Fuel designed to deal with the smoke problem (4)
I believe the answer is:
flue
'deal with the smoke problem' is the definition.
I can't tell whether this definition defines the answer.
'fuel designed' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'fuel' anagrammed gives 'FLUE'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for flue that I've seen before include "Tube" , "Chimney pipe to draw off smoke" , "Passage for air" , "Vent pipe for smoke, etc" , "Chimney channel" .)