Principles of heat in relation to plumbing systems

Conduction

Conduction happens when heat travels through or along a material (one molecule to the next).

Heating copper tube to solder, or heating coil in a DHWC.

Copper is a very good thermal conductor. Plastics tend not to be good thermal conductors.

Convection

Can only take place in a fluid or gas.

Convection occurs because when molecules are heated,  they heat and rise, and when they cool they fall. This is the main way a DHWC heats the water up by.

Radiation

This is heat transfer via infrared light. It transfers heat from one body to another without heating the space in between.

Heat is measured in 0C or scientifically in Kelvin (K).

Certain situations mean that heat needs to be retained – and at other times emitted – but always controlled. Hot water cylinder pipes need insulating to keep the heat in, so the hot water does not lose its temperature (efficiency).

Cold water mains pipe needs to be insulated to stop condensation forming on the pipe. White cars are more common in hot countries, as white reflects the sun’s heat. In solar panels, shiny surfaces are needed to absorb the heat from the sun.

Dark colours absorb heat – unpainted cast iron.

Light colours reflect heat – polished aluminium.

Heat remains in the pipework when it is insulated and therefore increases efficiency and reduces running costs.