Nordic Pure’s 16x25x3 MERV 13 Air Bear Cub Replacement Plus Carbon filter is meant to replace the filter for any system that requires a 3” depth. Unlike other filters where the nominal and actual sizes differ by a fraction of an inch, the Air Bear Cub Replacement has a nominal and actual depth of 3 inches exactly. Keep that measurement in mind when you are measuring your filter’s housing to determine what filter is best for you. Nordic Pure 3” MERV 13 Air Bear Cub Replacement Plus Carbon 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 tobacco and fireplace smoke are captured and removed. MERV 13 air filters are comparable to air filters with the MPR rating of 1900-2200, FPR rating of Blue, and APR rating of Diamond. Particles in indoor air are measured in microns; for scale, a human hair is about 70 microns wide. Each Nordic Pure 3” MERV 13 air filter will capture more than 90% of 1.0-10.0 micron contaminants and up to 75% of .30-1.0 micron contaminants. The effective life of your air filter depends on both the inside and outside conditions in which you live. We recommend that you change your air filter every 3-6 months to maintain maximum efficiency and indoor air quality.