Factory original Aprilaire No. 401 fits the Spacegard / Aprilaire 2400 air cleaner. Comes in money-saving 2-pack for reduced product and shipping costs. Manufacturer recommends replacing at least once a year.
Or, if you would like to upgrade your air cleaner have nearly double the air cleaning ability, you can purchase Aprilaire's upgrade filter kit. Plus, this upgrade kit makes it easier to replace your filters since pleat spacers are no longer needed.