What causes the natural draft in a chimney or vent system?

Natural draft in a chimney or vent system is primarily caused by the height of the vent or chimney. As warm air rises due to its lower density, it creates a negative pressure at the bottom of the vent or chimney, drawing in cooler air from the appliance that is being vented. This principle of thermodynamics allows for the continuous movement of air and combustion gases, facilitating efficient ventilation.

The greater the height of the chimney or vent, the stronger the natural draft, as taller structures enhance the temperature differential and further amplify the upward movement of air. This is crucial for ensuring that exhaust gases are effectively expelled from the building and that fresh air is drawn in for combustion processes.

While pressure difference is related to how natural draft operates, in this context, it is the height of the chimney that is the defining factor. Mechanical force and fan operation refer to artificially induced drafts, which do not pertain to natural draft mechanisms.