What is “a ton” of air conditioning capacity? Does it mean 2,000 pounds of air conditioning? Actually, in the HVAC industry, “ton” is not a measurement of weight; it’s how much heat an air conditioner can remove from your home in one hour.One ton of air conditioner capacity is equivalent to 12,000 Btus per hour. One Btu, or British thermal unit, is the amount of heat it takes to increase the temperature of one pound of water by one degree. It’s about the same amount of heat given off by a birthday candle.
So how did air conditioner capacity come to be called “tons” of cooling power? It dates back to the late 19th century before modern air conditioning existed. Back then, ice for cooling indoor spaces was harvested from lakes and rivers – by the ton.
One pound of ice requires 143 Btus of heat to melt completely. That’s actually quite a bit of heat, especially considering that one pound of melted ice (water) only requires one Btu to rise in temperature by only one degree. That means, once the ice reaches 32 degrees F and melts, it only takes 180 more Btus to reach boiling (212 degrees F).
If you have one ton (2,000 pounds) of ice, it takes 286,000 Btus to melt it completely. 286,000 Btus can be applied as quickly or as slowly as you want in order to melt the ice, but when measuring air conditioner capacity, it’s calculated by the hour. So if it takes one day to apply 286,000 Btus, simply divide that figure by 24 hours to get 11,917 Btu per hour. That rounds up nicely to 12,000 Btus, or one ton of air conditioning power.
Due to differences in nominal and actual capacity along with indoor/outdoor operating conditions compared to actual operating conditions, tonnage estimates can be off. That’s why it’s important to conduct a load calculation when sizing a new air conditioner.
To learn more about air conditioner capacity and other HVAC information, please contact us at Overland Park Heating & Cooling in Greater Kansas City today.
Our goal is to help educate our customers in Overland Park, Kansas about energy and home comfort issues (specific to HVAC systems).
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