How to select the correct filter size for your swimming pool

Sand, Cartridge, and Diatomaceous Earth (DE) Filter Systems

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How to select the correct filter size for your swimming pool

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There is a lot of confusion about various filters, many different opinions, and several important facts to consider. The first is that a pool can be properly maintained with any of the filter systems available: Sand, Cartridge, or Diatomaceous Earth (DE). Here is a brief description of each type:

Sand Filters

Water is pushed through a bed of filter sand and removed through a set of lateral tubes at the bottom. The filter area of a sand filter is equal to the area of the filter itself.

For example, a 24″ filter will have 3.14 square feet of filter area. Only the top 1″ of sand is actually used to filter the water. The principle behind this filter is that water is pushed through the filter sand, somewhat like an espresso machine. Dirty water goes in the top and clean water exits out the bottom. As the filter sand becomes plugged with debris from the pool, the pressure increases on the filter and the water flow drops. In order to clean the filter, you just run it in reverse and dump the waste water; this is referred to as “backwashing” the filter.

Once the filter is backwashed, you move to the rinse mode and that repacks the sand and then back to filter. This has to be done manually every few weeks. From a hydraulics standpoint, a backwash valve is typically the most inefficient piece of equipment you can add to a swimming pool system. Should the sand ever become really dirty, it is easily and inexpensively replaced. In terms of particle size filtered out, sand is the least effective method as it can allow smaller particles to pass back into the pool.

Cartridge Filters

This one is easy to understand. Water passes through a filter material and the filter captures the debris.

This is just like the water filters used under your sink. Cartridges have much more available area to filter than sand. Most start at 100 square feet, and the majority of the cartridge filters sold are larger than 300 square feet so they don’t clog up as quickly and therefore you touch them less frequently. There are two types of cartridge filters in general. In the first case, there are filters elements that are inexpensive to replace and as such, they don’t tend to last as long. Then there are other filters that have very expensive elements and these last 5 or more years.

In both cases, cartridge filters are designed to run at lower pressure than sand. This puts less back-pressure on the pump and hence you get more flow and turnover for an equivalent pump size. Generally, these filters have to be cleaned once or twice a season by simply hosing them off, so you don’t touch them as often. In terms of particle size filtered out, a cartridge is somewhere between sand and DE.

DE Filters

Diatomaceous earth is mined and is the fossilized exoskeletons of tiny diatoms. They are used to coat “grids” in the filter housing and act like tiny sieves to remove debris. They are very small and as such can filter out particles as small as 5 microns.

Diatom filter area is sized between sand and cartridge at around 60 to 70 square feet are most common. Once the filter pressure rises, the filter is backwashed just like a sand filter and then “recharged” with more DE powder. Typically it is poured in a slurry into the skimmer and it then coats the filter grids. DE filters run at higher pressures than cartridge filters and as such can lead to some inefficiency and flow loss.

Now with that background, which swimming filter is best? You can use this question to gauge who you’re talking to in a pool store. Just ask: “Which swimming pool filter is best” and then listen for the answer. There is only one correct answer to that question: can you please define best? If the answer is any of the three, someone is trying to simply sell you something.

  • If you want bulletproof – sand is a great choice.
  • Low maintenance would lead one to a cartridge.
  • The cleanest water might lead you to DE.
  • All three types of swimming pool filters work.
  • You can add a little DE to a sand or cartridge filter to increases its ability to filter small particles.
  • Flocculants can be added to the pool water to create big particles out of small particles (think – flocks of birds are easier to see).
  • Cartridges that become fouled can be replaced.

Go With a High-End Cartridge Filter for Your Pool

Which filter should you choose? Go with a high-end cartridge filter for your pool. The reason is that no one really wants to have another item on the to-do list and good cartridge filter can last a season. Be sure that you:

A Swimming Pool Chemical Calculator

Common Filter Media Rate
High-Rate Sand: 5 – 20 gpm/ft 2
Cartridge: 0.375 gpm/ft 2
Diatomaceous Earth(DE): 2 gpm/ft 2

It is always recommended to oversize the pool filter. Adequate filtration is the primary source of clean clear pool water. An undersized filter can lead to numerous problems, including cloudy pool water, increased chemical demands, pH swings, and unsafe swimming pool water.

