Pressure drop

Pressure drop is the reduction in pressure across part of a heating-water circuit as water flows through pipework, valves, heat emitters, filters or other components. In heat pump design it is read with required flow rate, pipe bore, velocity and available pump head because too much pressure drop can stop the circuit carrying the required heat or trigger flow problems. MCS guidance links pipe internal bore with fluid velocity and frictional resistance, and Energy Saving Trust warns that longer runs of smaller-bore pipework affect pressure drop and flow rate. The term is not a pipe-size instruction, a pump-setting value, a heat loss calculation or proof that the heating system is correctly designed.