Manufacturers list their equipment in BTU’s, not tons. If you can still read the model number on your outside unit, the BTU rating will be somewhere in the beginning of the number. Divide the number by 12 to find tonnage. examples:

  • you see a 24,¬† divide by 12 = 2 ton system
  • you see a 36 in the model number, divide by 12 = 3 ton system

Systems come in 2, 2.5, 3, 3.5,4, and 5 tons so you are looking for:

24, 30, 36, 42, 48, or 60 in the serial number. Older units can be difficult to size if the data plate or sticker is missing. If the model number doesn’t make sense try Google search with the number, it usually returns results on the fix it forums.