How To Size a Pool Filter

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Before you can select the correct 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.

Related Article: How to Size an Above Ground Pool Filter

Step by Step

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Step 1

SIZE POOL - A standard pool circulation rule is to be able to filter all that water in your pool at least once a day. Customers generally run their single speed pump for an 8 hour period, so they require a pump/filter system that will recycle their pool water in an 8 hr period. The first step then is to calculate the total gallons in your pool. 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

Step 2

DETERMINE GPM REQUIRED - After you have the number of gallons in your pool (20,000 gallons for this example), you will have to calculate the Gallons Per Minute (GPM) required to filter 20,000 gallons in 8 hours. To come up with this flow rate first divide your calculated gallons by 8 for 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

DETERMINE Feet of Head - As water flows through the system piping between the pool and the pump, it will meet with resistance to flow according to factors like the length of the piping, number of turns (elbows) and the diameter of the piping. This resistance is called "Feet of Head or "Head". 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. However for a rough estimated use the average of the lengths of the suction lines 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.

Step 4

DETERMINE PUMP SIZE - Now that you have determined your pools required GPM and its Feet of Head, you have the information required to select your pool.'s pump size. Go to the description page of the style of pump you would like to purchase. Many pump manufacturers will provide a chart on this description page showing the HP required for your particular GPM and Foot of Head requirement. 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 that will handle 42 GPM with a 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 certain it can handle the flow coming from the pump. So in this case, instead of getting a filter rated at exactly 42 GPM, you should select one that is a little higher – around 60 GPM would be fine.

Step 6

OTHER CONSIDERATIONS - There are a couple of other considerations that 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 a 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.

Step 7

DETERMINE 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 horse power 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

Comments

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(1 to 40 of 119)

 Posted: 7/19/2019 

I have a Hayward Ec65a filter, is this big enough for a 18x36 pool?
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InyoPools Product Specialist  Posted: 7/22/2019 

Yes, the Perflex EC65 should be enough for a pool that size.
 Reply

 Posted: 7/13/2019 

What pump and filter would you recommend for a 22x52 above ground pool?
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InyoPools Product Specialist  Posted: 7/16/2019 

How To Size an Above Ground Pool Pump and Filter System
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 Posted: 7/9/2019 

I have a 38400 gallon pool and I need to know the size pump and filter I need for it. Thanks Nick
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InyoPools Product Specialist  Posted: 7/11/2019 

Given the bare bones of information provided on y9our system. i suggest a Pentair IntelliFlo and a four cartridge Clean & Clear Plus 420 sq. ft.
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 Posted: 7/4/2019 

I have a 24ft above ground pool that needs a new sand filter. Currently running a 1hp pump with this. Suggestions?
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InyoPools Product Specialist  Posted: 7/5/2019 

A 16-inch tank or larger sand filter should work fine. We have this guide: How to Size an Above Ground Pool Filter
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 Posted: 6/13/2019 

We have a above ground pool 30/15 the filter is 62in/24in, our question is how much sand goes into the filter.
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InyoPools Product Specialist  Posted: 6/14/2019 

What is the model number of the filter? Then we can look up the specs or owner's manual to find the sand requirement.
 Reply

 Posted: 6/13/2019 

Hi I have a 24 round pool going from sand to de earth .My pump is a two speed 1hp to 1 1/2 what size filter should a get .was looking at haywood eac40
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InyoPools Product Specialist  Posted: 6/13/2019 

An EC40AC would be the best-sized filter for that pool and pump combo.
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 Posted: 6/11/2019 

I have a filter and person is replacing the pump. He said the filter is not big enough for the pump. It a rectangle 30,000 gal pool. He wont tell me the size I need but I can replace that.
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InyoPools Product Specialist  Posted: 6/14/2019 

Do you want a sand, cartridge, or DE filter?
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 Posted: 6/10/2019 

i have a 21 ft round above ground pool. 10k gallons in it with a 1hp pump and the sand filter just took a poop as it is spitting sand into the pool. if i considered getting a cartrige filter set up what ones would i be looking at? i mean i know if i was to get another sand filter a 14 - 19 would be appropriate. but looking at the cartridge filters i have no idea. thank you
 Reply

InyoPools Product Specialist  Posted: 6/14/2019 

A pool that size would require a 75 sq ft cartridge filter, or larger. You can take a look at the following guide for a size chart for each filter type:  How to Size an Above Ground Pool Filter
 Reply

 Posted: 6/5/2019 

Hi I have an above ground oval shaped 10k gallon pool. Based on the guide you provide I feel like Hayward EC40C92S would be the right fit. Does that make sense to you? Thanks in advance!
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 Posted: 6/13/2019 

I HAVE A 30 FOOT ABOVE GROUND POOL WITH 21000 GALLONS OF WATER WHAT SIZE PUMP AND FILTER SHOULD I HAVE AND IS IT OK TO KEEP PUMP RUNNING ALL THE TIME ?
 Reply

InyoPools Product Specialist  Posted: 6/13/2019 

This guide will give you above ground pool equipment sizing suggestions: How To Size an Above Ground Pool Pump and Filter System
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InyoPools Product Specialist  Posted: 6/6/2019 

