At home, I have the fireplace to blacken (9)
I believe the answer is:
denigrate
'blacken' is the definition.
(I've seen this before)
'at home i have the fireplace' is the wordplay.
'at' says to put letters next to each other.
'home' becomes 'den' (an animal's home).
'have' says to put letters next to each other.
'the fireplace' becomes 'grate' (grate can mean a fireplace).
'den'+'i' is 'deni'.
'deni'+'grate'='DENIGRATE'
'to' is the link.
(Other definitions for denigrate that I've seen before include "Blacken" , "Disparage" , "Unfairly criticise" , "Bad-mouth" , "put down" .)