The Energy Chronicles

Air Conditioning Tons and Where They Come From?

When speaking about air conditioners and their capacity, they are often measured in terms of tons. At first hearing you may think this is referring to its weight. However, this is actually referring to how many tons of cooling the air conditioning system can provide or in other words how many BTUs can be removed from the space every hour. A ton of cooling is equivalent to 12,000 BTU per hour and 1 BTU is about equal to the amount of heat that gets produced from lighting one match and burning it all the way through. So why use tons and not BTUs when describing air conditioners?

Back before air conditioning was invented, people who were able to afford it would use blocks of ice to keep their homes cool in the summer and also use these blocks to keep food refrigerated. This ice would have been taken from areas such as lakes during the cold winter months. Essentially a ton (2,000 pounds) of ice would require 286,000 BTUs to completely melt. If the ice were to melt over the course of an entire day (24 hours), it would be absorbing heat at a rate of 11,917 BTU per hour (taking 286,000 BTU divided by 24 hours in a day). Rounding this number up comes to 12,000 BTU per hour or one ton of air conditioning capacity. So there you have it, tons of air conditioning.

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