A natural draft system is primarily used to facilitate what type of gas flow?

A natural draft system is primarily designed to facilitate flue gas exhaust. The operation of such a system relies on the principles of buoyancy and temperature differentials between the flue gases and the outside air. As the flue gases rise due to their lower density compared to cooler air, they create a negative pressure in the exhaust stack or chimney, allowing the combustion gases to be drawn out of the system naturally.

This passive operation is effective for removing combustion byproducts, ensuring that the air quality within the heating space remains safe and that the heating appliance operates efficiently. Proper venting of flue gases is crucial because it prevents the accumulation of harmful gases, such as carbon monoxide, within the living spaces.

Fresh air intake relates more to systems that require controlled ventilation or air supply for combustion, which is not the primary function of a natural draft system. Similarly, excess pressure release and draft control can be associated with different components or systems, but they do not specifically define the primary purpose of a natural draft, which focuses on the exhaust of flue gases.