mjb1032
It depends on the size of the rooms and how much heat-load they are subject to. An 8000 btu air conditioner can work great for a big living room on the shady side of the house. But put it in an upstairs room with sun streaming in from 4 windows and it won't keep up. Remember A/C's perform two functions they COOL and DEHUMIDIFY the air. If you think bigger is better its not, too large an A/C unit in a room will get it cool, but it will feel "clammy", because the unit will turn off before it's had sufficient run-time to dehumidify the room. It should say on the box what room size it's for. 5000 would cover an average bedroom. 18000 would do your whole apartment. Any of the major brands these days make decent units. Keep it clean, and it'll last for years.