Sizing an central air conditioning unit for a 2,000 square-foot structure requires more than just the basic measurements of area. AC units are gauged based upon the amount of heat the unit can pull out of the air. Different rooms house different cooling needs due to the amounts of heat generated in those rooms. Sizing a unit requires looking at the cooling needs of the house and weighing the cooling options.
Calculating Square Footage
A Realtor will list a structure as 2,000 square feet based upon the usable areas, ignoring such rooms as the hallways or laundry rooms. Calculating square footage for cooling needs requires including hallways, but excluding other structures. Measure the length and width of each room, including hallways and bathrooms, that will be impacted by the AC unit. Multiply the two measurements together to get each room's area in square feet. Do not measure closets or other rooms that will be unaffected, such as attics and basements. Keep each room's measurement separate.
Converting Area to BTUs or Tonnage
BTUs (British Thermal Units) are the measurement of how much heat is pulled out of the air by the air conditioner. Tonnage is calculated by dividing the BTUs by 12,000. Most central AC units are rated by tons. Convert each room's square footage to BTUs first. A room of 100 to 150 square feet equals 5,000 BTUs; 150 to 250 square feet equals 6,000 BTUs; 250 to 350 BTUs needs 7,000 BTUs. Multiply the square footage by 25 for rooms larger than 350 square feet. Add 4,000 BTUs for kitchens, and 1,000 BTUs for bathrooms, laundry rooms, or other moist and hot rooms. Add each room's BTUs together to get the total BTUs. Divide the total by 12,000 for tonnage. A 2,000 square foot structure has a bare minimum BTU need of 50,000 BTUs and a tonnage of 4.1 tons. The needs will be higher depending upon what type of rooms are present in the structure.
Shopping for Units
Not all central AC units, called split-systems, are the same. Split-systems are ranked by tonnage but have additional specifications, depending on the manufacturer. Contemporary trends for energy saving and conservation have driven manufacturers to develop units that boast minimal impacts to the electric bill. Other types of units are advertised as having a limited impact on the environment. The sound quality of a unit is another consideration. Always ask about the levels of sound for both the external unit and the control unit inside the building.
Central units offer overall climate control, which is most often the preferred method of cooling. Installation costs can be monumental if duct work and electrical lines need to be installed. Ductless systems and window units use zone control which cools only specific areas. Installation costs for those two types are minimal. Zone control is ideal for houses or buildings where sections of the structure are largely unused. Limiting the areas that are cooled can drastically lower your electric bill.