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How to Choose The Right Pool Pump

Categories: How To Guides, Pumps, Energy Efficiency
With so many technical terms to know and different models to consider, it’s no wonder that many of us end up at the mercy of the local pool store or our weekly maintenance guy for help navigating all of the available information in hopes of making an informed and intelligent pool pump buying decision. Below we’ve put together some helpful information on how to find the best pool pump for your needs - hopefully this will eliminate some of the confusion when it comes to purchasing this important piece of pool equipment.

Before we get started, I’ll give you a chance to get out of reading this article… The simple way to address this topic is to purchase one of the new variable speed pumps we have available. These pumps will work on any pool, regardless of plumbing size, filter type/size or feet of head, etc. All terms we would rather not concern ourselves with! And most utility companies offer a rebate if you install one. The most popular variable speed pump on the market that will work on almost every residential pool in the industry is the Intelliflo by Pentair.
Okay, back to picking out the right pump…
There are two very important things to remember -
  1. Not all pumps are the same and not all horse power ratings mean the same thing. For example, a 2HP pump from 15 years ago is not necessarily as efficient or has the water flow of a 2HP pump manufactured today. Additionally, all 2HP pumps made today are not the same. There are variations that alter the performance drastically. Don’t be alarmed, all you need to know is that even though the horse power might be the same, the performance is often much different and you might not be comparing apples to apples. 
  2. Your current pump may have not been sized correctly to begin with. Pool builders are notorious for putting a 2HP pump in their proposal because the competition did, and they can’t put a smaller pump in for fear their bid will be viewed inferior. When in actuality, you want the lowest horse power available that will give you the performance and circulation required for your system. If a 1HP pump will provide the circulation your pool needs and will turn the water over as recommended, why pay more for a 2HP in up-front costs as well as on-going operating costs?
Below are the five steps to selecting the best pump for you:
STEP 1 – Determine the gallons in your pool and the desired turnover rate.
A healthy turnover rate is 8-10 hours for most residential pools with heavily used pools having a turnover rate slight shorter (5-7 hours).
STEP 2 – Determine your minimum flow rate.
Divide your gallons by the turnover rate desired
For example: 24,000 gallons / 8 hours = 50 gallons per minute (GPM)). 50 GPM is the minimum flow you need from your pool pump.
Pool Size Turnover Rate  Minimum Flow Rate
35,000 Gallons 6 Hours 97
35,000 Gallons
8 Hours
24,000 Gallons 6 Hours
24,000 Gallons
8 Hours
18,000 Gallons
6 Hours
18,000 Gallons
8 Hours
STEP 3 – Determine your maximum flow rate.
The flow rate of your system is limited by two factors –
  1. The size of pipe/plumbing.
  2. The equipment your pool has, specifically your filter. 
The first thing to check is your size of plumbing. Here is the max flow that the most popular plumbing sizes can accommodate (per line):
PVC pipe maximum flow rates by size 
1.5" 2" 2.5" 3"
44 GMP 73 GMP 120 GMP 160 GMP
For example: If you have two 1.5” suction lines (such as a skimmer and main drain) then your maximum flow rate will be 88 GPM (44 GPM per line).
If you have 1.5” PVC plumbing that can handle a max of 44 GPM (per line) and you install a pump that has a flow rate of 100 GPM, it will do you no good since the pipe size can’t handle that amount of flow.
In fact, this will actually damage your system’s plumbing, the pump can cavitate as it “starves” for water. Components inside the filter can deteriorate at an accelerated rate as well.
In the diagram below, you will see this pool has two skimmers and a main drain. So, if the system is plumbed with 1.5” PVC, the maximum flow rate would be 132 GPM (44 GPM x 3 lines) while in in pool mode. When the valves are turned to spa mode, the maximum flow rate would be 44 GPM as there is only one suction line from the spa.
Another factor that needs to be considered when you’re looking at aspects of your system that limits flow, is your pool filter. The type of filter (cartridge, DE or sand) and the size will determine the amount of flow they can handle. See the chart below for a better illustration of maximum flow rates as well as best flow rates.
  • If you have a spa attached to your pool then you want a pump that will produce the GPM closer to the max flow.
  • If you have a pool only, then the lower, best flow rate GPM is what you want your pump to provide.
DE Filter
Square Feet 24 36 48 60 72
Max Flow 48 72 96 120 144
Best Flow 36 54 72 90 108
Cartridge Filter
Square Feet 100 200 300 400 500
Max Flow 38 75 112 150 150
Best Flow 30 50 75 100 125
Sand Filter 
Tank Diameter 19 21 24 30 36
Max Flow 40 50 60 100 140
STEP 4 – Calculate the resistance (head) of your system.
Again, don’t be alarmed. Even though this calculation is based on many different factors:
  • Do you have a heater, chemical feeder or salt system
  • The amount of turns in your plumbing, size of plumbing
  • Distance from the skimmer to the pump, etc.
We have a few easy steps to determine an approximate amount of head or resistance your system has.
A good estimate is to take the amount of feet from where your suction lines are (skimmers or main drain) back to where your pump will be located. The total amount of return piping should give you a good idea on how many feet of head your pump will have.
STEP 5 – Choose your pump.
Every pump will have a performance or curve chart as you see below.
For example, if you had 60 feet of head and needed a flow rate of 80 GPM then pump “D” would be the best choice for your system. Follow the line for 60 from the left across until it intersects 80 from the bottom of the chart and you see they cross closest to the “D” line.
Now that you have calculated your pool size in gallons, determined the best turnover rate for your pool, know your approximate feet of head and know the flow rate best for your pool, you are now ready to shop for pool pumps! Click here to view our selection of pool pumps.
If you are still are uncertain and would like some help, give us a call at 888-836-6025 and we’d be more than happy to assist you. And, remember the variable speed pump option.
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Pool Supply Unlimited is an e-commerce company that loves water. We love to pump it, filter it, heat it, chlorinate it, light it up and stare at it while we're barbequing a fat, juicy steak. There are real pool professionals working here. Our guys have seen thousands of pools in their careers, no exaggeration. We are based in San Antonio, TX and can land most products to your door (within the 48 contiguous states) in less than a week.
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