Tonnage is the cooling capacity of an air conditioner or heat pump, where one ton equals 12,000 BTUs (British thermal units) of heat removed per hour. The term comes from the heat needed to melt one ton of ice over a full day. Most homes use systems between 1.5 and 5 tons, sized by an ACCA Manual J load calculation.
Why it matters to you
An oversized system cools the air quickly and shuts off before it removes much humidity, while an undersized one runs nonstop on the hottest days. Correct sizing shapes comfort, humidity and equipment wear more than almost any upgrade.
Practical guidance
Ask for a Manual J load calculation instead of accepting the old unit's size or a square-feet-per-ton rule of thumb. Insulation, windows, air sealing and duct condition can all change the right size for your home.