Maximum pump gpm must be used when calculating the minimum required filter area. Exceeding the filter media rate will result in many negative effects to the equipment and poor pool water quality.

RESULTS SHOWN HERE

More About Pool Filter Size and Filter Media Rate

Choosing the right filter:

Each pool filter media has its own unique advantages and disadvantages. Selecting the right one requires consideration of user load, pump max gpm, flow rate, filter media rate, installation location, filter size, maintenance and local code requirements on turn over rate.

An improperly sized filter can lead to cloudy and dirty water. Ensuring the main drain cover is in place, and intact is impossible in cloudy pool water. Being able to visually inspect the main drain cover is important. Not being able to see a swimmer in distress at the bottom because of cloudy pool water is extremely dangerous.

High-Rate Sand Filter Media:

Pool filter sand media is one of the oldest methods of purifying water. Debris, algae, and contaminants get trapped between the sand particles as the pool water passes. High-Rate Sand filters clean particles down to 25-100 micron range. High-Rate sand filter maintenance requires backwashing to clean out the debris and prevent channeling.

Cartridge Filter Media:

Pool cartridge filters clean down to the 10-15 micron range. Replacement and maintenance are easier compared to a sand filter. There is no need for backwashing, cartridge filters are easily removed and cleaned or just replaced. These filters reduce energy cost by the reduced pressure required to operate. Saving on energy and equipment use.

Diatomaceous Earth(DE) Filter Media:

Diatomaceous Earth or DE provides the best filtration at 1-2 microns. DE’s made from fossils called diatoms. Its a fine white powerer that is poured into the skimmer and trapped by a fabric forming a thin layer that traps debris and contaminants but allows water to pass. Maintenance can be tricky and should be handled by a professional for best results.

Maintenance:

Take note of the pressure side psi when first installing the filter. Once the pressure rises over 10 psi past original installation pressure, its time to clean the filter.

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POOL CHEMICAL CALCULATOR APP

Track and chart chemical test history for multiple pools. Save pool equipment configuration. Save operating notes, warranty details and manufacturer support info for each piece of equipment.

How to select the correct filter size for your swimming pool

How to Select an Inground Pool Filter

Hello and welcome back to our pool equipment selection series. We’ve already walked you through the process of sizing up the pump. The next step will be to select the type of filter that can handle the size of the pool and the pump. There are three filter types common on residential pools, and they are Sand, Cartridge, and DE. Each have their pros and cons; we will talk you through the basics of each type then we will dive into the finer points. And again, don’t forget to check out part one of the pool equipment selection series in which we discuss how to select and properly size your inground pool pump.

Sand FiltersHow to select the correct filter size for your swimming pool

We’ll start with the most common, Sand filters. These are the most popular filter found in backyards today. They’re known for being the least expensive as well as being easy to maintain. A #20 silica sand is used as the filter media to sift your pool water clean. The S and filter’s order of operation is pretty simple; the filter tank is filled halfway with sand allowing water to filter down through the sand, where it is then collected by an array of laterals.

There are two types of sand filters; Top Mount and side mount. This is determined by where the valve is mounted to the tank. Top mount sand filters are usually cheaper than side mount, but the side mount is more convenient when it comes time to change the sand. The reason being is that on a top mount you have to disconnect the pipes to remove the valve. On a side mount filter, you don’t need to. However, a side mount will take up more space on an equipment pad. If space is limited, go with the top mount.

Sand filters are the least efficient when filtering your water because they can only catch dirt particles 20-40 microns wide. If you’re a pool water aficionado, you will want to look to one of our other options like the Cartridge filter! The cartridge filter is quickly becoming the favorite for new installations because it takes up the least amount of space, it’s easy to clean, and it filters down to 10 microns; which is half the size of what a sand filter can catch.

