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.

Click Here to View Available Pool Filters

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.

Click Here to View Available Pool Filters

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 146)

 Posted: 11/12/2020 

I have a 16000 gallon inground pool with an old DE filter that needs replaced. I am thinking of going to a cartridge filter. My pump is a 1HP uprated to 1.25 and I would like to know what size cartridge filter I need. Would a 150 square foot do the job for me?
 Reply

InyoPools Product Specialist  Posted: 11/16/2020 

Yes, a 150 square foot filter like the ProClean Plus 150 sqft Pool Cartridge Filter - PCCF-150 or the Clean & Clear Cartridge Filter 150 sqft would be great for your setup. That size provides an outstanding balance of flowrate and filtering capacity, which should make maintenance easier.
 Reply

 Posted: 10/14/2020 

Have to replace my Hayward Perflex Extended Cycle D.E. Filter, can it be replaced with a Hayward W3C1200 Swim Clear Catridge Pool Filter. Pool 17'2" X 35'4"
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InyoPools Product Specialist  Posted: 10/19/2020 

yes, the W3C1200 can replace your Perflex DE filter.
 Reply

 Posted: 9/26/2020 

We have a 16 by 32 above ground pool how big should R cartridge filter be.
 Reply

InyoPools Product Specialist  Posted: 10/6/2020 

A 16' X 32' above ground pool would require at least a 90 square foot cartridge filter. For future commenters, you can refer to this guide for sizing an above ground pool filter: How to Size an Above Ground Pool.Filter
 Reply

 Posted: 7/27/2020 

That was very very helpful
 Reply

InyoPools Product Specialist  Posted: 8/21/2020 

You're welcome! Thank you for reading.
 Reply

 Posted: 7/26/2020 

I am needing to replace my cartridge filter for my above ground 18’ round pool. The cartridge size I have has been discontinued (c-7399). This cartridge has been rated for 100 square foot pool filters. I can find a 50 square foot one that looks to have the same dimensions but we are concerned it might not be enough filter. I can also find a 75 square foot that is 1/4 inch taller or a 181square foot that could work too. Is going up to the 181 going to stress the pump out?
 Reply

InyoPools Product Specialist  Posted: 9/8/2020 

If the 181 matches the exact dimensions, then that would be the ideal option. The larger you go, the higher the flowrate it can handle, and the longer you can go between cleaning. Going with a lower square footage filter could give you pressure problems.
 Reply

 Posted: 4/21/2020 

Hi! I’m replacing my DE filter for a Hayward Cartridge filter but no sure which one do I have to select. My pool is small: Width - 8’8”, Length - 19’, Shallow End - 3, Deep End - 6 based on this numbers I was able to calculate that is approximately 5,643 Gallons. Actually the pool has 1HP pump.
 Reply

InyoPools Product Specialist  Posted: 4/24/2020 

What id the model number of your DE filter? I can get a better estimate of what size you need by comparing a cartridge model to the DE you currently have.
 Reply

 Posted: 4/25/2020 

Thanks for your reply. Unfortunately I do not have that information. It is a very old WaterCO DE Filter installed back on 2005. Sorry to not able to provide additional information.
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 Posted: 4/9/2020 

I live in AZ and am looking to replace a sand filter with a cartridge or DE filter. Pool is about 25k gallons, pump is Hayward Super Pump 1.5 hp with about 30 ft of head. What is your recommendation for a filter?
 Reply

InyoPools Product Specialist  Posted: 4/15/2020 

For a pool that size, matched with a 1.5 HP pump, I'd choose a cartridge filter size of 125 square feet or higher. The plus side of going with the bigger filters, you can go longer between cleanings.
 Reply

 Posted: 3/28/2020 

Hi, I have a pool with 48,750 total pool volume with a 3 hp pump and a Hayward filter W3C4030 which has 425 sq ft of filtering. it seems as though the filter is too small for this system ? or else the pump is too big ? there is 2 1/2 piping on this system a 2 heat pumps and one gas heater all in Parallel each with valves tees and 90's and I don't know how many under going to the pool. Debating weather to buy a larger filter ?
 Reply

