Sizing a Domestic Water Booster Pump — Flow and Total Dynamic Head
A booster pump is specified by two numbers — flow rate and total dynamic head. Get both and the pump curve does the rest.
Design flow
Use the peak probable flow from the fixture-unit calculation for the zone the pump serves. For a packaged multi-pump set, divide the duty across 2–3 pumps plus one standby so the set modulates with demand.
Total dynamic head (TDH)
- Hstatic — vertical distance from the pump to the highest fixture (m).
- Hfriction — pipe and fitting losses along the longest run at design flow (m). Estimate 1–5 m per 100 m of pipe depending on velocity, plus fitting equivalent lengths.
- Hresidual — minimum pressure needed at the top fixture: ~100 kPa (10 m) for taps, ~140 kPa (14 m) for flush valves and instant heaters.
- Hsuction — positive pressure available at the pump inlet (e.g. head from a rooftop break tank); subtract it.
Worked example
10-storey residential zone, pump in the basement, top fixture 34 m up, longest run 60 m, peak flow 3.2 L/s, fed from a ground cistern at atmospheric pressure.
Hfriction = 60 m × 3 m/100 m + fittings 6 m = 7.8 m
Hresidual = 14 m (flush valves present)
TDH = 34 + 7.8 + 14 − 0 = 55.8 m ≈ 56 m
Select a booster set delivering 3.2 L/s at 56 m head, with the operating point in the middle third of the pump curve for efficiency.
Also specify
Pressure vessel volume, VFD or staged control, low-water cut-off, non-return valves, and the motor kW from the pump’s curve at the duty point.
EngEst Pro computes total dynamic head from your building geometry and pipe runs and matches a booster pump duty point — the Plumbing Calculator lists the pump set, pressure vessel, valves, and controls in the BOM.
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