duct vs flue

duct

noun
  • a pipe, tube or canal which carries gas or liquid from one place to another 

  • a vessel for conveying lymph or glandular secretions such as tears or bile 

  • a tube or elongated cavity (such as a xylem vessel) for conveying water, sap, or air 

  • a layer (as in the atmosphere or the ocean) which occurs under usually abnormal conditions and in which radio or sound waves are confined to a restricted path 

  • an enclosure or channel for electrical cable runs, telephone cables, or other conductors 

verb
  • to enclose in a duct 

  • to channel something (such as a gas) or propagate something (such as radio waves) through a duct or series of ducts 

flue

noun
  • A pipe or duct that carries gaseous combustion products away from the point of combustion (such as a furnace). 

  • In an organ flue pipe, the opening between the lower lip and the languet. 

  • An enclosed passageway in which to direct air or other gaseous current along. 

How often have the words duct and flue occurred in a corpus of books? (source: Google Ngram Viewer )