Nordic Pure’s 20x25x5 Lennox X6673_X6675 Replacement MERV 15 Plus Carbon 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 15 Plus Carbon air filters are made by adding a hand cut flat panel infiltrated with activated charcoal to our standard pleated filter to greatly reduce unwanted odors. Each time air passes through a Nordic Pure pleated furnace filter, airborne dust, pollen, mold spores, pet dander, smog, dust mite debris, and bacteria are captured and removed. Particles in indoor air are measured in microns; for scale, a human hair is about 70 microns wide. Each Nordic Pure 4” MERV 15 air filter will capture more than 90% of all airborne contaminants from 1.0-10.0 microns, and up to 95% of all contaminants from .30-1.0 microns. It is important to note that because of this high filtration and air flow restriction, HVAC systems should be rated to handle filters of MERV 15 and above, which are not typically used in residential settings. The effective life of your air filter depends on both 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.