Field Scenario

A general contractor on a job site suggests using a venting component from a different manufacturer than the fireplace itself, since it “looks identical” and is what he has extra of from another job.

What You Actually Do

You decline and use only the components listed as compatible by the fireplace manufacturer, explaining that “looks identical” does not mean tested-and-listed-as-compatible — different manufacturers’ venting systems can have different wall thickness, joint design, or thermal performance even when visually similar.

Why This Matters

Mixed-brand venting systems are a real, documented cause of installation failures and are specifically called out in most manufacturer instructions as prohibited — this is exactly the kind of “reasonable-seeming” shortcut that removes the tested safety basis of the whole system.

What a Strong Response Includes

• Declining a non-listed substitution regardless of visual similarity or convenience.
• Explaining the specific reason (loss of tested compatibility), not just citing a rule.
• Sourcing the correct listed component rather than proceeding with what’s on hand.