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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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(41 to 80 of 244)

 Posted: 11/23/2021 

Hi, We are having a inground pool installed, 25x15 retangular, 3.5x4x6 depth, 12,600 gallons. The basic install includes a Hayward 3030' Sq. Ft. Cartridge Filter (Eco-Smart), Hayward Tri-Star VS900 1.8hp "Energy Efficient" Variable Speed Pool Pump. The builder is recommending a Hayward 4030' Sq. Ft. Cartridge Filter (Eco-Smart) and Hayward Tri-Star VS950 1.8hp "Energy Efficient" Variable Speed Pool Pump. Do I need that additional upgrade or are we good with the basic setup? The pool is just for two people 95% of the time.
 Reply

InyoPools Product Specialist  Posted: 11/23/2021 

You should be OK with the base package listed. The Hayward C3030 is already oversized for a pool that size.
 Reply

Anonymous  Posted: 11/23/2021 

Thank you Matt! One more question. Is the Hayward 400K BTU High Efficiency Elect Ign Nat. Heater (Draft Induced) overkill or right sized for the pool?
 Reply

InyoPools Product Specialist  Posted: 11/23/2021 

For me, you can't really go overkill on a heater because you always want the pool to get to your desired temp as quickly as possible. Going with the 400k BTU will get the pool to temp quick(er than the smaller models), which means you don't have to run the pump as long. My only concern with the Hayward heaters is the amount of moving parts in their design. As the H-series ages, the blowers, the board, sensors, and such need to be replaced. My preferred heater model is a Raypak 2100 Series P-R406A-EN-X. It is atmospheric and not an induced draft, which means no blower. Their design is much simpler, and Raypak specializes in heaters. You may be familiar with Raypak, as they are also known as Rheem.
 Reply

 Posted: 11/13/2021 

I currently have an inground pool and just purchased a Hayward W3SP2315X20 Max-Flo XL Inground Pool Pump, 230V, 2HP. My filter is an old sand filter that I hate. I need to purchase a new filter (not sand) but I am not sure what size will be compatible with my pump. My pool is small about 18,000 to 20,000 gallons. I need to know what size filter will be suitable for my pump.
 Reply

InyoPools Product Specialist  Posted: 11/15/2021 

If you want better filtration and easier maintenance, you can't go wrong with a cartridge filter. Your pool is a pretty good size; it's midrange; I would use a four-cartridge system. You could use a 240 sq ft or larger four cartridge filter. I suggest something like the Crystal Water 325 sqft Pool Cartridge Filter - 570-0325-07
 Reply

 Posted: 11/15/2021 

Thank you so much Matt for your assistance.
 Reply

InyoPools Product Specialist  Posted: 11/16/2021 

You're welcome!
 Reply

 Posted: 11/4/2021 

What size Hayward Cartridge filter do I need for a 11,700 Saltwater in ground pool running a 1.85HP Hayward pump? I currently have a 48 sq ft DE filter that I would like to change to a cartridge filter system
 Reply

InyoPools Product Specialist  Posted: 11/10/2021 

The Waterway Pro-Clean 125 Sq Ft Filter - PCCF-125 would be suitable for a pool of your size, with that pump horsepower. In addition, it should extend your time between cleanings by a significant margin.
 Reply

Anonymous  Posted: 11/4/2021 

We have a 13000 gallon pool, using a TR60 sand filter and a 1 HP Hayward. The pump needs to be replaced, and we want to change to a cartridge filter system. Is the Pentair 240 the right size, and Pentair 1.5 VS superflow? Also would it be better to switch to VS or replace with another Hayward 1 HP?
 Reply

InyoPools Product Specialist  Posted: 11/10/2021 

The Pentair 240 Clean & Clear Plus with a 1.85 Hayward VS are well matched. That should give me good everyday filtering and high-end performance if you ever need to do any heavy-duty chemical treatments or cleaning.
 Reply

