As houses in Singapore are getting smaller with smaller kitchens, We believe that it deserves to be well ventilated rather than recirculated(Using recirculated Hood rather than venting it out with Ducting). The common practice here in SG is letting the hood recirculate: which technically means whatever the hood sucked up will be let out at the top of the hood through some vents(Chimney hood). Although generally, a good hood can filter out a high percentage of grease(90-95%) with its metal washable filters, and also lower the level of cooking odor by its Non washable active carbon filters(not all hood comes with it). Do take note that these filters do nothing to control the level of Carbon Dioxide, Carbon monoxide, Carcinogens(Cancer causing agent), heat ....Etc Etc....and who knows what burning LPG (Gas) emits. If you ever cook in a kitchen with a recirculating hood, you should know how bad it felt.