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How to Choose the Right Pool Pump for Your In-Ground Pool

11 Aug 2023

Not only is your pool pump is a vital piece of equipment to your swimming pool, but it’s also vitally important that your pool pump is the appropriate size for your pool. Too big and it will soak up more energy than necessary, resulting in higher energy bills each month. Too small though, and it will fail to sufficiently filter your pool. Having the right pump will be vital to maintaining your pool in the long run.

When determining what type of pool pump is right for your inground swimming pool, follow this rule: You need a pump that can filter all of the water in your pool within eight hours.

How do you figure that out? It’s as easy as following a few equations and taking some measurements. Let us help!

Welcome to Math Class

How much water is in my pool?

The first calculation necessary for determining what type of pool pump you should buy is to figure out how many gallons of water are in your pool. The equation will vary slightly based on the shape of your pool. Follow the appropriate example for your pool:

  • Rectangular pool: Gallons = Length x Width x Average Depth* x 7.5
  • Circular pool: Gallons = Diameter x Diameter x Average Depth x 5.9
  • Oval pool: Gallons = Longest diameter x Shortest diameter x Average depth x 6.7
  • Kidney-shaped pool: Gallons = (Longest width + Shortest width) x Length x Average depth x 3.38

*To determine the average depth of your pool, add the depth of the deep end to the depth of the shallow end and divide it by 2.

Note that pool features like fountains, spas, waterfalls, or in-floor cleaning systems are not factored into the above equations.

How fast should my pool pump filter water?

Once you know the total number of gallons in your pool, divide that number by 8 to figure out how many gallons per hour (GPH) your pool pump should filter. You’ll notice when you start looking at pool pumps that most advertise gallons per minute (GPM). To convert your GPH number to GPM, divide it by 60.

How much resistance should my pump be able to handle?

Now it’s time to measure Total Dynamic Head (TDH), which is a measurement of resistance. A simple way to think about TDH (more commonly called Feet of Head) is that it is essentially the amount of resistance that your pool pump experiences when it pulls water from your basin and pushes it back into the pool.

To determine feet of head, measure the length of the pipes in your pool, add the totals together and divide them by 3, You’ll need this number when you’re choosing a new pool pump.

Let’s Play the Matching Game

Is my pool pump the right size for my filter?

The pool pump and pool filter work together, transporting water from the pump to the filter. If your pool filter is too small to keep up with the amount of water flowing through an oversize pump, then the water flow will back up. This puts excess pressure on the pump and quickly wears out the pump motor.

To protect against this problem, make sure that the GPM for the pump does not exceed the max flow rate for the filter. Just to err on the side of safety, many pool owners buy an oversize filter rather than risk having a filter that’s too small for their pump.

Are my pipes the right size for my pool pump?

Regardless of how many GPM your pump is designed to handle, the pipe size connected to the pump will ultimately determine how quickly water can flow through it. For example, if you have a 100 GPM pump, but you have 1-1/2″ pipe, your pump will only flow at 60 GPM.

Take note of the numbers below to make sure that your pipes and pump have the same GPM capabilities.

1-1/2″ pipe has a max flow rate of 60 GPM
2″ pipe has a max flow rate of 100 GPM
2-1/2″ pipe has a max flow rate of 140 GPM

Can We Help?

That’s a silly question. Of course, we can help! Just tell us when and where by contacting us to schedule a service for your swimming pool. If we haven’t already met, we look forward to working with you and your pool!

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