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How does a hot-water heating system circulate heat through radiators?

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heating In a thermoelectric generating system a heat source—usually fueled by coal, oil, or gas—is used within a boiler to convert water to high-pressure steam. The steam expands and turns the blades of a turbine, which turns the armature of a generator, producing electric power. A condenser converts any remaining steam to water, and a pump returns the water to the boiler.

A hot-water heating system circulates heat by using a boiler to heat water, which is then transported through a network of steel or copper pipes to radiators or other heat emitters located throughout a building.1

The circulation process works as follows:
* Movement: While early systems relied on gravity—where cooler, denser water would sink back to the boiler to displace and force lighter, heated water upward—modern systems utilize motor-driven pumps to drive the water through the pipes. This allows for greater flexibility in the placement of the boiler relative to the radiators.1
* Heat Transfer: As hot water flows through the hollow sections of a radiator, it transfers its heat to the metal surface. Ambient air from the room enters at the bottom of the radiator, is heated by the sections, and rises vertically to discharge at the top, creating a current of air that warms the room.2
* Return: Once the water has given up its heat to the room, it cools and is returned to the boiler to be reheated and recirculated.1

To function correctly, these systems must include valves to allow trapped air to escape and provisions to accommodate the expansion of water as it heats.1