Lesson 5
Flow, Pressure & Resistance
See why the radiator nearest the boiler can steal the far one’s heat, and why turning a TRV up doesn’t push more water through.
Builds on
Flow, push and resistance
In Dev’s house the radiator nearest the boiler is too hot to touch, while the one in the far bedroom is barely warm. Same water, same boiler. To see why, you need three ideas:
- Flow: water moving through the pipes. Heat, Power & the Water Equation measured it in litres a second; heating specs often use litres a minute (0.2 L/s is 12 L/min).
- Pressure difference: the push that drives the flow, made by the pump.
- Resistance: everything that fights the flow, such as pipes, bends, valves and the radiators themselves.
More resistance means less flow for the same push. More push means more flow through the same resistance.