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When inspection reveals that an existing chimney is not safe for the intended purpose, it shall be rebuilt to conform to nationally recognized standards, lined or relined with suitable materials, or replaced with a gas vent or chimney suitable for venting. The chimney passageway must be checked periodically to ensure that it is clear and free of obstructions. Do not install a manual damper, barometric draft regulator, or flue restrictor between the furnace and the chimney. Never connect a Catego