When considering air conditioner units for a home or business, you must assess the cooling capacity accurately. If your air conditioner has too little cooling capacity, it will not keep up with the changing temperatures and humidity outside. If it has too much, it will adjust temperatures too far too quickly, swinging the building between hot and cold and wearing out the unit. Cooling capacity is measured in tons or BTUs, and you can calculate it from the unit's label. Using some rules of thumb, you can calculate the ideal tons of cooling for a building as well.
Find the unit's A/C data tag. It will show various pieces of information about the unit, including the serial number.
Look on the tag to see if there is a number for Tons, BTUs, BTUHs, or MBTUHs. If there is a number in Tons, that is the tons of cooling capacity. If there is a number in any of the other three, that is the cooling capacity in British Thermal Units. All three -- BTUs, BTUHs, or MBTUHs -- are variations of the same unit, with MBTUH being 1,000 BTUs. Convert this number to tons of cooling by dividing it by 12,000. For example, 24,000 BTU = 2 tons.
Decode the cooling capacity from the serial number or model number of the unit, if the cooling capacity is not explicitly labeled. Encoding schemes vary, so you will have to look up how it works for your unit's manufacturer. This information should be available on the manufacturer's web site, or you can call technical support.
Calculate the tons of cooling capacity needed for your building using the following rules of thumb. For a commercial building, you should have one ton for every 400 square feet. For a residential building, you should have one ton for every 500 to 1,000 square feet.