Use the Airpura Replacement HepaBarrier Filter only in the AirPura C600 Airborne Chemicals Air Purifier (not included) and the AirPura T600 Tobacco Smoke Air Purifier(not included). This special HepaBarrier traps particles and dust after the carbon bed. Change HepaBarriers every 12 months. Change T600 filters at the same time as the carbon filter. For private home use change intervals will usually be less frequent. Note: Filters are not returnable unless deemed defective after inspection by the manufacturer. Please be careful to order the correct size filter for your AirPura air purifier. AirPura will replace any defective filters.