Accumulair MERV 13#401 Replacement Media for Aprilaire Model 2400 Accumulair #401 Accordion filter for Aprilaire/Space-Gard Model No. 2400 Reaches 99% efficiency on particles 3 microns or larger Improves efficiency and increases longevity of HVAC systems when properly used and maintained Improves air quality in the home! This is an aftermarket filter.