucked in through the drives since they are under a slight positive pressure.

Try disconnecting your front fan sometime (or partially blocking the intake) then blow some smoke into the front areas of your computer case. The low pressure inside the case caused by the power supply and/or rear case fan will pull air in through your drives.

I see this all the time of systems that have run for months (all my systems run 24/7, so I see this rather quickly if there's a problem).