In school, kids learn that one ton is equal to 2,000 pounds. Logically, if you had a 4-ton air conditioner or heat pump, you would expect your 8,000-pound piece of equipment to arrive on a flatbed truck! But thank goodness that is not the case! The tonnage or weight assigned to air conditioners and heat pumps has to do with the fact that people used to cool spaces with blocks of ice.
Before modern air conditioning, people rated their capacity to cool indoor spaces by the amount of ice that melted. When ice melts, it pulls heat energy from its surroundings. It takes 143 BTUs (British Thermal Units) to melt one pound of ice. The heat is transferred to the ice, which causes it to melt. In order to melt one “ton” of ice, you need approximately 12,000BTUs/hr. Do you see the ice/air conditioner connection yet?
Here are the numbers:
- One British Thermal Unit (BTU) = the amount of heat you get from burning one kitchen match all the way down to the end.
- One ton = the ability to cool 12,000 BTUs in an hour