BestAir AXP-213-13R Aprilaire/SpaceGard 20 x 25 x 4 Series 3000 MERV 13 Furnace Filter. Filters out unwanted particles including dust lint mold particles pollen bacteria and virus carriers while allowing cleaner air to flow through. Minimum Efficiency Reporting Value (MERV) of 13. Using our best tech and design this BestAir Filter is manufactured to trap up to 99% of Airborne Particles from 0.3 to 10.0 microns. Actual Size: 15 3/4 x 24 3/4 x 4 1/4 Fits Aprilaire? & Spacegard? Models 1210 3210 4200 2210 and 2200*/2120* *Models require the OEM upgrade kit #1213