Photo: Prydumano Design on Unsplash
Heat pumps and air conditioners are sold in "tons". One ton is 12,000 BTU per hour of cooling — a unit of measure that dates back to the cooling effect of melting a ton of ice in a day. Residential systems usually range from 1.5 tons (18,000 BTU/h) to 5 tons (60,000 BTU/h); mini-splits start as small as 9,000 BTU/h per indoor head.
The square-foot rule is a shortcut, not a method
You will often see "one ton per 500 square feet" or "20 BTU per square foot". Those rules ignore insulation, window area, air leakage, orientation and climate — the factors that actually determine load. Two 2,000 ft² homes, one a 1960s ranch in Ohio and one a new build in Georgia, can have heating loads that differ by a factor of three.
What a Manual J calculation does
ACCA Manual J is the industry-standard method for calculating heating and cooling loads room by room. It takes the home's envelope, local design temperatures, internal gains and duct location into account. Many utilities and state rebate programs require one. If a contractor sizes your system by looking at the old unit's nameplate, ask for a Manual J.
Why oversizing hurts
- Short cycling: an oversized single-stage unit satisfies the thermostat in a few minutes and shuts off, wasting energy on start-up losses.
- Poor dehumidification: short cooling cycles don't run long enough to pull moisture out of the air, leaving the house cool but clammy.
- Higher cost: bigger equipment costs more to buy and may need larger ducts.
Why heat pumps change the sizing conversation
An air conditioner is sized for summer. A heat pump has to handle winter too, and in cold climates the heating load is usually the larger one. Variable-speed heat pumps solve the dilemma: they can be sized for the winter load while throttling down to 30–40% capacity in mild weather, so they don't short-cycle. That's why this site lists capacity at 47°F, 17°F and 5°F for every model — the cold-weather numbers are what you size against in northern states.
Reading capacity on our model pages
Each model page shows rated cooling capacity, the nominal tonnage, and heating capacity at three temperatures. When several indoor units can be paired with the same outdoor unit, the figures shown are the maximum certified values for that outdoor model; your exact pairing may be slightly lower. Use the model directory filters to narrow down by tonnage.