With recirculation, the purified air is sent back into the kitchen. This is traditionally done using a carbon filter which is mounted inside the hood. The food dose is first sucked through the hood's grease filter, as with normal extraction, where all the grease particles are filtered out.
And then the air is sent through the carbon filter, which, with the help of the active carbon inside the filter, binds the smell to the filter. And then the cleaned air is led out into the kitchen again.
This is done using different methods, depending on the type of hood the carbon filter is installed in. In the case of wall-hung hoods, there are usually grooves in the hood's chimney - via these the air is returned to the kitchen.