The flow rate for your swimming pool is determined by calculating the pool's capacity in gallons and dividing it by your desired turnover rate (typically 6-8 hours).
Here's a breakdown of the calculation:
Steps to Calculate Pool Flow Rate:
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Determine Your Pool's Capacity (in Gallons): This is the total volume of water your pool holds. You'll need to use different formulas depending on the pool's shape:
- Rectangular/Square Pools: Length (ft) x Width (ft) x Average Depth (ft) x 7.5 = Gallons
- Round Pools: Radius (ft) x Radius (ft) x 3.14 x Average Depth (ft) x 7.5 = Gallons (Remember Radius = Diameter / 2)
- Oval Pools: (Length (ft) / 2) x (Width (ft) / 2) x 3.14 x Average Depth (ft) x 7.5 = Gallons
- Irregular Shapes: It's best to break the pool into sections of known shapes, calculate the volume of each section, and then add them together. Alternatively, consult your pool's documentation or a pool professional for the volume.
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Choose Your Desired Turnover Rate (in Hours): The turnover rate is how long it takes for your entire pool volume to circulate through the filter. A good target is typically between 6 and 8 hours. A faster turnover rate generally results in cleaner water, but also requires a more powerful (and possibly more expensive) pump. We'll use 8 hours as an example in the following calculations.
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Calculate Required Gallons Per Hour (GPH): Divide the pool's capacity (in gallons) by your desired turnover rate (in hours).
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Pool Capacity (Gallons) / Turnover Rate (Hours) = Gallons Per Hour (GPH) -
Example: Let's say your pool holds 20,000 gallons, and you want an 8-hour turnover rate:
20,000 Gallons / 8 Hours = 2,500 GPH
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Calculate Required Gallons Per Minute (GPM): Divide the GPH by 60 to convert to gallons per minute.
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Gallons Per Hour (GPH) / 60 = Gallons Per Minute (GPM) -
Example: Using the previous example of 2,500 GPH:
2,500 GPH / 60 = 41.67 GPM
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Therefore, in this example, you would need a pump capable of delivering at least approximately 42 GPM to achieve an 8-hour turnover rate for a 20,000-gallon pool.
Important Considerations:
- Plumbing Resistance: The calculations above provide a minimum GPM. Friction in your pool's plumbing (pipes, fittings, filter, heater, etc.) reduces the actual flow rate. You may need a slightly larger pump to compensate for this resistance. Consult with a pool professional for accurate plumbing loss calculations.
- Filter Requirements: Your filter will also have a maximum flow rate. Ensure your pump's GPM does not exceed the filter's maximum rating. Using a pump that is too powerful for your filter can damage the filter.
- Variable Speed Pumps: Many modern pumps are variable speed. They allow you to adjust the flow rate to optimize energy efficiency and filtration. In these cases, make sure the pump can achieve the minimum GPM needed for your turnover rate, but you can run it at lower speeds for much of the time.
- Professional Advice: It is always a good idea to consult with a pool professional to determine the best pump and filter for your specific pool setup. They can take into account all the factors that affect flow rate and recommend the most appropriate equipment.
In summary, calculate your pool's volume, determine your desired turnover rate, and then perform the division steps to find the necessary GPM for your pool pump.