Yes, you are correct.
 Reply

 Posted: 5/9/2019 

Hello. I have a in-ground/deck spa. It's a kidney shaped, 11ft x 7ft. I guess-ti-mate that it's about 900-1000 gallons. It's plumbed with 1.5 inch flex pipe and 6 Jacuzzi jets. The 2.25hp motor along with a Jacuzzi CFR-50 cartridge filter and Jacuzzi pool style pump is located about 15 feet away from the tub along with a 2hp blower. The motor is shot. My plans are to replace the motor, pump, and possibly the seemingly, undersized filter. I read somewhere that for spa purposes, I should figure roughly 1/2HP per jet. (1/2hp x 6 jets= 3HP). But a 3HP pump moves over 200 gpm which seems too much for the 1.5 inch plumbing and the 50 gpm filter. In your opinion, would you instead go with something around 1.5hp to 2hp pump??? If so, should I go with larger filter to handle the flow rate? By the way, I have no prior knowledge or history of the spa performance before the motor/pump failure. Thank you so much in advance for any advice you can give.
 Reply

InyoPools Product Specialist  Posted: 5/9/2019 

Typically spa jets need 10-25 GPM per jet depending on the style of the jet. If we size the pump on the high side (25gpm per jet), it would be 150 gpm. You could keep your existing 2.25HP pump and go with a larger filter like the Hayward C1750, which can handle 175 gpm.
 Reply

 Posted: 5/10/2019 

Hi Robert. Thanks for getting back with me about sizing a filter and pump for my spa. I was just looking at the specs on the Hayward C1750 on the INYO website. It says the C1750 is capable of handling 120 GPM, just short of the 150GPM you had mentioned. To handle a higher flow rate, would a sand or DE filter work for my spa or should I stick with a cartridge filter? Also, as using my exsisting pump, INYO is one of a few sites that still have parts for my older "R" series Jacuzzi pump. It would take about $100.00 to replace the seals and such in my existing. Plus the motor would run another $400.00. Again, in your opinion, would I be better off getting something new, like the AquaFlo Gecko Alliance XP2e Pump 3.0HP 230V, 2SPD, 56FR - 2"x2" SIDE DISCHARGE - 05334012-2040 "OR" renewing my old pump??? Even though, if I did go with the spa type pump, I would need to get a separate leaf trap to attach. Thank you again for your help and opinions.
 Reply

InyoPools Product Specialist  Posted: 5/10/2019 

We would recommend sticking with a cartridge filter. The C1750 can handle the flow from a 3Hp pump. I'd buy a new pump instead of investing in the rebuild of a pump that's been discontinued.
 Reply

 Posted: 5/13/2019 

Okay, thanks Robert. I'll go with the Hayward C1750. One last question, based on my size tub and the 6 jets, Do you feel the AquaFlo Gecko Alliance XP2e Pump 3.0HP 230V, 2SPD, 56FR - 2"x2" SIDE DISCHARGE - 05334012-2040 would "over power" it with it's 240 GPM? My thoughts are 1) the pump is close to 20 feet away 2) the pump is about 4 or 5 feet below the spa water level AND 3) the 2 inch fittings will need to be reduced down since the tub is plumbed with 1.5 inch flex PVC. With these factors, I thought a slight increase in HP rating would be appropriate. Does my reasoning make sense? If not, would you recommend a different type of pool/spa pump or possibly step down in horsepower? Thanks again for your help.
 Reply

InyoPools Product Specialist  Posted: 5/14/2019 

Honestly, I would stay with the current 2.25HP. A 3HP seems overkill for the 1.5" plumbing and 6 jets. 
 Reply

 Posted: 5/16/2019 

Thank you Robert. I very much appreciate your thoughts, direction, and advice with the sizing of a pump for my spa.
 Reply

Anonymous  Posted: 5/7/2019 

Hi what’s the best filtration system to use for a above ground pool size 12 / 24 oval
 Reply

InyoPools Product Specialist  Posted: 5/7/2019 

Are you asking about the type of filter: sand, DE, or cartridge? Or what size filter to use? The size of filter depends on which type you are installing. We have a simple guide on above ground filter sizing, called: How to Size an Above Ground Pool Filter
 Reply

 Posted: 4/24/2019 

I have a 30ft x 4ft round pool. What would be the best filter and pump. Want it to filter and clean as best as possible. Had cartridge filter before, do I stick to that? Just found i was cleaning it a lot. Open to suggestions. Thanks
 Reply

InyoPools Product Specialist  Posted: 4/24/2019 

For help sizing an above ground pump and filter system, give this guide a read: How to Size an Above Ground Pool Filter
 Reply

Anonymous  Posted: 4/24/2019 

Hi I am just wanting a reccommedation on which filter to consider. I have already found the size I need. Thanks
 Reply

InyoPools Product Specialist  Posted: 4/25/2019 

The most popular brands are Pentair and Pureline. Out products also having customer reviews and ratings to help you on your search.
 Reply

 Posted: 4/13/2019 

I have a 10,000 gallon inground pool. Currently running a 1 how Hayward super pump with a salt generator as well as a Hayward heat pump. My issue is that the heat pump requires a certain flow rate In order to kick on, when cartridge is not cleaning the heater doesn't kick on.. what filter /pump size should I use to replace old filter
 Reply

InyoPools Product Specialist  Posted: 4/18/2019 

Hello Ray - Does the heat pump kick on when the cartridge is clean? Does it only kick off when the cartridges start to get dirty? What is the make and model of your filter?
 Reply

Anonymous  Posted: 4/13/2019 

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