How To Size a Pool Filter

WRITTEN BY:  Inyo Pools

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Before you can selct the correct filter for your pool, you must first select the correct pump for you 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 inbalance 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 buildup may cause cracks in the filter tank causing iit to explode. This guide covers how you should size your pool filter correctly.

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 th 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 13 of 13)

Inyopools  Posted: 06/26/2017 11:31 AM  Latest Inyo Product Specialist

Anonymous (ec40ac) - A filter should be able to handle about 25% more GPM water flow than the system's pump. The EC40AC filter is designed for 40 GPM. 1 HP pumps can generate up to 50-70 GPM, so you will need a larger filter.


Anonymous  Posted: 06/23/2017 16:16 PM  Latest

I have a 27'x 52" above ground round pool. Currently using a Hayward ec40ac 1hp de filter. Is this adequate?


Inyopools  Posted: 06/20/2017 11:34 AM  Latest Inyo Product Specialist

Anonymous (filter size) - The size of your filter really depends on the size of your pump. You want something about 25% larger than the average GPM of your pump. Assuming you have a 2 or 2.5 HP pump, I would recommend a filter with a 400-450 Filtration Area and a Flow Rate of 150 GPM.


Anonymous  Posted: 06/19/2017 17:54 PM 

I have a 30,000 gallon in ground pool with and average depth of 5.5'
What size cartridge filter do I need?


Inyopools  Posted: 06/17/2017 13:44 PM  Inyo Product Specialist

James - Your C1200 Star Clean Plus Cartridge Filter is a good match for your 1 1/2 HP Super Pump. The typical water flow for a 1 1/2 HP Super Pump is 70-80 GPM. The C1200 is designed to handle up to 120 GPM.


James  Posted: 06/16/2017 12:47 PM 

I have a hayward 1 1/2 super pump with a hayward c1200 star clear plus hooked to a hayward heater. This is all to a roughly 15000-17000 gallon pool and seperate spa. Is this to small of a filter


Inyopools  Posted: 06/09/2017 0:07 AM  Inyo Product Specialist

Fritz - Assuming your current DE filter is something like a Hayward Pro Grid DE Filter 48 Sq Ft with a designed flow rate of 96 GPM and your current pump is 1 1/2 HP uprated, I'd recommend something like the Hayward Star Clear Plus 120 Sq Ft. Filter 1.5" Ports. If you have a 2 HP uprated pump, I'd recommend the next larger filter. We recommend getting a filter with a GPM capacity that is 25% larger than the pump's capacity.


Fritz  Posted: 06/06/2017 23:38 PM 

I have a 16'x32'pool with an average depth of 6'
The pool has an old DE filter that needs replacing.
I want to change over to a cartridge filter, what size would I need. Currently it's a 48sq ft


Inyopools  Posted: 06/05/2017 15:33 PM  Inyo Product Specialist

Kevin - A Pentair CCP430 filter is much larger than you need for a 17,000-gallon pool. With a 150 GPM or 9000 GPH rating it could turn over your pool in two hours. Most people try to turn their pool water over 1-2 times a day in 8 hours. I'd recommend going with a CCP320. Dealers usually recommend having a filter whose capacity is at least 25% greater than the normal GPM of the pump. To turn your pool over 2 times a day in an eight-hour period, you would need a GPM of 71 GPM (17,000 x 2 = 34,000 / 8 = 4,250 GPH / 60 = 71 GPM). I'd recommend the Pentair Whisperflo Pump 1 1/2 HP Uprated motor- WF-26 to deliver that GPM. A CCP320 filter with a 120 GPM capacity your gives you an operating buffer of 69% (120/71). You can always have a filter larger than you need. It can't have a GPM smaller that what the pump generates.


Inyopools  Posted: 06/05/2017 11:22 AM  Inyo Product Specialist

Mayates - To match your 1 ½ HP pump, you have the option of something like the Hayward S180T (18") or the S210T (21"). On filters, we usually recommend the larger one. It will last longer and require less frequent cleaning.


Mayates  Posted: 06/04/2017 15:33 PM 

I have a 27' round above ground pool with a 1-1/2HP pump. Need to replace sand filter. What size sand filter would we need? Thanks


Inyopools  Posted: 03/18/2015 10:23 AM  Inyo Product Specialist

Fads - Depending on what type of filter you want, I would go with something like a Pentair Clean & Clear Cartridge Filter 100 sq/ft or a Hayward Sand Filter with Top Mount Valve 18" Tank. These are a little larger than required but for filters we recommend a larger size. They will last longer and require less frequent cleaning.


Fads  Posted: 03/17/2015 9:59 AM 

i have a whisper 24 1 hp and a circular pool 22'x48'' what size filter is a match for that pump