Nordic Pure’s 20x25x5 Lennox X6673_X6675 Replacement MERV 8 rated air filters are the newest filters made by Lennox with a slightly decreased height and width, but the same actual depth of 4 3/8”. This filter is a new standard size that will fit both old and new systems. As always, we ask you to measure your filter’s housing to ensure the proper fit. 5” Lennox X6673_X6675 Replacement MERV 8 rated air filters are made of electrostatically charged synthetic materials that attract and capture most airborne particulates in your workspace or office. Each time air passes through a Nordic Pure pleated furnace filter, lint, dust, pollen, dust mites, mold spores, odors and other contaminants are removed. MERV 8 air filters are comparable to air filters with the MPR rating of 600-800, FPR rating of Green, or APR rating of Gold. Particles in indoor air are measured in microns; for scale, a human hair is about 70 microns wide. Each MERV 8 filter captures up to 85% of airborne particles as small as 3.0-10.0 microns. The effective life of your air filter depends on the inside and outside conditions in which you work. We recommend that you change your air filter every 3-6 months to maintain maximum efficiency and indoor air quality.