The Honeywell universal True HEPA replacement filter is 99.9% effective at capturing particles such as household dust, smoke, pollen, mold spores, and cat dander. This universal filter is designed to replace Honeywell True HEPA filter model No. HRF-11, 20500, and 20590. Filters should be replaced every 1 to 5 years depending on use. For use with Honeywell air purifier model series: 10500, 10590, 17000, and 50100. For air purifier Model No. 10500 (or HEPA filter Model No. 20500) 2 Model No. HRF-D1 filters are needed. For air purifier Model No. 1700 (or HEPA filter Model No. 20500), 2 Model No. HRF-D1 filters are needed. For air purifier Model No. 17005 (or HEPA filter Model No. 20500), 2 Model No. HRF-D1 filters are needed. For Air Purifier Model No. 17352 (or HEPA filter Model No. 83154) 2 HRF-D1 filters are needed. Each Model No. HRF-11 contains 1 HEPA filter and 1 gasket.