Pool pump: the features that matter
The right pump is not the most powerful one, but the one that delivers the flow your filter and pool need, against the real resistance of the circuit, with as little energy and noise as possible.
Flow rate and head: the two numbers that matter
Flow rate is measured in m³/h and shows how much water the pump moves. Head is measured in metres of water column and expresses the resistance the pump has to overcome: friction in the pipes, bends, valves, the filter, any heating or disinfection unit, and the difference in height.
The two are linked. Every pump has a performance curve: the higher the resistance, the lower the flow. That is why the flow rate in the catalogue is not what you will get in your pool. The technician estimates the resistance of your circuit and chooses a pump that, at that point, delivers the flow needed to complete the water circulation in a reasonable time.
Horsepower on its own tells you little. An oversized pump pushes the water through the filter too fast, so it filters worse, makes more noise and wastes electricity.
Pre-filter and self-priming
In front of the impeller, pool pumps have a pre-filter: a basket, usually with a clear lid, that catches leaves, hair and anything the skimmer missed. If it is not emptied regularly, the flow drops and the pump struggles. Also check the lid's seal: if air gets in, the pump loses suction.
Self-priming means the pump can draw water even if it sits a little above the pool's water level, once its housing has been filled with water. Even so, the best position is close to the pool, at water level or slightly below. The pump must never run "dry".
Single-phase or three-phase
Most home pools run on single-phase pumps, which connect to the house's standard supply. Three-phase pumps are used for larger pumps, in pools at holiday accommodation, or where the property already has a three-phase supply. The choice depends on the power needed and the supply available, and is coordinated with the electrician so the line has the right protection.
| Feature | What to check |
|---|---|
| Flow at the real head | That it matches the pool volume and the filter's limit |
| Voltage | Single-phase or three-phase, depending on the property's supply |
| Pre-filter | A large basket, a lid that opens easily |
| Housing material | Plastic or cast iron, resistant to pool chemicals |
| Speed | Fixed or variable |
| Noise | The noise level stated by the manufacturer |
Noise and position
The pump is the noisiest part of the equipment. Noise is reduced by:
- the right size, so it does not work harder than it needs to;
- mounting it on a solid base with anti-vibration pads;
- an enclosed, well-ventilated plant room, away from bedrooms and from the boundary with your neighbour;
- a variable-speed pump, which runs at low speed most of the time.
If a pump that used to run quietly starts whistling or rattling, it may be drawing air, have a clogged pre-filter or worn bearings. Do not leave it for later.
Fixed or variable speed
A conventional pump always runs at the same speed. A variable-speed pump adjusts its speed to the task: low for everyday filtration, high for backwashing the filter or vacuuming. Either way, the running hours are set with a timer; how many are needed is covered under pump running hours. The type of pump is chosen during the site survey, together with the filter and the rest of the equipment.
Questions
Why is the pump running but not drawing water?
Usually air is getting in: a low water level at the skimmer, a worn seal on the pre-filter lid or a clogged basket. Switch it off, fill the pre-filter with water, check the lid and start it again.
If I fit a bigger pump, will the pool get clean faster?
Not necessarily. The pump has to match the filter and the pipes; a flow above what the filter can handle makes filtration worse and increases noise and energy use.
See also
Pool filter
Sand, glass media or cartridge pool filters: how each one works, how to choose the size and what the pressure…
Variable-speed pump
Variable-speed pool pumps: why lower speed for more hours means less energy use and less noise, and how to…
Pump running hours
How many hours your pool pump needs to run: the turnover cycle, setting the timer by season, which hours of…