I'll bet the "fireplaces" are zero clearance units that cost the builder only about $1200 each. They provide a nice ambience when used, but they're really not for heat, and that's why you don't smell woodsmoke.

The exterior of our stone fireplace on the roof has some stones that have fallen off and need to be replaced. The problem is that there is a 3 inch gap between the fireplace frame and where the stones sit. Someone tried to put standard concrete to fill the gap in the past but it obviously didn't work. Any advice?

Our last house had zero clearance, Masonite exterior. Crap. ALL of the townhouses have full brick exterior, clay liners thru top of chimney so I assume they are actually Masonary. We have very nice Masonary surround and hearth, actual metal flue thingy. Never used it. The townhouse across the street ALL have the Masonite cexterior chimney stacks so I know they have zero car stuff.