 Posted: 10/24/2021 

We have 8500 gal pool. The current equipment is a 1HP pump and a 36 Sqft DE filter . We need replace them. The company recommend 1.5HP speed variable pump. How big DE filter do we need? 36 sqft or bigger?
 Reply

InyoPools Product Specialist  Posted: 10/25/2021 

Because it is a variable speed, you are a lot more flexible on filter size. With single speed, you need to have a filter that can handle a pump going full-bore all the time. The variable speed will be running at its lower speeds for most of the time. With your pool's size and the fact that it is a VS pump, a 24 square foot DE filter would be fine. The larger Waterway Crystal Water 36 sq ft - 570-0036-07 will allow you to go longer between backwashes.
 Reply

 Posted: 10/18/2021 

We have an 23,000 gal pool. We had all new equipment installed this summer. The company recommended a 1.65 HP pump and a 90 sq ft hayward cartridge filter. As new pool owners, we went with their advice. Recently, a different pool company told us that the cartridge filter is way undersized for our pool... what are your thoughts? what size cartridge filter should we have?
 Reply

InyoPools Product Specialist  Posted: 10/19/2021 

I have to answer a question with a question, is it working for you? If it is, then it's okay. However, if you are experiencing pressure issues or need to clean the cartridge frequently to keep the filter pressure down, you may have undersized it. You have an entire pool season's worth of experience with the filter; did you have any concerns about the filter before the new pool tech mentioned it?Different pools have different variables. For example, a 15,000-gallon pool that experiences a heavy swimmer load would require a larger filter than 90 square feet. But a 25,000-gallon pool in a screened enclosure may be okay with just a 75 or 90 square foot filter.
 Reply

Anonymous  Posted: 9/18/2021 

My pool is in ground. It’s 18x30, goes from 3ft feet deep to 5.5ft. What size filter should I have. The pool contractor is trying to give me a 320
 Reply

InyoPools Product Specialist  Posted: 9/20/2021 

Your pool is about 15,000 gallons, which means you could use a cartridge filter as small as 100 square feet. But if you go with a smaller filter, you will need to clean it a lot more often than if you got a 4-cartridge model like the 320. You could find a middle ground by using a 175 sq ft Hayward Star Clear Plus or 200 sq ft Waterway ProClean Plus model. These single cartridge models are darn big, and they only have a single cartridge, so maintenance and upkeep should be cheaper than the 4-cartridge model.
 Reply

 Posted: 9/15/2021 

I've got a 13,000-15,000 in ground gunite pool with a Hayward 18x18 sand filter and a 1.0 HP pump. Reading that the newer 18" Hayward sand filters have problems splitting at the seams. Recommendations on other brands that offer 18" filters? Best cartridge filter to replace the sand filter?
 Reply

InyoPools Product Specialist  Posted: 9/16/2021 

We currently do not have another 18" sand filter, the closest we have is the 19" tank, Sand Dollar Top Mount Filters SD40 1.5" MPT W/Valve. A suitable cartridge filter would be a 90 square foot model like the Hayward Star Clear Plus 90 Sq Ft. Filter 2 Inch Ports.
 Reply

Anonymous  Posted: 9/7/2021 

30,000 gallon with automatic cover. Stays covered when not in use. Replacing pump and filter. The Polaris pb4-60 booster pump. Pool used 4 months a year. Thinking canister since it is easier. Have de now. Thinking Pentair products. Thinking the 420 or 520 with whatever pump makes sense, but really not sure what would be the best match.
 Reply

InyoPools Product Specialist  Posted: 9/8/2021 

The Clean & Clear Plus 420 or 520 would be good choices for that setup. I suggest going with a larger VS pump, like the Hayward TriStar VS Pump 2.7 HP - W3SP3206VSP. Your pool is covered most of the time, so you should be able to use the low RPMs schedule to keep your water clean. But, you will have the luxury of high-end performance if you need to do any chemical treatments that require turning over your water several times.
 Reply

