Carton Model: CBCF001. Recirculating filters are designed to absorb cooking odors before recirculating air into your kitchen. To ensure the best performance of your extractor, you should replace the carbon filter every 2 to 4 months, depending on use. Please note that recirculation filters are not designed to absorb large amounts of water or steam, they are designed to clean the air of impurities such as smoke or odors. Reasons for carbon filters You don't need to open your hood/hood outside, no holes in the wall. Recirculating cooker hood is used. Carbon Filter suitable for these hoods: CBCS6903-OW & CBCB6903-OW