I currently own:
2 i5's
1 i7'
1 dual xeon 5650 server
1 dual xeon 5650 server
1 xeon 5650 server
1 i3
1 fx 8350
They are all in the same room, and with a little ventilation do just fine, although yes it will heat up the room.
My problem is power consumption, doing the math it's almost better for me to rent a dedicated server rather than run my own, but when I bought mine for goldfarming I had no idea what any of this was.