flues is a form of:

Flue



noun
1.
(a passage for smoke or hot air, a chimney, a pipe or tube for carrying away smoke or gases) បំពង់ (ផ្សែង ។ល។)
ENGLISH MEANING
noun
1.
An inclosed passage way for establishing and directing a current of air, gases, etc.; an air passage
2.
A compartment or division of a chimney for conveying flame and smoke to the outer air.
3.
A passage way for conducting a current of fresh, foul, or heated air from one place to another.
4.
A pipe or passage for conveying flame and hot gases through surrounding water in a boiler; -- distinguished from a tube which holds water and is surrounded by fire. Small flues are called fire tubes or simply tubes.
5.
Light down, such as rises from cotton, fur, etc.; very fine lint or hair.
6.
In an organ flue pipe, the opening between the lower lip and the languet.