Computer Case Fan Airflow Direction

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

Threaded View
I want to install two additional fans in my case but I need some
questions answered first,

1.  My case (Centurion 5 CAC-T05 US) has an intake on the front and an
exhaust on the rear. I will install an additional intake on the front.
 Should the side fan be exhaust, or intake?

2.  What direction does the CPU fan blow air: on to the cpu, or draw
air away from the CPU?

3.  Same question as above, only pertaining to the graphics card fan?


Re: Computer Case Fan Airflow Direction

On Tue, 02 May 2006 00:31:08 GMT, no@spam.invalid (Jackpine) wrote:

Quoted text here. Click to load it

Pretty sure it blows in --- towards the heatsinks. There are long
discussions about this on the net.  Some claim they got lower temps
with the fan blowing out on the CPU. Others argue it takes a shroud
around the CPU to effectively blow hot air off the heatsinks away from
and careful design so its better to have the fan blow down into the
heatsinks and then outward away at the sides. There are other
arguments given but all the ones Ive had blow downward.

Frankly I would love to see the definitive case fan setup guide.
People always say you need equal force from fans blowing in and out to
keep dust from settling in the case. I have tons of problems with
dust.  After a few months theres dust clogging the window screens.
I look in my PC and the graphics card and CPU fans can get really
clogged. I just cleaned all of those thngs in the last few months.

If you go by a simplistic formula --- if you have one in and one out
and you add two more ---  I suppose they should be similar in air flow
and one should in and one out. So two in at the front and one out in
the side and one out in the rear. The problem is does the one on the
side sucking air out cause any problems?

Does it suck a lot of the cool air coming in from the front
prematurely? I dont know. Doest it cause any turbulence in the case
that disrupts the normal flow of air from the bottom of the intake to
the top outtake in the PS?  The usual diagrams of in from bottom and
out the back at the top seem simple enough but I wonder how side fans
fit in the scheme of things.

Re: Computer Case Fan Airflow Direction

how do u measuere the fans.  i know mm,  what do u acutually measure
on the fan.

Re: Computer Case Fan Airflow Direction

On Tue, 02 May 2006 15:31:20 GMT, no@spam.invalid (korky122) wrote:

Quoted text here. Click to load it

They have a cfm figure which shows how much airflow or air it moves. I
have no idea if its accurate or not but thats the only thing I see on
it to compare fans since obviously various fans have different speeds.

Re: Computer Case Fan Airflow Direction

On Tue, 02 May 2006 00:31:08 GMT, no@spam.invalid (Jackpine)

Quoted text here. Click to load it

You should leave it as it came.

That's almost always as an intake.  However, the side fan
actually makes the front/bottom of a case harder to cool,
but since you are adding the front fan you will likely be

Quoted text here. Click to load it

Which way does your CPU 'sink fan move the air?  You want
the side fan to compliment that airflow pattern.  If the
side fan is nearly directly overtop of the CPU 'sink fan and
the 'sink fan exahusted out of the sink (which is less
common), then you would orient the side fan to also blow out
of the chassis, keeping the airflow in the same direction.
It is far more common to have the CPU 'sink fan blowing into
the sink instead, and so most case side fans also blow in,
are intakes.

Quoted text here. Click to load it

Leave it as it came.  They don't just randomly throw the fan
on there, it's out of the box the way it's supposed to run.
If you mean that you have a second side case fan for the
video card, IMO that's too much side intake (as it's
typically also meant to be an intake fan) and should
consider just blocking the hole for the CPU intake fan and
using only the one nearer the video card (keeping the air
intake the furthest away from the exhaust areas in the
middle and upper rear to provide benefit to the most parts).

The side-intake over the CPU was mostly initiated by Intel
so they could package cheaper heatsinks with their
hot-running P4 CPU.  If your CPU stays cool enough without
the side intake you don't need it at all, though it might
help cool the northbridge too but less often are they a
problem if the CPU is cool.

Site Timeline