The Goodman GMVM97 High-Efficiency Gas Furnace with modulating gas valve and a variable-speed circulating blower provides efficient and economical performance. Unlike single-stage gas furnaces that operate 'all on' or 'all off,' a Goodman modulating gas furnace typically runs at the lowest possible speed to precisely maintain a constant, steady temperature in your home. A modulating gas furnace optimizes its heating output to maximize indoor comfort and lower energy costs. When operating at low-speed levels, your Goodman gas furnace consumes less energy to keep your home comfortable. In addition, the 98% AFUE rating on this gas furnace means that 97 cents of every $1.00 of heating energy expense warms your home.