A room air purifier is provided is provided that has a housing that defines a floor supply duct inlet, a room air inlet, and an outlet. An air mixing chamber within the housing is in direct communication with said room air inlet and said floor supply duct inlet. A filter is disposed in the housing. A fan is disposed in said housing between the outlet of the filter and the outlet side of the filter. An air channel panel is disposed in a filter inlet area between the air mixing chamber and the filter. Various sensors may be deployed to control temperature, and to prevent unpurified air from exiting the room air purifier. Optionally, an additional wall supply inlet may be placed in fluid communication with the air mixing chamber to provide a second extra-room source of air.