How to Know How Many Hours to Run a Pool Filter

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Last Updated: December 18, 2023 References

As pool owners know, all of its systems need maintaining so that the water stays crystal clear and refreshing. Water clarity is a combination of maintaining the chemical balance of your pool and proper filtration. Make sure you’re running your filter properly by running it longer when it’s hot out, and during the day. You can also determine how long you should run the filter in your pool specifically, based on its volume and the speed of its filter.

Method 1

Method 1 of 2:

Calculating Run Time per Day

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1
Determine the volume of your pool. How long you run the filter depends on the pool size to filter ratio. Calculate the volume of your pool by multiplying the length by the width by the average depth in feet.
- Multiply this number by a standard multiplier, which is 7.5 for rectangular and square pools and 5.9 for other shapes.
- Example: 16*32*5*7.48 = 19,149. This would give the volume of the pool in gallons for this 16x32 inch pool that has an average depth of 5 feet.
- If your pool has different areas of depth to it, calculate the volume of each area of depth before adding them all together to find the total volume of your pool.
2
Find out the flow rate of the pump. Include the resistance to flow in your plumbing system. You can estimate your pool plumbing resistance to be 20ft/lbs for small pools, and 40ft/lbs for large pools or installations where the pool pump is far removed from the pool area.^{[1]
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- The pump manufacturer can tell you the flow rate for certain resistances.
- An average 1 HP pump will move about 50 gallons per minute. This would be 3,000 gallons per hour.
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3
Calculate the turnover rate for your pool. The minimum recommended turnover for a pool is 2 complete turnovers in any 24 hour period. Use this equation to see how long you should run your filter: (Pool Volume ÷ Filtration rate) x 2 = Hours to run filter. This will tell you how many hours to run your pump to filter the water a full 2 times.^{[2]
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- For example, using a pool volume of 19,149 gallons and a filtration rate of 3,000 gallons per hour:
  - (Pool Volume ÷ Filtration rate) x 2 = Hours to run filter
  - (19,149 ÷ 3000) x 2 = 12.766, or about 12 hours and 45 minutes for a full 2 cycles.

Method 2

Method 2 of 2:

Following Basic Rules for Filtering

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1
Run your filter 1 hour for every 10 °F (−12 °C) it is outside. A general rule of thumb you can follow year-round is running your filter dependent on the temperature. In the winter, you’ll be running it 6 or fewer hours, while in the summer, you might have to go a full 12.^{[3]
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- If you’re experiencing temperatures of 80 °F (27 °C) or greater, you should be running your filter about 10-12 hours regardless.^{[4]
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2
Run your filter during the daytime when your pool water is hottest. These warm temperatures are when algae is most likely to start growing in your pool water. Run the filter with chlorine the entire length of the day in these cases to avoid any chances of algae turning up in your pool.^{[5]
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- Although running your filter at night may save you energy, it does nothing to prevent the algae from forming during the day when it’s actually got a chance to, unlike at night.
3
Feel free to safely run your filter 10-12 hours a day. Your pool filter is intended to be run for up to 12 hours a day consistently. You can run it on its lower settings normally, and then on the higher settings when you’re adding the chlorine or other cleansers to the water.^{[6]
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- This way, you’ll be ensuring you’re filtering out the entire contents of your pool at least 2 times a day.
- If you have a small filter, you will need to run the filter longer depending on how many gallons the filter can process in a given time. Don’t worry about running it for too long, it’s better to overrun your filter than not run for long enough.
4
Clean out or replace pool filters after long periods of use. Over the course of a pool’s life, you’ll need to have the filters cleaned out if they’re dirty or clogged with debris. Otherwise, you may find you’re having to run your filters for longer to achieve the same effect.^{[7]
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- Here are instructions detailing how to Clean a Cartridge Type Swimming Pool Filter.

Community Q&A

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Question

Do I need a 220 line to run a 3/4 hp pump?

Community Answer

220 is more efficient than 120 and will help keep the energy usage lower. Run time depends on size of pool and hydraulics. Residential In-ground pools are generally hydraulically built to run 8 hours a day for proper turnover rate, with a temperature of 80 degrees. Every 10 degrees warmer than 80 degrees pump should be run 1 hour longer. For example, 90 degrees run 9 hours. This is for a single speed pump running 3450 rpm.

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Question

How long should the filter pump run after the two 12 hour turnovers?

Community Answer

Let the filter rest for about a day, then run the filter in 6 - 8 hour intervals every day that you want to use your pool.

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My pool was clear while the sand filter was running, but when I scrubbed, the walls were green again. Any suggestions?

Pool Lady

Community Answer

Check the balance of your water. It may just need to be super-shocked. Depending on the size of your pool, a bottle of vitamin C tablets could solve your problem. Just a note, know what you need before you go to buy your chemicals. Pool stores sell chemicals. It is how they survive.

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Add your chemicals at night when the sun is not depleting the chlorine in your pool.

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Regularly examine the water for bugs, plant material, dirt, and other contaminants. Skim the surface with a net, and vacuum the bottom and sides.

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Run your pool pump at night for cooler operation of your pump.

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