Tons is a shorthand phrase that refers to the total cooling capacity of the unit in BTU’s. A 3-, 4-, or 5-ton unit doesn’t refer to the weight of the equipment, but instead to the amount of heat the air conditioner can remove from the home in one hour. The term “tons” stems from a time before air conditioning when people cooled their homes with ice that had been harvested from lakes and rivers in the winter.
There’s a complicated mathematical formula involved in converting the weight of that ice into energy, but in the end a “ton” of air conditioning capacity represents roughly 12,000 BTU per hour. So a 2-ton unit has 24,000 BTU/hr capacity and a 3-ton has 36,000 BTU/hr, and so on. Check out our extended glossary to learn more about other HVAC terms.