How to Pick the Right Size Swimming Pool Pump

Choose Wisely, Save Money and Turn Your Blue Swimming Pool Green

Smooth curve and water jets of swimming pool.
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No one likes to walk out in his or her yard and find a green swimming pool -- or do they? In this instance, we're not talking about literally letting your swimming pool water turn green. Instead, we are talking about creating an enticing pool that is easy on the environment and on your budget, as well. Armed with just a little information, you can save money on your monthly utility bill, streamline your pool maintenance, and your swimming pool water will never look better!

However, before we start the transformation there are a few terms and concepts to understand. The overall goal of the pool circulation system is to cycle the water through the pool filter system, where dirt and debris are removed and water is sanitized and returned to the pool, clean and inviting. The heart of the system is the pool pump. An American National Standard, ANSI/APSP-5 Standard for Residential In-ground Pools, provides guidelines for maintaining proper water cleanliness. In it, we find that a "turnover" is the amount of time it takes to move a volume of water, equal to the size of your pool, through the filtration and sanitation process once.

How Much Pump Do I Need?

If your pool volume is 15,000 gallons, then one turnover would be equal to 15,000 gallons. This turnover is required every 12 hours, or twice a day. Pumps, on the other hand, use a slightly different description of "gallons per minute" or GPM. Think of this a little like the miles per gallon (MPG) quoted as gas mileage on your car. Our goal is to meet or exceed our minimum required turnover and to use the least amount of energy doing it.

Here is the problem: most pools are designed to sell, not to operate. It has become very popular to "sell on horsepower" or how powerful a swimming pool water pump is, not how efficiently it operates. Many pool builders routinely sell against their competition by quoting a "bigger" pump as a "free upgrade." As a result, the vast majority of pools have pumps that are severely oversized. Water pumps of 1, 1.5, and 2 horsepower are very common -- and for the average size pool, very oversized.

Oversizing pumps have become such an issue that the State of California (a big pool state), recently enacted a law to control how big of a pump could be placed in a swimming pool. While it might not seem possible, it's actually less expensive to run your pool water pump 24/7 if you have the correct pump in place. Unless you have a two-speed, or variable-speed pump, chances are you cannot operate around the clock. The savings with one of these pumps can be so large, you might want to invest in one, and you certainly want to consider if it is time for a replacement. One other key advantage of these pumps -- you can't hear them. Not only will you save money, but when they operate, they simply don't make any noise.

Calculating Your Swimming Pool Water Pump Needs

Now it's time for a little arithmetic. Get out your calculator to figure out what you need to properly circulate your pool water and squeeze out the most efficiency. Using the example below, substitute your pool's volume and do the math:

Remember: Pool Volume (gallons) × 2 = gallons required daily for a 12-hour turn


  • We have a pool that holds 15,000 gallons of water.
  • 15,000 gallons × 2 turnovers/day = 30,000 gallons/day
  • We need to circulate 30,000 gallons of water every 24 hours - but remember, a pump has specifications of Gallons Per Minute (GPM)

Now convert that to GPM:

  • 30,000 gallons ÷ 24 hours = 1250 gallons/hour
  • 1250 gallons/hour ÷ 60 minutes = 20.8 gallons/minute (GPM)

A 15,000-gallon pool needs about 20 GPM output if we want to run it 24 hours per day.

Most people run their pool on an 8-hour on/16-hour off (stagnant) cycle. That means for the majority of the day, the pool water is just sitting there, not circulating. It is during this stagnant period that bad things happen:

  • Algae outbreaks
  • Debris build-up
  • pH swings

Not only will running your pool around the clock cost less, but it will also be much easier to maintain. The reason is that you will no longer let the pool sit idle, where it drifts out of that "perfect pool water" condition. This makes you think back to that 2 HP upgraded pump you received when building your pool. Perhaps it wasn't such a good deal, after all!

If you are in the market for a swimming pool, keep this in mind when evaluating proposals. The most important factor for any pool water pump is not how much it costs to buy it -- it is how much will it cost to own and operate. The best choice will be to upgrade to a multi/variable-speed pump. It is good for your budget and it is good for the environment.

Pool Pump Operating Costs

Pump Size GPM (varies with plumbing) Cost/Hour Cost/24 Hours Cost/7 Days Cost/30 Days Cost/Year Cost/8 hours day for 1 year
0.5 HP 40 $0.03 $0.72 $5.04 $21.60 $262.80 $87.60
1.0 HP 60 $0.06 $1.44 $10.08 $43.20 $525.60 $175.20
1.5 HP 68 $0.09 $2.16 $15.12 $64.80 $788.40 $262.80
2.0 HP 76 $0.12 $2.88 $20.16 $86.40 $1,051.20 $350.40
3.0 HP 85 $0.18 $4.32 $30.24 $129.60 $1,576.80 $525.60

Updated by Dr. John Mullen