Metal grease filters are required for exhaust and recirculation hoods to filter grease and other solid particles from the air being drawn in. To maintain high effectiveness, they should be cleaned by hand or in the dishwasher approximately once a month. Whether you have an open living kitchen or a small closed kitchen, to ensure a consistent and pleasant indoor climate, the air should be completely exchanged 6 to 12 times per hour. To achieve this, the air flow rate or the performance of the range hood must match the volume of the room.