hearth vs open fireplace

hearth and open fireplace both are nouns.

Word	Noun	Adjective	Verb	Adverb
hearth	Yes	No	No	No
open fireplace	Yes	No	No	No

As nouns, hearth and open fireplace are synonyms defined as:

hearth and open fireplace: an open recess in a wall at the base of a chimney where a fire can be built

Other synonyms of hearth include fireplace.

hearth (noun)	open fireplace (noun)
home symbolized as a part of the fireplace	an open recess in a wall at the base of a chimney where a fire can be built
an open recess in a wall at the base of a chimney where a fire can be built
an area near a fireplace (usually paved and extending out into a room)