The Pool Pro’s Guide to Pump Sizing Smarter

Choosing a variable speed pump shouldn’t feel like a guessing game. We walk through a simple, field-tested way to size the right unit by matching your current single-speed horsepower to modern total horsepower (THP), accounting for plumbing size, distance, and voltage, and then using RPM control to hit your flow goals without wasting energy. No fluff—just practical rules you can apply the moment you step onto the equipment pad.

We start by translating old-school horsepower labels into today’s THP ratings and explain why you can safely choose equal or slightly higher THP and run it slower for quiet, efficient filtration. You’ll hear how pipe diameter, elbow count, elevation, and equipment distance shape total dynamic head, and why most backyard pools don’t need elaborate TDH calculations. We compare VS and VSF pumps, demystify how auto-flow control can handle minor resistance changes, and outline clear ranges: what to buy if you’re replacing a 1 HP, 1.5 HP, or 2 HP single-speed. We also unpack voltage realities on older 120 V systems so you don’t overbuy a pump that can’t deliver its full potential.

Chasing WEF numbers? We put them in perspective. The big savings come from programming your pump to lower daily speeds and only ramping up for spa jets, heaters, or cleaners. If your pump doesn’t report flow, we recommend adding a FlowVis meter so you can set precise gallons per minute and know your turnover isn’t guesswork. Finally, we cover brand matching—why sticking with Pentair, Hayward, or Jandy to match your existing automation can save you time, wiring headaches, and re-plumbing.

If you want a clear path to better circulation, lower noise, and smaller power bills, this conversation gives you the checklist: match THP to your old HP, size up rather than down, ignore small WEF differences, use a flow meter to set RPM, and keep your brand ecosystem consistent. Subscribe for more practical pool insights, share this with a friend who’s shopping for a pump, and leave a review to tell us what sizing questions you want answered next.

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Chapters

• 0:51 Sizing Goals And Who This Helps
• 1:03 Coaching Program And Resources
• 2:31 Builder Choices And Exceptions
• 4:30 Total Dynamic Head Explained
• 6:48 Plumbing Size And Distance Factors
• 8:42 When To Measure And When Not To
• 10:03 Variable Speed THP Versus HP
• 11:42 Matching Old HP To New THP
• 13:19 Older Pools, Voltage, And Limits
• 14:59 VS Versus VSF And Smart Flow
• 16:17 Practical THP Ranges To Use
• 18:24 Bigger Is Fine If You Dial It Down
• 20:08 WEF Ratings And Real Savings
• 21:49 Use A Flow Meter To Set RPM

