A factory-built fireplace has been installed with a masonry chimney above it. This combination is:

A factory-built fireplace is a listed appliance, meaning it was tested and certified as a complete system: firebox, connector and chimney together, with specified clearances to combustibles. The listing is what establishes safe operation, and it is specific to the components tested. Placing a masonry chimney above such a firebox substitutes an untested flue for the one the appliance was certified with, changing draft characteristics, flue temperature and the clearances the assembly was designed around. The result is an installation outside its listing, and for the inspector that is the finding — not a judgment about whether it will draft adequately. A listing may occasionally permit a specific masonry arrangement, which is why the answer is conditioned on what the listing says rather than being an absolute prohibition.

A factory-built fireplace must be installed with the chimney system it is listed for. Substituting a masonry chimney puts the installation outside its listing unless the manufacturer's listing specifically permits that arrangement, so the condition is reported for evaluation.

Factory-built (zero-clearance) fireplaces are listed appliances certified as complete systems with specified chimney components and clearances. Installing components outside the listing voids the basis for the appliance's safety certification, which inspectors report as an installation concern.

Listed Means Listed Together. The firebox and its flue were tested as one system. Swap a part and you are no longer inside the listing that made it safe.

Watch for absolute words. 'Always,' 'never' and 'required whenever' are usually wrong on listing questions, because the listing itself is the authority and it can permit exceptions.

• •Assuming masonry is always an upgrade over a listed metal flue
• •Believing correct flue diameter cures a listing mismatch
• •Stating an absolute prohibition rather than deferring to the listing