Cooling fans

[Taffy Apple]

I'm building a PC and seems I'm gonna have a bash at overclocking I also bought 2 box fans.

Its a dumbass question I know, but are they supposed to be blowing cool air in to or warm air out of the box? Or could I have 1 blowing in and another blowing out, so I get airflow thru the box?

 

[_Korruption_]

What kinda box fans?

 

[Taffy Apple]

Just a pair of zalman brushless power coolers. I'm just not sure which way round they need to go!