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Fan Suction

Last response: in Components
March 24, 2010 7:09:23 AM

Are case and PSU fans intended to blow hot air from the case or suck cold air in to the case? I ask because I have several fans and they are blowing in different directions.

More about : fan suction

a c 92 ) Power supply
March 24, 2010 7:26:08 AM

General rule is front/low fans pull air in, while back/high fans suck air out. Side fans can be found doing either. This is because warm air rises, so you want the fans higher up blowing out. A blow hole fan at the top of your case should always be blowing out. I wouldn't worry to much about this unless your temps are high.
March 24, 2010 7:36:11 AM

Thanks! Very helpful :) 
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a b ) Power supply
March 24, 2010 12:08:47 PM

You need fans for both functions. The MUST be in balance - in fact, total air flow will always establish its own balance. You cannot exhaust air from the case without adding air to the case from outside - you can't manufacture air out of nothing! So what goes out WILL come in. Your task in setting it up is to help that process so that supply is nearly equal to exhaust. Then comes the great debate over whether the net balance should have slightly more intake (so the case interior is slightly pressurized and air leakage out of holes goes OUT of the box), or should intake be slightly less than exhaust so air leakage is INTO the box? I'll refrain from offering my opinion here, in the interests of NOT hijacking your thread into another debate.
a c 248 ) Power supply
March 24, 2010 12:09:21 PM

Typically the air flow is bottom/front to top/rear. The fans at the bottom/front of a case are intake fans and the fans at the top/rear are exhaust fans. Power supply fans are always exhaust fans. A case fan on the side panel is usually, but not always, used as an intake fan. Depending on the fan's location it may provide additional cooling for either the video card or the cpu.

Scroll down to the bottom of this web page to see an animation of typical airflow in a modern case:

March 24, 2010 2:40:31 PM

I have a power supply at the bottom of my atx case. A corshair vx550w, but there are also case fans at the top both extracting air from the case... Do you think this is ok?

To make for better air flow I usually remove my side panel.
March 24, 2010 2:43:37 PM

Thanks for your help though everyone!
a c 248 ) Power supply
March 24, 2010 4:45:29 PM

Yes, it is okay to have two exhaust fans at the top/rear of the case. That is the correct design configuration in modern pc cases.
a b ) Power supply
March 24, 2010 4:51:01 PM

This guide is also a very good starting point on the basics of case airflow:

A bottom-mounted PSU is handy, particularly if your case has a grill which allows it to intake cool air. A dust filter is recommended however since obviously the floor or whatever your PC is on will be the dustiest part of your room.