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How To Size a Pool Filter

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Before you can select the correct pool filter for your pool, you must first select the correct pump for your pool. Your pool filter must be matched to your pool pump. If the filter is too small relative to the pump. the pump will generate more water pressure in the filter than the filter is able to handle. This imbalance will quickly break down the filtering material of the filter which will greatly diminish the effectiveness of the filter. In more extreme cases, the high-pressure build-up may cause cracks in the filter tank causing it to explode. This guide covers how you should size your pool filter correctly.

Click Here to View Available Pool Filters

Related Article - How To Size an Abo



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Step 1

Pool Size - We suggest having a pump and filter that can cycle through your pool's volume within 8 hours. Depending on filtering and water chemistry demands, you may run the pump longer or shorter, but 8 hours is a good baseline mark.

To calculate your pool's volume in gallons, use the formula listed in this step's image. The formulas are listed according to pool shape. For example, if you have an L-shape, divide your pool into two rectangles, calculate their volume then combine the sums.

See our guide on How to Size a Pool Pump for Your In-Ground Pool for the formulas required to size your pool. For this guide, we will assume a typical in-ground pool size of 20,000 gallons.

Related Article - How To Size an Above Ground Pool Pump and Filter System

Step 2

Determine Required Gallons Per Minute (GPM) - After you have the number of gallons in your pool (20,000 gallons for this example), you will have to calculate the GPM required to filter 20,000 gallons in 8 hours.

To calculate this flow rate, first, divide your calculated gallons by 8 Gallons Per Hour (GPH). Then divide that number by 60 to get Gallons Per Minute (GPM). For our example of 20,000 gallons that's: 20,000 / 8 hours or 2,500 GPH divided by 60 mins/hour or 42 GPM.

Step 3

Calculate the Pool's Feet of Head (Feet of Water) - The pump's actual flow rate is determined by two factors, the horsepower rating the amount of pressure needed for the pump to prime itself. This resisting force, also called the Feet of Head, accounts for factors including pipe size, length of pipe, number of turns (elbows,) and rise in height the water has to overcome to reach the pump.

As Head increases, your pools actual GPM will decrease. Calculation of Head can be involved and is generally done during the initial installation of the pool. For a rough estimate, average the suction lines' lengths between the pool and the pump. Most basic in-ground pools have a Head of 40' to 50'.

We will assume 45' for this example.

Related Article - How To Size an Above Ground Pool Pump and Filter System

Step 4

Determine Pump Size - Now that you have determined your pool's required GPM and its Feet of Head, we can select the pump.

Go to the description page for your pool pump of choice. The pump's description should include its flow chart. A pump's flow chart lets you see the pump's estimated flow rate according to the specific horsepower and your plumbing's Feet of Head.

For example, say you wanted the popular Hayward Super Pump. An abbreviated version of the Hayward Super Pump Performance Page is shown at the left. Based on the data above, we are looking for a pump to handle 42 GPM with 45 Feet of Head. According to the chart for 50 Feet of Head (closest above to 45'), we need a pump between 3/4 HP (31 GPM) and 1 HP (50 GPM). Since we always go to the higher GPM, we would select the 1 HP pump.

Step 5

Determine Filter Size - The size of your pool filter is directly related to the pool pump you have selected. If your pool filter is too small for the pump, there will be additional strain on the pump motor as it tries to push water through and meets resistance at the filter. This will eventually burn out the pump motor, and your filtration will also be compromised.

We recommend over-sizing the filter to be absolutely confident it can handle the flow coming from the pump. So, in this case, instead of getting a filter rated at precisely 42 GPM, you should select one that is a little higher – around 60 GPM would be fine.

Click Here to View Available Pool Filters

Step 6

Other Considerations - A couple of other considerations should be mentioned in your selection of a pool pump and filter. The above calculations are based on a basic pool configuration with no extra water features: fountains, spas, waterfalls, solar heating, and in-floor cleaning systems. The features generally require higher GPM rates which equates to higher HP pumps/filters.

Also if your pool requires greater than 60 GPM you may need at least 2" diameter suction pipes. Suction pipes of 1 1/2" have a physical limit of 60 GPM. 2" pipes can handle up to 100 GPM.

Related Article - PVC Pool Pipe Dimensions

Step 7

Determining AG Pool Filter Size - The size of your system is mostly determined on the size of your above ground pool. The gallons found inside your pool will give you the horsepower needed for your pump. A simple rule to follow is you should be able to clear all of the gallons of your pool in an 8 hour period of time. You can use the following as a guideline.

