Aerostar 13x21 1/2x1 MERV 13 Pleated Air Filter, AC Furnace Air Filter, 4 Pack (Actual Size: 12 7/8" x 21 1/2" x 3/4")

Nominal Size: 13x21 1/2x1; Actual Size: 12 7/8" x 21 1/2" x 3/4" Comparable to MPR 1500 to 1900 Ultimate Allergen Defense and Honeywell Allergen Elite FPR 10 Designed to filter microscopic particles such as lint, dust mites, spores, pollen, pet dander, fine dust, smoke, and bacteria. Simple to install and a cost-effective step towards a healthier home environment. For best results, change your filters every 60 to 90 days but increase frequency to 30 days during peak summer and winter months 100% synthetic electrostatic media for high efficiency with low air flow resistance