What is prohibited from being installed at the termination of factory-built chimneys?

The correct choice indicates that decorative shrouds are prohibited from being installed at the termination of factory-built chimneys. This prohibition is likely grounded in safety concerns and functionality. Decorative shrouds can obstruct the proper venting of exhaust gases, leading to potential backdrafts or buildup of harmful gases, which compromise the safety and efficiency of the chimney system.

In contrast, metal caps are specifically designed for chimney tops to protect against rain, debris, and animals while still allowing for proper venting. Insulation materials are typically used in conjunction with factory-built chimneys to maintain necessary temperatures and prevent issues like condensation, which wouldn't be a concern at the termination point. Flue pipes are essential components of chimney systems for directing exhaust but their proper installation is reinforced by code regulations, indicating that they must adhere to established standards for safety and operation.

Thus, the guidance against decorative shrouds serves to ensure that factory-built chimneys operate safely and effectively by allowing adequate exhaust and preventing obstruction at their termination points.