Glossary
BTU and ton
A BTU (British Thermal Unit) is a unit of heat: the energy needed to raise one pound of water by one degree Fahrenheit. An air conditioner's capacity is expressed in BTU per hour it can remove from the house, and one ton of cooling equals 12,000 BTU per hour. A 3-ton unit removes 36,000 BTU per hour.
What a BTU and a ton are
A BTU is a small unit of thermal energy. An air conditioner is described by how many BTU of heat it can pull out of the house in an hour. Because the numbers get large, the industry uses the ton: 12,000 BTU per hour. The name comes from the amount of heat a ton of ice absorbs as it melts over a day.
Residential units typically range from 1.5 to 5 tons. That number, along with SEER, appears on the label and in the contractor’s proposal.
Why it matters in Florida
The right size does not depend on square footage alone. It depends on insulation, windows, orientation, duct leakage, humidity and how many people live in the house. That calculation is called Manual J, and it is what a serious contractor runs before proposing a tonnage.
In Florida, humidity changes the equation. An oversized unit cools the air quickly and shuts off before it has pulled out the moisture: the house ends up cold and clammy, and the compressor starts and stops all day, which burns more kWh and wears it out. A correctly sized unit runs longer cycles, dehumidifies, and uses less.
Common mistake
Replacing the old unit with “the same tonnage” or a bigger one “just in case.” If the house has gained insulation or better windows since the last one went in, it probably needs fewer tons, not more. Ask for the Manual J in writing before accepting a size. We explain it in the right size air conditioner.
Full guide: Right-sizing an air conditioner in Florida: Manual J, tons and humidity →
Updated