intake fans help reduce dust wedged in cracks, but exhaust fans in the back and top are the most important for system temperatures. That said fans can be had pretty cheap, so why not put one or two in the front (I only had exhaust for a couple years, but once I put a dedicated graphics card I added intake fans). The intake fans also dropped my hard drive temps.
The only fan that should be exhaust is the one on the back of the case and it should be faster than your intakes.
i've never used the top fans before...but i imagine the hot air can make things uncomfortable for the user if the tower is close enough, especially over long gaming sessions?
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