Mine is on the floor....very little space, but it's there. The "intake vent" (or whatever you call it) is facing out so I get fresh air. Mine has a humidifier with water in it. Do NOT place one of these overhead. :) :) Why??? Because you'll drown!!!! Seriously, the moisture builds up inside the tubing and will drain down onto your face. :) :) Yeah, happened to me!!!!!
One other: The electric cord is a smidgen too short to reach the outlet....which is in the ceiling. I have a little wooden "stand" that was for a totally different purpose.....but is wonderful for sitting the machine on it. It's sorta like a mini side table (Super MINI)