How many btu to cool a 400 sq ft room?

Answer 1

While the question is not very well framed, the following information probably permits an answer to the intended question:

The rule of thumb is 2-1/2 tons of refrigeration per 1000 square feet.

1 ton = 12000 BTU/hour

... so 400 ft2 x 2.5 tons/1000 ft2 x 12000 BTU/hr∙ton = 12000 BTU/hr

Note that the appropriate answer is in terms of RATE of cooling (BTU/hr) not total energy (BTU)

It is impossible to answer the question as asked because the total energy required to cool the room would depend on several factors not provided with the question, for example:

• the beginning and ending temperatures
• height of the room - so that the volume of the room could be calculated
• humidity of the air
• degree of insulation
• whether the room contained only air or also furniture, equipment, people,etc.