A thimble for a chimney connector is permitted if it is:

A thimble for a chimney connector must be firmly cemented in place with high-temperature cement to ensure a secure and reliable installation. This requirement is critical because thimbles are designed to allow the installation of a chimney connector pipe through a wall while providing a safe passage for flue gases. The use of high-temperature cement guarantees that the thimble can withstand the extreme temperatures generated during the operation of the heating system, ensuring minimal risk of heat transfer to surrounding materials, which could potentially lead to fire hazards.

A loose-fitted thimble could result in leaks of flue gases or might allow for the movement of the chimney connector, compromising the system's overall integrity. Likewise, thimbles made of flexible material would not provide the necessary stability and support for the chimney connector. Lastly, installation at any angle is not permissible, as it is essential for the thimble to be correctly aligned to maintain proper flue gas venting and prevent back-drafting, which could lead to dangerous conditions in the home.