Accumulair FC12X36_4 MERV 6 Rating Air Filter/Furnace Filters, 12x36x1 (11.5 x 35.5) - 4 pack Nominal size is 12x36x1. Actual size is 11.5 x 35.5. MERV 6 Rating. Each filter lasts up to 3 months. Economical, high-capacity media makes this filter an ideal upgrade from standard fiberglass throwaways. Captures a wide variety of airborne allergens including dust, mold, pet dander, and dust mites. 4 Pack of Air Filters