Important Note: Almost ALL furnace filters have a different "actual size" than the nominal size printed on the air filter. It's best if you measure your air filter for the EXACT size and compare it to our "Actual Size". With the 4" and 5" air filters there is a wider variance between the nominal and actual size depending on the manufacturer. If you are replacing a 4 3/8 depth 20x25x4 filter in your Honeywell unit you should order our 20x25x5 Honeywell Replacement air filter that measures 19 7/8 x 24 7/8 x 4 3/8 (19.63x24.88x4.38). Nordic Pure 20x25x4 Pleated Air Filters MERV 12 are made of electrostatically charged synthetic materials that attract and capture most airborne particulates in your home. All Nordic Pure pleated air filters are manufactured using a heavy duty, moisture resistant beverage board frame. There is a metal mesh support grid bonded to the pleats for extra support. MERV 12 furnace air filters are comparable to HVAC filters with the rating of MPR 1500-1900. This high-performance HVAC replacement filter will help keep your air conditioning and heating systems running efficiently, saving money on utilities and costly maintenance. It is important to regularly change your furnace air filters especially during any home improvements for fresh, clean air in your home or office. We recommend that you change your air filter every 3-6 months to maintain maximum efficiency and economy. From the Manufacturer Nordic Pure 20x25x4 MERV 12 Pleated AC Furnace Air Filters: Actual Size: 19-1/2-Inch by 24-1/2 -Inch 3-3/4-Inch. IMPORTANT NOTE: Almost ALL filters are a fraction of an inch smaller than the nominal size printed on the filter. It is best if you measure your filter for the EXACT size and compare it to our "Actual Size" listed above. With the 4-Inch and 5-Inch filters there are many different exact sizes for the different HVAC manufacturers. Because of this, your filter may say 20x25x4 on it but really be the same as our 20x25x5. This is why we ask you to measure your filter so you aren't surprised if the filter doesn't fit! You may also want to look at our Honeywell replacement 20x25x5 filter. Just check the "Actual Size" before ordering. Changing your air filter is the first step in insuring your HVAC system runs at its optimal level this season. Generally, you should change your 4-Inch air filters every 3 to 6 months. Particles in indoor air are measured in microns, which are 1/1000 of a millimeter. A human hair is about 100 microns wide. A MERV 12 Nordic Pure air filter captures airborne particles as small as 0.3 microns! Nordic Pure air filters do not kill germs, however, the filter media does not permit the growth of bacteria or mold. As a result, it is not necessary to add any potentially irritating chemicals to the air filter to kill germs. Nordic Pure air filters are made out of an electro statically-charged synthetic material that draws airborne particulates to it like a magnet. Electrostatic filters help trap airborne particles to protect your family from allergy causing pollen, fine dust, smoke particles, airborne plant spores, bacteria, and some viruses.