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Optimal Fan Placement and Direction for Air-Cooling a Computer

This may sound dumb but this is a genuine question.

I just bought an extra fan for the case and installed it. It's working fine. I would like to know the orientation of the fan placement.

Currently, it is blowing air out of the case. Is this the correct placement?

Apologies for not including a picture earlier. Here it is:

enter image description here

The fan is blowing air to the other side of the case. The side which is not shown in this photo.

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marked as duplicate by Oliver Salzburg Jan 9 '13 at 16:30

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Are you talking about the actual CPU (a chip on the motherboard beneath a heatsink), or the case (box which contains all the computer parts and holds them together)? – Darth Android Jan 3 '13 at 19:23
I'm sorry for not being clear. What I referred to was an extra fan for the case. Please have a look at the photo. Thanks! – Abhishek Sha Jan 3 '13 at 19:38
I might be mistaken (it's a little difficult to tell from the photo) but do make sure that the fan is properly secured to the case with all four screws. Not doing so is going to increase vibration in the fan (possibly coupling the vibrations to the case), which at the very least is going to significantly increase the noise made by the fan and very well might reduce its lifespan considerably. – Michael Kjörling Jan 4 '13 at 8:54
Another thing to keep in mind is that it is a good idea to push more air into the case than you pull out. And have those fans pushing air in covered with a dust filter. This way the chance of dust being sucked in through other non-filtered places is smaller and your case will (hopefully) remain a lot cleaner. – Svish Jan 4 '13 at 12:07

It depends on the rest of your setup. There are many ways to route the airflow though a case, but all of these follow the next steps.

  1. Air needs to enter somewhere. (Either via under pressure because all other fans are blowing air outside the case, or by using a fan which suck in relative cold outside air.
  2. Air flow must pass over some components which get hot. The CPU is the most obvious, but not the only one. (e.g. chipsets can get hot. Drives usually require at least a slow airflow to remain cool. Dedicated graphical cards often require a lot of cooling, ...)
  3. You do not want airflows to 'bump' into each other, working against each other. Usually this is solved by letting all cold air in at one end of the case and out at the other end. Since most graphical cards dump the heat at the rear, the most common design is to let cold air in at the front, and push hot air out at the rear.

If this (common case from point 3) is the case then orient the CPU fan to assist the airflow. If not, mount it in another way so it assists the common airflow and so it does not dump its (now hot) air on other components which need cooling.

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Am I doing it right? According to the photo? – Abhishek Sha Jan 3 '13 at 19:33
@AbhishekSha Appears correct – Kruug Jan 3 '13 at 19:55
Dunno, looks backwards to me from the point-of-view that it should be blowing air out the back of the case, not pulling it in from there. – martineau Jan 3 '13 at 20:36
@martineau Looking at the arrow on the side of the fan, it appears to be pointing out of the case, which is the direction of the fan's airflow. – Kruug Jan 4 '13 at 3:13
@Kruug: Indeed...I hadn't noticed that, so stand corrected. – martineau Jan 4 '13 at 11:46

Air should be taken away from the CPU.

Air should also (ideally) flow from the front of the computer to the back.

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The key word is flow... as in Air Flow.

You need a good, solid, relatively uninterrupted flow of air into and subsequently out of the computer case. I am not sure, but I believe in this case, where you use the term CPU, you actually mean the computer case.

Typically, there is at least one fan mounted in the front of the case drawing air in. It is usually positioned near the hard drives and forces air against or over them to increase cooling there. Your power supply, or PSU, usually also has at least one fan inside of it, positioned to draw air from within the computer case and push it out of the back of the case. Thus, a single fan pulling air into the case from the front, and the fan within the power supply pulling air out of the case will create a flow of air through the case.

It is better to create negative air pressure within the case... that is to say, it is better to have more fans pulling air out of the case, than it is to have more fans pushing air into the case. However, you do not want to put fans in spots so as to have them compete against each other. Your overall goal is to have air move across as many components as possible, to draw the heat they generate away and out of the case. Most cases will have at least one spot on the back of the case to mount a fan... and you would mount a fan there to move air out of the case... or in the same direction as the air is moving from the PSU fan typically above this spot.

If the case has a mounting position on the side for a fan, the direction of air flow from this spot depends on the design of the case, how many other fans you have already mounted in the case, and the direction of airflow. For example, there are cases that have a mounting spot on the side of the case directly across from where the processor (or CPU) is expected to be, and some of these cases actually include a vent hose to be mounted around the fan you put on the side of the case, to force air directly onto the CPU heatsink.

CPU fans... meaning the fans mounted to the heat sink that sits on the processor, will pull air from inside the case, and push it down into the heat sink. This of course, deals with the heat sink design that has a fan sitting directly on top of the heat sink. More modern heat sink designs now will mount a fan on the side of the heat sink, so that air is pushed across it, rather than down on top of it. This design tends to work in conjunction with a fan being mounted at the back of the case... where the air being pushed across the heat sink is then pulled directly out of the case by the rear mounted fan.

In short, where you mount this fan, and what direction it moves air, depends completely on your existing case design. You should, however attempt to put it somewhere that it will remove warm air from within the case.

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Thank you for the very detailed reply! – Abhishek Sha Jan 3 '13 at 19:36

Better computer cases have the desired direction of the airflow marked somehow, either printed embossed on the case itself, or specified in the manual.

Usually, rack-mounted cases draw cold air from the front, and eject it from the back. With consumer cases, this is also most often the case, but not always. If your case lacks any documentation about how the air should flow, just examine the existing fans, and orient your additional fan in a way that it adds more airflow in the same direction.

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Unfortunately, my case is ancient. I do not have any documentation. Please have a look at the photo that I've just uploaded. Thanks! – Abhishek Sha Jan 3 '13 at 19:34

This ways so that the hot air can be blown out:

enter image description here

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This photo is very informative. The photo that I've just added is a similar setup. Do you feel that it is right (from my photo)? – Abhishek Sha Jan 3 '13 at 19:35
your picture shows a top blow cooler which is not as effective as the setup from my picture, but you understood the point. – magicandre1981 Jan 3 '13 at 20:27

A general answer to your question:

When adding fans to a case, you usually have a certain order (I'm only talking case fans, not CPU, GPU, or other component fans):

  1. The primary exhaust. A fan placed near the CPU (the hottest component) blowing out of the back of the case. Note that the power supply is also blowing out the back of the case, so we vent all hot air out the same side. (If your PSU were venting in another direction, you may want disregard my advice.)
  2. The primary intake. A fan near the front of the case that pulls in air from far away from the exhaust.
  3. Extra exhaust/intakes. These need to be placed to support the main airflow from the front to the back of the case. (So you might have them at the top sides of the case to pull in air over the HDD. Or you could have additional exhausts at the back or over the GPU.)
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