What is the result of a difference in temperature of the gas inside a chimney compared to outside?

The phenomenon of natural draft in a chimney is primarily driven by the difference in temperature between the gases inside the chimney and the outside air. When the gases produced by combustion are heated, they become less dense and rise within the chimney due to buoyancy. This rising hot gas creates a pressure difference, pulling in cooler air from outside to replace it, thus promoting a flow of air through the system.

In a natural drafting system, this process does not require any mechanical assistance or devices, relying purely on the principles of thermodynamics and air density. The greater the difference in temperature between the hot gases and the cooler outside air, the stronger the natural draft becomes, enhancing the efficiency of the combustion process and ensuring proper exhaust of gases.

Understanding this principle is vital for maintaining safe and effective operations in boiler systems, as inadequate draft can lead to dangerous situations, including the buildup of carbon monoxide or other harmful gases within the structure.