21x21x1 Aerostar Air Filter

Square 21x21x1 returns are uncommon enough that you've probably struggled to find this size at a hardware store. This Aerostar measures 20 7/8" x 20 7/8" x 3/4" actual, sized for a nominal 21x21x1 slot. Pleated synthetic media construction with an electrostatic charge built into the fibers. MERV 8 handles standard household dust and pollen. MERV 11 captures pet dander, smoke residue, and most common allergens. MERV 13 takes care of fine particulates including bacteria, virus-sized aerosols, and wildfire smoke. The pleats provide substantially more surface area than a flat fiberglass filter would offer at the same nominal size, which is what extends the service life to 60 to 90 days under typical residential conditions. The electrostatic charge improves capture of sub-micron particles - the size range where mechanical filtration runs out of options. Manufactured in the USA by Con-Air Industries, Orlando, Florida. Cardboard frame, reinforced for shape retention under blower suction. MERV 13 in this depth reaches its pressure-drop limit faster than lower grades and wants a change closer to every 30 to 60 days under typical load. If anyone in the household has asthma or chronic respiratory issues, MERV 13 is worth the more frequent change schedule for the improvement in indoor air quality.