Funny you should ask. I keep it in my bedroom. At idle it's quiet. As long as the temp in the room is comfortable to cool, the fan often shuts off. But the machine isn't exactly stock any more.
Initially, it was stock with a standard 5.25 cd drive and 3.5 HD installed. Both remnants from older systems. Everything is pretty tightly packed. The hard drive obscures the heat sink on the motherboard limiting convection, and generating it's own contribution to the heat profile. The box was typically warm to the touch, and the fan ran constantly.
I removed both drives and replaced them with
this and a 2.5" hard drive.
I was able to mount the 2.5" drive in dvd adapter chassies. It would have been nice if the bottom plate had been designed for that, but a little work with a drill press did the job. The drive reports temps about 106f.
I also did some surgery to case, specifically I removed the sheet metal where the 3.5" drive was mounted. That was a matter of drilling out a couple of pop rivets. This gave maximum clearance above the monolithic cpu/northbridge heat sink, improving convection air flow.
When the cpu is running hard, the fan goes on high, many screensavers cause this condition, even so, the air coming out is cool to the hand, so I suspect the fan could be toned down some.
Late last night, the CPU load while watching a DVD, caused the fan became obtrusive. I pulled the cover off, unplugged the fan, then leaving the cover off, I finished watching the movie. The only noise then being the dvd and hard drives chatting back and forth.
The case is well sealed, fan exhausting out the left back side, with air only being allowed in thru a grill on the right side. When in the stand, the right end is down.