How to Select & Size a Booster Pump System for Buildings and Apartments (Head, Flow Rate)

Head (measured in meters of water column, m) is the sum of three components. The first is static lift: water must rise to the highest fixture, estimated at approximately 3.5 m per floor. The second is residual pressure at the outlet so that showers and faucets operate with sufficient force, typically requiring an additional 10–15 m. The third is pipe friction losses from friction, fittings, and valves — this depends on pipe length and diameter, and a safety margin is usually added.

An approximate formula for initial estimation: Head ≈ (number of floors × 3.5 m) + (10–15 m outlet pressure) + pipe losses. For example, a 10-story building: 10 × 3.5 = 35 m, plus 12 m outlet pressure, plus estimated pipe losses of ~10–15 m, gives approximately 57–62 m of head. This is an indicative figure for selecting the pump range; the final design requires detailed hydraulic calculations based on actual drawings.

For very tall buildings, pressure zoning is typically applied (dividing the system into multiple zones by height, each zone with its own pump system or intermediate tank) to prevent excessive pressure at lower floors that could damage pipework and fixtures.

A common mistake is to add up all the fixtures in the building — this gives an oversized figure because not all taps are open at the same time. More accurately, the design flow rate is calculated based on the number of water-using fixtures operating simultaneously during peak hours, taking into account a simultaneity factor. The more apartments there are, the lower the relative proportion of fixtures in simultaneous use.

In practice, you estimate the peak flow rate (m³/h) of the building, then select a pump system so that this flow rate falls within the pump’s efficient operating range. A multi-pump system running in alternation or in parallel on demand is well suited here: at low demand, only one pump runs at reduced speed; at peak hours, the remaining pumps cut in one by one, maintaining stable pressure while avoiding overcapacity operation.

A VFD booster pump system adjusts pump speed to maintain stable discharge pressure that tracks actual demand. Compared to on/off mechanical switching with a pressure tank, this approach reduces pressure fluctuations when opening or closing taps, limits hydraulic shock, and saves energy because the pump only runs at the power actually needed rather than always running at full load before switching off.

In multi-pump systems, the multi-master configuration provides each pump with its own dedicated VFD. When one VFD encounters a fault, the remaining pumps continue to operate independently — providing good redundancy, suitable for facilities requiring continuous water supply such as apartment buildings, hospitals, and hotels. Dooch equips these booster systems with NQ/NSQ/XQ Drive VFD series.

For small and mid-scale buildings, horizontal booster pump systems are usually sufficient and cost-effective. The Dooch 2DHF (multi-stage) and 2DHM (single-stage) series serve up to approximately 58 m³/h at up to 68 m of head — meeting the needs of many low-rise apartment buildings and small office towers. For high-rise buildings or mixed-use complexes requiring higher flow rates and head, multi-stage vertical booster pump systems (Dooch IOP/XQP/NSQP/NSQ/N747D) are more appropriate, reaching up to 1,740 m³/h and head up to 330 m, with multi-master VFD for high redundancy.

For small buildings or households that only need a single booster pump, the Dooch NSQ/SQ2-DHF/DHM or DHJ/DHJA (self-priming) series can be used, with power ratings of 0.37–5.5 kW, paired with a VFD or pressure switch. Figures outside the ranges stated above should be confirmed per specific model and operating conditions.