How Many BTUs To Cool a Room? A 115 volt, 10,000 BTU Window Air Conditioning unit is capable of cooling a 500 square foot room without much strain on the unit. So a good rule of thumb is 20 BTUs per square foot. So for example, if your room to be cooled is approximately 10 x 25 you would have a 250 square foot space to cool, and would require a 5,000 BTU uni ...