What principle does gravity distribution for heating rely on?

The principle that gravity distribution for heating relies on is indeed natural convection to circulate air through the home. In systems that utilize gravity distribution, the heating relies on the natural tendency of warm air to rise and cooler air to descend. As warm air is generated by a heat source, it rises, creating a pressure difference that allows cooler air to be drawn in from the lower parts of the space. This movement of air helps to circulate the heat throughout the room without the need for mechanical means or forced circulation, making it an efficient way to distribute heat in a building.

This method is particularly effective in older heating systems where the design takes advantage of the natural thermodynamic principles guiding air movement. It contrasts with systems that rely on forced circulation of water, where pumps are used to distribute heated water through radiators or other means, or with high-pressure steam systems, which employ steam to transfer heat. Similarly, electrical resistance heating functions through a different mechanism by generating heat directly through resistive elements, rather than relying on convection currents.