Rheem Classic Plus Super Quiet 80 2-Stage Uplfow/Horizontal Gas FurnacesA Furnace That ''Grows'' To Meet Your Comfort NeedsThe Rheem Classic Plus ® Super Quiet 80 Gas Furnace has two stages of heating to save energy and keep your home at its comfortable best. Most furnaces are either “off or “on at 100% capacity, no matter what your heating comfort needs may be. The Rheem Classic Plus Super Quiet 80, however, operates at 70% and 100% capacity. Most of the time, this furnace operates in its energy saving “low-heat stage to deliver a gentle and steady flow of heating comfort. On the coldest days, when you need more heat, the furnace automatically switches to “high-heat stage to deliver the maximum heating comfort. The temperature of your home stays at the comfort level you select ‚¬â€œ wherever you set the thermostat.