Size and Selection of Swimming Pool Pumps

The first thing you need to know is that not all horsepowers are equal. Every pump has different flow characteristics, and the flow rate will vary by manufacturer and model.

But the question cannot be answered without some other key insights, namely your Pool Type, Turnover Rate, Filter Design Flow Rate and estimated Resistance, in Feet of Head.

What’s Your Pool Type?

Above ground or in ground? Aboveground pool pumps are meant to operate below the water level, on the ground next to the pool. Inground pumps are “self-priming” and can lift water several feet.

Simple or Complex Pool? A small pool with 1 or 2 skimmers and a main drain can use a smaller pump, but pools with attached spas, waterfalls, solar heaters or built in cleaners may need a larger pump.

Turnover Rate?

The Turnover Rate is the time it takes for all of the water in the pool to pass through the filter. An 8-hour turnover rate is considered standard.

Pool Volume in Gallons ÷ Turnover Rate in Minutes = Flow Rate

The formula for Turnover requires that you know your pool size – in gallons. If you have paperwork from your pool builder, this may list the amount of gallons in the pool. If not, break out the calculator, and a measuring tape, if needed.

  • Round Pools – Diameter (ft.) X Diameter (ft.) X Average Depth (ft.) X 5.9 = Total Pool Gallons
  • Oval Pools – Length (ft.) X Width (ft.) X Average Depth (ft.) X 6.7 = Total Pool Gallons
  • Rectangle Pools – Length (ft.) X Width (ft.) X Average Depth (ft.) X 7.5 = Total Pool Gallons

Average depth is calculated by adding the deepest part of the pool to the shallowest part of the pool, and dividing by 2. For instance, if the shallow end is 3′ deep, and the deep end is 8′, the average depth is 5.5. (3+8 / 2 = 5.5)

Sample Desired Flow Rate calculations, based on an 8 hour (480 minutes) turnover rate:

10,000 (gals) ÷ 480 (mins) = 21 GPM

25,000 (gals) ÷ 480 (mins) = 52 GPM

35,000 (gals) ÷ 480 (mins) = 73 GPM

Pool Filter Design Flow Rate?

Every pool filter is designed to work best with a certain flow rate of water. If the filter design flow rate is exceeded, it results in poor filtration and filter damage. Lower flow rates do not generally pose a problem, however.

Larger pool filters with more surface area will have higher design flow rates, but every pool filter is different, from 30 gpm to 150 gpm, depending on size and type of pool filter.

design-flow-rate

Find your Design Flow Rate on the pool filter label, owner’s manual, spec sheet or brochure. You can also find this Performance Data listed on our pool filters pages.

Now that you know your Pool Type and your particular pool filter’s Design Flow Rate, you are halfway to finding the perfect pump for your pool!

Estimated Resistance?

pool diagram buildapedia

OK, here’s where it gets a bit tricky, stay with me… Every pool system has a total resistance that the pump must overcome. The water has to be pulled and pushed through pipes that bend and twist and it’s forced through impellers and filters, squeezed through heaters and valves, as well as lifted vertically, from the water level to the pump level. The amount of lift, and all of the pipes, fittings and equipment adds-up to the Total Resistance, measured in Feet of Head.

A simple pool with one skimmer and no heater has a fairly low resistance level, in the 15-20 ft/hd (Feet of Head) range. Add another skimmer, a heater and maybe a spa and more complex pools can be much higher, in the 45-60 ft/hd range. Most inground pools probably fall in the 25-45 ft/hd range.

Total Resistance is made up of all the pipe lengths, turns of the pipe, and all of the equipment that the pump must pull and push water through. Resistance is measured in Feet of Head. To calculate the system resistance, add together these two sums:

  • Multiply the clean filter pressure by 2.31 to measure resistance after the pump
  • Multiply the pump vacuum by 1.13 to measure resistance before the pump
  • Add the two together to compute the total resistance in the system.

Now, most pool owners don’t have a vacuum gauge installed before the pump. If you can get of a vacuum gauge (not a pressure gauge), unscrew the front pump drain plug, and thread the vacuum gauge in its place. Turn the pump on and take your reading.

