Pool Filter Flow Rate Calculator

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Pool Filter Flow Rate Calculator

High-Rate Sand (20 GPM per sq. ft.) Cartridge Filter (0.375 GPM per sq. ft.) D.E. (Diatomaceous Earth) (2 GPM per sq. ft.)
function calculateFlowRate() { var volume = parseFloat(document.getElementById('poolVolume').value); var hours = parseFloat(document.getElementById('turnoverTime').value); var filterType = document.getElementById('filterType').value; var resultDiv = document.getElementById('flowResult'); if (isNaN(volume) || isNaN(hours) || volume <= 0 || hours <= 0) { resultDiv.style.display = "block"; resultDiv.innerHTML = "Please enter valid numbers for pool volume and turnover time."; return; } // Calculation: GPM = Volume / (Hours * 60) var totalMinutes = hours * 60; var gpmNeeded = volume / totalMinutes; var filterSize = 0; var sizingUnit = "sq. ft."; var note = ""; if (filterType === "sand") { filterSize = gpmNeeded / 20; note = "Sand filters require backwashing when pressure rises 8-10 PSI above baseline."; } else if (filterType === "cartridge") { filterSize = gpmNeeded / 0.375; note = "Cartridge filters offer high clarity but require manual cleaning of the elements."; } else if (filterType === "de") { filterSize = gpmNeeded / 2; note = "D.E. filters provide the finest filtration (down to 3-5 microns)."; } resultDiv.style.display = "block"; resultDiv.innerHTML = "

Calculation Results

" + "Required Flow Rate: " + gpmNeeded.toFixed(2) + " GPM (Gallons Per Minute)" + "Minimum Filter Surface Area: " + filterSize.toFixed(2) + " " + sizingUnit + "" + "
" + note + "
"; }

How to Use the Pool Filter Flow Rate Calculator

Maintaining a crystal-clear swimming pool depends on one critical metric: the turnover rate. The turnover rate is the amount of time it takes for your pump and filter system to circulate the entire volume of your pool water exactly once. Most health departments and pool professionals recommend a turnover rate of 8 hours for residential pools.

Calculating Your Required GPM

GPM stands for Gallons Per Minute. This is the speed at which water moves through your filtration system. To find your required GPM, follow this formula:

Flow Rate (GPM) = Total Pool Volume ÷ (Turnover Hours × 60)

Example Calculation

Suppose you have a 20,000-gallon pool and you want a standard 8-hour turnover:

  • 8 hours × 60 minutes = 480 minutes
  • 20,000 gallons ÷ 480 minutes = 41.67 GPM

In this scenario, your pump and filter must be capable of handling at least 41.67 gallons every minute to successfully clean the water within the 8-hour window.

Understanding Filter Sizing and Media Types

Once you know your GPM, you must select a filter that can handle that flow without creating excessive back-pressure. Different filter types have different "design flow rates" per square foot of surface area:

Filter Type Flow Limit Filtration Quality
High-Rate Sand 15-20 GPM per sq. ft. 20-40 Microns
Cartridge 0.375 GPM per sq. ft. 10-15 Microns
D.E. (Diatomaceous Earth) 2.0 GPM per sq. ft. 3-5 Microns

Important Considerations

  • Pipe Velocity: Ensure your plumbing can handle the flow. For 1.5-inch PVC, the maximum recommended flow is typically 42 GPM. For 2-inch PVC, it is 73 GPM.
  • Oversizing: It is almost always better to "oversize" your filter. A larger filter has more surface area, which means less frequent cleaning and lower stress on your pool pump.
  • Variable Speed Pumps: If you use a variable speed pump (VSP), you can run the pump longer at a lower GPM to save electricity while still achieving the desired daily turnover.

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