The easiest place to find AC tonnage is on the AC unit itself. Go outside to the condensing unit and look for a data plate mounted to the side. Up near the top of the label, you’ll see the model number (M/N) and serial number (S/N). The model number is where you can find the size of AC you’re looking for.
Not all air conditioning companies do this, but most will give you a 2 or 3 digit section in AC model number that says how many thousands of BTU/hour your air conditioner can cooling of your house.
If the model number on your air conditioning system lists the tons, no more calculation is needed as you now finally found the right AC tonnage of your cooling system.
Divide the BTUs on the label by 12,000. You need to use this number as the divisor because there are 12,000 BTUs per ton. The result of this calculation will be the tons of your central air conditioning system. For example, assume that your system is labeled as having 60,000 BTUs. Dividing 60,000 by 12,000 will give you 5 tons. This is the most accurate method on determining the size of your central air conditioning system when your label does not indicate the tons on it directly.
If you don’t want to do the math, here are the numbers you’re looking for and their corresponding tonnage:
18 = 1.5 tons
24 = 2 tons
30 = 2.5 tons
36 = 3 tons
42 = 3.5 tons
48 = 4 tons
60 = 5 tons
The 3 digits in the model number tell you the nominal capacity in thousands of BTU/hr. Since each 12,000 BTU/hr is equivalent to 1 ton of air conditioner capacity, it’s easy to figure out how many tons of nominal capacity your AC has.
Finding AC tonnage from model number is very important and detrimental to the proper operational status of an Air Conditioning System.
If your system happens to not have the BTU or the tons information detailed, identify the AC model number on the label. Then contact a local HVAC contractor and provide them with the model number. Most HVAC contractors can look up the tonnage of the system by using the model number.