In the absence of a vacuum gauge, you can estimate the suction side vacuum to be something close to 1/3 of the pressure side reading. For example, if your filter pressure x 2.31 = 30, assume that the vacuum reading would equate to 10 ft. of head. Total resistance = 40 ft. of head.

Another way to calculate the suction side resistance, in the absence of a vacuum gauge, is to add up all the bits of pipe and valves before the pump.

  • For each 1.5 in. skimmer or main drain, add 2 ft. of head, or 1 ft., if the piping is 2 in. diameter.
  • For each 10 feet of 1.5 in. pipe used, add 1 ft. of head, or .5 ft. for each 10 foot run of 2 in. pipe.
  • For each 90 degree fitting or valve between the pool and the pump, add 1 ft., or 0.5 ft. for 2 in. pipe.
  • For a check valve installed before the pump, add 2 ft. of head.

To roughly calculate the amount of resistance, measured in feet of head, that your pump must overcome, here’s a rough approximation method that can be used. Add up all of these resistances to find the total resistance in your system.

Pool Filter – 10 ft
Pool Heater – 10 ft
Pool Cleaner – 10 ft
Pool Piping – 1 ft per 10 feet
90 degree fittings – 1 ft each
Inline Chlorinator or Purifier – 2 ft
Directional Valves – 1 ft each
Skimmers & Drains, 2 ft each
Wall Returns, 2 ft each

Add these all up, to calculate the total feet of head measurement that your new pool pump must overcome. Then – refer to the manufacturer’s website, and look for an image or a link to the Pump Performance Curve for the particular swimming pool pumps you are interested in.

It’s an important part of the pool pump selection process, because you want to match the pump to both Design Flow Rate and the amount of Resistance it has to overcome.

whisperflo flow chart

We use pump flow curves, or pump performance charts to find the Sweet Spot, where Resistance and Design Flow Rate intersect.

For example, the SPX2610X15 will pump 90 gpm at 30 ft of head, with a clean filter and baskets. On the other hand, a Whisperflo 1-HP (purple line) will pump 80 gpm at 60 ft of head, as shown right.

Bringing it All Together

The best pool pump for you then, is that particular pump that can deliver the flow rate to match your pool filter’s design flow rate while overcoming the resistance in your system.

That may be the exact same pump that you are replacing. Unless you had real performance problems with your pool pump, the best pump for you may be the same make, model and horsepower pump.

Bigger is not Better! If two pump curves come close, choose the smaller pump. When it comes to pool pumps people tend to think bigger is always better. Indeed, this is not true with pool pumps. A larger pump will cost more money to operate and if too large – it will start to cavitate, making lots of noise, and overworks the motor. Pool pumps that are too large also compromise filtration and can even damage a filter that is too small.

The same pool pump will also match up to the plumbing pipes, but a different pump will have a slightly different height and depth where the pipes connect.

hayward-VS-pumps-arent-actually-GREEN-colored

Another option with less math involved, is to buy a variable speed pool pump. You can set multiple speeds to match your existing equipment, and at the same time cut your electrical usage in half. Prices on VS Pool Pumps have come down to the $750 range.

One More Tip: Remember that not all horsepower pumps are equal. Every pump, regardless of horsepower, has it’s own flow rate. A WhisperFlo 1 hp for example, can produce nearly double the flow rate of the Super Pump 1 hp; and that’s not always a good thing! Don’t oversize the pool pump – you’ll save energy, wear and tear and filter the water more effectively.

29 thoughts on “Size and Selection of Swimming Pool Pumps

  1. I have the Pentair QUAD DE 60 shipped this morning.
    Do you think Pentair QUAD DE is to much for the pool and pump or return it for something smaller but no sand filters. The pool comes with water features… 2 bubblers and 2 deck jets. Thank you.

    • The Quad 60 is a large filter, very large for 6600 gallons. Perhaps the pump is very large too, and needs a large filter? That is sometimes the case when there are water features, which require more flow, from a larger pump, and the larger pump needs a larger filter. Returning the filter may be costly in shipping and possibly restock fees.

