Allergy Be Gone carries a large inventory of Honeywell Replacement Air Purifier Pre-Filters to use inside your round Honeywell HEPA (High Efficiency Particulate Air) filters. A pre-filter increases the overall filtration efficiency of your air purifier. Pre-filters prepare your air for final filtration, working to rid the air you breathe from pollen, mold spores, pet dander, dust, smoke and other irritants that regularly float invisibly through the climate in which you live. To operate at maximum efficiency, all air purifiers should be run continuously. Scientific research has determined that indoor air pollution will quickly revert to pretreatment levels when an air purifier is turned off. Genuine Activated Honeywell Enviracaire carbon pre-filters maximize the life of your HEPA filter and often take less than five minutes to change. For most Honeywell Tower air purifier models, the Honeywell HRF-B1 Premium Odor Reducing Air Purifier Pre-Filter will trap larger air particles and help to reduce odors and even certain harmful gases.