What must all forced mechanical draft systems be?

All forced mechanical draft systems must be gas tight to ensure that any combustion gases produced during operation are contained and directed properly within the system. A gas-tight system prevents any leaks that could allow harmful gases, such as carbon monoxide or unburned fuel, to escape into the surrounding environment. This is crucial for safety and efficiency, as these gases can pose serious health risks or contribute to air pollution if not managed properly.

Being gas tight also enhances the efficiency of the system, as it ensures that the draft created by the mechanical components is effectively utilized to draw the combustion gases out of the equipment being used, such as boilers or furnaces. This design characteristic is essential for maintaining proper airflow and ensuring optimal combustion conditions.

While features like proper ventilation, insulation, or adjustability may contribute to the overall performance of a mechanical draft system, they are not fundamental requirements like being gas tight. It is the primary concern for safety and performance that makes a gas-tight seal a necessity in forced mechanical draft systems.