Air Conditioner - Sizing Guidelines

It is critical that the capacity of a room air conditioner be the right size for the room being cooled. An improperly-sized air conditioner can result in a cold, clammy environment or an inadequately cooled room. The comfort level in a room is often more a factor of low humidity than low temperature.

  • An oversized unit (a larger BTU unit than a room requires) results in the compressor running for short periods of time and being off for long periods of time. As cold air leaves the air conditioner in a small room, it is deflected off of the walls back to the air conditioner and prematurely cycles the unit off. This results in cold spots and hot spots and very little loss of humidity.

  • An undersized unit (a lower BTU unit than a room requires) results in the compressor staying on most of the time and the unit not adequately lowering the humidity level and temperature in the room.


Factors to consider when sizing an air conditioner:

  • For sizing guidance, first visit: Air Conditioner Buying Tips

  • For additional assistance matching your room size and shape to the air conditioner size, visit: Energy Star Room Air Conditioner Buying Guide.

  • Heat/Cool units can be used as the sole source to cool a room but are not recommended to be the sole source of heat for a room in very cold climates. Since the heat is intended more for supplemental heating, size the air conditioner for its cooling capacity and not the heating capacity.