COOLING RULES OF THUMB Air conditioning capacity requirement: A simple rule of thumb for climates such as South Florida: one ton per 400 sq .ft. (Commercial) or one ton per 500 to 1000 sq .ft. (Residential) 600 standard ROT.

CFM per ton. Most air conditioners produce 400 cubic foot per minute per ton.2 ton provides 2ton X 400CFM/ton=800 cfm.

A 1200 sq .ft. house may require a 2-ton unit. Or count the supply outlets: 8 outlets @ 100 cfm (estimated) = 800cfm = 2 tons needed. Do not buy an air conditioner that has more tons or BTU's of capacity than you actually need.

Can an air conditioning system have too much capacity or be OVERSIZED.

Yes. If a system is over sized for a building it may be able to drop the indoor temperature so rapidly that the cooling cycle is too short to permit adequate reduction in the humidity level. Remember that indoor comfort is a function of both temperature and relative humidity. Also, since an oversized air conditioning system will be cycling on and off more frequently, not only is the building actually less comfortable but it may also be harder on the equipment, thus shortening its life. Turning electric motors on and off is hard on them. It costs more to start than to run long cycles. Example would be driving on the highway or driving in the city. Stop and go costs more.

A properly sized Air Conditioning system should run nearly continuous on the hottest days of the year according to Energy Efficient Building in Florida.

How to Determine BTU's or Tons of Cooling Capacity of an Air Conditioner from its Data plate. One ton of cooling is 12,000 BTU (British Thermal Unit) BTU is a standard unit of the amount of heat it takes to raise the temperature of 1 pound of water 1 degree Fahrenheit. Your outside condensing unit should have a model number on the data plate. 2te036aeg1 036 would indicate 36,000 BTU /12,00 BTU per ton=3 ton.

012 =12,000 BTU=1 ton cools 600 square foot

018=18,000 BTU=1.5 ton cools 900 square foot

024=24000 BTU=2 ton cools 1200 square foot

030=30,000 BTU=2.5 ton cools 1500 square foot

036=36,000 BTU=3 ton cools 1800 square foot

042=42,000 BTU=3.5 ton cools 2100 square foot

048=48,000 BTU=4 ton cools 2400 square foot

060=60,000 BTU=5 ton cools 3000 square foot