Booster pump sizing for buildings

Reviewed by the Calcwise engineering team ·

Get an indicative peak flow and total head for a domestic water booster set in a residential building.

L/s
Sum of fixtures: ~1.2 L/s with one bathroom, ~1.6 L/s with two
m
From the pump to the highest fixture
bar
Typically 1–1.5 bar (15–20 psi)
Advanced options
m
Pipes and meter
bar
0 if drawing from a tank
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How it is calculated

Qc = 0.682 × Qt^0.45 − 0.14 (Qt ≤ 20 L/s)
Qc = 1.7 × Qt^0.21 − 0.7 (Qt > 20 L/s)
H = static height + minimum pressure + losses − mains pressure

Not every fixture is used at once, so a simultaneity factor is applied to the total installed flow (Qt) to get the peak flow (Qc). US designers often use fixture units (Hunter's curve) for the same purpose.

The cut-in pressure must cover the height and the minimum pressure at the worst fixture; the cut-out pressure is usually set 1–1.5 bar (15–20 psi) higher.

Frequently asked questions

What peak flow does a 12-apartment building need?

With 1.2 L/s per apartment, the installed flow is 14.4 L/s and the peak flow about 2.1 L/s (34 GPM).

How many pumps should a booster set have?

At least two identical pumps in duty/standby or alternating operation, so supply continues if one fails.

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