The most common and most likely answer to this crossword clue is the 9 letter word FIREPLACE
I've seen this crossword clue in The Daily Telegraph
F
I
R
E
P
L
A
C
E
Buddy explains!

The straight part
We know that "hearth/art" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hearth/art = fireplace.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FIREPLACE mean?
FIREPLACE noun- An open hearth for holding a fire at the base of a chimney.