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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: 3/13/2023 

I have a 30,000 gallon in ground pool. What are the standards for the correct cartridge filter size?
 Reply

InyoPools Product Specialist  Posted: 3/16/2023 

What is the model number of your pump? As we mention in the guide, that is an important part to sizing a filter.
 Reply

Anonymous  Posted: 7/27/2022 

Currently have an above ground pool 27x52 round. Think it's 18,637 gallons. Just got a 1hp pump to combine with a waterway 22inch sand filter running basic pool sand and a rx clear 150sq foot cartridge filter to plumb inline after the sand filter then to a hayward cl200 chlorinator all on 1.5inch intake and return plumbing. Pool chemistry is on point. Question is will this finally take care of the algae issue. thinking of running the pool cotton ball filters in both pool skimmer and pump skimmer too. Will this setup filter the 19k gallons in a 6hr period adequately and with the least maintenance possible? Did I go to small on the pump hp? I know 1.5 is recommended, but with maybe 30ft of head to include the return pipe as well this should easily be 60gpm?
 Reply

InyoPools Product Specialist  Posted: 7/28/2022 

The pool filter and pool pump's flow rate are vital to a pool, but balanced water chemistry is the most critical part of preventing alga blooms. Algae won't grow in a properly balanced and chlorinated pool. You could be filtering 150 GPM, but if the pH, Alk, Hardness, and Chlorine levels are out of whack, it'd be all for not. Make sure you have a working chlorinator on the system. Filters remove debris; chlorine kills organic materials like algae and bacteria.
 Reply

 Posted: 6/27/2022 

Could you tell me what size pump filtration system I should use for 10, 000 gallon pool the is 18x48 Round above ground pool
 Reply

InyoPools Product Specialist  Posted: 6/29/2022 

What type of filter do you prefer, sand, DE, or cartridge?
 Reply

 Posted: 4/18/2022 

Not sure how many gallons is pool but i think it’s 15,000 to 20,000 gallons i have 1hp pump what size of filter should I get on both cartridge filter / DE filter
 Reply

InyoPools Product Specialist  Posted: 4/20/2022 

I suggest a Clean & Clear 150 sq/ft Cartridge Filter or a four cartridge Hayward Swimclear Cart for cartridge. Filter 325 sqft. For a DE filter option, I'd lean towards Crystal Water 36 sqft D.E. Pool Filter - 570-0036-07.
 Reply

Anonymous  Posted: 4/10/2022 

I have a 45k gallon pool currently have a old de60 filter and 2.5 hp pump want to put new filter and variable speed pump what size should i go with and is it a good idea to switch to a cartridge filter
 Reply

InyoPools Product Specialist  Posted: 4/14/2022 

You can stick with the same filter or get a new filter in a similar size. You'll be changing the pump, but not the size of your pool. A 45k gallon pool is on the very high end of residential pools. You should stay with a larger filter unless you want to clean the filter more often; nobody wants to do that. If you want to switch to a cartridge, pick a four-cartridge system. For a 45k0gallon pool, I'd choose the  Crystal Water 525 sqft Pool Cartridge Filter - 570-0525-07
 Reply

 Posted: 4/2/2022 

I have a in-ground kidney shaped pool that we have used the cartridge style filter, but want to change it over to a sand filter. Question is what size of filter do I need with approximately 29,000 gallons of water?
 Reply

InyoPools Product Specialist  Posted: 4/4/2022 

If you already have a filter, I can use the current model information to find a suitable replacement. What is the size or model number of your current filter?
 Reply

 Posted: 4/4/2022 

We currently have a cartridge style filter, a Pentair Plus, model CCP520. Wanting a sand filter to replace with that will allow me to backwash and clean the filter without the need of replacement of cartridges.
 Reply

InyoPools Product Specialist  Posted: 4/14/2022 

What is your pool size in gallons, or length, width, and depth measurements?
 Reply

