Breaking up coal for furnace (6)
I believe the answer is:
cupola
'furnace' is the definition.
(cupola is a kind of furnace)
'breaking up coal' is the wordplay.
'breaking' is an anagram indicator.
'up'+'coal'='upcoal'
'upcoal' with letters rearranged gives 'CUPOLA'.
'for' acts as a link.
(Other definitions for cupola that I've seen before include "Round domed roof" , "Small dome on a roof" , "Dome - furnace" , "St Peter's roof" , "Rounded dome" .)