Day and NightA (R) P102-1919-6 6"""" HEPA filter Fits Day and NightA (R) whole house HEPA air cleaner model P102-550. Measures approximately 19.5"""" x 19.5"""" x 6"""". For optimum performance change filter every 2 years. AirFilters.com Do you struggle with ridding your home of unwanted airborne particles? Well, there is no need to worry anymore with the Day and NightA (R) HEPA replacement air cleaner filter. HEPA stands for High Efficiency Particulate Air. For a filter to be classified as a HEPA filter, it must first satisfy certain standards created by the United States Department of Energy (DOE) . To be a true HEPA filter it must remove 99.97% of all particles greater than 0.3 of a micrometer from the air that is processed through the filter. HEPA filters are currently the most efficient filters available for air cleaners or even HVAC units. HEPA filters are designed to attract and capture tiny unseen particles that may be present in your indoor environment. Some of these particles may be dust, pollen, dust mites, pet dander, or cock roach allergens. If you desire optimum filtering performance in your air cleaner, then the Day and NightA (R) HEPA replacement air cleaner filter is the right choice for you. Start breathing cleaner and healthier air right away!