Pool & spa
Pool Pump Electricity Cost Calculator
What the pump actually costs to run, worked from horsepower, a nameplate or a measured wattage, with the variable speed comparison that drives the decision.
Result
The variable speed saving comes from pump affinity laws rather than from a better motor: flow falls roughly in proportion to speed while power falls with roughly the cube of it, so running at half speed for twice as long moves the same water for a fraction of the energy. That is why the saving is large enough to change the economics of a replacement. The figure here is the saving you enter rather than a promise, and the actual result depends on your plumbing, filter and required turnover. This does not account for a pump that is oversized for its plumbing, which is common and wastes energy before any of this applies.
Get a Free Business AuditHow the calculation works
Three routes to the pump's power draw, because the figure you have depends on where you looked. Horsepower converts at 745.7 watts of shaft output divided by motor efficiency to give input power. Nameplate amps times volts gives it directly. A measured wattage needs no conversion. From there it is kilowatts times run hours times days times your rate, and the variable speed comparison applies the saving you enter.
What moves the number
- Run hours per day, which is the lever most owners can actually move.
- Motor efficiency, since input power is shaft power divided by it.
- Whether the pump is single or variable speed.
- Electricity rate, which varies enormously by region and tariff.
Where this one goes wrong
The variable speed saving comes from pump affinity laws rather than a better motor: flow falls roughly in proportion to speed while power falls with roughly the cube of it, so running at half speed for twice as long moves the same water for a fraction of the energy. That relationship is why a variable speed pump usually repays itself on a pool that runs daily. Nameplate amps are a rated maximum and service factor ratings can push the plate figure above normal running draw, so a measured reading at your usual speed gives a better answer than the plate.
Before you quote
- Prefer a measured reading over the nameplate where you can get one.
- Apply motor efficiency when working from horsepower.
- Check your actual tariff rather than using a national average rate.
Where the rules come from
Questions
About this calculator
How much does it cost to run a pool pump?
Work it from your own pump and rate rather than a typical figure, because the spread is very wide. A single speed pump running long hours on an expensive tariff can be one of the largest loads in a house, while the same pool on a variable speed pump at a low rate costs a fraction of it.
Why does a variable speed pump save so much?
Because power rises with roughly the cube of speed while flow rises in proportion to it. Halving the speed cuts flow in half but cuts power to around an eighth, so running twice as long at half speed moves the same water for far less energy. That relationship, not motor efficiency, is where the saving comes from.
Should I use the nameplate amps?
It is a reasonable starting point but it is a rated maximum, and service factor ratings can make the plate figure higher than normal running draw. A measured reading at your usual speed is better if you can get one, which is what the measured wattage method is for.
Can I just run the pump fewer hours?
Up to a point, but the pool still needs enough turnover to filter and to distribute sanitiser, and cutting hours too far shows up as water quality problems rather than savings. Reducing speed rather than hours is what the affinity relationship rewards.
The formula
watts = horsepower x 745.7 / motor efficiency; annual cost = watts / 1000 x hours per day x days x rate
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How to use this calculator
- Work the draw out from. Enter your own figure; the page starts at Motor horsepower.
- Motor horsepower. Enter your own figure; the page starts at 1.5.
- Motor efficiency (%). Input power is shaft power divided by efficiency, so a less efficient motor draws more for the same work.
- Run hours per day. Enter your own figure; the page starts at 8.
- Months the pool runs. Enter your own figure; the page starts at 12.
- Cost per kWh ($). Enter your own figure; the page starts at $0.17.
The result updates as you type, so you can try a figure, see what it does to cost to run for a year, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Work the draw out from | Motor horsepower |
| Motor horsepower | 1.5 |
| Motor efficiency | 80% |
| Run hours per day | 8 |
| Months the pool runs | 12 |
| Cost per kWh | $0.17 |
| Saving if you ran variable speed | 65% |
What comes out
| Result | Value |
|---|---|
| Cost to run for a year main result | $694.59 |
| Power draw | 1,398 |
| Cost per month running | $57.88 |
| Kilowatt hours per year | 4,086 |
| Cost per year on variable speed | $243.11 |
| Saving per year from variable speed | $451.49 |
| Cost per day | $1.90 |
The pump draws 1,398 watts and costs $694.59 a year at 8 hours a day. A variable speed pump at the same turnover would cost $243.11, saving $451.49 a year.
How sensitive the answer is
Holding everything else steady and changing only cost per kwh, this is what happens to cost to run for a year. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Cost per kWh ($) | Cost to run for a year |
|---|---|
| $0.09 | $367.73 |
| $0.13 | $531.16 |
| $0.17 example above | $694.59 |
| $0.26 | $1,062 |
| $0.34 | $1,389 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Work the draw out from
- Choose from Motor horsepower, Amps and volts from the nameplate, A measured wattage.
- Motor horsepower
- A number, between 0 and 20, starting at 1.5.
- Motor efficiency (%)
- Input power is shaft power divided by efficiency, so a less efficient motor draws more for the same work.
- Run hours per day
- A number, between 0 and 24, starting at 8.
- Months the pool runs
- A number, between 1 and 12, starting at 12.
- Cost per kWh ($)
- A money amount, between 0 and 5, starting at $0.17.
- Saving if you ran variable speed (%)
- Pump affinity laws mean halving speed cuts power far more than half, so the saving comes from running longer at a lower speed.
What the results tell you
| Result | What it is |
|---|---|
| Cost to run for a year | The headline result. A money figure. |
| Power draw | A number. |
| Cost per month running | A money figure. |
| Kilowatt hours per year | A number. |
| Cost per year on variable speed | A money figure. |
| Saving per year from variable speed | A money figure. |
| Cost per day | A money figure. |
Keep going
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