Short definitions of the physical-science terms that underpin plumbing and heating calculations.
Plumbing calculations rest on a handful of physics terms. These plain definitions make the formulas in the worked examples easier to follow. They are general explanations for revision.
- Pressure: force acting over an area, measured in pascals (Pa) or bar. In plumbing it drives flow.
- Head: the vertical height of a column of water above a point; more head means more static pressure.
- Density: mass per unit volume. Water is about 1000 kilograms per cubic metre, so 1 litre is about 1 kilogram.
- Flow rate: the volume of water passing a point per unit time, for example litres per second or litres per minute.
- Velocity: how fast the water moves along a pipe; for a given flow, a narrower pipe means higher velocity.
- Specific heat capacity: the energy needed to raise the temperature of 1 kilogram of a substance by 1 °C; for water it is about 4.2 kJ/kg per °C.
- Conduction, convection, radiation: the three ways heat moves — through solids, by moving fluids, and as radiant energy.
- Thermal expansion: the increase in volume of water (and materials) when heated, which is why heated systems need somewhere for the extra volume to go.
Keep these definitions handy when working through calculations, and confirm any values you rely on against your course material.
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