Central Air Conditioning Intake Sizes

Air Intake

• Air conditioning systems rely on circulated air from in your home and a supply of fresh air from outside. These two intake sources pass through the system, over the evaporator coils and into your home through the ventilation ducts. The size of the air intake will correspond to the volume of the air conditioned to supply your house.

Air Volume

• The volume of air flowing into your home ranges from 1 to 4 cubic feet per minute per square footage of floor space. The differences depend on the location of the room because rooms with exterior windows or doors require a greater volume of cooled air.

Air Intake Size

• The area of the air intake is dependent upon the volume of air for the home divided by the velocity of the air in the system. The formula for the area is cubic feet per minute divided by the feet per minute. This will determine the square footage of the air intake needed. Use this to determine the size needed for the fresh air intake for your central air conditioning system.

Return Air Intake Ducts

• The air return for an air conditioner brings air back into the system to supplement the air from the outside. Compared to the cold air coming through the ventilation ducts, the return air is warm. This means that it takes up a larger volume than the cold air, and the duct return air duct and vent should be sized accordingly. Ideally, the return air ducts will be 20 percent larger than the ventilation ducts, according to "Modern Refrigeration and Air Conditioning" by Andrew D. Althouse, et al.