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Convective heat transfer, often referred to simply as convection, is the transfer of heat from one place to another by the movement of fluids. Convection is usually the dominant form of heat transfer in liquids and gases. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes of unknown conduction and advection.
Gas boiler heat exchanger enables heat transfer from one source to another over a solid surface. If we speak about a condensing type, here the process includes the heat from fuel gases that is used for heating water that is returning from radiators to the boiler.