This Lennox X0444 air filter is the pleated air filter replacement for the PMAC-12C air filter cabinet and measures 17” X 28” X 6”. The Lennox X0444 furnace filter has a MERV 10 rating, which means that it filters out 85% of particles down to 3 microns. Filters Out: This includes – pollen, dust mites, mold spores, some bacteria, dust, smoke and more. This is a significant upgrade from a 1” furnace filter. This filter should be replaced every 9-12 months depending on the air quality in your home.