The Honeywell Universal True HEPA Replacement Filter captures up to 99.97% of particles such as household dust, smoke, pollen, mold spores, and pet dander from the air that passes through the filter. Filters should be replaced every 1-5 years depending on use. Each HRF-F1 contains 1 HEPA filter and 1 gasket For use with Honeywell Air Purifier Model Series: 11520, 12520, 13520, 17200, 18150, 17400, 50150, 50200, 50250, 50300 For air purifier models 11520, 17200, 18150, 50150 (or HEPA filter no. 21500) two HRF-F1 filters are needed For air purifier models 12520, 17400 (or HEPA filter no. 22500) two HRF-F1 filters are needed For air purifier models 13520, 50250 (or HEPA filter no. 24000) three HRF-F1 filters are needed For air purifier model 50200 (or HEPA filter no. 23500) two HRF-F1 filters are needed Filters should be replaced every 1-5 years depending on use *From the air that passes through the filter. Overall particle reduction is dependent on many factors, including the amount of air processed, the pollutant type and the pollutants' introduction rate into the environment