This will be my first time purchasing a window unit, and I'm a little confused. Most charts indicate that a 7,000 BTU unit is appropriate for a ~250 square foot room, however from what I can tell, these do not exist (only 6,000 and 8,000 BTUs are available). Also, none of the guides I see mention ceiling height, which I figured would be important (i.e. cubic footage seems more appropriate than square footage). Finally, many say that getting a unit that is too powerful actually won't cool as effectively, but don't really explain what this means exactly - if I put a 20,000 BTU unit in a 100 square foot room, would the room really be warmer than it would be with a 5,000 BTU unit? Or do they just mean that it would be overkill?
Finally, some 6000 BTU units, like the GE AEL06LS say that they are only appropriate for 150 square foot rooms, and I don't understand why.
Anyway, my room that is 233 square feet, with ~9.5 foot ceilings. Would it be best to get a 6000 BTU unit or a 8000 BTU unit?