They are fault tolerant insofar as they have hot-pluggable, redundant power supplies, redundant network cards, error correcting memory, RAID arrays, hot-pluggable nics, hot-pluggable fans, hot-pluggable disks.
Having one of these servers working in a reasonably well ventilated room IS keeping it in a reasonable environment.
They are well cooled, that's why they have multiple fans - that's why they are noisy.
The problem only arises when they can no longer reject the excess heat into the environment - or to put it in plain English, the room gets too hot. That simply won't happen running one single server (even with 4 CPUs) in a normal, reasonably well ventilated room.
How many PCs could you have working in your front room before they start doing "misterious" things? One? Two? Four? Eight?
You really haven't a clue, do you?