Well, 1300 sq. ft. of it is a finished basement, walk out on one side and built into a hill so the walls are naturally cool, the 5000 btu Haier is keeping te lower level comfortable, and if the house starts the day cool, the other one will keep things comfortable upstairs until late afternoon if it is in the north side living room window. That's why I think we could get along fine with 3 of them. The house has thick plaster walls and ceilings, that once cool, will keep the house cooler all summer. If the plaster gets hot, it takes about 3 days to get the house cooled off to a comfortable temperature with just the central. When we moved in last summer, the A/C had not been run at all until mid July, and it took a good 36 hours to make the house bearable with the central and one window unit. Once the temperature is regulated, the units can cycle on and off even in the 96 degrees we had today. I just think three window units at about 4.5 amps each cycling on and off individually would be more efficient than the central unit, which is set at 71 ish, comes on at 73, and turns off somewhere between 66 and 68. The central unit is also about 20-22 years old, so is probably less than efficient.