 Posted: 3/28/2022 

I just bought a 15x30 above ground pool. Now, I need a pump/filter package. What should I use?
 Reply

InyoPools Product Specialist  Posted: 3/28/2022 

What kind of filter do you want?Related Article - How To Size an Above Ground Pool Pump and Filter System
 Reply

 Posted: 3/23/2022 

Hello. I'm looking to get a new filter and pump for our older gunite pool. The pool is roughly 32 by 16 (about 20,000 gallons). I'm looking to purchase the Hayward C3030 cartridge filter and the Hayward 2HP pump. Do you think these two pieces of equipment would be compatible? I'm also looking into heat pumps, and wanted to see if you had any recommendations. Thanks!
 Reply

InyoPools Product Specialist  Posted: 3/24/2022 

The Hayward SwimClear C3030 Cartridge can accept the Hayward Super Pump or the Super II, 2HP options. We suggest either the Hayward HeatPro or Rapypak Classic Series heat pumps. If I were to choose between the two, I'd lean towards the Raypak Classic.
 Reply

 Posted: 3/21/2022 

I’m replacing my sand filter and want to change to a cartridge. My pool is 18,000 gal, 1 hp pump. What size filter would you recommend? Would 200 sq ft be adequate or would 420 be better!
 Reply

InyoPools Product Specialist  Posted: 3/21/2022 

The 200 sq ft or 420 sq ft would work well for a pool of that size. Both filter options would mean less maintenance over the course of a season. The 420 sq ft option may only need to be cleaned at the beginning and the end of the swimming season. We recommend the ProClean Plus 200 sqft Pool Cartridge Filter - PCCF-200 or the Clean & Clear Plus 420 Cartridge Filter - EC-160301 in those respective filter sizes.
 Reply

 Posted: 3/14/2022 

Hi - I have an in-ground, rectangular pool that is 20' x 10', and the depth ranges from 3' to 5-1/2'. I believe the gallon size is about 14,000 gallons. Currently I have a Hayward Pro-Grid DE filter, that I hate (model #DE2420). My pool pump is a Century V-Green pump (I actually bought it from you). I would like to change my filter to a cartridge type. Can you tell me what size would be best? Also, what salt water system could I add at the same time? Thanks!
 Reply

InyoPools Product Specialist  Posted: 3/14/2022 

I would switch to a 120 square foot cartridge filter, something like the Star Clear Plus 120 Sq Ft. Filter 1.5" Ports - W3C1200 (2"-Port Model). The 120 sq ft option is a good size and should give you plenty of swim time between cartridge cleanings. You can go bigger, again the plus-side being you can extend the time between having to clean your filter.
 Reply

 Posted: 3/14/2022 

Thank you Matt. I also am interested in converting my pool to salt water. Could you recommend a system for that? Thanks! Cynthia
 Reply

InyoPools Product Specialist  Posted: 3/14/2022 

A 14,000-gallon pool could use a 20k rated system. We suggest the POWERCLEAN Salt Ultra 320 - 52000-220-000. 
 Reply

 Posted: 3/7/2022 

I have a 2hp motor and a c751 75ft sq cartridge Hayward filter system. I wanted to go to a Hayward 120 sq ft filter system. Do you see a problem with going to a bigger filter system?
 Reply

InyoPools Product Specialist  Posted: 3/7/2022 

There shouldn't be an issue with upgrading from a Hayward C751 to a C1200 - 1.5" Port or 2"-Port, 120 sq ft option. The larger filter should allow you to go longer between cartridge cleanings. 
 Reply

 Posted: 2/12/2022 

We have an in ground pool that is 13,500 gallons. It has a Hayward DE filter that was set up with an automatic pool cleaner which we have no longer use. It has a 2hp 2 speed motor. I would really like to simplify the controls and go with a smaller motor. What size single speed motor would I need and can I replace just the motor or would I need to replace the pump too. Currently we run it on high 4 hours and on low 4 hours and it does a good job when operating correctly.
 Reply

