Where there's smoke (4)
I believe the answer is:
flue
'where there's smoke' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for flue that I've seen before include "Chimney shaft" , "Passage for air" , "Chimney channel" , "Smoke-duct in a chimney" , "Fuel (anag.)" .)