Compatible Models: 210 furnace air filter compatible with AprilAire Whole House Air Purifiers models: 1210, 1620, 2210, 2216, 3210, 4200. NOTE: Not Fit for 1213 Upgrade Kit (Model 2120, 2200). Nominal Air Filter Size: 20 x 25 x 4 inch. Nominal size is an industry standard filter size system, not the actual size. It can help you identify the correct replacement filter easily. USA Newest Patent Design: 4 foldable metal bars greatly improve the support stability of the filter replacement. The 4 anti-friction pads (at the top and bottom) prevent friction between the filter element and the furnace during installation. High-Efficiency Filter: 210 air filter is MERV 11 rating. It is made of high-quality filter material, and have been tested before leaving the factory. It is suitable for home, offices, schools, hospital and so on