Also, that port on the left side at the front - is that a clean-out, or an optional horizontal feed?
Satamax Antone wrote:You have about 3 cubic metre of stone, that's about 8 metric tons (well counting like massonry, if it was pure granite, it would be heavier) So, that's plenty enough.
Now, you have to decide how you want it to look, and if it is possible to keep the chimney as is, and have enough ISA (internal surface area.) for it to skip the front bell as i have drawn it. Can you calculate the ISA of the fireplace and chimney?
Allen had a point about insulating the stonework on the outside. I would go strawbales and cob. But i'm sure there's other options.
Might be a good investment to preserve the look of the fireplace, covering the fireplace opening, and still be able to see the flame, maybe even the burn tunnel if it were also made of ceramic glass. The glass is stable up to 1400d F.