flue

A flue is an enclosed passageway designed to direct a current of air, flame, or smoke. In the context of engineering, it most commonly refers to a channel within a chimney that carries smoke and hot gases from a fireplace or furnace to the outside air. This passage also helps to create and maintain a draft, which supplies air for the fire.12

Flues are essential components of heating systems, ensuring that combustion byproducts are safely expelled from living spaces. Industrial chimneys, often free-standing structures, utilize large flues to vent gases from furnaces and power plants. The mixture of gases resulting from combustion and passing through a flue is known as flue gas.234