How is a range hood that re-circulates air considered?

A range hood that re-circulates air is considered deficient because it typically does not effectively remove cooking odors, smoke, and grease from the kitchen. Instead of venting air outside, a re-circulating hood uses filters to clean the air and then releases it back into the kitchen. This can lead to a buildup of heat, humidity, and pollutants in the cooking area, diminishing indoor air quality and making it less effective in maintaining a clean and healthy environment. While re-circulating hoods might be convenient due to their easier installation and lack of ductwork requirements, they are often not the best solution for efficient ventilation compared to ducted range hoods. Therefore, from a performance and effectiveness perspective, their inability to expel air outside renders them deficient.