An unvented gas log heater shall not be installed in what type of fireplace?

An unvented gas log heater is specifically not suitable for installation in a factory-built fireplace. Factory-built fireplaces are designed with specific clearances and components that are intended for vented appliances only. The materials and construction of these fireplaces can potentially trap combustion gases, leading to dangerous levels of carbon monoxide and other pollutants within the living space.

The design and ventilation of factory-built fireplaces do not accommodate the introduction of an unvented appliance, which relies on natural air for combustion and does not have a venting system to expel combustion byproducts. This makes using an unvented gas log heater in such fireplaces both unsafe and non-compliant with safety codes.

In contrast, other fireplace types, like wood-burning ones, open hearth, and traditional stone fireplaces, may not have these strict limitations, as they are often used with vented appliances and can provide the necessary airflow for combustion gases to be safely vented outside.