I've taken me off the 'solution ' so others get a crack at replying, many seeing that green ' solved ' marker will pass on by.
To be a little more technical. cooling has two options:
Negative pressure, here you'll have more OUT than IN, ( 2x140mm exhaust, 2x120mm intake for example ) it works and is no real problem, the extra OUT will find air to pull through the case so temperatures remain fine, the only problem is that the OUT can draw air from unfiltered sources, not all cases filter ALL the incoming air, so you can end up with a rapid build up of material in the heatsink fins, increasing maintenance, especially if you have several furry pets in the house.
Positive pressure: As I suggested, here there's more IN than OUT, all the IN air is filtered and the excess IN air will find a way out, but it can be a little noisier, located in the front, the intake fan noise is usually not damped out so if you're after a really quiet system, the choice of fan is more critical than for a negative pressure system.