On Land

Environment Information
At Rill Architects we run ArchiCAD on macOS. If you work at Rill, this is your stuff. If you don't, but you work in ArchiCAD, you may find something interesting. Anybody else, I don't know.

As long as I can remember, we've used a polygon wall for a fireplace, with a 3D-only wall or slab above to take the chimney to the ceiling. This method has been developed pretty far.

This new method isn't going to give you the 1" chimney section for CDs, but for schematics, it feels a little simpler.

Draw a thick (24" at least) rubble wall from floor to ceiling. Use the layer A Fireplace.

Schematic FP 1

Draw a slab with the shape and thickness of the firebox. Use the layer X SEO Show2. (If you don't have this layer, make it. It's a weird one. It should show in working plan, A1 plan, and working model and section/elevation. It should be hidden in A2 Section Elevation. I.e., It's visible in plan, visible when working on the model, and hidden in the output sections. It should always be set to wireframe.)

Bring the slab forward as necessary.

Schematic FP 2

SEO-subtract the slab from the wall.

In the output section, the line at the base will be hidden.

Schematic FP 3