Every forced air heating and air conditioning system requires a filter of some kind to protect the equipment. This filter rack connects to the side of the air handler when a side-return is used. When a filter is installed in the rack, your equipment is protected from the damaging effects of large dust particles present in every home's air. For best heating and cooling system performance change your air handler filter every 1-2 months. Instead of purchasing this filter rack, you can upgrade to an Air Cleaner which will capture much smaller dust, pollen, dander, and spore particles. These air cleaners may reduce the incidence of associated illnesses and allergy symptoms.