How heat energy moves through metals, liquids, and room spaces in domestic heating.
Under C&G Unit 203, plumbers must understand how heat energy is transferred to design and troubleshoot central heating and hot water systems. Heat moves from hotter areas to cooler areas in three primary ways:
- Conduction: The transfer of heat through a solid material by direct molecular contact. In plumbing, this is how heat passes from the burner flame through the copper or steel heat exchanger wall into the water, and how heat spreads along metallic copper pipework. Metals are excellent conductors of heat.
- Convection: The transfer of heat through a fluid (liquid or gas) by the movement of the fluid itself. As water or air is heated, it expands, becomes less dense, and rises, while cooler, denser fluid sinks. This creates convection currents. In plumbing, convection is the driving force behind natural gravity circulation in open-vented systems and how room air is warmed by radiators (which draw cool air in at the bottom and release warm air at the top).
- Radiation: The transfer of heat energy by electromagnetic waves (infrared radiation) without requiring any physical medium. Heat from the sun travels this way. Although called "radiators," modern hot water radiators actually transfer about 70-80% of their heat via convection and only 20-30% via direct radiation to room surfaces.
*Original revision guidance; confirm definitions and examples against C&G Unit 203 course specs.*
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