How to use the pool pump energy cost calculator
- Enter the pool volume, the turnovers per day you want and the pump's flow and power at full speed.
- Enter the speed to compare, as a percent of full speed, and your electricity price.
- Read the monthly cost at your speed against full speed, and the run time needed.
- Use the table to compare several speeds for the same amount of water moved each day.
Formula
Water per day = pool volume x turnovers per day
Flow at speed s = full flow x s; power at speed s = full power x s^3
Hours per day = water per day / (flow x 60)
Energy per day (kWh) = power x hours / 1000
Cost per month = kWh per day x days x price per kWh
s is the speed as a fraction of full speed. Because the hours scale as 1/s and the power as s^3, the energy for a fixed amount of water scales as s squared.
A 15,000 gallon pool, once a day
At full speed the pump moves 60 gallons per minute and uses 1,800 W. Turning over 15,000 gallons takes 4.17 hours and 7.50 kWh a day, which costs $38.25 a month at 30 days and $0.17 per kWh.
At 50% speed the flow is 30 gpm and the power is 1,800 x 0.5 cubed = 225 W. The same water takes 8.33 hours and 1.88 kWh a day, which costs $9.56 a month, 75% less. At 40% speed it costs $6.12, and at 30% speed $3.44, though it must run for 13.89 hours.
Why slower can use much less energy
For a centrifugal pump the affinity laws say flow rises in proportion to speed, while the power needed rises with the cube of speed. Halving the speed halves the flow but cuts the power to one eighth. To move the same water you run twice as long, so you use a quarter of the energy. This is the reason variable-speed pumps are sold on their electricity savings, and the table shows how the saving grows as speed falls.
The saving has limits. The pump must still produce enough flow for the filter, heater, cleaner or chlorinator, and the system pressure changes with speed. Running 24 hours a day at a very low speed gives no room for more circulation when you need it.
Checking against your pump
The laws are an idealization. Real pumps have losses that do not follow the cube law exactly, and the actual flow at a given speed depends on the pipe, filter and valves in your system. Compare the answers with the pump maker's performance charts if you have them, and use measured watts from the pump display for the best match.
Related tools: the pool volume calculator to find gallons, the electricity cost calculator for other appliances, the electric bill breakdown calculator, and the pool chlorine calculator.
Assumptions and limits
- Flow is proportional to speed and power to the cube of speed, which is an approximation for a fixed system.
- The flow and power at full speed are values you supply. The defaults are examples.
- The electricity price is a flat rate with no time-of-use differences, and the default is an example.
- Speeds below 20% of full speed are not calculated because most pumps cannot run that slowly.
Frequently asked questions
How many turnovers per day do I need?
It depends on the pool, the weather, the number of swimmers and local guidance, so the page does not choose for you. Many owners aim for about one turnover a day, and the field takes any value you prefer.
Where do I find my pump's flow and watts?
The pump data sheet or label gives flow and power at several speeds, and many variable-speed pumps show watts on the display. Use the numbers for full speed in your own plumbing, not the maximum on the box.
Does a single-speed pump match the full speed row?
Yes. A single-speed pump always runs at full speed, so the 100% row is its daily energy and cost for the same turnover. The other rows show what a variable-speed pump could do.
Is the saving guaranteed?
No. It is the result of the idealized pump laws with your numbers. The real saving depends on the pump and the plumbing, and can be smaller or larger.