The standard size of AC units is in tons. That means the capacity to cool in equivalent tons of ice.
The other standard is BTU. Stands for British Thermal Unit. One unit is the amount of heat needed to raise by one degree F, a pound of water.
Calculating heat load has to be done with many factors--desired temperature differential, amount of insulation, amount of exposure to sun and wind, cubic foot volume of area, shape of area, internal restrictions to air flow in the area to be cooled, occupants, and any heat producing machinery.
· 1 decade ago