A 2,600-square-foot home needs a four-ton or five-ton air conditioning unit, depending on the climate zone in which the home is located, according to AC 4 Life. Homes in the Southwest or South need five-ton air conditioners, while other zones can use four-ton units.
The size of an air conditioning unit is calculated by dividing the unit's BTU rating by its BTUs per ton. It is important not to buy an air conditioner that is too large for a given space. A unit that is too big will short cycle and cycle on and off repeatedly, resulting in reduced system life, increased operating costs and a failure to dehumidify the space.