How to Calculate Pool Pump Size

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Pool Pump Sizing

Many pool owners will opt for the most powerful pump they can afford for their new pool or to replace an old one. However, there is more to sizing a pool pump, so you should not just pick the most powerful model you come across.

If the pump is larger than what your pool needs, it will use more power than necessary and can also overpower your filtration system as the two are not compatible.

On the other hand, going for a smaller pump than your pool needs means you get inadequate water circulation and cleaning, leading to other problems like algae blooms.

The good news is that pool pump sizing is not that difficult. This guide looks at the key steps to follow to ensure you choose the right pump for your pool.

Calculate Pool Volume

The first step in pool pump sizing is to calculate your pool's volume. Any pool pump you choose should be able to handle the amount of water in your pool.

If your pool has a manual, it will include essential information like the pool volume, meaning you will not need to do any calculations. Also, most reputable pool equipment and fixtures suppliers provide online calculators that you can use to calculate your pool volume quickly.

However, you can still calculate your pool volume without a calculator. All you need to do is measure the length, width, and average depth and use then use the formula below:

Volume = Length x Width x Average Depth x 7.5

For those with L-shaped pools, you will need to divide the pool into sections and then calculate the volume of each before adding the figures you get.

However, here is the formula for calculating volume for round or circular pools:

Volume = Diameter Squared x Average Depth x 5.9

Determine Minimum Flow Rate

Once you know your pool's volume, the next step is to determine the minimum flow rate. Minimum flow rate is the minimum amount of water you need the pump to push every minute to ensure you still attain your daily turnovers.

Turnover is the time it takes to complete the cycle, or in simpler terms, the time it takes all the water in your pool going through the filtration system. Most pool types will require at least 2 turnovers per day, with the typical cycle length being 6 hours, 8 hours, or 10 hours.

To ensure efficient water circulation and cleaning, you need to know the minimum flow rate that your pump should have to attain the minimum daily turnovers.

You can use online pool calculators to determine the minimum flow rate by inputting the number of turnovers you want, pool volume, and pump run times or cycles.

As you decide on the minimum flow rate that you will need for your pump, also make sure you consider other things like the electricity bills and pool chemistry.

Using a low flow rate pump means you have to run it longer, which increases your electricity bills, but it often results in a more balanced pool. Therefore, you have to strike a good balance between energy efficiency and balancing pool chemistry to ensure you get the optimal pool pump size.

Determine Maximum Flow Rate

The maximum flow rate for your pool pump largely depends on things like the plumbing system and other things like the filters. Therefore, here you will not need to do any complicated calculations.

1. Plumbing System

When it comes to the plumbing system, the size of your pipes will determine the maximum flow rate they can handle.

The larger the pipes, the higher the pressure they can handle and hence the higher the flow rate they can accommodate. For example, the large 2.5-inch pool pipes can take a maximum flow rate of 120 GPM, while the smaller 1.5-inch ones will only support up to 43 GPM.

It is important to note that your plumbing system can have different pipe sizes, and so you have to check all of them as you try to figure out the maximum flow rate. The right idea is to use the maximum flow rate of the smallest pipe in the system.

2. Filters

Most swimming pools will use cartridges, DE, or sand filters. Each of these filter types can handle a varying maximum flow rate.

Besides the filter type, the surface area of the filter will also affect the flow rate. The smallest sand filters will have a surface area of around 1.8 square feet and can support up to 40 GPM.

A small cartridge filter with a 100 square foot surface area handles up to 38 gallons per minute. On the other hand, a 24 square foot DE filter, which is one of the smallest, has a maximum flow rate of up to 48 GPM.

Calculate Total Dynamic Head

The TDH (total dynamic head) is another crucial element that you will need to consider as you are sizing your pump after determining your flow rates.

TDH is a measure of the total resistance on the pool's hydraulic system. It includes the resistance on filters, pumps, heaters, pipes, and any other fixture or accessory that can affect how water flows to and from the pump.

TDH will also consider the maximum vertical height you need to pump the water as it is also some form of resistance that will work against the pump.

It is not always easy to accurately measure a pool's TDH, but you can still estimate it. The best way to do it is by measuring the vacuum pressure at the pump and clean filter pressure and then adding the numbers you get to get the TDH.

The higher the TDH for your system, the more powerful the pump you will need to ensure efficient water circulation since it needs to overcome more resistance as it moves water.

Other Factors to Considers

Once you know the flow rates and TDH, choosing the right pump size should be easy. Most pump manufacturers will indicate the maximum and minimum flow rates plus the TDH their pumps can handle in a flow chart. And so you should have an easy time deciding what will work for you.

That said, there are still a few other things that pool owners still need to take into account as they decide the best pool pump size. They include whether you have water features in the pool or not. Water fountains, waterfalls, and bubblers affect the water flow rate, and so you need to factor them in when deciding what to buy.

Other things like frequency of pool usage, how you use the pool (heavy or light), and environmental factors such as heavy debris accumulation and inclement weather also matter. These things often mean you need to circulate your pool water more to keep it clean, and so you require a larger and more powerful pump that can handle the increased demands.

Bottom Line

Every pool needs to have the right pump size to ensure optimal water circulation. With the right pump size, you will also eliminate unnecessary strain on your filters and other things like the plumbing system.

While many pool owners will often opt to replace their pump with the exact size and even model, this does not always work well. The best idea is to determine what your pool needs by looking at the volume, minimum and flow rate, and the TDH.

With a few quick calculations and a little shopping around to compare the many models out there, you should end up with the proper pump size for your swimming pool.