Computer case upper back fan.

[bishy76]

So I have a very standard case and I can put one fan on the upper back of the case. I have a cpu fan obviously and a fan that is part of my gpu. I plan on buying a fan for the upper back slot and am wondering if it should be blowing in or sucking air out of the case?

 

[R_1]

the upper rear of the case is usually the exhaust. heat rises. heat from the CPU and heat from the GPU will rise and unless forced out of the case...
if the power supply is above the exhaust fan it will allow cooler air to get to the PSU, by forcing heated air out before getting to PSU. do not rely on the PSU as the sole exhaust source - doing this will force hotter air across the PSU.