A system which delivers a ton of cooling is one that 12,000 BTU/hour, where BTU is a unit of cooling/heating energy. The appropriate number of tons for a desired space depends on the size of that space. The cooling capacity required is also dependent on the following:

· the number and size of the windows
· the direction the room faces
· the available shade
· how well the room is insulated
· how many people use the room
· what appliances (computers etc.) are in the room