Definition of "flue"

It has frequently been a subject of inquiry, whether the ancients were acquainted with chimneys, or open fire-places. In the houses discovered at Herculaneum and Pompeii, there are no chimneys; they all appear to have been warmed by furnaces and flues.

1815, Robertson Buchanan, A Treatise on the Economy of Fuel, and Management of Heat, Especially as it Relates to Heating and Drying by Means of Steam, Appendix, p. 307.

Besides the usual run of machines, planers, millers, automatics, centre lathes, cranes, etc., there were several power stations, the rolling mills for strip material and for 60 ft. rails, and all the steel furnaces with their complicated systems of flues. If variety is the spice of life, then there was plenty here.

1944 November and December, A Former Pupil, “Some Memories of Crewe Works—II”, in Railway Magazine, page 341