Ventilation is an essential for all rangehoods:
You must duct all rangehoods to the outside either through the roof
Under the eave or out the back wall.
A lot of rangehoods in the past were ducted into the ceiling cavity.
This is not only dangerous but ineffective in exhausing effeciently.
For a rangehood to exhaust successfully it must be ducted outside wether, that be through the roof or out the back wall!heat resistant metal ducting should always be used.
The best ducting is rigid ducting it allow all the ehausted vapours to escape .
It is not always possible to employ rigid ducting one, it is costly & secondly you may have roof beams that require you to go around in this case you need to use semi rigid metal ducting. If ducting through the roof you will have different needs for a tile roof from that of a metal roof.
Rangehoods plus has venting kits to suit both metal roofs & tile roofs