The program described herein monitors four homes throughout the United States using, first, a standard efficiency, natural-draft, electronic ignition (IID) gas furnace and, secondly, a high efficiency (noncondensing) induced-draft, III) gas furnace. This paper presents these field data and related analysis from the 1979-80 through the 1982-83 heating seasons, with emphasis on the energy-efficiency improvement of the induced-draft gas furnace.