Question : Problem: Direction of coolong fans installed in PC case

Hi there,

I apologise in advance for what is probably a very simple and well known question, but...

In my PC at home there are three cooling fans installed, one at the top, one at the back and one that is situated at the side directly over the CPU.  Upon taking the cover off last night I noticed that there was a LOT of dust in the unit, particularly around the CPU.

I understand that these fans are there for cooling purposes, but my question is - are they there to draw hot air out or to blow outside air in?  I am thinking that currently they may be blowing air in hence the amount of dust, so which is better?  There are arrows on the fans which I assume either indicate the direction of air flow once running, or the direction that they need to face.  

Can someone let me know what the arrows indicate and which way the fans should be installed?

Thanks!

Answer : Problem: Direction of coolong fans installed in PC case

The fan on the back of your computer is almost always the exhaust fan to draw hot air out.  The fan over your cpu is to blow outside air in.  Typically fans at the top are exhaust fans as well.