• Above Ground Pool up to 24 Ft. Round = 1 HP pump
• Above Ground Pool over 24 Ft. Round = 1 ½ HP pump

Related Article - How To Size an Above Ground Pool Pump and Filter System
 

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Anonymous  Posted: 4/13/2019 

I have a 21x52 above ground around 11,000 gallons of water what replacement filter/pump would you recommend!
 Reply

InyoPools Product Specialist  Posted: 4/17/2019 

We'd recommend the Jacuzzi Laser model 94084958. This has a 1HP pump and a 19" sand filter.
 Reply

 Posted: 3/27/2019 

I am looking to replace my DE cartridges (fell apart last season) and after researching, wondering if it's just more efficient to purchase total new filter/pump (pump on it's last leg as well). what would you recommend for a 30' above ground ??? Love DE - had sand when installed but would never run clear...switched over and have had the best luck with DE over the last 6-7 years with no issues. Thanks!!!
 Reply

InyoPools Product Specialist  Posted: 3/28/2019 

We cover the recommended sizes for above ground filters in this article. Give it a read: How To Size an Above Ground Pool Filter
 Reply

 Posted: 3/25/2019 

I have a 24 x 52 above ground pool. Want to change from cartridge filter to D.E. I like the Hayward D.E. Perplex EC40 and EC50. Which one would be best for the size of my pool. We run it about 8 hours per day.
 Reply

InyoPools Product Specialist  Posted: 3/26/2019 

The EC40 would be sufficient for a 24' above ground pool. However, I would go with the EC50. The EC50 wouldn't have to be cleaned as often.
 Reply

Anonymous  Posted: 3/18/2019 

What size sand filter for a 18x 33 aboveground oval pool?
 Reply

InyoPools Product Specialist  Posted: 3/25/2019 

Check out our guide titled "How to Select Above Ground Pool Filters".
 Reply

 Posted: 2/16/2019 

We are going to install a 24' X 50' in ground pool w/liner. What kind of pump and filter would you recommend? What are the different kinds of filters? Is a sand filter the best? Which ones are the easiest to maintain? Thank you for your help
 Reply

InyoPools Product Specialist  Posted: 2/18/2019 

Hello David - We did a selection series on pumps and filters. These should answer all of your questions. Check out the blogs/videos titled "How to Select an Inground Pool Pump" and "How to Select an Inground Pool Filter".
 Reply

Anonymous  Posted: 1/18/2019 

how do you measure the pool filter. moved into a house with existing but not sure if the measurement is from the ground up or just the sand filter plastic tub.
 Reply

InyoPools Product Specialist  Posted: 1/18/2019 

Sand filters are measured by the diameter of the tank.
 Reply

 Posted: 11/28/2018 

Looking for a pool pump and filter replacement. My pool is 16x32 at 19,000 gallons. I have a solar heater as well. Currently I have a SVL56 waterway 1.5hp and 1.10 SF pump and a prclean pccf-200 filter rated at 75gpm. I am looking to replace this combo with a 1.65hp Haywood SP2303VSP maxflo and a Haywood C17502 SwimClear Plus pool filter. Will this combo be an adequate replacement for what I currently have?
 Reply

InyoPools Product Specialist  Posted: 11/28/2018 

Hello Eric - Yes, the Hayward Max-Flo VS SP2303VSP and the Hayward Star Clear Plus C17502 would be great replacements for your 19,000 gallon pool.
 Reply

 Posted: 3/31/2019 

i have a 20,000 gallon in ground pool. What is the size cartridge filter I should buy?? 1.5 hp pump motor thank you
 Reply

InyoPools Product Specialist  Posted: 4/1/2019 

Hello Edward - I'd recommend the same equipment that Eric had suggested. A 1.65 variable speed pump and a cartridge filter that is 150 square feet or higher.
 Reply

Anonymous  Posted: 11/5/2018 

I have an above ground doughboy pool that is 21 ft wide by 41 ft long and is3 feet deep on one end and 6 feet deep on the other end. What pump and filter would you recommend?
 Reply

InyoPools Product Specialist  Posted: 11/6/2018 

Thank you for contacting Inyo. We'd recommend the Hayward model CC15093S for your 21'x41' above ground pool. This system has a 1.5HP pump and a 150 square foot cartridge filter. The pump comes with a standard 3-prong plug. We also carry a version with a twist-lock plug.
 Reply

 Posted: 8/7/2018 

Hello Chuckee - As we mentioned in step 4 of the guide, the flow rate of a pump is determined not only by its horsepower but by the plumbing system's feet of head. A 2 HP pump may only push 55 gallons per minute (GPM) if the feet of head is high enough. Where as on a different pool, a 1 HP pump can push 90 GPM. But to answer your question, you need to know the feet of head of your system and the flowchart of your specific pump to determine if it will match the Hayward C1200. Luckily, the C1200 has a flow rating of 120 GPM, making it pretty hard for any pump to test its limits.
 Reply

 Posted: 7/20/2018 

The Hayward EcoStar Owner's Manual states the following regarding the Drive Error: Prime Failed:

Indicates that the pump was not able to prime within 15 minutes of startup.
Plumbing and fittings should be checked for potential air leaks and corrected.