InyoPools Product Specialist  Posted: 3/31/2020 

I cannot tell what the issue is from your comment. Is there a back pressure problem? The Hayward Swimclear Cartridge Filter 425 sqft can handle 150 gallons per minute (GPM) flow rate, and can turnover 72,000 gallons in 8 hours. That is more than enough for that pool size.Also, how long have this pump and filter been installed together? If this is a recent pressure issue and they have been working fine for a year or more, then you may just need to clean the filter.
 Reply

 Posted: 3/28/2020 

I have a 12x24 oval pool and am looking to replace the cartridge filter system (the pump works fine, so only looking to replace the filter system). I have found some I like, but they talk about "square foot" and I'm not sure what that means.
 Reply

InyoPools Product Specialist  Posted: 3/31/2020 

What size is your current filter? Whether it be sand or DE, we can get an idea of what type of filter rate and capacity is required.
 Reply

 Posted: 12/25/2019 

Hi, I have a pool of 8x12, about 3,120-150 gallons. Have calculated a 3/4 pump. A 12” sand filter would be sufficient or what you recommend me?
 Reply

InyoPools Product Specialist  Posted: 12/26/2019 

Yes, that would be sufficient for an above ground pool of that size.
 Reply

Anonymous  Posted: 10/6/2019 

What size pool sand filter and pump do I need for my round 14x48 above ground pool?
 Reply

InyoPools Product Specialist  Posted: 10/7/2019 

The answer could be found on the related article: How to Size an Above Ground Pool Filter linked at the beginning of the page.But for a pool that size, you would need about a 14" sand filter or larger.
 Reply

 Posted: 7/19/2019 

I have a Hayward Ec65a filter, is this big enough for a 18x36 pool?
 Reply

InyoPools Product Specialist  Posted: 7/22/2019 

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

 Posted: 8/14/2020 

I have the same pool size, 18x36 and i use the same filter, EC-65A for over 20 years. Same pump, 1.5. Now my filter just broke and has a crack. I'm going to replace it. I just need the connection from the filter to the pump. Can you help me? It used to work well all the time but I guess it's time to change the filter. Thank You.
 Reply

InyoPools Product Specialist  Posted: 8/27/2020 

Are you referring to PVC plumbing that goes from the pump discharge port to the filter's intake? We do not carry  PVC rigid pipe, but it should be available at any local hardware store. If you are referencing a part of the filter, can you see what you need in this parts diagram?  Replacement parts for Hayward Perflex D.E. FIlters EC-65, EC-65A, EC-75 & EC-75A
 Reply

 Posted: 8/14/2020 

I have the same pool size, 18x36 and i use the same filter, EC-65A for over 20 years. Same pump, 1.5. Now my filter just broke and has a crack. I'm going to replace it. I just need the connection from the filter to the pump. Can you help me? It used to work well all the time but I guess it's time to change the filter. Thank You.
 Reply

InyoPools Product Specialist  Posted: 9/1/2020 

Do you need a piece of PVC rigid pipe, flex PVC, or a union? Those are usually the only things between the pump and filter. Do you see a picture of the part you are referring to in the following link? Hayward Perflex D.E. FIlters EC-65, EC-65A, EC-75 & EC-75A Parts Diagram
 Reply

 Posted: 7/13/2019 

What pump and filter would you recommend for a 22x52 above ground pool?
 Reply

InyoPools Product Specialist  Posted: 7/16/2019 

How To Size an Above Ground Pool Pump and Filter System
 Reply

 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
 Reply

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.
 Reply

 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?
 Reply

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
 Reply

 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.
 Reply

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
 Reply

InyoPools Product Specialist  Posted: 6/13/2019 

An EC40AC would be the best-sized filter for that pool and pump combo.
 Reply

 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.
 Reply