Can a Pool Pump Be Too Powerful?
SwimmingPoolSteve.com is user-supported. In order to keep this resource about pools and spas available for free to all readers I earn commissions for purchases made through links on this page. For more information see the full disclaimer page. By using this website you are agreeing to the terms and conditions.
Can a Pool Pump Be Too Powerful? The answer may surprise you to hear that pool pumps being too powerful is an exceedingly common problem! There are a few converging factors which cause this to be the case but this article will help you to understand why pumps are so commonly overpowered and what the potential concerns of this situation are. In short, people tend to shop with a "bigger is better" mindset. Equipment manufacturers want to sell a lot of equipment so they lean into this shopping mentality. Pool pumps are a fairly complex technical subject which appears simple enough on the surface level, and finally, every pool is unique and there is a wide variation on design and installation details both from pool type to pool type but also geographic and climate considerations.
If you were to hire an engineer to evaluate your backyard, residential swimming pool and determine the most efficient and appropriately sized pump motor for your pool filtration system, likely most pools would end up with something along the lines of a high-head 3/4 horsepower (0.75hp) motor. However, the most popular pumps being sold right now range in size from 1.5 to 3.0 horsepower. Some of these brands and models are incredibly powerful with a potential rate of flow so high it can damage your other pool equipment as well as exceed safe recommendations for things like suction line water velocity which potentially then creates an entrapment hazard in your pool.
How to know if a pump is too powerful for your pool? - There are a few good metrics to look at when evaluating the size of a new pool pump, but also a few seemingly intuitive comparison metrics which are deceptive by design, specifically horsepower ratings. The average pool owner with a failing 1.5 horsepower pump most likely will look towards another 1.5 horsepower pump to replace it with. The problem here is that horsepower ratings are easily (and purposefully) skewed by equipment manufacturers to make their equipment sound good, or have a large (horsepower) number on the label, because by and large that is what pool owners want and expect to see. Unfortunately the horsepower rating on the pump will do little to tell you what the pump is capable of delivering for flow...only how much power the pump is capable of consuming. Service ratings are multipliers that apply to pool pump motors which can be compared to "sprint mode" where the pump operates at a higher (horsepower) rating than the actual motor rating. So right away simply comparing horsepower is not good enough, but further to this the hydraulic design of the pump wet end and impeller is far more important anyway. To summarize, the horsepower ratings are misleading, and they do not actually correlate with how much water the pump will move...which is actually the main thing you need to know to evaluate whether a pump is too powerful or not.
Comparing pump flow rates - Once you look past the horsepower rating and start comparing the actual flow rate potential of each pump you are way ahead of the curve, pun intended, to understanding how to size a pool pump correctly. Every pump manufacturer provides a performance chart or performance curve for the pump which show the expected flow rate (in gallons per minute) versus resistance to flow (measured in feet of head). So for a given resistance to flow you can compare two different pumps to see how much actual flow (in GPM) the pump will deliver. If you want to see a list of many of the most common pumps compared like this check out the chart near the bottom of this page on variable speed pool pump reviews. Your challenge now will be to determine what the resistance to flow in your specific pool will be. That will be hard to do. You can measure a momentary picture of the total dynamic head using a vacuum gauge and a pressure gauge while the existing pump is operating...or you can infer / estimate the resistance to flow based on generalized information. Neither of these methods are perfect but this is how it is done, short of hiring an engineer to calculate the total dynamic head of the pool system design which is seldom done outside of commercial pool applications.
