How Long Should a Pool Pump Run, and What Does It Cost?
The pool pump is usually the biggest electricity user among your pool equipment, and it is also the one piece of equipment the water cannot do without. Run it too little and the pool clouds or turns green. Run it far more than it needs and you pay for hours that do nothing useful. This guide explains how to work out the right run-time for your pool and how to calculate what it costs, using the figures on your pump and the rate on your own electricity bill.
Turnover: the idea behind run-time
The key idea is turnover. One turnover is the time it takes for the pump to push a volume of water equal to the whole pool through the filter once.
Two numbers decide it: the volume of your pool and the actual flow rate of your pump. The volume you can work out from the pool's dimensions. For a rectangular pool it is length × width × average depth × 1,000, in litres, where the average depth is the shallow end plus the deep end divided by two.
The flow rate is harder. A pump's manual shows a flow curve, usually in cubic metres or litres per hour, but the real flow in your system is lower than the maximum on the box. Every metre of pipe, every bend, the height the water has to be lifted and the state of the filter all add resistance. A filter that needs backwashing slows the flow noticeably.
Here is an illustration. Suppose your pool holds 48,000 litres and your pump actually moves about 10,000 litres an hour through your plumbing. One turnover takes 48,000 ÷ 10,000 = 4.8 hours. If the flow is lower because the pipe runs are long or the filter is dirty, the same turnover takes longer.
The general aim is to turn the whole volume over at least once a day, and more in summer, when the water is warmer, the sun is stronger and the pool is used more.
Summer and winter hours
As general guidance for a typical home pool:
- In summer, most pools need somewhere around six to eight hours a day, and more after heavy use, a storm or a chemical treatment.
- In winter, when the water is cold and the pool is hardly used, fewer hours are usually enough, provided the water stays clear and the chlorine holds.
Two things can push the number up. If you have a salt chlorinator, it only makes chlorine while the pump runs, so the hours must be long enough to produce the chlorine the pool needs, not just to filter it. And if your pool has trees around it or a busy household using it, the filter has more work to do.
The water is the final judge. If it stays clear and the chlorine reading holds, your hours are probably right. If it starts to dull, add time before you add chemicals.
Reading your pump's power figure
To calculate running cost you need the pump's power in kilowatts. Look for the nameplate on the motor. It is usually a metal or foil label on the side of the motor body.
Many labels show two figures. The input power, sometimes marked P1, is what the pump draws from the wall. The output power, sometimes marked P2, is what the motor delivers to the shaft. For cost, you want the input figure, because that is what the meter measures. Output power is often the number printed on the box, and it is lower than input.
Older pumps may be rated in horsepower. One horsepower is about 0.75 kW, so a pump sold as 1 hp is roughly a 0.75 kW motor, and its input power will be somewhat higher than that.
If the label only gives volts and amps, multiplying the two and dividing by 1,000 gives a rough upper estimate in kilowatts. The real figure is a little lower, because motors do not use the full product of volts and amps as useful power.
Working out what it costs to run
The method is simple, and it works for any electrical appliance:
- Kilowatts × hours per day = kilowatt-hours (kWh) per day.
- kWh per day × days in the month = kWh per month.
- kWh per month × your rate per kWh = monthly running cost.
Your rate is on your electricity bill or prepaid statement from Eskom or your municipality. Tariffs differ between suppliers and between blocks of use, so use your own figure rather than one from an article or advert.
A worked example, in kWh only:
- A pump with an input power of 1.1 kW running 8 hours a day uses 1.1 × 8 = 8.8 kWh a day.
- Over 30 days that is 8.8 × 30 = 264 kWh for the month.
- The same pump running 5 hours a day in winter uses 5.5 kWh a day, or 165 kWh over 30 days.
Multiply those kWh figures by your own rate and you have your answer. Remember that a salt chlorinator, a heat pump or a booster pump for a pressure cleaner all use electricity too, and each can be calculated the same way from its own nameplate.
Time-of-use tariffs
If your account is on a time-of-use tariff, electricity costs different amounts at different times of day. Running the pump in the cheaper periods can lower the monthly cost without cutting the hours the pool needs. Your supplier publishes the peak and off-peak periods for your tariff.
Balance this against what the pool needs. In summer, running at least part of the day while the sun is on the water helps, because that is when chlorine is used up fastest, and a salt chlorinator only produces chlorine while the pump is running.
Timers: set them and check them
A timer is what turns a good plan into a daily habit. Mechanical timers use pins or tabs around a dial; digital timers are programmed with on and off times. Splitting the day's run-time into two or three blocks is often better than one long block, because it keeps the water moving through the day and limits the damage if one block is lost to an outage.
Timers are the weak point when the power goes off. A mechanical timer stops while the power is off and runs late afterwards, and some digital timers lose their programme. Our load-shedding and pool pump guide covers how to plan run-time around outages and what to check when the power comes back.
Variable-speed and energy-saving pumps
A standard pool pump runs at one speed: full speed. A variable-speed or energy-saving pump lets you choose a lower speed for day-to-day filtration and a higher speed only when you need it, for backwashing, vacuuming or running a suction cleaner.
The reason this matters comes from the way pumps behave. When a pump slows down, the flow it delivers drops roughly in step with the speed, but the power it draws drops much faster than that. So a pump running at a moderate speed for longer can move the same total volume of water in a day while using considerably less electricity than a single-speed pump running flat out for a shorter time. Slower flow through the sand also tends to filter a little better.
Whether a variable-speed pump is worth it for your pool depends on how many hours you run and on your tariff. The honest way to decide is to take the manufacturer's input power figure at the speed you would actually use, run it through the calculation above, and compare it with your current pump. You can browse options in our energy-saving pumps department.
When the pump is working harder than it should
A pump that has to fight to move water uses power without doing the job. Common causes are a full weir or pump basket, a filter overdue for a backwash, a partly closed valve, or worn bearings in an ageing motor. A loud whine, a hot motor, a pump that trips or air bubbles in the pump basket are signs to look into. Our article on pool pump problems and when to replace a pump goes through the warning signs.
If the pump needs attention, our pool pump repair service is R850 for diagnosis and repair, with any parts quoted before they are fitted.
Getting help
If you are not sure how many hours your pool needs, or whether your pump is the right size for your pool and filter, send us a WhatsApp on 081 577 5051 with a photo of the pump's nameplate, the filter and the pool. We can help you work out a sensible run-time and whether a different pump would suit your pool.