Computer case fans?

The one in the front, or side should suck the air in, the one in the back blows it out. It's done in this way to flow air in a steady stream over the components. It picks up the heated air off of the processor fan, and heatsink, plus cools down the Northbridge/Southbridge chipset. I have a 4-1/4" inch fan blowing in, thru a tuned port that comes down in size, to fit across a 3"x3"x3" solid copper finned heatsink, with a 3" fan on top. I have a 4-1/4" fan sucking air out the back. ( I took the fan/heatsink combo off the other day to clean the top of the cpu, and bottom of the heatsink, to apply fresh thermal paste. Forgot how heavy that sucker was! I'll bet that heatsink weighs a pound or more!! Looks like it was a solid copper block, that had fins machined on it, down to leave a 3/8" thick plate at the bottom! Heavier than a full can of pop. lol!)

The back should blow out and the front should blow in. This should be the only way to do it. I've never heard of someone having both front and back blow out; the fans are going to cancel each other out by fighting for the air.

BTW the back fan SHOULD blow out because nearly all power supplies dump a lot of heat in the back of the computer. By having the back fan blow in, you're only carrying the heat back in the computer - it's counterproductive.