My furnace is an outdoor wood boiler. We used to have 2 chimneys inside. One was attached to an old cast iron wood cookstove. The other was a fireplace adapted to hold an indoor wood stove. BUT, last year we tore both chimneys down because the mortar was literally dried up. (We were able to jiggle the bricks free by hand, or gove a very light tap with a hammer.) I'm surprised they hadn't fallen down on their own, actually. I miss having the wood heat inside. We hope to rebuild the chimneys next year.