14 inch by 20 inch by 1 inch Electrostatic Filter. The NaturalAire Standard has an ASHRAE 52.2 rating of MERV 8. This filter is convenient to use and easy to replace. Ordinary furnace filters are designed to protect heating and cooling equipment from the insulating properties of relatively large airborne particles. The NaturalAire Standard goes far beyond that, removing even those microscopic particles that can stain walls and furnishings, or worse-aggravate seasonal allergies. Synthetic wire backed media in clay covered frame. Lasts up to 90 days.