503.5.6.1 Chimney lining.
Chimneys shall be lined in accordance with NFPA 211.
Exception: Where an existing chimney complies with Sections 503.5.6 through 503.5.6.5 and its sizing is in accordance with Section 503.5.5, its continued use shall be allowed where the appliance vented by such chimney is replaced by an appliance of similar type, input rating and efficiency.