Priming issues could be an issue with blockages or air leaks. A checklist of things to check on your plumbing system can be found in this guide: How To Determine Why a Pool Pump Won't Prime. Also, try cleaning the cartridge to alleviate any pressure issues.
 Reply

 Posted: 7/19/2018 

Hello Jeff - Something like the Hayward model S166T92S would be sufficient for an 18' above ground pool. This is a 1HP pump with a 16" sand filter.
 Reply

 Posted: 7/18/2018 

Hello Janet - We would recommend a sand filter that is 18" or larger.
 Reply

 Posted: 7/17/2018 

I'm not sure if our new pool filter has been properly sized. Our old pool filter was replaced with Pentair CC100 a month ago, and we got the Hayward EcoStar Variable Speed pump. Our inground pool is bean-shape about 39ft x 18ft with spa. We also got a new heat pump 35000btu. The issue we been experiencing, the pool pump stops with Priming Drive Error about every 15 minutes when we set the valves to flow to the spa. We also noticed that the initial filter gauge was about 22 psi then goes to about 27psi to 30psi. Usually the gauge is at 8psi when the valve is set to waterfalls and about 12psi when set to main pool only. What do you think is about ISSUE? I'm guessing it might be the CC100 being too small. I appreciate any recommendation. Thanks, Mel
 Reply

 Posted: 6/17/2018 

what is the biggest pump I can safely use on a hayward 120 sq.ft.filter without causing damage
 Reply

 Posted: 5/26/2018 

Hello we have a 18 foot round above ground pool that is 4 feet deep. We were looking to get a sand filter and pump. What do you suggest for which sand filter and pump combo to get? We were looking for hayward. Thank you!
 Reply

 Posted: 5/18/2018 

I have an 18’ x 52” round pool. I bought a 1.5 hp pump and it blew the sand from my filter into my pool. What size sand filter do I need to get?
 Reply

 Posted: 5/18/2018 

Hello Lynn - You can get a filter without a pump. We'd recommend the Hayward C751 for your 27' above ground pool.
 Reply

 Posted: 5/17/2018 

We have a 27' diameter pool 5 foot deep. We currently have a sand filter with a 1.5HP Hayward motor (which we bought less than 2 years ago). We want to go to a cartridge filter. Can we buy a cartridge filter system without buying a new pump motor? If so, which one do you recommend for our pool?
 Reply

 Posted: 5/17/2018 

Hello Brooks - Your pool size would hold about 25k gallons. The Hayward S210S would be a little undersized. We would recommend the S244S.
 Reply

 Posted: 5/16/2018 

I have an 18x33 in ground pool. depth goes from 4 - 7 feet. What size hayward filter do you recommend? is the S210S sufficient or should I go with S244S?
 Reply

 Posted: 5/10/2018 

Hello TKG - Even though the DE2420 is advertised as an inground pool filter, it can be used on above ground pools. I agree that you would be stepping down if you went with the EC50. I'm not a fan of the DE "fingers" inside the EC50. If you ever have to replace the full set of fingers, it costs as much as a complete filter.
 Reply

 Posted: 5/9/2018 

hello, my above ground pool is 15x26 and 52in deep. so I generally estimate 12000 gallons. I have a 1.5HP Hayward power-flo lx pump, and a Hayward Pro-Grid de2420. The base is cracked so I have to replace the filter and am getting mixed reviews for what to replace with. Apparently this model filter is not commonly used for above ground pools, and I have been directed to a Hayward EC50. Seems like such a step down, but also much cheaper. Thoughts?
 Reply

 Posted: 4/30/2018 

Hello KR - Because of the 2.25HP pump, we'd recommend something like a Hayward S310T2. This is a 500 pound sand filter with a 30.5" diameter tank.
 Reply

 Posted: 4/30/2018 

have a 15X30 inground pool approx 20,000 gallons with a 2.25 HP pump. I'm replacing my DE filter with a sand filter. Recommendation on size and or make/model of sand filter to look at please.
 Reply

 Posted: 4/17/2018 

Hello Heather - The 21" Hayward S210T sand filter would be sufficient for your 18'x34' above ground pool and it will work with the SP1593 pool pump.
 Reply

 Posted: 4/13/2018 

Hello. I have an above ground 18'x34' pool. We have a 1.5 HP Hayward SP1593 pump and we need a new filter. Our old filter is a sand filter (Hayward S230T) but that is only sold as a combo filter/pump. Can we get the Hayward S210T filter to use with the SP1593 pump? I think they are both 200lb. sand filters. Not sure what the 21" and 23" difference means. Anyhow, what filter do you recommend?
 Reply

 Posted: 4/6/2018 

This would partly depend on the pump model and its horsepower, as mentioned in the how-to. For most most pools that size, a 75 sq. ft. cartridge filter would do the job.
 Reply

 Posted: 4/6/2018 

HI i wanted to ask what size Cartridge filter i need for a 10x16 oval above ground pool.
 Reply

 Posted: 3/9/2018 

ax3bl4d3 - We would recommend a Hayward Star Clear Plus 90 Sq Ft. Filter 1 1/2" Ports for your 1.5 HP Hayward pump.
 Reply

 Posted: 3/7/2018 

16x32 above ground with 1.5hp hayward pump. what size minimum cartridge filter should I look at?
 Reply