The Aprilaire 413 Furnace Filter is a MERV 13, 16″ x 27″ x 6″ air filter that is engineered to capture some of the worst allergy and asthma culprits! The MERV 13 rating means that it will catch at least 90% of all particles 1 – 3 microns in size and at least 85% of microns 3 – 10 microns in size. These particles include but are not limited to bacteria, tobacco smoke, proplet nuceli (sneeze germs), mold, hair spray, pollen, dust mites, pet dander, and more. The Aprilaire 413 Filter is a direct filter replacement for the 4400, 3410, and 2410 Aprilaire air purifiers. If you own the 2400 or the 2140 Aprilaire air cleaners you can use the 1413 upgrade kit to allow your cabinet to accept a MERV 13 filter. Using this upgrade kit will get rid of those annoying pleat spacers and will drastically improve the air quality within your home! Aprilaire recommends you replace the 413 air filter every 9-12 months, depending on the air quality in your home.