For optimal performance, recommended to change at least every 3 months.. Made in the USA. Actual Size: 19.5” x 24.5” x 3.75” | Nominal Size: 20 x 25 x 4 MERV 10 Efficiency with MERV 8 Air Flow (.25" W.C.) Electrostatic Air Filters for homes, business, schools, apartments, hotels and industrial Durable and sturdy galvanized metal backing
