Return Air Systems

Air Filter Grille and Chase Sizing

A properly sized return air system ensures adequate heat removal, extends the life of the air conditioning system and ensures the removal of excess humidity to provide you a high degree of comfort.

A properly sized return air system ensures adequate heat removal, extends the life of the air conditioning system and ensures the removal of excess humidity to provide you a high degree of comfort.

The objective is to get enough air volume across the evaporator coil at the appropriate velocity to remove the system-designed sensible heat (felt or measured heat) and latent heat (the heat that comes from a change in state, such as humidity). An undersized air return restricts airflow, causing inefficient operations, reduced comfort, increased noise and decreased reliability of heating and cooling equipment.

Return air filter grilles and return duct chases should be sized in accordance with the Air Conditioning Contractors of America (ACCA) Manual D to accommodate 200 square inches of gross grille area per ton at an equivalent static pressure of .05. A return air duct/duct chase should be consistent in diameter from filter grille to return air plenum, which is usually located in the attic.

Be sure to check your return air filter(s) once a month. A good rule of thumb is to check your filter(s) every time you receive your monthly electricity statement. Fiberglass filters should be replaced every month, while pleated filters can last up to three months. We recommend that return air filters be free from any type of blockage, such as furniture or curtains.

Dust and dirt can block airflow, which forces the heating and cooling system to work harder. A clogged return air filter can increase the operating cost of an air conditioning system by more than 10%. This means that if total energy bills were $1,600, and 60%, or $960, was for cooling and heating, a customer could see potential savings of up to $96 each year — just by unclogging the return air filter. Extremely dirty filters may also cause permanent damage to heating and cooling systems.