Wonderful fireplace, we hear (5)
I believe the answer is:
great
'wonderful' is the definition.
(I've seen this before)
'fireplace we hear' is the wordplay.
'fireplace' becomes 'grate' (I've seen this before).
'we hear' shows a homophone (sound like).
'grate' is a homophone of 'GREAT'.
(Other definitions for great that I've seen before include "Extensive; excellent" , "Excellent (colloq.)" , "Dickens novel about Pip" , "The Plough" , "Brunel's third and last steamship" .)