What U.L. listing is required for factory built chimneys?

The correct answer focuses on the U.L. (Underwriters Laboratories) listing that is specifically necessary for factory-built chimneys. A U.L. 103 or 103 HT listing is required for these chimneys because it pertains to systems that are built to handle the higher temperature emissions typical of wood-burning appliances. This listing ensures that the product can safely withstand the heat generated during operation without compromising structural integrity or safety.

Additionally, U.L. 103 HT indicates that the chimney can handle higher temperatures than standard models, making it suitable for use with certain types of appliances that produce extreme heat, which is critical for safety and compliance with building codes. The specificity of this requirement reflects the stringent safety standards set for heating systems, highlighting the importance of using certified components in construction and installation.

In contrast, the other U.L. listings mentioned, such as 101, 102, and 104, do not specifically relate to the temperature and application requirements for factory-built chimneys, thus they cannot be used for this purpose.