Activated carbon filter for Sirius hoods: S-DD16 (2pcs), SM905 52cm, SM905 85cm (2pcs) Hood in circulation mode: In this mode, the extracted air passes through the grease filters and also passes through an activated carbon filter, which somewhat filters out unpleasant odors and vapors , then the purified air is returned to the kitchen air. In this case, the capacity, depending on the state of the carbon filter (wear and tear), is approx. It drops to 60-80%. This mode of operation is only recommended if there is no outlet. Activated carbon filters must be replaced every 3-6 months, depending on use.