      • The pump is the Pentair SuperFlo VS. Is this pump a good match for the Quad 60 in the case of 6600 gallon pool?

        • Well, because your pool is so small, and the water features are also small, without high water volume needs, you don’t need a big pump or filter. The Superflo is a good choice, and the quad 60 is a very excellent filter, one of the best available, for water quality and high performance. So if you want the best, you got it, and no need to return anything. Only if money/cost is a concern, you could use a smaller filter, but the Quad-60 is well matched to the Superflo VS pump, and I’m sure you’ll be very happy with both. It’s also able to handle the high flow of the Quick Clean program (high speed) of the Superflo VS, which can reach flow of 100-110 GPM. So, you’re all set, I’d say go with what you have on order. And you can run the pump on low speed most of the time, and may only need higher speeds for a 2-4 hrs per day. Experiment for the first few weeks, to optimize the programming, to meet your needs for heating, chlorinating, cleaning functions, and use of the water features at certain times of day.

  2. Thank you for your insight. I have Pentair SuperFlo VS Pump in my cart. I was hoping you can recommend a filter for me as well. 6600 gallon pool.

  3. I am looking to purchase pump and filter for inground 10’x 20′ pool with 2-inch pipe. What is your recommendation.

    • Hi Viktor, you should also consider the Design Flow Rate of the pool filter, printed on the label or in the filter brochure or specs. You don’t want a pump that is too powerful for your filter. A pump with 2″ inlet/outlet ports would also be desirable. Variable speed pumps can be adjusted in flow rates, and are required next year, so maybe that is the best route. For a small pool like yours, look at the Waterway 140, The Pentair SuperFlo or the Jacuzzi 160, all which have 2″ ports.

  4. Earl Campbell

    Hi Davy,

    Replacing my state-rite set up P2RA5F/US Motor EUSQ1152 set up and want to get something more up to date.

    I have a 14×28 kidney pool holding approx 10,000 gallons…current set up is 1.5″ piping. I have about 25 feet of pipes in the ground (a couple of 90 degree bends into the pump/water filter/water heater.

    If you could advise.

  5. I have a 21 ft above ground pool with a 1/3hp pool pump and a 14 in sand filter. I would like to upgrade the motor. Can I upgrade to a 1.5 hp or 1 hp pool pump. Please advise. Thank you.

    • Hi Rey, sounds like both the pump and filter are too small for the pool. You would not be able to put a larger pump on such a small filter. For a 21′ pool, I would recommend a 21″ sand filter, with a 1hp or 1.5hp pump. Something like the Hayward 21″ Sand filter system, our item E3231, would be a good size.

  6. Roy Bass

    I have an 18 foot / 48 inch intex with the stock paper filter and want to switch to a sand filter with enough GPH to run a good cleaning robot. Im adding a skimmer where one of the two current intakes are located on the pool. Whats the max GPH/Filter combination that you would suggest that wont harm the filter or pump. Would it be a good idea to change the intake/exhaust hose/outlet/inlet sizes ? Thanks for the assistance.

    • Hi Roy, the 16″ Intex sand filter would be a good size. I’m not sure that you can run a suction cleaner from it, but you can run a robot, which does not connect to the filter system. Such as the Aquabot S2-40i.

  7. Charles Sikes

    Changed my pump from 1hp to 1/2 hp and I cannot get it to fully prime. Checked for air leaks and cannot find any. Approx 19000 gallon inground with 1 skimmer and 1 sidewall return. Would an undersize pump cause this? Pump is a Dayton.

    • Hi CHuck, I would not think that size would be the problem, unless you have a large vertical lift, or lots of resistance in the system that it is having trouble overcoming. Go buy a Drain King at the HD/Lowes store nearby and put it on the end of a garden hose and push it down into the skimmer pipe, close the main drain valve, and turn on the garden hose. This will force water up into the pump. Let the pump and filter fill up, with the filter air bleeder open. Then, crack open the main drain a little bit, and with the drain king still pumping water from those, then as it starts to catch prime, crimp the hose and slowly pull out the Drain King.

