There are more than one type of window unit. Down south, like in the pictured setup, they are evaporative coolant systems, and what they do is spit out water out the back. They basically separate water from the air and the temps go down due to the dry cooler air coming back in. These types of window units do not let any air out, but they do spit some water out, which can smell. We always use these in a room within a room, not in a window to the outdoors. Put a large plastic tote on the floor where the water is spitting out occasionally, and fill it qtr or half full with tap water. The spit water mixes with the larger amount of tap water and you can't smell it. Don't oxygenate this water. The amount of actual water that comes out of those things isn't a large amount. We've used 1 window unit on a 5' x 5' room or tent with no problems, and they are only about $100 at walmart. Keep in mind this setup only works in high humidity, hot areas. And they do make a little noise when they run, but usually a room within a room keeps that problem at bay. Get one with a digital temp setting.