InyoPools Product Specialist  Posted: 2/14/2022 

I would need to know the make and model of the pool pump, or preferably the model number of your specific pump. As we mention in this guide, different pumps have different flow rates. Without that information, I cannot suggest a new HP. Also, I would need to know the feet of head for your system to estimate the flow rate of the new motor and drivetrain parts.
 Reply

 Posted: 2/14/2022 

Matt The only info on the pool pump is that it was made for Blue Haven Pools. I’ve been told that it is identical to a Hayward Super II pump. The replacement motors I’ve purchased are AO Smith STS1152R I don't know what the feet of head is but if it helps the pipe is 2" and runs about 40' from the pump to the skimmer. The deepest part of the pool is 5-1/2 feet and the bottom of the pump sits level with the top of the pool. I hope this help. Your help is greatly appreciated.
 Reply

InyoPools Product Specialist  Posted: 3/7/2022 

If your goal is to run the pump more efficiently, you should run the dual-speed at low rpm for 12 hours a day. Of course, that number will have to be higher in the summer months, but it would still be significantly cheaper to schedule it that way than to switch to a single-speed motor. There's no upside to going to a smaller single-speed motor when you already have a dual speed. You'd be spending money to buy a less-efficient motor that restricts your filtering capability to one speed. If you want a simplify your controls, get a different controller to interface with the motor.
 Reply

Anonymous  Posted: 2/7/2022 

I've damaged to hood on my Hayward StarClear C751 and don't see that model being offered. Pool is 22000 gallons and currently using a 3/4 hp Hayward pump. Is my best option to go to a 90 sqft Hayward? What else is a good replacement? I am in Columbus Ga.
 Reply

InyoPools Product Specialist  Posted: 2/14/2022 

The Hayward Star Clear Plus C751 is no longer offered through online dealers. However, the next size up, W3C9002, is available and would work for your application. The main difference between the C751 and C900 is the latter is taller and has a higher square footage cartridge. The larger cartridge can go longer between cleaning and handle a higher flow rate.
 Reply

 Posted: 2/1/2022 

Hello, I changed my inground pool to a 6 000 gallons inground pool and I have a 1.5 hp super pump with 2 inch pipes. Which sand filter do you suggest ? My Jacuzzi Laser 225 cracked before changing the pool.
 Reply

InyoPools Product Specialist  Posted: 2/1/2022 

What do you mean by "changed the pool"?
 Reply

 Posted: 2/2/2022 

We had a way bigger pool, which had approximately 18 000 gallons instead of the new one which has 6 000 gallons but we don’t want to change the 1.5 Hp motor. Which sand filter do you suggest to be big enough for the motor ? The pipes are 2 inches. Thank you
 Reply

InyoPools Product Specialist  Posted: 2/2/2022 

I suggest using a similarly sized filter to your old Jacuzzi Laser 225. A suitable option would be the Hayward Pro Series - W3S220T. The filter needs to be sized for the pool and the pump's output. You may have a smaller pool, but the pump will push about the same amount of water unless your plumbing dynamics have severely changed.
 Reply

 Posted: 1/20/2022 

I have an old Hayward DE filter that cracked on the top lid. It is Model # DE-4800. I would like to replace it with a Cartridge filter what is a comparable cartridge filter in terms of performance? The pool size is ~ 20k gallons.
 Reply

InyoPools Product Specialist  Posted: 1/24/2022 

A similar performing cartridge filter to the Hayward MicroClear DE4800 would be the Hayward Swimcleare 325 sqft - W3C3030
 Reply

 Posted: 1/7/2022 

Hi, we have a 30x60 inground pool with a 2hp super pump. Our old sand filter needs to be replaced. What size and type (not sand) filter would you recommend? We estimate 85000 gallons
 Reply

InyoPools Product Specialist  Posted: 1/7/2022 

What is the model number of your current filter? Knowing that information explains what type of flow rates and capacity that is necessary, regardless of the filter media type.
 Reply