Which type of fireplace should not have an unvented gas log heater installed?

A factory-built fireplace, also known as a pre-fabricated or manufactured fireplace, is not suitable for an unvented gas log heater installation. These fireplaces are typically designed to work with vented systems to safely expel combustion gases and byproducts. Unvented gas log heaters produce carbon dioxide and moisture during operation, which can accumulate in a confined space without proper ventilation.

Factory-built fireplaces often have specific construction materials and designs that do not accommodate the additional risks posed by the emissions of an unvented system. Furthermore, the safety codes and manufacturer instructions typically mandate that unvented appliances be installed only in locations that provide adequate ventilation, which factory-built fireplaces often lack.

In contrast, open hearth, masonry, and freestanding fireplaces may have design characteristics that allow for more versatility regarding venting options, making them potentially suitable, with proper precautions taken. Therefore, the installation of an unvented gas log heater in a factory-built fireplace would not conform to safety standards and could create hazardous conditions.