A recirculating range hood works by drawing in air from the cooktop and circulating it back into the kitchen. The hood has a fan that pulls air through a filter, which removes smoke, odors, and grease particles. The filtered air is then circulated back into the kitchen through the vents in the hood.
Recirculating range hoods are not as effective as ducted range hoods at removing smoke and odors from the kitchen. However, they can be a good choice if you cannot or do not want to install a ducted system.