Honeywell 21500 Enviracaire True HEPA Filter Fits Model 11520 series and model 17200 Overall particle reduction depends on many factors including the amount of air processed, the pollutant type and the pollutants' introduction rate into the environment. True HEPA filter lasts one to three years used regularly Honeywell supports the American Lung Association Maintain Honeywell performance rating with Honeywell replacement parts