Intake or exhaust?

[Mercuryaces]

I've got only one fan in my case besides my CPU and GPU fans, it's located in the back, should it be intake or exhaust, also, would it be a good idea to have more? If so, where?

[Oshino Shinobu]

If you only have the one, make it intake. You would want more in most cases though. Two intake fans in the front and have the one at the rear as an exhaust is a good setup. 

[zombienerd]

I recommend intake (with a filter) for single fan operation.  It really doesn't matter to airflow whether it's being pushed in or sucked in, but it does matter to dust where the air comes from and goes.

 

As for amount, you should usually have at least 2 filtered fans on intake duty and 1 on exhaust.  This creates positive case pressure which prevents dust from getting sucked in from every crack.

 

All that said, if your temps are good, and you don't mind cleaning every once in while, why spend more money?

[1234vietnam]

make it an intake. most people agree that the ideal setup is two in the front one on the back. 

 this video can probably help you out

[HazeTheBeater]

If its only one, It wouldnt really matter that much. I would say either on the front or the back. If its on the front put it in the upper slot and be mindful no hard drive cages are obstructing the airflow

 

[LogicalDrm]

Only single should be exhaust. However this depends also about your case and other parts. Like if you have top mounted, rather modern PSU and blower GPU, intake might be also fine. Otherwise exhaust as all your other components are throwing hot air back into case.