The Winix size 21 (115115) value pack is a great deal with 1 HEPA filter and 4 carbon prefilters. This value pack will last approximately one year. It fits Winix air purifier models P300, WAC5300, WAC5500, WAC6300, 5000, 5000b, 5300, 5500, 6300 and C535. If using model WAC9500 PlasmaWave Ultimate pet air cleaner, remove the complete original cartridge and replace it with the HEPA filter and carbon filter - the carbon filter will need to be on top facing the front.
Note: This listing is for a Winix 115115 Size 21 Value Pack (1 HEPA + 4 Prefilters) made by Magnet