So as it stands now (we're in the middle of a remodel), our family room has an exposed 70s style brick chimney with a clay thimble about 6ft off the floor. The brick is ~4ft wide and stretches floor to ceiling. This room originally had a wood stove in it which is why the thimble is there. We ran black iron pipe through the exterior and down through the new walls during the remodel for a hookup to a propane fireplace. Obviously we can't do an insert with a chimney setup, but what we want to know if we can do is this. Essentially build out from the existing brick what would be a new floor-to-ceiling hearth with a raised mantle, and room for a direct vent insert to be placed inside to achieve an effect similar to this: The plan obviously would be to build the structure, concrete/mortar the exterior with a mesh reinforcement, and then stone veneer the outside, but what I'm concerned about is the interior. I'm assuming you would have to have the interior lined with steel or some other heat reflective material, correct? Is this idea even possible? Our only option if not would then simply be a stoner veneer directly on the outside of the brick, and do a freestanding gas fireplace which I really don't want. Any thoughts on this?