How does stack height affect a natural draft furnace?

The height of the stack in a natural draft furnace is primarily significant because it directly influences the amount of draft generated. The draft refers to the pressure difference that causes flue gases to rise up the stack and allows fresh air to enter the combustion chamber. A taller stack creates a stronger draft due to the increased vertical distance the gases must travel, which enhances the natural convection process.

As the stack height increases, the temperature of the flue gases also rises, which creates a greater buoyancy effect. This increased buoyancy helps to draw more air into the furnace, improving combustion efficiency and promoting better heat transfer within the system. Thus, the stack height is crucial in ensuring that the combustion process operates effectively by facilitating the proper flow of gases.

While the other options may relate to certain aspects of furnace operation or environmental impact, they do not capture the central role of stack height in influencing the draft specifically. This makes the understanding of draft and stack height a foundational concept in boiler operation and efficiency.