Burning paintings maybe outside private room (6)
I believe the answer is:
'burning' is the definition.
(I've seen this before)
'paintings maybe outside private room' is the wordplay.
'paintings maybe' becomes 'art' (paintings are a type of artwork).
'outside' means one lot of letters goes inside another.
'private room' becomes 'den' (a secret room or location).
'art' placed around 'den' is 'ARDENT'.
(Other definitions for ardent that I've seen before include "Enthusiastic, eager" , "Passionate, fervent" , "'Fervent, impassioned (6)'" , "Loving and fiery" , "Fiery and passionate" .)