I have a portable air conditioner in my studio apartment. It works, but just barely. My electricity is included in my rent, so I don't know how much the electric bill is, but my landlord told me to keep the air conditioner off during the day when I am not home. But if I do that, when I get home, I can crank it all the way up, and my apartment doesn't get cool until about 2am. I thought about buying another one of the units, thinking maybe 2 won't have to work so hard to cool the place down as one does. I am just trying to find the most efficient way to stay cool. It's hot here in the desert this time of year!