Equipped with a naturally aspirating gas burner and a pilot light. The pilot light is unlike a standing-pilot. It does not run continuously. The pilot light is shut off when the furnace is not in operation -- when the thermostat is not calling for heat. The heat exchanger is more efficient than one inside a conventional furnace. There's no draft hood. There may be a small fan installed in the flue pipe to create an induced draft, so these furnaces are sometimes referred to as induced-draft furnaces. A mid-efficiency gas furnace is also equipped with automatic controls, blower and motor assembly, venting, and air filtering. Some mid-efficiency furnaces have a motorized damper installed in the exhaust flue pipe. A mid-efficiency furnace is about 20% more energy-efficient than a conventional gas furnace. A mid-efficiency furnace has an AFUE rating of 78 to 82%. The intermittent-pilot is the main distinguishing characteristic.