Chimney shafts not of metal; smoke flues not of metal for chimneys; ducts not of metal for ventilating and air-conditioning installations; ducts not of metal for central heating installations; smoke flues not of metal for chimneys; chimney cowls and chimney pots not of metal; clamps not of metal for chimney flues; reinforcements not of metal for chimney flues; grilles not of metal for ventilation