Upstairs, there's a study with a fireplace whose hearthstone was found by the house's current owners in a nearby stream.
From the post-gazette.com
We have a hearthstone stove in our dining room with circulating fans in top corners of doorways as well as ceiling fans.
From the dailyherald.com
Hearthstone, a real estate investment firm, and Builder magazine sponsor the annual awards to recognize and encourage the philanthropic work of those in the housing industry.
From the news-journalonline.com
More examples
A stone that forms a hearth
The Hearthstone Historic House Museum is a historic home in Appleton, Wisconsin, United States that has been converted into a museum. On September 30, 1882, it became the first residence in the world powered by a centrally located hydroelectric station using the Edison system. ...
Hearthstone in Danbury, Connecticut was built in 1895. It was listed on the National Register of Historic Places in 1987. It has also been known as Parks' Castle and as The Castle. The property includes four contributing buildings and three other contributing structures. ...
A flat stone used to form a hearth; By extension: The fireside, home life; A soft kind of stone used to whiten door-steps, scour floors, etc; To scour, as a floor, with hearthstone
(1) A large stone used as the floor of a fireplace. (2) Other naturally occurring or synthetic materials used to construct a hearth. (3) Figuratively, the fireside.