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Woodburning requires a larger flue and ceramic liner. Gas requires a chimney liner to prevent the acids formed from combustion from eating away the mortar. An 1800 chimney was most likely built for wood and coal burning. Then later a gas insert was installed. Before you burn wood have a chimney sweep inspect the chimney to see if it has a ceramic liner and that the flue size is large enough for woodburning, and that the use of the gas insert has not damaged the chimney.
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Yes it can. This would involve tearing out walls and the existing chimney and errecting a new chimney, Then reframing and drywall. The firebox might need reconstruction as well. Again, a chimney sweep can advise you on this.
General C&ontractor
35 years of troubleshooting construction, remodel, component & material failures. What to do next