# good or bad fan position?



## gophynna (Aug 12, 2005)

Okay, I'm going to ask my first question.. It'll probably be pretty newbish...

How do I tell which way is the intake direction and which way is the outtake?

Also, is this setup okay...and which fans should be blowing in which direction...

I have one fan on the top of my case inbetween the space where the psu and cdrom are.

I have another fan on the side panel of my case.

And I have a fan at the very back of my case just below the psu.

The psu is dual fan.

Which way should each of these fans blow for proper airflow?


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## Tumbleweed36 (May 14, 2005)

Hi,

You will get some disagreement on the fans on the top of the case and the side panel of the case. There should be no disagreement on the fan in the back of your case. 

The normal case should have the rear fan blowing air out and a front fan drawing cool air in. I would assume that the top fan would serve the same purpose and should be drawing cool air in.

the side fan is done differently by many people. In my opinion, I would have it drawing cool air in, but you have to be very careful that you don't create case turbulance. Therefore, how it impacts the normal airflow might depend upon how it fits in the total airflow. 

That is my personal opinion.


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## kodi (Jun 30, 2004)

The front fan should draw air inwards and all other fans should blow air out.
If the fans are working just try to place a piece of light grade cardboard over the fans,if the fans are notworking there usually is a small arrow on the side of the fan indicating the direction of the airflow

EDIT looks like we posted at the same time


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## toxict3arz (Oct 12, 2004)

i always thought .. back fan blows out and everything else blows in... am i wrong?


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## Tumbleweed36 (May 14, 2005)

Hi Toxict3arz,

No, you aren't exactly wrong in many cases (get the pun). Anyhow, if you have just tow or three fans, that is the rule. However, there are times when that is not always the case with certain top and side case fans. I think mainly though, that you are right on track with your assumption. 

The thing that must be preserved, is that you don't create a turbulance within the case. If some alteration needs to be made to fan direction to prevent turbulance, then take that action. An area that is widely misunderstood is the direction of the CPU/heatsink fan. It must blow DOWN  over the heatsink and CPU and NOT blow up drawing air from that area. That alone can acocunt for considerable temperature change with some units.

*Kodi,*_

Got you on that one. For once in my life I either typed faster than you did or just hit the button earlier. Anyhow, glad that I beat you for this time. Have a great evening._


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## Volt-Schwibe (Jan 12, 2003)

i remember almost arguing about that here at this forum.

i was saying it needs to blow onto the heatsink, and there was some seriously strong resistance to the idea.

since then, i have decided that the majority opinion is that it should blow towards the heat sink, and if someone wants to disagree, i just hope it doesn't cost them a processor.

this here is a diagram i had made to explain...

in figure1, we see a fan, and the airflow around it. the blue is where is is sucking in and creating a pocket of low pressure air, causing it to draw air in from all directions, and the red shows the high pressure stream of air blowing out of it. you will notice the output is a more tightly controlled funnel of air.

figure 2 shows the high pressure blast flying cleanly into and around the heatsink, reaching fully to the base.

figure 3 shows the low pressure suction drawing air past the heatsink fins, but only the tips... this makes for a higher heatsink base temp. (the colors are backwards in fig 3)


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## ebackhus (Apr 21, 2005)

In regards to an inverted (top exhaust) CPU fan solution, I've seen people put tape around the top of the heat sink to force airflow at the base of the heatsink, eliminating the problem. Now, I don't know if this is the greatest idea so I won't risk it on my PC. I also prefer the downward flow because it also sends air across the MOSFETs and RAM sitting nearby.


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## w00t (Jun 30, 2004)

I used temp tape (the stuff they wrap exaust in) for the heat sink once and it sucks do not do it, the pressure builds up in the enclossed space slows the fan and heat seems to just build up after the first minute. The air must pass over the heat sink then "carry the hot air away" not stay there. Also cool air for the mobo and related is critical.


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## ebackhus (Apr 21, 2005)

Which is also why liquid coolings can be a problem. Sure, you can OC like you're mad but there are other parts of your system that heat up as well. That's why more and more chipsets are coling with sinks and fans.


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