      • Charles Sikes

        Thanks for the prompt repy Davy. I already have a drain king so I will try that. When in this process due I turn the pump on? My filter does not have a bleeder valve, it sounds like it is automatic. I assume your solution is the see if there are any air leaks I can’t find?

        • Hi Charles, The Drain King can help in priming a pump that is difficult to prime – and it can also be used to pressurize the suction lines and then with a plug in the pump or with the filter valve on closed, or return valves closed/deadheaded, or even the wall returns plugged… you will begin to see any air leak voids, begin to leak water, somewhere in front of the impeller. Leaks after the impeller will be under pressure and will not be air leaks, but water leaks.

      • Charles Sikes

        Put the drain king in and found another problem, water coming out of the drain when the valve was on closed. I realize I need to change the spider gasket but could this be what is not allowing my pump to fully prime even though it is on the return side?

        • The spider gasket should not have any effect on the pump priming. But putting the filter valve on recirculate or waste does make it easier to prime the pump. Less resistance cuz the water is not going thru the filter.

          • Charles Sikes

            Got the suction line pressurized and the basket lid is where the leak is. Brand new pump and the manufacturer is sending me a replacement. Thanks for your help.

  8. Hello, I need to replace my old Jandy 3HP VS pump. I did not enjoy my experience with the first generation VS Jandy pump. Plus there is literally no support or knowledgeable pool techs in my part of Texas who know anything about Jandy products. I want to purchase a Pentair VS Intelliflo pump. There are so many Pentair pumps that I cannot figure out what to purchase. Even after I read all of your blogs. HELP. I am looking at the Pentair Intelliflo VS+SVRS 3HP 011057.

    My pool is basically rectangular, 40,000 gallons, with a waterfall. The waterfall has a dedicated Jandy pump on a dedicated line. (I know, overkill, but I listened to a pool renovater who was pushing Jandy). The pumps and DE filter (hayward 60/20) are approximately 20 yards in a straight line from the pool.

    The pool is 4′ in the shallow and 12′ in the deep. I ran the Jandy for a minimum of 12 hours per day at between 450-650 most of the time and increase my pump speed for parties and heavy use for a few hours a day, and to assist the pool sweep. I was running a Jandy salt chlorinater (no longer, because EVERYTHING in the vicinity rusted). The pool sweep is also on its own booster pump. Do you have a recommendation? I would like to purchase the right pump for my needs this time around.

    My other question is about the multivalve port. I have replaced the spider gasket twice, and now it is leaking again. I wish to replace it for a new one. Any thoughts about using one with a slide valve or should I stick with the traditional hayward multipart?

    Thank you for any help you can provide in advance.

    T

    • Hi Teri, let’s start with the valve, yes, I’d replace it with the Slide valve (aka Push-Pull valve), mainly because of the much lower resistance (which will reduce your cost of running a VS pump), but also because they are so simple and rarely give any trouble. The downside is they are only Filter or Backwash, no Recirculate setting (useful if your filter is broken), and no Waste (useful if you ever need to vacuum to waste). The Hayward filter can use a Slide Valve SP0410X502S, which will require some replumbing to fit. I’d also recommend using Sweep Elbows in place of regular 90’s, again to reduce resistance.

      For the pump, you could use the Pentair Superflo VS, which would work well for your size pool, if you were to run it longer than you currently do, perhaps low speed for 12 hours and high speed for 4 hours daily. The Pentair Intelliflo VS has a more advanced controller, with some diagnostics and 8 speeds, instead of Superflo’s 3 speeds. IntelliFlo is a great pump, there are three models, VS, VF and VS+SVRS. The VF model senses flow and pressure and can self-adjust speeds to accomplish certain tasks, and SVRS (as you likely know) will shut down if it senses increased vacuum pressure, as though the drains might be blocked. VS+SVRS is a good safety feature to have, especially if you have kids using the pool.

