For a bit of time, I ran an over clocked FX 8320 and crossfire 7970's. The heat that machine put out was tremendous. I only had a wall mounted AC unit so I had to practically take my shirt off when I loaded it up.
This was back when I was a student and had the FX and one GPUs. Getting an internship meant that I had the money for an upgrade, and the cheapest, most straightforward was to get a second GPU, or so I thought. Wasn't even that cheap because I had to put both the GPUs under water to keep them from overheating when both in the same PC.