 Posted: 8/27/2021 

I have a 2.0 HP Whisperflow Pump on a 12-15,000 gallon pool with an 20 year old Pentair Triton 2 Sand Filter. I'd like to go to a cartridge filter setup, any suggestions?
 Reply

InyoPools Product Specialist  Posted: 9/1/2021 

What is the model number of your current filter? An example of the model number formats for your filter would be the TR100, or 140264
 Reply

 Posted: 9/1/2021 

I have already removed the sand filter and replaced with a Pentair 420 Cartridge Filter. It works great.
 Reply

InyoPools Product Specialist  Posted: 9/1/2021 

Awesome!
 Reply

 Posted: 8/24/2021 

i have a 20000 gallon pool with a 1 1/2 hp motor, currently have a 60 sqft de filter and want to convert to sand. what size sand filter do i need?
 Reply

InyoPools Product Specialist  Posted: 8/25/2021 

To replace a 60 sq ft DE filter, I would suggest a 30-inch tank or larger. This will give you a close enough flowrate to the DE filter while also big enough to prevent excessive backwashing. I recommend either the Pentair Tagelus Top Mount Filter TA100 w/Valve - EC145240 or Hayward Pro Series Side Mount Sand Filter 4.91 sq. ft Less Valve
 Reply

 Posted: 8/14/2021 

Looking to replace my sand filter with a cartridge filter. 12000 gallon in ground pool. 1 1/2 Hp pump. 2 inch plumbing. What would be your recommendations
 Reply

InyoPools Product Specialist  Posted: 8/17/2021 

You could go with a 90 square foot filter or higher.
 Reply

Anonymous  Posted: 8/10/2021 

Hi ?? I have a 14x48 round pool and I’m trying to find out what filter pump I can get for this pool the one the pool brought is not that good
 Reply

InyoPools Product Specialist  Posted: 8/11/2021 

A 3/4 HP pump like the Pureline Pure Pro XL Pump - PL1500 should work.
 Reply

 Posted: 8/5/2021 

Hi, I have a 12,000 gallon In ground pool with a 3hp variable Pentair pump, but have a 320sq ft Pentair clean n clear plus cartridge filter. Is the filter to small for my pump and pool? If so which one do you recommend? I’m running for 8-10 a day at 2800 .
 Reply

InyoPools Product Specialist  Posted: 8/6/2021 

That pump and filter are a fine match with one another. If anything,  they are oversized for your pool. You should get plenty of life out of the cartridges between cleanings.
 Reply

 Posted: 8/2/2021 

I have an inground pool with a spill over spa. I'm probably close to 40k gallon for both. I have a Pentair single phase 2hp pump with 2 inch plumbing. Can I use a Hayward Swim Clear 525 sqft cartridge filter for my pool? I usually run my pool 12 hours a day.
 Reply

InyoPools Product Specialist  Posted: 8/3/2021 

Yes, the Hayward SwimClear 525 sq ft would be plenty of filter for a pool that size.
 Reply

 Posted: 7/21/2021 

I have an 18,000 gallon fiberglass pool that is 40x16 shallow end is 4' 1.5 and deep end is 6'5.5" what size cartridge filter do I need
 Reply

InyoPools Product Specialist  Posted: 8/3/2021 

For a pool that size a 120 square foot filter like the Star Clear Plus 120 Sq Ft. Filter 1.5" Ports or the Waterway Pro-Clean 125 Sq Ft Filter
 Reply

Anonymous  Posted: 6/12/2021 

I have Haywood 1100 filter need new filter should I get Haywood 1200 or newvswimclear Haywood sizec100s orc1505s
 Reply

InyoPools Product Specialist  Posted: 6/17/2021 

Ether would work. I always suggest going with the same size or bigger when replacing a filter to prevent any pressure issues. Plus, if you go bigger, you may go longer between cleanings.
 Reply