      If you have any followup questions, feel free to email me swimmers -@- intheswim.com – Davy

    • Thank you for the advice. I have another question. Is there a major difference or an important one between a variable flow pump versus a variable speed pump for my size pool? Also, is a 3HP pump what I should be using?

      • Hi, the IntelliFlo VF automatically determines the minimum flow rate for circulation, filtration, heating, cleaning, spa jets, or water features. It senses pressure differences, and adjusts flow accordingly. The Variable speed pump, or Intelliflo VS does not have the built-in sensors, and will operate at the speed you set it at, or per the program it is running. You don’t really need the ful-size 3-HP Intelliflo pumps, you could use the SuperFlo VS, which is closer to 1.5 HP, as long as you run it long enough to circulate all of the pool water thru the filter at least once per day. Most people that have a 2-speed or variable speed pump run the pump nearly all the time, but on a very low speed for like 20-hrs per day, and high speed for 4-hrs per day. You could run it less of course, again as long as you turnover all of the water at least once. This can be determined by computing the flow rate at different pump speeds, in a gallons per minute rate, and doing the math over the course of the day. The SuperFlo has less pre-set speeds, and fewer diagnostic bells and whistles, but would work fine on your pool, running a few hours longer than the Intelliflo, but that depends on speed actually, it could run less than the Intelliflo, it all depends. One thing for certain is that a 3 HP pump will draw more amperage, and cost more to run than a 1.5 HP pump, if both ran at the same speed. So it depends on you, both will work fine for your pool, if you are looking to save some money, go with the SuperFlo (the Chevy), but if you want the bells and whistles, buy the Intelliflo (Cadillac). Both will get you where you want to go, just one has a bit more style, or more features.

  9. Is a Intex Krystal Clear 1500 GPH Sand Filter Pump & Saltwater System overkill for a small Summer Waves 10’x30″ (1200 gallon capacity)?

    Or is it mostly about budget and how much ease of maintenance means to you and your budget?

    • Hi Dennis, I don’t think it’s overkill, because it will save money on chemicals, and can be run for fewer hours per day, and best of all, it will keep the pool from getting cloudy, green and possibly unsafe to swim in. Bigger filters always good. Never a downside to having a larger filter. However, you could also use the 1000 GPH system and be pretty happy with that, on a 10′ x 30″ pool. When you go to 1500 GPH systems, the filter hose is a 1.5″, so you need Intex Type B adapters for 1500 and above, and for 1000 GPH and below size systems, they use the 1.25″ hose. So for the smaller pools, 8, 10, 15 – your wall port size is 1.25″ and need adapters to use a filter of 1500 GPH or higher. There are two types, one that uses the old 1.25″ hose to connect to pump and filter, and one that uses the 1.5″ hoses, to connect to the 1.25″ wall ports. (We don’t currently sell these adapters at InTheSwim.com)

  10. Hello, I have a pool of approximately 15k gallons with 2-inch pipe. I am about to buy a pump in my local store but the only ones available at the moment are TriStar VS 950 (SP32950VSP) and MaxFlo VS 500 (SP23520VSP), both work for me since I have no waterfall or anything special. What really interests me is energy efficiency.

    The question based only on those two models, which would be the most efficient in energy consumption? I know that the TriStar line is more efficient than the MaxFlo, but since it is a smaller motor, it consumes less?
    For example, if the two pumps are working at 2300 Rpms, MaxFlo VS 500 will it consume less for being a smaller motor or will TriStar consume less for being simply more efficient despite being a larger motor?

    • HI Steven, with a pool your size, and with a filter that is appropriately sized for your pool, the VS950 would be way too big, to the point where it could damage equipment or possibly be hazardous. The VS950 produces almost 3x the flowrate of the Maxflo VS500 – and that’s not a good thing, in your case. Lower flow and pressure is always better. With regards to energy efficiency, it’s the amps that you really pay for, and you are correct that the larger motor will have a higher amp draw, and thus be less efficient. MaxFlo VS500 all the way, baby! 🙂

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