The pump is the piece of pool equipment that uses the most electricity. A variable-speed pump is not magic: it takes advantage of a very specific law of physics. We explain it without complicated formulas and tell you when switching is worth it and when it is not.
The cube law, in plain words
In a centrifugal pump, flow is proportional to speed, but power is proportional to the cube of speed (the so-called affinity laws). If the pump runs at half speed:
- It moves half as much water per hour.
- It draws 1/8 of the power (½ × ½ × ½).
- To move the same total volume it needs twice the hours, so in theory it uses a quarter of the energy.
Illustrative example (round figures, not a specific model): a 1 kW single-speed pump running 8 hours uses 8 kWh. Moving the same water at half speed for 16 hours, the theoretical ideal would be about 2 kWh. In practice the saving is smaller because of motor and plumbing losses, but it is still large.
Half the speed, far less power
How much do you really save?
The US ENERGY STAR programme states that a certified variable-speed pump can use up to 70% less energy than a single-speed one. That is a maximum: it depends on how many hours you filter, the installation and the speeds you program.
Is there an EU rule that requires it?
At present there is no specific EU ecodesign regulation for pool pumps; the Commission lists them among the products it is studying in its working plan. So switching is a money-saving decision, not an obligation.
When it pays off and when it does not
- It pays off if you filter many hours a day, if the pool is large or communal, or if your current pump is near the end of its life.
- It pays off less in small pools with few filtration hours or pools used only a few months a year.
- Watch out: at low speed some equipment (salt chlorinator, heat pump, robotic cleaner) needs a minimum flow. Program higher-speed periods for them.
To find out what flow your pool needs, try our pump and filter calculator.
Frequently asked questions
How much does a variable-speed pump save?
ENERGY STAR states it can use up to 70% less energy than a single-speed pump. Real savings depend on filtration hours, the installation and programming.
Why does it use less if it runs longer?
Because a centrifugal pump’s power is proportional to the cube of its speed: at half speed it draws one eighth of the power, so even running twice as long it uses about a quarter of the energy in theory.
Is switching to a variable-speed pump mandatory?
No. At present there is no specific EU ecodesign regulation for pool pumps; it is a money-saving decision.