Understanding flow and safety limitations - There are a few concerns and considerations about the flow your pool pump will generate. Yes, you definitely want enough flow to be able to effectively clean and filter your water, and for all of your peripheral equipment like gas heaters or electric heat pumps to operate (they have minimum flow rate requirements) but largely your concerns will be with having too much flow versus having too little flow. One hard number that you can and should look at would be the maximum design flow rate for your pool filter. Every pool filter will have a maximum GPM that they should not exceed. Some filters like sand filters have relatively low maximum design flow rates versus cartridge and D.E. filters which commonly have higher maximum flow rates. In any case, the filter most likely represents the piece of equipment on your pad which can least handle high flow situations and for most pools the maximum design flow rate for your filter represents your total maximum flow rate recommended for your system. Aside from the equipment operation and longevity consideration, the main concern for a pool pump being too powerful is the exceeding of safe suction line water velocities as well as maximum designed flow rate for fixtures such as main drains and skimmers. The Virginia Graeme Baker Act outlines the maximum safe suction line water velocity in any pool to be no more than six feet per second. For reference 6fps velocity in PVC pipe is:
1.5" pipe @ 6fps = 38 GPM
2" pipe @ 6fps = 65 GPM
2.5" pipe @ 6fps = 90 GPM
3" pipe @ 6fps = 138 GPM
4" pipe @ 6fps = 238 GPM
Count the number of active suction lines connecting to your pool pump. Then reference the size of each pipe. Add the totals together to see your maximum safe suction line (total) water velocity. A pool with no main drain suction and only one skimmer suction line would have a rather low maximum flow rate, dependent on the pipe size being used for the line. PVC pipes and pool pumps can and will move water far in excess of the numbers you see here for VGBA recommendations. It would be pretty easy to exceed safe suction line water velocity in many residential pools, due to both the pump being too powerful, but also the plumbing system using too few pipes, or pipes that are smaller in diameter. In addition to the pipes themselves you also have the actual fixtures themselves:
Average pool skimmer maximum design flow rate = 55 GPM (with some high flow models being 75 GPM)
Average pool main drains set are rated for 125 GPM (floor mount) or 75 GPM (wall mount)
You are probably starting to see more clearly now how a pool pump can be too powerful and what will happen when you try to use a pump that is too large for your pool. You will potentially damage your equipment like your filter, and you can create unsafe amounts of flow rate leading to entrapment safety hazards in the pool. A lesser note but still worth noting is that you will also damage the efficiency potential of your filtration system with a "too large" pump. Water moves very efficiently at laminar flow rates below 6fps but extremely inefficiently at velocities faster than this where turbulence and friction compound logarithmically.
When determining whether a pump is too powerful or not start by learning the maximum (and minimum) flow rates for each piece of your pool equipment. Note the maximum design flow rate of the filter as this likely will be the least able to handle high flow. Count the number of suction lines you have in the pool, as well as noting the size of each pipe, and then add up the total flow rate for these all based on six feet per second of water velocity. Also double check your main drains and skimmers maximum design flow rate. Finally, compare performance curves for each pump you are looking at, and ideally compare these to the performance curve for the existing pump you have.
Measure the total dynamic head of your pool or estimate your resistance to flow (in feet of head) of your unique pool system, and then compare new pumps to the amount of resistance / flow the last pump had. Realistically this is a job best left for a swimming pool professional, but hopefully this additional information will help you to make a more informed decision about the next pump you buy for your pool.
You might also be interested to read this article about How much power does a pool pump use?
Top content from www.SwimmingPoolSteve.com
Pool and spa chemistry crash course
New pool owner guide
The Swimming Pool Steve blog
Have a question - ask Steve
Swimming Pool Steve is an award winning, second generation swimming pool and spa specialist from Ontario Canada. With over 10,000,000 views on the Swimming Pool Steve YouTube Channel, winner of the 2018 Pool & Spa Industry Leadership award and author of hundreds of pool and spa articles both online and in print Steve is committed to helping pool and spa owners as well as pool and spa industry workers learn more about the technical side of building, renovating, repairing and maintaining all types of swimming pools and spas. Follow Swimming Pool Steve on Facebook, Twitter and YouTube.
Endorsed Brands From Swimming Pool Steve
The following links and products are to affiliates of the Swimming Pool Steve website. These are brands, products and services hand selected by Steve for endorsement. Please note that these endorsements can include monetary compensation, affiliate links and referral fees to Swimming Pool Steve, however there is zero additional cost to you should you use one of these products or services. Income generated from these links helps to keep this pool and spa resource available for everyone. To have your product or service considered for listing here as an endorsed brand email SwimmingPoolSteve@gmail.com.
Amazon Disclosure Statement - As an Amazon Associate I earn from qualifying purchases.
www.ClearComfort.com
Clear Comfort's patented hydroxyl-based advanced oxidation systems (AOP) represent the pinnacle of water care technology available to pool and spa owners. To put a complex technology simply, if you are looking for the best possible water care system for your pool or spa then you are looking for a Clear Comfort AOP system.
- Swimming Pool Steve
www.PoolPartsToGo.com
New Black + Decker variable speed pumps are available online from www.PoolPartsToGo.com and they are a drop in replacement for many popular pump models including Pentair Superflo and Hayward Super Pumps. With an adjustable platform base, union connections included and a very strong warranty these pumps offer an impressive value to pool owners.
- Swimming Pool Steve
www.PoolSupplyWarehouse.com
Pool Supply Warehouse has a large stock of swimming pool equipment, chemicals, maintenance items and consumables needed for caring for your swimming pool. They offer fast shipping and by shopping with this retailer you are helping to support Swimming Pool Steve directly.
- Swimming Pool Steve
www.PoolSuppliesCanada.ca
When it comes to ordering pool and spa supplies online in Canada www.PoolSuppliesCanada.ca is by far the best option. They carry everything from chemicals to replacement pumps to entire pool kits, with free shipping options and more "in stock" items than any other Canadian online retailer.
- Swimming Pool Steve