How to select the correct filter size for your swimming pool

How to select the correct filter size for your swimming pool Pentair Clean and Clear Plus, Quad Style

Cartridge Filters

Cartridge filters are made in either single or quad style. The single cartridge has one filter element that can range from 25 to 200 square feet of filtering material. These types are great for small to medium sized pools, which have lighter bather loads. The quad or four cartridge filters are designed for medium to large pools that expect more debris. if you have a smallish pool but still plan on a few pool parties, consider getting the quad cartridge because the higher square footage will permit you to go longer between cleanings without sacrificing water clarity.

Diatomaceous Earth

Speaking of water clarity, last but not least we have the DE or Diatomaceous Earth filters which are the Cadillac of pool filters, as they can catch particles as small as 1-3 microns. These filters use DE powder which is fossilized shell of diatoms, a type of ancient algae….. I guess algae is kind of good for your pool in some ways.

The DE powder is introduced to the filter by pouring it into your skimmer. The powder then coats the fabric covered grids and as water passes through, VOILA, no more dirt.

That covers the three different types of filter.

How to Size a Pool Filter

To prevent excessive cleaning, we suggest sizing your filter properly or better yet, oversizing your filter. The two factors you’ll want to consider are designed flow rate and turnover capability. In our pump example, we used a pool that was 23,000 gallons. To accomplish the 8-hour turnover rate, the pump must push 48 GPM. Using those numbers, we need a filter with a designed flow rate over 48 GPM and a turnover capability greater than 23,000 gallons.

Remember, When you oversize a filter, you are helping yourself in two ways, one you can go longer between cleanings, and two you put less stress on your filter and your pump, giving them both a longer lifespan.

And before we close out filters we should touch on the two types of filters valves used on Sand and DE filters: Slide and Multiport.

Now, this is a multiport valve which more common than its counterpart the slide valve; this is due to its versatility. The multiport valve has up to 8 settings, but we will stick with the most common, which are:

How to select the correct filter size for your swimming pool Hayward SP714T Top Mount Valve Label

  • Filter
  • Backwash
  • Rinse
  • Recirculate
  • Close

The Filter setting is the normal cleaning cycle of your pool water. Backwash is the cleaning cycle for the filter; it works by reversing the flow of water through the tank.

After the backwash comes the Rinse, because backwashing loosens can leave dirt in your pipes we need a way to flush it out before returning to regular filtration. The rinse returns the water flow to normal patterns within the filter but still directs the water to waste until pipes are clear. How To Backwash a Pool Sand Filter , How To Backwash a Hayward DE Filter

Then we have Recirculate which allows you to run your pump to circulate the water while bypassing your filter media. You would use this setting if you were adding a chemical that required the filter to be bypassed or… let’s say there was a crack in the filter, you could place the filter in Recirculate and keep the water moving.

And Closed is used when you want to stop all flow of water past the pump, For example if you need to service something down the line like a chlorinator or a heater.

And this slender guy is the slide valve. Slide valves are designed for side mount filters. They only have two positions; filter and backwash. Slide valves are mainly used on equipment pads with restricted space or if the pool owner prefers a simple set up.

There are a few primary factors that go into finding the right size pool pump. Below, we’ll run through how to easily figure it out step-by-step and choose your pool pump confidently.

How to Figure Out What Pool Pump Size You Need

  • Calculate the volume of your pool
  • Calculate minimum flow rate
  • Determine maximum flow rate
  • Determine your flow rate range
  • Add in Total Dynamic Head (TDH)
  • Settle on your final specs

Pool Volume

First up, you need to figure out how many gallons of water are in your swimming pool. This calculation differs based on pool shape, but is pretty straightforward. Use our pool volume calculator below and then we’ll start calculating the minimum flow rate you need for your pump.

All good? Okay, let’s move on to the next step.

