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If you have at least a bit of an idea on how AC ratings work, you might already know that a 4-ton capacity air conditioner doesn’t actually weigh 4 tons, or even 8,000 pounds because an AC’s number of tons doesn’t refer to its weight at all. This number, in actuality, refers to the amount of heat the air conditioner unit is able to remove from a house within an hour. Cool, right?

Now we know what a ton means when we are talking about ACs, but you may very well still be wondering why ton is the unit of measurement used for air conditioner capacity. It’s a good question, and we have the answer. Just keep reading!
British Thermal Unit (BTU)
A British Thermal Unit, or BTU, is used to measure the amount of heat coming from the unit. One BTU is roughly equivalent to the level of heat produced by a burnt match. Neat, right? One ton of air conditioner capacity is equivalent to 12,000 BTUs per hour. This basically means that a 4-ton air conditioner can remove 48,000 British Thermal Units from the house per hour. WHOO!
Before air conditioners were invented, people used large blocks of ice to cool their homes in the summer, as well as refrigerate food. People harvested ice during the winter from frozen lakes and rivers.

Of course, you’re probably asking how on earth this relates to ACs being specified in tons, but it does. Keep reading and we’ll show you.

About 143 BTUs are required to melt a pound of ice at 32 degrees fahrenheit. So this means that if you have a one-ton (2000 pounds) block of ice, it will take around 286,000 BTUs to melt it completely. If that block of ice melts evenly over an entire day, the heat rate is going to be 11,917 BTU/hour. Round it all up, and we get 12,000 BTU per hour. Or one ton of air conditioner capacity. Now that’s COOL!

A lot of people may know that a ton is used to measure AC capacity, but not many are aware that the term originally referred to blocks of ice. And now you know!

Stay frosty out there!