Case Fan

Posted on 2000-05-05
Last Modified: 2013-11-10
Okay, this may sound a little stupid, but should my case fan be pulling in air, or pumping it out?  It's attached to the front of the case, if that makes any difference.
Question by:Shish
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Expert Comment

ID: 2783137
Front case fan pulls air in.

Expert Comment

ID: 2783564
ok well actually it depends on what type of power supply you have running. If your power supply blows air out (newer ones should) then you want the fan on the case to be pulling air in. If your power supply blows air in (pulling air) then you case fan should be pushing air out.
Think of it as a wind tunnel. The ideal is to create circulation not pressure. If one fan is blowing the other should be sucking - otherwise they will be working against each other.
LVL 12

Expert Comment

ID: 2783950
garzajd: What makes you say newer power supply fans should blow air out? I thought ATX power supplies were all designed to pull air in to help cool the processor.
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Expert Comment

ID: 2784162
I agree with garzajd on that one.

It is not a question of blowing air in or out, but of cooling the components.  

The cpu fan and heat sink draw heat from the processor and into the
inside of the system case . Other components also release heat inside
the system case.  Whether the "hot" air is blown out or "cool" air is drawn
in should not matter, and depends on the venting design of the case.

A fan in the front of the components would act like an exhaust fan, while
one in the rear would act like a supply fan. Both woould be pushing air in the same direction.

LVL 48

Expert Comment

ID: 2784529
>> garzajd: What makes you say newer power supply fans should blow air out? I thought ATX power supplies were all designed to pull air in to help cool the processor.

The ATX specification says the power supply fan shoud draw air in.  Some manufacturers implement it the other way and use the power supply fan to draw air out.  Their reasoning is that the power supply heats the air up so why should you cool the processor with heated air.

Accepted Solution

sterl9 earned 50 total points
ID: 2784641
garzajd is correct on this. The older ATX power supplies had air being drawn into the case, the newer ones suck the air out of the case. You have to get the warm air OUT of the system case and suck cool air into the system case to keep it cool.

Expert Comment

ID: 2799857
Sorry sterl9 he's not talking the power supply fan. If you'd read the question correctly it's a chassis [CASE] fan.
The correct way for Case fan blowing is into the computer to FORCE cool air across the hot components,The excess air is forced out through the side vents.
The chassis [CASE] fan must suck air IN!

LVL 12

Expert Comment

ID: 2800039
Fixingit: I disagree. If the power supply fan is already pulling air into the case (as it is on my machine at home) it makes more sense for the chassis fan to pull air OUT--that way you get a forced draught through the case, which is going to be preferable to forcing air in at both places. (For your information I tried both ways round on my chassis fan at home, and pulling air out kept the internals much cooler than pulling it in).

Expert Comment

ID: 2800084
pjknibbs:As sterl9 pointed out OLDER ATX Power Supplys sucked air IN, newer ones blow OUT. The reason they blow air OUT is because blowing the already hot air from the Power supply over the Motherboard and components defeats the COOLING process.
LVL 12

Expert Comment

ID: 2800310
Fixingit: How does that invalidate my comment? Quite apart from anything else, I've *tested* this (on a machine drawing air *in* through the power supply) and I can categorically say that the ambient temperature in the case was a good 10 degrees cooler when the case fan was extracting air than when it was acting as an intake. I'd *much* rather run my case fan in intake mode because it's a lot less noisy when I do so, but I lose most of the benefit when I do, so what's the point?

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