Climate and Insulation

• The climate in which you live is a consideration when sizing central air conditioning systems as well as the level of insulation. If you live in an area with humid conditions, that humidity can leak into the home through windows and doors, which increases the cooling capacity needed. If you live in an area with less humid conditions, the cooling load needed is lowered. Of course, the amount of outdoor heat and humidity coming into the home will depend on the level of insulation in your walls and attic. Contractors use a computer program to calculate the climate and insulation levels for your area and home.
  
  

Windows

• The number of windows in the home, the location of the windows in regards to sun and shade and the size of windows are considerations when determining the correct central air conditioning size. Besides measuring the wall lengths in shaded areas of the home or walls that are in sunny areas, the window size and locations are needed to correctly size a central air-conditioning system. Generally, 10 percent more BTUs are needed for rooms and windows with sunny conditions and 10 percent less BTUs for rooms with shade.
  
  

Occupants

• The number of occupants in a home is another consideration. The number of people in the home over two will raise the size of central air conditioner needed to cool the home. The general size of the air conditioner cooling capacity is based on two people. For each additional person that will be in the home, you add 600 BTUs for each person to the total BTUs needed.
  
  

Heat Generating Appliances

• Central air conditioning filters through the entire home, so you need to determine what appliances, lights or other heat-producing items are in the home affecting the heat and cooling of the room where the items are kept. Because the home has a kitchen, you would add 4,000 BTUs to the total needed to cool the home. For other appliances or lights generating heat, you add the total wattages of all together. Contractors use a computer program to calculate how many extra BTUs are needed for additional appliances and lights not located in a kitchen.
  
  

Other Considerations

• The ceiling height of the rooms and the level of comfort required are other considerations when determining the size of a central air-conditioning system. The comfort level is determined by how cool you need the house. These calculations are entered into a computer program to give you the correct sizing information.