What type of door is prohibited on a factory-built fireplace unless specifically tested and labeled for such use?

A gasketed fireplace door is prohibited on a factory-built fireplace unless it has been specifically tested and labeled for such use because these doors are designed to create a tight seal that can trap combustible gases or heat within the fireplace unit. If they are not manufactured to meet specific safety standards, they could pose a risk for the accumulation of hazardous conditions.

Factory-built fireplaces are subject to stringent testing and labeling requirements to ensure they operate safely and efficiently. Gasketed doors that have not been properly tested may not provide the intended safety measures, leading to issues such as overheating or improper venting of combustion gases, which could result in dangerous situations like chimney fires or smoke infiltration into living areas.

In contrast, options such as glass doors, screen doors, and metal doors might not have the same restrictions because they can be designed to function properly and safely with factory-built fireplaces, provided they meet the safety codes and standards required. Thus, it is essential to adhere to these regulations to prevent potential fire hazards and ensure the safety of the fireplace installation.