How can the draft through a natural draft furnace be increased?

Increasing the draft through a natural draft furnace is fundamentally tied to the principles of thermodynamics, specifically the relationship between temperature and the movement of air. In the case of natural draft systems, the draft is created by the difference in density between the hot gases inside the stack and the cooler air outside. When the temperature of the stack rises, the density of the gases within the stack decreases, causing them to rise more quickly. This enhanced movement of the hot gases increases the draft.

By raising the temperature in the stack, the buoyancy effect is amplified, resulting in a stronger upward draft. This increased flow of air assists combustion by ensuring that a sufficient amount of oxygen is drawn into the furnace, thereby enhancing the efficiency of the system.

In contrast, decreasing the stack temperature would slow down the draft, while reducing furnace pressure might affect the combustion process but would not directly increase draft. Adding insulation to the stack helps maintain temperature but does not directly contribute to increasing the thermal difference needed to enhance the draft on its own.