Heard fireplace is wonderful (5)
I believe the answer is:
great
'is wonderful' is the definition.
(I've seen this in another clue)
'heard fireplace' is the wordplay.
'heard' shows a homophone (sound like).
'fireplace' becomes 'grate' (grate can mean a fireplace).
'grate' is a homophone of 'GREAT'.
(Other definitions for great that I've seen before include "Very large in size, quantity, etc." , "Important - splendid" , "cracking" , "Chief - weighty" , "Extensive; excellent" .)