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—Pumps, filtration and plant

Sizing a pool pump

The right pump moves enough water through the system without wasting energy. Bigger is not better; matched is.

A circulation pump is chosen to move the pool’s volume through the filter within a reasonable time, known as turnover. The required flow is then compared with the resistance of the system: pipe sizes and lengths, bends, valves, the filter, heaters and any chlorinator all add resistance. A pump is selected whose performance meets the flow at that resistance.

Equipment guides are about choosing, sizing and installing plant, not about day-to-day pool care.

An oversized pump uses more energy, can push water through the filter too fast for good filtration and makes more noise. Features such as infinity edges, spas and water features may need their own pumps or a variable-speed pump that can run at different rates. Sizing should be calculated, not guessed from the old pump’s label.

01Summary

What matters most here

  • Flow and resistance

    Both decide the pump.

  • Oversizing wastes energy

    And can harm filtration.

  • Features add demand

    Spas and edges may need their own pumps.

02Detail

What goes into the calculation

  • Pool volume

    Length, width and average depth.

  • Turnover

    How often the volume should pass through the filter.

  • System resistance

    Pipes, fittings, filter and heater.

  • Filter rating

    The maximum flow the filter is designed for.

  • Features

    Extra flow for spas, jets or edges.

03Before you start

Information to provide

  • Pool dimensions

    Including depths.

  • Equipment list

    Filter, heater and chlorinator models.

  • Pipe sizes

    If known.

—In practice

How to use this

Gather the pool’s volume, the pipe sizes and lengths, and the equipment in the circuit — filter, heater, chlorinator, features. Ask for the required flow and the system resistance to be worked out, and for a pump chosen to meet them efficiently. Check the pump’s flow also stays within the limits of the filter and any heat pump it feeds.

Mistakes worth avoiding

Choosing the largest pump
An oversized pump wastes energy, is noisier and can push more water than the filter is designed to handle.
Ignoring the pipework
A pump’s real performance depends on the system it pushes against. Pipe sizes and bends are part of the calculation.

04FAQ

Common questions about this

Should I replace my pump with the same size?
Not automatically; the original may have been over- or undersized.
Why not choose a bigger pump?
It uses more energy and can push water through the filter too fast.
Do features need separate pumps?
Sometimes, depending on their flow requirements.
Can a variable-speed pump cover several needs?
Yes, by running at different speeds for different tasks.

05Read next

More pool guides on this

Filed under pump & filtration systems. Every pool guide is listed on the pool guides page.

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