The Goodman GMSS96 High-Efficiency Gas Furnace with single-stage gas valve and a single-speed circulating blower provides efficient and economical performance. A single-stage gas furnace provides more consistent airflow through constant rotation. Energy efficiency is key to controlling the cost of heating your home. The 96% AFUE rating on this gas furnace means that 96 cents of every $1.00 of heating energy expense warms your home.