That's just back fill for an old coal gas insert (if that's piping I see on the left there - otherwise it's coal - but it's pretty shallow makes me think gas). See how deep the builders opening is so you know what you're working with and what your options are. Before removing the rubble I'd be getting a flashlight and shining up there and get on the roof and shine down to see what chimney size you're dealing with or if it's been blocked up and also the condition of the brick and mortar or any other defects in the chimney structure. You'll undoubtedly need a liner if anything but an electric appliance. Maybe even some rebuild on the chimney. Check all that out first.
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u/ThatllBtheDayPilgrim 1d ago edited 1d ago
That's just back fill for an old coal gas insert (if that's piping I see on the left there - otherwise it's coal - but it's pretty shallow makes me think gas). See how deep the builders opening is so you know what you're working with and what your options are. Before removing the rubble I'd be getting a flashlight and shining up there and get on the roof and shine down to see what chimney size you're dealing with or if it's been blocked up and also the condition of the brick and mortar or any other defects in the chimney structure. You'll undoubtedly need a liner if anything but an electric appliance. Maybe even some rebuild on the chimney. Check all that out first.