Response to a furnace (6)
I believe the answer is:
retort
'response' is the definition.
(I know that retort is a type of response)
'to a furnace' is the wordplay.
I cannot quite understand how this works, but
'to' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for retort that I've seen before include "Chem. flask; sharp answer" , "Respond" , "Lab. vessel; quip" , "one used in lab" , "Snappy reply" .)