Minimum Flow Rate

Once you have the approximate number of gallons of water in your pool, we have to figure our minimum flow rate for the pump, using a Gallons Per Minute (GPM) calculation. GPM takes into account your pool size and the number of “turnovers” you need per day (your turnover rate). For both traditional chlorine pools and saltwater pools, the industry standard is 2 turnovers per day.

Before we get into the calculation, you have a few options here. You can choose to run your pump 24 hours per day (decreasing your GPM needs) or twice a day in different segments. The typical two-a-day segments are: 6 hour cycles, 8 hour cycles, and 10 hour cycles. So, let’s calculate the minimum flow rate we need for all four of these options.

The ultimate goal is efficiency here – balancing electricity bill savings with pump horsepower and balanced water chemistry. Running at low horsepower for longer periods of time results in a more balanced water chemistry, but can be a sink on your electricity bill. The opposite is true for higher horsepower and shorter run times.

This is where variable speed pool pumps come in handy – they can speed up and slow down when you need them to, resulting in a much safer pool chemistry and energy efficient setup, which is a nice savings on that electric bill.

Okay, let’s move on to the next part of our pool pump sizing – figuring out your maximum flow rate.

Maximum Flow Rate

Fortunately, you don’t have to do a bunch of fancy math to figure our maximum flow rate. It is completely dependent on your plumbing system and other pool equipment, all of which should have documentation on maximum flow rates. We’ll start with filters.

Filters

There are three types of pool filters (sand, cartridge, and DE) and all of them have different maximum flow rates based on their surface area. Make sure you stay below the maximum flow rates for your filter system or you could end up damaging it. Here are the flow rates for common filter types and sizes.

Sand Filters

As a general rule of thumb, sand filters typically fall between 19-22 Max GPM per square foot of surface area.

  • 1.8 square feet surface area = 40 GPM
  • 2.3 square feet surface area = 50 GPM
  • 3.1 square feet surface area = 60 GPM
  • 4.9 square feet surface area = 100 GPM
Cartridge Filters

Cartridge filters are a lot bigger and a little less exact. Typically, you’re going to average 0.3 to 0.35 GPM per square foot of surface area.

  • 100 square feet surface area = 32-38 GPM
  • 200 square feet surface area = 55-75 GPM
  • 300 square feet surface area = 80-112 GPM
  • 400 square feet surface area = 100-150 GPM
DE Filters

DE filters are a little rangy as well. Plan for approximately 1.75 GPM per square foot of surface area, assuming the middle of the ranges below.

  • 24 square feet surface area = 36-48 GPM
  • 36 square feet surface area = 54-72 GPM
  • 48 square feet surface area = 72-96 GPM
  • 60 square feet surface area = 90-120 GPM

Now that we have filters settled, let’s move on to maximum flow rates for plumbing.

Plumbing

You never want to put more pressure in your pipes than they can handle. The maximum flow rate of your plumbing setup depends on the pipe size and should be clearly labeled on your system. If not, you can use these common values or ask your contractor.

  • 1.5″ pipes = 43 GPM
  • 2″ pipes = 73 GPM
  • 2.5″ pipes = 120 GPM

Heads up: your plumbing setup may be different across your entire pool environment. For example, the pipes leading to your spa could differ from the main pool area. Always remember to take the lowest of the maximum flow rates for sizing up your pool pump. Otherwise, you could risk damaging the setup for part of your pool environment.

Min and Max Flow Rate Range

Almost there! Now that we have the minimum and maximum flow rates for your pool setup, put them together to get to your flow rate range: one of the two main specs for determining the pool pump size you need.

So, let’s say you have a 15,000 gallon inground pool. With two turnovers per day, your minimum flow rate comes to 20.8 GPM.

Let’s also say that you have a 2.3 square foot sand filter (50 GPM max) and 1.5″ plumbing (43 GPM). You have to take the lower of those two values to make sure you don’t overwork any components of your pool, so your maximum flow rate comes to 43 GPM.

In this example, our flow rate range comes out to 20.8-43 GPM.

Let’s figure out the last main spec you need for your pool pump: total dynamic head.

