Flues of metal for use in building

Chimney flues; Filtering installations for flue gases; Fittings for flues; Flues; Flues incorporating fans; Flues incorporating fans and/or extractors; Flues for ventilating apparatus; Flues incorporating extractors; Flues for heating apparatus; Flues for heating boilers; Heat exchangers for the removal of flue gases; Heating apparatus incorporating flues; Recuperators for pre-heating combustion air in heating systems by the use of hot flue gas