20X21.5X1A (Actual Size) Enviroflow Air Filter (Merv 8 ) (4 Pack) Nominal Size 20x21.5x1. Actual Size 20 x 21.5 x 1 MERV 8 Rated. Electrostatic pleated media, which performs better than regular fiberglass fibers Traps dust and allergens such as pollen, mold, pet dander, and dust mites Pack of 4 Filters Each filter lasts up to 90 days