Total Dynamic Head (TDH)

Total dynamic head is a resistance metric – it tells you the total amount of resistance in the hydraulic system of your pool. The filter, pump, pipes, heater, backwash valve, return, and other accessories have an effect on how water flows throughout your system. Most inground pools will be somewhere around 50 TDH. Above ground pools typically fall around 30 TDH. We’ll go into more specifics on TDH in another post.

Final Specs

Okay, we now have everything we need! All pool pump models will have charts with horsepower estimates based on flow rate ranges and total dynamic head. In our inground pool example, we need a pool pump with a 20.8-43 GPM flow rate range and 50 TDH (also called Feet of Head).

There you have it! Be sure to check out our recommendations for the best single and variable speed pumps as well, and my article on how long to run your pump every day.

Questions? Shoot us a message and we’ll be happy to help.

How to select the correct filter size for your swimming pool

Step 1

Your first step is to determine the number of gallons of water in your pool. The formulas for calculating the gallons depend on the shape of your pool.

For a RECTANGULAR POOL:

Measure the length (ft), the width (ft) and the average depth. The average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by two.

The formula for calculating the total gallons in a rectangular pool is: Gallons = Length x Width x Average Depth x 7.5.

For example (see picture): your pool is 30 ft long and 15 ft wide. The pool’s shallow end is 4 ft and its deep end is 8 ft. So, the pool’s average depth is 4 plus 8 = 12 divided by 2. This gives you 6 ft. The pool’s capacity is 30 ft x 15 ft x 6 ft x 7.5 = 20,250 gallons. Go to Step 5.

How to select the correct filter size for your swimming pool

How to select the correct filter size for your swimming pool

Step 2

For a ROUND SWIMMING POOL:

Determine the number of gallons of water in your round pool, measure the diameter of the pool and its average depth. The average depth is determined by adding the depth at the shallowest part to the depth at the deepest part and dividing by two.

The formula for calculating the total gallons in a round pool is: Gallons = Diameter x Diameter x Average Depth x 5.9.

For example (see picture): your pool is 25 ft in diameter, the pool’s shallow end is 3 ft and its deep end is 7 ft. So the pool’s average depth is 3 plus 7 = 10 divided by 2. This gives you 5 ft. The pool’s capacity is 25 ft x 25 ft x 5 ft x 5.9 = 18,428 gallons. Go to Step 5.

How to select the correct filter size for your swimming pool

Step 3

For an OVAL SWIMMING POOL:

To determine the number of gallons of water in your oval pool, measure the longest diameter, the shortest diameter and the average depth. The average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by two.

The formula for calculating the total gallons in an oval pool is: Gallons = Longest diameter x Shortest diameter x Average depth x 6.7.

For example (see picture): Your pool’s longest diameter is 25 ft, shortest diameter is 15 ft and the pool’s average depth is (3 + 7) / 2 = 5 ft. The pool’s capacity is 25 x 15 x 5 x 6.7 = 12,563 gallons. Go to Step 5.

How to select the correct filter size for your swimming pool

How to select the correct filter size for your swimming pool

Step 4

For a KIDNEY-SHAPED SWIMMING POOL:

To determine the number of gallons of water in your kidney-shaped pool, measure the largest width, the smallest width and the average depth. The average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by two.

The formula for calculating the total gallons in a kidney-shaped pool is: Gallons = (Longest width + Shortest width) x Length x Average depth x 3.38.

For example (see picture): Your pool’s length is 25 ft, longest width is 15 ft, shortest width is 10 ft and the pool’s average depth is (3 + 7) / 2 = 5 ft. The pool’s capacity is (15 + 10) x 25 x 5 x 3.38 = 10,563 gallons.

Step 5

Now that you have calculated the number of gallons in your swimming pool, you want to determine how many gallons per hour (GPH) you need to pump to clean all the water in your pool in eight hours. To come up with this flow rate, simply divide your calculated gallons by eight. For the RECTANGULAR swimming pool example the GPH required is 20,250 gallons / 8 hours or 2531 GPH.

