Chimney shaft
I believe the answer is:
flue
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">chimney shaft</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for flue that I've seen before include "Chimney vent" , "Smoke duct" , "Chimney-shaft" , "Conduit for smoke" , "Chimney channel" .)