A 4-ton Carrier air conditioning unit is a split system residential air conditioner that can remove 4 tons of heat from a home in one hour. Heat is measured in BTUs, and 12,000 BTUs equal 1 ton. This unit can remove 48,000 BTUs per hour.
A split system consists of two pieces, a condenser that cools the air and sits outside the house to vent heat and an air handling unit that is inside to disperse the cooled air. Residential air conditioning units are available in sizes of 1 to 5 tons, while industrial units are available in sizes of 10 to 75 tons.