Convection

Currents created by heating air, which then rises and pulls cooler air behind it. Also see radiation. Process of heat carried from one point to another by movement of a liquid or a gas (i.e., air). Natural convection is caused by expansion of the liquid or gas when heated. Expansion reduces the density of the medium, causing it to rise above the cooler, more dense portions of the medium. Gravity heating systems are examples of the profitable use of natural convection. The air, heated by the furnace, becomes less dense (consequently lighter) and rises, distributing heat to the various areas of the house without any type of blower. When a blower is used, the heat transfer method is called "forced convection."