Amaircare 8 inch annual filter kit has 3 carbon media pre-filters and 2 carbon inner filters for older portable Amaircare 2500 and 2550 series air purifiers. Units include black, santex white and sandstone units. Replace air filters regularly for maximum air filtration needed to keep allergies and asthma under control. Replacing these air filters keeps the HEPA filter and the unit performing at a high level. 12 month supply for most uses. Pre-filters removedust and odors from the air. Replace the prefilters every 3 months. The inner filters are pure carbon blanket media that remove Volatile Organic Compounds (VOCs) including paint fumes, cleaning solvent fumes, etc. Replace the inner filters every six months.