Step 6

Most pool pump specifications are expressed in gallons per minute (GPM). So, to convert from GPH to GPM, divide your GPH by 60 minutes – 2531 GPH / 60 = 42.2 GPM.

How to select the correct filter size for your swimming pool

Step 7

Having calculated your required GPM, you next have to figure out the average Feet of Head for your pool pump. Check out our blog on How to Calculate Feet of Head. PLEASE NOTE, WE ARE CURRENTLY REVIEWING OUR PROCEDURE FOR ESTIMATING FEET OF HEAD. CURRENT ESTIMATES ARE TOO HIGH.

How to select the correct filter size for your swimming pool

How to select the correct filter size for your swimming pool

Step 8

You now have the information required to select the size of your pool pump. 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. 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 calculated above for a typical RECTANGULAR pool, we are looking for a pump that will handle 42GPM with a 47 Feet of Head. According to the chart for 50 Feet of Head (closest to 47′), we need a pump between 3/4 HP (31 GPM) and 1 HP (50 GPM). Since we always go for the higher GPM, we would select the 1 HP pump.

Step 9

The full performance page for the Hayward Super Pump can be found at this link, Hayward Super Pump. For the location of performance pages for other pump models, contact an Inyopools sales representative at 1-877-372-6038.

Step 10

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 encounters resistance at the filter. This will eventually burn out the pump motor and your filtration will also be compromised. We recommend selecting the filter so that it is oversized 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 11

There are a couple of other considerations that should be mentioned in your selection of a pool pump. The above calculations are based on a basic pool configuration with no extra water features like: fountains, spas, waterfalls, solar heating, and in-floor cleaning systems. These features generally require higher GPM rates which equate to a higher HP pump. 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.

There are three common pool filter types – sand, cartridge and Diatomaceous Earth (D.E.). All three of these pool filter types will keep your pool and spa clean, but you should consider the needs of your specific application, your other equipment and plumbing size before making a selection.

When choosing a filter type and size, we recommend enlisting the help of a pool professional to ensure the proper products are selected for your pool. Our pool pros will take into consideration the weather conditions in your area, the types of debris that can land in your pool, and they will also evaluate your entire application – how many gallons your pool has, your plumbing size and the needs of and types of other pool equipment you have.

Tip: An undersized pool filter will render it ineffective and lessen its life; the larger the filter, the longer the time between cleanings.

Pool System Plumbing

The first thing you want to check is the pool system plumbing. For instance, the maximum flow rate through a 1.5 inch PVC pipe is 44 gallons per minute (GPM). Even if you have a pump that can move 100 GPM, it won’t do you much good if the piping will only allow 44 GPM through it. An oversized pump not only wastes energy and money, but it may damage other equipment in the process.

The Right Filter

The correct filter size depends on the size of the pool. To maintain good water clarity, you must run the pump long enough each day to filter and sanitize the water in your pool. All filters have a GPM design rating and a turnover rate. A turnover rate of 8 or 10 hours is a typical sizing rate for residential pools.

All filters have flow requirements. D.E. filters are normally rated at 2 GPM per square feet (sq. ft.) of filter area for maximum flow. This means a 48 sq. ft. D.E. filter will have a maximum flow rate of 96 GPM, and a 60 sq. ft. model will be rated at 120 GPM. So if you have a pump that is going to flow 100 GPM, you would need to go to the 60 sq. ft. D.E. filter.

For a sand filter, it is best to look at the flow requirements of each filter as they can vary from 15 GPM per sq. ft. and higher. Just make sure the filter you choose can handle the flow rates needed.

Cartridge filters are becoming increasingly popular due to their eco-friendly operation. These filters don’t need to be backwashed and can save thousands of gallons of water each season. You should always adhere to the manufacture’s maximum flow rates and be sure not to size a cartridge filter too small as that may cause short cleaning cycles. The best way to determine flow rates for cartridge filters is to use the formula of 3x the flow rate for minimum, and the manufacture’s rating for maximum. The larger the cartridge filter, the longer the cycles between cleaning becomes.

