Size a replacement flue liner correctly for a wood stove insert installed into an existing masonry fireplace

Steps

1. Identify the wood stove insert's flue collar/outlet size and the appliance manufacturer's specified minimum liner diameter and height requirements from its listing/installation manual
2. Do not default to matching the liner to the existing masonry flue's original size — insert liners are sized to the appliance outlet, which is typically smaller than the original masonry flue
3. Confirm the liner (rigid or flexible, insulated as required) is listed for solid-fuel use and, where applicable, listed to UL 1777 for masonry-flue installations
4. Verify the installed liner height and any offsets meet both the appliance manufacturer's draft requirements and NFPA 211 requirements for chimney height above the roofline
5. Insulate the liner per the liner manufacturer's instructions where required to maintain adequate flue-gas temperature and draft, particularly in oversized masonry chases
6. Perform a post-install draft check and video scan to confirm proper appliance performance before returning the unit to service