The definition of a flue is a duct, pipe, or opening in a chimney for conveying smoke and combustion gases to the outside atmosphere. It is an essential part of a heating system, as it allows the safe and efficient removal of smoke and combustion gases from the home. The flue also helps to ensure that the combustion gases are properly vented and not allowed to accumulate in the home. The flue should be inspected regularly to ensure that it is in good working order and that there are no blockages or obstructions. In addition, the flue should be cleaned regularly to ensure that it is free of soot and other debris that could cause a fire hazard. Proper maintenance of the flue is essential for the safety of the home and its occupants.