Kitchen hoods are broadly classified into ducted hoods and ductless hoods. Two main types exist, ducted and recirculating (ductless). Some types also use steerable propellers or ducted fans. The assembly ducted air directly into the engine. Conditioned outdoor air is ducted to the terminal unit in the space. The boilers were ducted into four funnels located amidships. Most fume hoods for industrial purposes are ducted. A large variety of ducted fume hoods exist. The boilers were ducted into four funnels. The boilers were ducted into a single funnel. Both ships' boilers were ducted into a single funnel located amidships. The boilers would have been ducted into two widely spaced funnels. MARIN has done extensive research on ducted propellers. This is not a problem with the much cooler exhaust from ducted fans. The boilers were ducted into a pair of funnels.