For those who may be interested here's free a book with a lot of detail about the safe design and building of fireplaces and chimneys. The title indicates 1889, but if you look at the diagrams and photos in the book, that date is obviously wrong. The latest photos look like the early 1960s to me.
Farmers' Bulletin 1889 - Fireplaces and Chimneys
You can download it in several different formats.