Range hoods must be vented using metal duct. Given a choice between flexible metal duct and smooth metal duct, go with the smooth. The ridges found in flexible metal duct create turbulence and will diminish airflow.

Range hoods should be ducted to the outside of the home. While non-ducted filters trap some of the grease and odors from normal cooking, the humidity, smoke and heat will all be re-circulated back into the home. If the non-ducted filters are not regularly replaced, eventually the grease and odor catching effect will no longer protect your home from