I work for a company that (among many other things) designs and builds custom full stone masonry fireplaces. Almost all of our customers in Northern climates ar

I work for a company that (among many other things) designs and builds custom full stone masonry fireplaces. Almost all of our customers in Northern climates are heating huge mansions with two or three fireplaces and absolutely swear by them, to the point where the fireplaces are designed first and the rest of the residence is planned around them. Once you get all that thermal mass warmed up it radiates a surprisingly long time.