We have central air but the upstairs is always about 5* warmer, so I bought a window unit for our bedroom and turn on the ceiling fan to circulate the extra cool. I dont turn it on until about an hour before bedtime and make sure the door is closed. Its sure alot less to run that if needed than to run the central. Sometimes we dont need the entire house cooled so I use it if needed just for that room ! They are pretty cheap and not much to run the newer models.