Air Conditioner Capacity Is Measured in Tons — Know the Reason?

Why is air conditioner capacity measured in tons? You may have wondered this, especially since you know your 4-ton capacity air conditioner doesn’t actually weigh 4 tons. Here’s what that 4 ton designation really means and why air conditioner capacity is measured this way.

We know that the air conditioner’s number of tons doesn’t refer to its weight. In fact, this number refers to the amount of heat the air conditioner can remove from a house within one hour. For example, a 4-ton air conditioner is able to remove 48,000 British thermal units (or BTUs) from the house per hour. One BTU is roughly equivalent to the heat that would be produced if you lit one match and burnt it all the way. One ton of A/C capacity is equivalent to 12,000 BTU per hour.

Now we know what a ton means, but we still haven’t answered the question of why the ton is the unit of measure for air conditioner capacity. Before the invention of the air conditioner, people who could afford it used large blocks of ice to cool their homes in the summer and refrigerate food. The ice was harvested during the winter from frozen lakes and rivers.

But how did the use of ice to cool buildings lead to the term “ton”? Basically, it takes 143 BTUs to melt a one-pound block of ice at 32 degrees. Accordingly, if you have a one-ton (2000 pound) block of ice, it takes 286,000 BTUs to melt it completely. If that block of ice melts evenly over the course of the day, it absorbs heat at the rate of 11,917 BTU/hour. Rounded up, we get 12,000 BTU/hour, or one ton of AC capacity.

Today most people know that a ton is used to measure A/C capacity, but not everyone knows that the term originally referred to blocks of ice! For more information on air conditioner capacity or any other home comfort issues, contact the pros at Climactic Conditioning Co., Inc. We’re proud to serve homeowners in and around Sarasota, Bradenton and Lakewood Ranch.