How To Calculate Pool Pump Run Time

If you have a pool, then you almost assuredly have a pool filter pump. But how long should you run the filter pump? Knowing that a pool pump filter system is the second highest energy consumer during the summer, (after AC units), we want you to get the most bang for your buck.

Let’s walk through a few common questions and then breakdown the calculation behind finding the ideal pool filter pump run time for your swimming pool. We will show you the standard calculation and a simple calculation.

What does the pool filter pump do?

To understand how much run time you need, it’s important to know exactly what your filter pump does for your pool. The pool filter pump is the heart of your pool filtration system. It circulates water from the pool and returns it back, distributing pool chemicals and filtering your water. It is recommended that you “turnover” or circulate all of your pool water through the pool filter at least once throughout the day. This will ensure that the chemicals are evenly distributed and your water stays clean and clear. If you don’t circulate the water, you run the risk of algae growth and water balance or clarity issues. This may lead to water that is unsafe for swimmers.

How many gallons of water are in my pool?

Before we start, let's understand how many gallons of water are in your pool. To find your pool’s volume, use one of these easy calculations. If you don’t want to calculate the pool volume, take a quick look at the table on this helpful article: Calculating Pool Volume.

Square and Rectangle Pools with Single Depth:

Length x Width x Depth x 7.5 = Approximate Volume (Gallons)

Square and Rectangle Pools with Variable Depths:

Length x Width x Average Depth x 7.5 = Approximate Volume (Gallons)

Average Depth: If the pool has a shallow end and a deep end, add the two depths together and divide by 2. (Example: The shallow end is 3' deep and the deep end is 8'. Using the Average Depth formula: (3+8)÷2=5.5' Average Depth.)

Round Pools:

3.14 x Radius x Radius x Average Depth x 7.5 = Volume (Gallons)

The Radius equals the diameter divided by 2. (Example: A 16' diameter divided by 2 = 8' radius.)

Note: Most round pools have a single depth.

Oval Pools:

3.14 x Length x Width x .25 x Average Depth x 7.5 =  Approximate Volume (Gallons)

Kidney-Shaped Pool:

(A + B) x Length x
0.45 x Average Depth x 7.5 = Approximate Volume (Gallons)

(“A” and
“B” = Width at two widest points)

Irregular Shaped or Free-Form Pools:

Longest Length x Widest Width x Average Depth x 5.9 = Approximate Volume (Gallons)

What is the Turnover Rate?

Now that we have the pool volume in gallons, we can calculate the Turnover Rate. The water flow of Flow Rate for all pool filter pumps is measured in gallons per minute (GPM), versus gallons per hour (GPH). Here is how to get that number: 

Total Pool Volume ÷ 8 = GPH

GPH ÷ 60 = GPM

Let’s do some math!

Now that we have gallons per minute (GPM) and pool volume, we can calculate the run time. The math is simple. For this example, let's say you have a 20,000 gallon pool and the pool pump has a GPM rating of 40. Grab that calculator and just “sub-in” your measurements for these:

40 (GPM) X 60 (minutes per hour) = 2400 gallons per hour

20,000 (gallons) / 2400 (gallons per hour) = 8.3 hours

In this case, the ideal pool filter pump run time is 8.3 hours per day for one circulation or “turnover” of water.

A simpler calculation

Here is a simple rule of thumb for operating your single-speed filter pump during the swim season when the temperatures and bather loads are high:

Run the circulation system one (1) hour for every 10 °F of air temperature if a single-speed filter pump is installed.

Example: If it is
100 °F, the pump should run 10 hours a day minimum. Of course, if the pool is
full of algae or a major weather event has occurred, the pump may need to run
24-hours a day.

Variable-Speed Pumps:

Variable-speed filter pumps should run longer, based upon the operating speed. Most pool owners run their variable-speed pump 12 hours per day (3-4 hours on high speed for the pool cleaning system and 8-9 hours on low speed for filtration). Keep in mind that  certain water features — Salt Water Chlorine Generators and heaters — may not operate properly or even turn on if the filter pump is running on low speed.      

Any further questions?

If you have any further questions about pool pumps, please visit your local Leslie’s pool store today!