Comfort systems use fans to push heated and cooled air through ducts into living spaces. Air also needs a way to circulate back to the central comfort system equipment, where it again gets heated or cooled and circulated back to the living spaces. Most homes use centrally located return ducts to capture and return  air back to the central comfort system. In contrast, a comfort return system uses separate ducts in each major room to capture and deliver air back to the central comfort system.