Transcript

SPEAKER_00: 1:03

Hey, welcome to the Pool Guy Podcast Show. In this episode, I'm going to try to give you some advice on sizing a variable speed pump. If you're thinking about converting your single speed pump to a VS Pump, or if you have a VS Pump now on your pool, you want to verify it's the right size. This podcast definitely is for you. Are you a pool service pro looking to take your business to the next level? Join the pool guy coaching program. Get expert advice, business tips, exclusive content, and get direct support. From me, I'm a 35-year veteran in the industry. Whether you're starting out or scaling up, I've got the tools to help you succeed. Learn more at Swimmipoollearning.com. Since every pool is different, sometimes it does pay to have a professional look at your pool before you upgrade the pool pump, especially if you wanted to do it yourself and you're undecided. Now there are some rules of thumbs you can work off of as far as pump sizing. The most obvious rule is that if you had a builder install a pump at your pool, they probably installed the right size pump. Usually they install the right size pump. I've only ran to a few pools where I thought the pump was undersized, and a few pools where I thought the pump was definitely oversized for the pool size. But generally speaking, the original builder, when they build the pool, will install a pump with the correct horsepower for your setup. For example, if you have a spa that's maybe 20 feet from the equipment area that's elevated, he may have put in a 1.5 or 2 horsepower pump to get the water to the spa flowing nicely versus a one-horsepower pump. And conversely, if you have an older pool, most of the time the builder had to put in a one horsepower pump because that's really all that your breaker could handle. Usually an older pool has the pump on a 120 volt breaker, and there's no way you can put anything with a higher horsepower because of the amperage. So technically that pump may be undersized because they were limited by the amount of voltage they could use for that pump, if that makes sense. They couldn't put in a 1.5 or 2 horsepower pump in that situation because of the voltage that was available at the at the time they were installing it. So that may be an exception to the rule that the builder put in the right size pump when he built the pool. Now, how would you size these pumps? Let me just start by saying that you can do a test for what's called total dynamic total dynamic head. And this is basically the resistance or how much resistance your particular pool setup has in regards to the efficiency of the pump running. Now, is this really necessary in the real world, like a backyard pool? Well, I mean you could you could have this done. You have to put you know a pressure gauge in front and also on the return, and then you have to see the difference in that number, and you can calculate the total dynamic head. Most pool pros don't bother doing that because most residential pools don't really have a very complex system. Now, yes, granted, there may be some pools with a single pump running the waterfall feature, the solar on the roof, different things where there's lots of elbows and lots of different elevation differences. But the main resistance is going to be elbows in your equipment area, and also the main thing is your pipe diameter. So if you have 1.5 inch plumbing, going to two-inch plumbing on certain aspects of your equipment area, not necessarily digging up the pool and replacing all the plumbing, but certain parts of the pool with two-inch plumbing can drastically reduce total dynamic head or the resistance of the water in your system. So that's something to consider that your plumbing size is probably the biggest factor. And then the other factor would be how many elbows and fittings and you know twists and turns you have before the water gets to the return. But it's really not a huge factor in backyard pools because typically the equipment is pretty close to the pool, maybe you know, 10 or 20 feet away. Now there are setups I've all I've also had these pools where the equipment is like 50 feet or 100 feet away. This becomes a little more challenging. But the building usually puts in a pretty powerful pump in that case for that to kind of compensate for the resistance of the water or the total dynamic head resistance that you're going to face with different plumbing situations. So, what I'm saying is that you can get a scientific analysis of your system done, and you can do it yourself in some cases. If you go online and look at the forms, they'll teach you how to get your total dynamic head, and then you can use that to go on the manufacture site and kind of chart the pump. Again, really not necessary because you can kind of just use some standard rules of thumbs for residential pools, commercial pools, yes, big projects where they have infinity spillways and water features and things like that, or solar on the roof. You may need to have this done to make sure you have the right amount of flow or a powerful enough pump and the plumbing is installed correctly. But again, usually at the build, the builder will account for all these factors from their experience of installing at other build. So let me touch on an aspect of variable speed pumps that you kind of need to know when you're sizing, and that is that they don't really have a horsepower rating, HP rating. So if you look at your current single speed pump, you'll see something on the label and it's gonna say 1.5 HP, and then it may show the amperage of that pump. Doesn't really matter at this point because the variable speed pumps nowadays, a lot of them can be dual voltage VS pumps, and I'll go over that in a minute. And that means that they can run off of 230 or 115 or if whatever you want to call it, 120 and 240. It's kind of weird that there's so many different ways of labeling the voltage. But basically, you don't have to worry about the amperage as much as the what they label the VS pumps with now, which is THP or total horsepower. So let me just explain that I'll use Penta and I as an example since they're pretty popular and