A flue vent connector or "stackpipe" (orange in our sketch) is the term used to describe the round metal vent or connection pipe connected between the combustion gas exhaust port of an oil or gas fired heater or a wood or coal stove and the chimney that ultimately vents the combustion gases to the outdoors. [Click to enlarge any image]
Also known as the gas flue the exhaust stack is the pipework on the furnace that removes toxic gases from the furnace into the outside air. Replacing this kind of flue is rather complicated. It may not be suitable for an amateur to do as doing it incorrectly can lead to exhaust fumes building up in the home.
BOILER STACKS AND CHIMNEYS - Reprinted Courtesy of the National Board of Boiler and Pressure Vessel Inspectors Any boiler using a combustible fuel source requires a stack or chimney. The stack or chimney aids combustion in natural draft boilers by helping to ensure a steady supply of combustion air which mixes with the fuel.
The stack is nothing but chimney which is used to disperse the hot air at a great height emissions & particulate matters that are emitted from the various types of stacks like boiler flue gas etc. At these heights the polluted air disperses in a very large area so that concentrations at the ground are within permissible limits and not harmful for humans animals and vegetation.