Nordic Pure’s 20x25x5 Lennox X6673_X6675 Replacement MERV 15 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 15 rated air filters are made of electrostatically charged synthetic materials that are ideal to reduce airborne contaminants in your workplace or office. Each time air passes through a Nordic Pure pleated furnace filter, airborne dust, pollen, mold spores, pet dander, smog, dust mite debris, smoke, and bacteria are captured and removed. Particles in indoor air are measured in microns, which are 1/1000 of a millimeter (a human hair is about 70 microns wide). Each MERV 15 air filter will capture more than 90% of all airborne contaminants from 1.0-10.0 microns, and up to 95% of 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 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 economy.