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How to Choose a Pool Pump

If you are like most a pool owners, shopping for pool pumps can be a very daunting task. With so many terms to know and items to consider, it’s no wonder that many of us end up at the mercy of the local pool maintenance guy or pool shop. In order to level the playing field as you work to find out just what you need and what you don’t, we’ve put together some helpful information on how to find the best pool pump for your needs.

Flow Rate & Head

There are two key elements that play into determining what pool pump (and how strong it needs to be) will best work for your system:  “flow rate” and “head”. Flow rate refers to how much water can be moved in a determined amount of time and is measured in gallons-per-minute (or GPM). The term “head” refers to the amount of resistance to flow that exists in your pool plumbing system. Head is usually measured in “feet of resistance” or “feet of head”. The items in your pool's circulation system (such as the pool heater, automatic pool chemical feeder, etc.), as well as the amount of bends in your piping, size of piping, and distance the water must travel all play a role in determining your total head.

Pump manufacturers carry details related to flow rates and head that can help you determine which pool pump you need. It’s also important to keep in mind that these two calculations are not independent of each other. Your determined/desired flow rate will play a part in determining your head, as many elements within a pool’s plumbing loop offer different levels of head depending on how much water you’re trying to pass through them in any given moment.

Calculating Flow Rate: To calculate flow rate, you first need to determine your desired turnover rate, or how often your pump filters an equivalent amount of water to the total amount in your pool. It’s recommend that your pool have 1-2 turnovers a day with a turnover time of about 5 hours. The steps below will help you calculate your flow rate.

  1.  Determine the amount of water in your pool or your pool's total capacity.
  2.  Divide the number of gallons of water in your pool by the number of hours you want per turnover (say, 5).
  3.  Then divide this number by 60 to determine your need flow rate per minute (GPM).

Example: Let’s say we have a 20,000 gallon pool and have a desired turnover rate of 5 hours. Your desired flow rate would be would be: (20,000/5) = 4,000 gallons per hour/60 = 66.66 GPM (apprx. 67 GPM).

Calculating Head: As mentioned above, your total head is comprised of a variety of factors and is actually broken into multiple parts, as head does have a dynamic component to it. These calculations can become very complex very fast. Don’t worry however as there are a few tips for estimating fairly accurately your total head. *Note: For estimating feet of head below, courser filters allow for lower-end estimations.

  1. Determine the amount of pipe between the pump and pool return. This is your starting feet of head. 
  2. If you use a filter, cut this number in half.
  3. If your return line pipe size (diameter) changes (reduced diameter), determine the percentage change and add that many feet to your calculation (20 feet of pipe that connects to a 50% smaller diameter pipe adds 10 feet of head).
  4. 90-degree turns in piping add around 1-2 feet of head.
  5. Other items along the line will usually add around 2-12 feet of head. Sometimes these products will tell you how much resistance is built depending on your flow rate. If you have that information or can contact a manufacturer and get it, it will help to make your estimation that much more accurate.
  6. For each foot below the water surface your return line is, add 1 foot of head to your calculation.

Buying the Pool Pump

 Now that you’ve calculated your flow rate and head, you’re ready to start looking at pool pumps. Check out manufacturer’s specs related to each pump in these two areas to determine the best pump for you. If you’re still not feeling confident enough to make the decision alone – contact us! We’d be happy to help you select a pump and answer any other pool equipment or pool supply questions you might have.

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