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A/C Capacity Measured in Tons? Here’s the Story

If you’re having a new air conditioning system installed in your Orlando area home, and your HVAC technician says your home requires a three-ton A/C, you may be surprised at the need for such a heavy piece of equipment. The fact is, in air-conditioning parlance, the word “ton” is a measurement of A/C capacity, not the weight of the equipment. A three-ton A/C unit doesn’t weigh three tons but, rather, is capable of providing approximately three tons of cooling capacity per/hour. Here’s the story.

More than 100 years ago, when blocks of ice were used to keep food cold, they were also used to provide a basic type of air conditioning in homes/businesses. With Willis Carrier’s 1902 invention of the first modern-day air conditioner, ice blocks were no longer needed to cool indoor air. To measure A/C capacity, however, the relative cooling power of ice blocks was adopted as a measurement and continues to be used today.

A block of ice cools its surroundings by absorbing heat until eventually melting to water. It’s been determined that, during this melting process, a one-pound block of ice will absorb a total of 143 BTUs (British Thermal Units) before melting completely. One BTU is equal to about the amount of heat produced by burning a single kitchen match.

Carrying out this calculation further, one ton (2,000 pounds) of ice will absorb 143 x 2,000 BTUs before completely melting. That’s a total of 286,000 BTUs. A one-day time period is used to factor total cooling capacity. Dividing 286,000 BTUs by 24 hours then gives the per/hour figure, which is 11,917. This was rounded up to 12,000 BTUs, which now expresses the A/C capacity of a one-ton unit. If your HVAC technician is recommending a three-ton A/C system, he’s likely determined by his Manual J calculations that your cooling load is 36,000 BTUs per/hour.

Founded in 1969, Rinaldi’s Energy Solutions, located in Orlando, is a community-based, family-owned business proudly serving Central Florida. For expert A/C advice, sales and service, contact the professionals at Rinaldi’s.

Our goal is to help educate our customers in Orlando, Florida and surrounding areas about energy and home comfort issues (specific to HVAC systems).  For more information about A/C capacity and other HVAC topics, download our free Home Comfort Resource guide.

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