it's pretty easy to kind of correlate each one of these Penter VS pumps with the total horsepower. So let's just say you get a superflow VS, and let's say you have an older one that's gonna be 1.5 total horsepower, but the newer ones, if you had one within the last couple years, the total horsepower is actually 2.2 now. So the superflow VS has a 2.2 total horsepower. And if you have a 1.5 horsepower single speed pump at your property, then this pump would be perfect for you because you could modulate it to be 1.5 horsepower because the total horsepower is 2.2. So you could set the speed down to where you would get the same kind of power out of it as a 1.5 horsepower pump running at the full 3450 rpms if that makes sense. So let me back up for a minute. A single speed pump runs off of 3450 rpms, and a variable speed pump, of course, you can change that speed, you can put it at 2100 rpms or 2800 rpms, so you can actually match that 1.5 horsepower gallons per minute flow rate with a 2.2 horsepower VS pump. So that's actually a perfect size pump for you. You can even get away with a straight 1.5 total horsepower pump. So if you do need to run the full speed, let's say for a spa so you can get the jets going, you can easily do that with a 1.5 total horsepower VS pump as well. Now, if you had a 2 horsepower pump, you're still within range with the 2.2 horsepower pump, but you may want to go to a total 3 total horsepower pump, which would be the Intelliflow 3. By the way, they also make a 1.5 Intelliflow 3 pump. Or you can just get the Whisper Flow VS, which is 2.6 horsepower, which is plenty of horsep total horsepower, I should say, which is plenty when you're replacing a two horsepower pump. So basically, you want to try to match the current horsepower you have now, either the 1.5 or 2 horsepower to a VS pump that's within the total horsepower range. Now, I was speaking earlier about the older pools. Typically, they have 1.5 inch plumbing and they have a one horsepower pump. Which VS pump should you get? Well, I wouldn't recommend getting a three horsepower pump because if the voltage is 120 volts, it's going to modulate that down anyway, and it's going to run maybe off of 1.5 or 1.6 total horsepower, and you're not going to get the the full three total horsepower because that requires more voltage. The dual voltage pumps, as you get to the higher horsepower, will just modulate the total horsepower down, and so you're not going to get the again the three total horsepower from maybe an Intelliflow 3 pump, and you might as well not even get that in that case. But if you have a 1 horsepower single speed pump now with your pool, you can easily install a 1.65 or 1.5 total horsepower pump, and you have you'll have no problem with that at all. One thing you should also note is that a lot of pumps are going to say VS for variable speed or VSF variable speed and flow pumps. Basically, a VSF pump automatically adjusts their speed to maintain flow for optimal pool performance. So they're a little bit smarter than just your straight VS variable speed pump. And a VS pump just sets the run at different speeds based on how demanding the pool task is. Basically, a spa, or if you want to have a cleaner running at a different speed. So that's the only difference. There's really not much difference between a VS or VSF pump. It's just that the VSF pump automatically does some adjustments for you, which again goes back to the you know not needing to really know your resistance too much because the pump will compensate for that. And that goes into just about any setup in the backyard. Most of the time, the builder will put in a separate pump for a waterfall feature, or the builder will install a booster pump for a spa if the equipment is pretty far away and he really wants to get that power of the jets going and doesn't want to rely on the main pump for that. So I think sizing is basically just finding out where your current pump is and then finding a VS pump with the total horsepower that matches that as close as possible. Again, one horsepower, 1.5 horsepower pump, 1.65 is perfect. 1.5 horsepower, you can get away with a 1.5 horsepower. I'd rather you get a 1.65 or 1.85 or a 2 total horsepower pump if you have a 1.5 right now. And if you have a 2 horsepower pump, you know, a 2.6 or 2.4 or a 3 total horsepower pump vs pump is perfectly fine in your setup, and you shouldn't have any problems if you kind of stay within those parameters. You don't want to go down in the total horsepower because there's a reason why you have a 1.5 horsepower pump at your property. For example, my backyard pool has a one point had a 1.5, and so I went with a uh 3.0 horsepower pump. I could have gone with a 2. You know, 2.0 or 2.5, whatever, but I just went straight to a 3 because I can run my pump actually the match the 1.5 horsepower if I wanted to. And of course I have two-inch plumbing, and the reason why I had a 1.5 in was because I have a spa that's fairly far from the equipment, and there's no booster pump. And so for that to kind of get the power, the 1.5 horsepower pump was installed originally on my pool. And then when I switched to VS, I just went straight to a 3, which you can do. I mean, I could have gone with a 1.85 or a 2.2, but I went straight to a 3 because it was just easier at that time. They didn't have a lot of different choices when I when I was upgrading. They had a 1.85, 1.5, or 1.65, then they had a 2.7 or a 3. And again, you can go bigger, you're not gonna have much of a problem because you can change the speed of these pumps to mimic the speed of your old 1.5 horsepower or one horsepower pump. Let me talk just a little bit about the WEF efficiency number here. You're gonna see this a lot because the Department of Energy kind of put this number on all the pumps out there, and some people push your push a VS pump based on the WEF number. And I would just ignore anyone who's telling you that you should get this pump because it has a higher WEF number. The higher the number, the more energy efficient that pump is, it's gonna save you some energy. The way they kind of get the numbers is that it's gallons per