We have small (2200 sq ft) but tall (10 ft ceilings) old old house. No central air yet - we're waiting for the furnace to go out which the furnace guy says will happen pretty soon - so we have 3 window units. Highest bill so far was $250. We have timers so they turn off when we go to work but come back on at noon or so so the house doesn't have a chance to heat up too much. With the humidity here no way we could turn them off longer. We set them on high and hope for the best - we average mid-upper 60's. In winter we set heat at 60 and turn down at night - we cannot sleep in a hot room! So what we pay in the summer we save in the winter....