Ducting is only required for external venting cooker hoods. Ducting isn’t needed for carbon filter units as they simply remove particulates before recycling the air into the room.
With an external venting cooker hood, if the hob is installed on an external wall the installation of the ventilation ducting is relatively straightforward. The cooker hood must vent outdoors. The ducting has to be sleeved through the drilled holes and pass through each section of a cavity wall with no joints.
If the cooker hob is installed on an island or against an internal wall the ducting needs to run either through the ceiling or flooring void, or be surface mounted, before venting outdoors.