watt hour. So if the pump moves seven gallons per watt hour, it's gonna have a seven wef number. If the pump moves eight point five gallons per watt hour, whatever that is, I have no idea what that is, you're gonna have a 8.5 rating. In a nutshell, these ratings don't make a huge difference. For example, the Superflow VS is rated with a WEF of 9, the whisper flow is a WF of 8.4, and the Intelliflow 3, depending on if you get the 1.5 horsepower, it's a 7.1, or the 3 horsepower, it's a 9.4. The amount of money you're saving over the course of the year is pretty nominal. I would say if you're going from a 9.4 down to a 8.4, you're probably gonna save maybe$20 or$30 more a year on a little bit of an efficient pump because there's not a huge difference between you know seven gallons per watt hour and eight point five per watt hour, and the savings is pretty minimal. You know, it's not it shouldn't be a deciding factor, in other words, what the WEF number is. The best way to save energy is to run your pump at a lower speed, and yes, a higher horsepower pump, like a three horsepower total horsepower VS pump, will move more water at a lower speed than a 1.5 horsepower VS pump, but it's really nominal and you don't really notice the difference, and it's not gonna be something to be really concerned about. If you're going from a single speed pump to a VS pump, no matter which one you choose, you're gonna save money by running that one at a lower speed or lower percentage of output, and it's gonna save you money by doing that versus the actual WEF number of the pump that you purchase. One thing I do recommend if you don't have a VS pump that has the flow built in, like the IntelliFlow 3, you would have to get a flow meter on your system. This will help to maximize your energy savings. I think the Flow Viz is my go-to flow meter because if you have a Jandy check valve, you can just retrofit that in there. And then I've placed them on different parts of the pools before the pump, after the filter, you know, before the heater, anywhere on your system. It's not gonna be a huge difference in measuring the gallons per minute, in my opinion. You may be off by two or three gallons per minute, but it's a great way to know that if you put your VS pump, no matter what total horsepower, let's just say you have a you know three total horsepower VS pump, and you want to know what to set it at for 40 gallons per minute, because you want to get the right circulation for your pool, and you're just guessing otherwise. And so with the flow vis flow meter, you put it at 2100 RPMs, and it'll tell you how many gallons per minute is going through the system. Let's just say, for sake of argument, it's 40 gallons per minute, then you put it to 1800, then it drops to 23 gallons per minute, and you'll be able to adjust your speed of your pump based on the gallons per minute to maximize your energy efficiency and also get the turnover necessary in your pool set at that speed. So without a flow meter, you're kind of just guessing, you know, what exactly is the speed. For example, when I had a single speed pump on my pool, it was a 1.5 horsepower. With the flow vis flow meter, it was pumping about 65 gallons a minute at the full speed. So if I put my three horsepower VS pump, you know, at 2800 RPMs, let's say, I can probably achieve that 65 gallons per minute pretty easily, and even more at the three horsepower rate. And then just briefly, I'll touch on the brands of pumps. Truly, I think they're all pretty good. You know, some people prefer prefer Pentair or Jandy or Hayward. I'm gonna say that if you have a Penthair pump now, just get a Pentair VS pump. If you have a Whisperflow, then I think the perfect VS Pump would be the Pentair Whisperflow VS. And then if you have a Jandy pump, well, simply go with the Jandy VS pump. You may not have to do much re-plumbing in the case of both the Pentair and Jandy pump. If you get the same kind of pump with the VS on the back, and with Hayward, if you have a TriStar, just get the TriStar VS. It just makes sense to get the same brand you have already. Switching brands may not be logical, especially if you have an automated system, the pump communicates better with the branded automated system you have already. So I'm not a big fan of going from say a Jandy pump to a Pentair pump or a Pentair pump to a Jandy pump. I would just say if you have a Hayward pump, get a Hayward VS pump. If you have a Pentair pump, get a Pentair VS pump, single speed pump, I should say. And if you have a Jandy single speed pump, just get a Jandy VS pump. These manufacturers kind of all use the same drives in some cases, they all use the same sentry motors, so it's not like there's a huge difference between one brand over the other. And they're all pretty reliable now, and I would say you may have some preferences with the controllers and things like that, but at the end of the day, I think it's just easier to go with the same brand you have there now and put the same brand in in the VS version. And so, to recap to make it easy for you, try to go with the similar total horsepower VS pump with the one you have already, and then don't really worry about the WEF number, just be more concerned with how long you're gonna run at a lower speed to save energy. Always go up with the total horsepower and not down. In other words, if you don't want to go below your single speed pump that you have currently, you want to stay above that with your total horsepower, and don't worry too much about the resistance and total dynamic head and all those things. I don't think it's super critical for a residential pool, and it's not something that you should be obsessing about. And if you're looking for other podcasts, of course, you can subscribe to my YouTube channel Monday through Friday, and there'll be a podcast there for you. Also, if you go to my website, swimmingprolearning.com, on the banner there's a podcast icon. I have over 1700 podcasts there available. And if you're interested in the coaching program, you can learn more at poleguidecoaching.com. Thanks for listening to this podcast. Have a rest of your week. God bless.