You can keep your Mac Pro running for a long period of time but you have to take 3 things in consideration:
Temperature: Keep your Mac Pro cool with an air conditioner at a fixed temperature.
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i'm not too sure about the ambient temperature... don't the mac already run itself cool (not to mention dead silent)... maybe for laptops or imacs, but i'm pretty sure the mac pro is more impervious to warm sorroundings (i live in a very hot, very humid environment and so far so good)