A factory-built fireplace is not just a box in a wall. It is a tested, listed system, and the installation has to stay within the conditions of that listing. Distinct from factory-built chimneys (IMC 805 / UL 103).
903.1 General
Factory-built fireplaces must be listed and labeled, installed in accordance with the conditions of the listing, and tested in accordance with UL 127. The listing is part of the installation criteria, not just a product label.
903.2 Hearth extensions
Hearth extensions for approved factory-built fireplaces must follow the fireplace listing. The hearth extension must also be readily distinguishable from the surrounding floor area. Listed and labeled hearth extensions must comply with UL 1618.
903.3 Unvented gas log heaters
An unvented gas log heater cannot simply be placed inside a factory-built fireplace. The fireplace system must be specifically tested, listed and labeled for that use in accordance with UL 127.
903.4 Gasketed fireplace doors
Gasketed fireplace doors are prohibited unless the fireplace system has been specifically tested, listed and labeled for that installation under UL 127.
Field tip
The fireplace, hearth extension, gas log heater and door may each look acceptable separately. The installation still has to match the tested and listed system. Hub: 903 hub. Next: IMC 904.
Code basis
2024 IMC model-code education from the owner-provided Daily Code Talk. Confirm adopted edition. Not a fireplace design. Distinct from 805 factory-built chimneys.