How to select the correct filter size for your swimming poolWhy Work with A Pool Professional?

This is quite a bit of information to digest and your best bet is to talk to a pool professional to ensure you are using the appropriate products for your investment. With the help of a pool professional, you can be well on your way to receiving the best water clarity and to using the most efficient products in terms of energy use and water conservation.

Remember: Installing a filter too small for the output of the pump could cause costly damage to your filter.

Need some help locating a pool professional near you? Check out our dealer and servicer locator.

How to select the correct filter size for your swimming pool

Operating the correct sized above ground pool filter in your pool will help you save money and energy. In contrast, choosing one that is too large or too small can cause issues with the entire system. Read on to learn how to calculate the proper size for your above ground pool filter.

Step 1 – Measure the Size of Your Pool

If you have an above ground pool, you will need to measure the diameter and the center depth. Most above ground pools do not have a “deep end” that is substantially deeper than other parts of the pool. You then need to calculate the number of gallons of water in your pool. Do this by multiplying the total volume of your pool times 7.48, the amount of water in a cubic foot of space. For a 24-foot diameter pool with a center depth of 48 inches, the pool holds about 14,000 gallons.

Step 2 – Calculate the Gallons to Be Filtered in Eight Hours

How to select the correct filter size for your swimming pool

An excellent pool filter will clean all the water in the pool in eight hours. This is the minimum rate you want the pump to be able to work at. When we divide 14,000 by eight, we get approximately 1,750. Then divide that answer by 60. This yields the gallons per minute that must be pumped to filter all the water in eight hours. For our 14,000 gallon pool, the gallons per minute minimum is 30.

Step 3 – Determine the Maximum Flow Rate

Different pipe diameters can handle different flow rates. A 1-1/2 inch diameter pipe can carry about 45 gallons of water per minute. This is well above the minimum requirement for a 14,000-gallon pool. Choose a pool filter and pump with 1.5-inch piping, that is rated for a GPM between 30 and 45. Keep the pipeline as straight as possible, with few turns and rises. Most above ground pools use a powerful one horsepower pump and filter system to achieve the desired gallons per minute filtering rate. However, for the pool size in our example, a 3/4 horsepower filter will achieve the GPM rate desired with no problems.

Step 4 – Filter Systems

How to select the correct filter size for your swimming pool

There are three main filter systems used for both inground and above ground pools: diatomaceous earth (DE), sand, and paper cartridge. Any of these will keep your pool clean. If you desire a filter that has minimal maintenance with maximum performance, invest in a diatomaceous earth or sand filter. You will never have to change, clean or buy cartridges. The only maintenance needed is to backwash the filter, which is described in the filter manual. Choose the largest-capacity filter you can afford that will operate well with the flow rate of your pool. This will ensure the best performance with the least amount of maintenance time.

Step 5 – Install Your Pool Filter

Be sure your pool filter is set on a solid concrete base to reduce vibration. House the electrical system of the pump under a watertight cover to prevent electrocution.

Step 6 – Other Items to Install with Your Pool Filter

For non-cartridge filters, you will need to install a backwash hose, a sight glass pipe, and an air relief valve. Add a pressure gauge to all pumps that measure up to 60 psi. A pressure of 10 psi or more shows the filter needs cleaning.

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The swimming pool pump market can appear very complicated, so we have created 5 easy steps to help you choose the best pump.How to select the correct filter size for your swimming pool

Normally, you may consider replacing pumps like for like, however if the pump has failed prematurely, it may have been the incorrect pump and we recommend following our 5 easy steps to choosing the correct swimming pool pump. There is a tendency for people to buy bigger pumps than necessary. This is not recommended as you will suffer higher running costs, and run the risk of overpowering the filter, straining the pump and causing early failure.

The importance is not necessarily the power of the pump (HP or kW) but the flow rate.

According to swimming pool experts, as a general rule, all the water should be filtered within an 8 hour period.

To choose your swimming pool pump you need to know how many litres of water are in the pool, and then match this with the flow rates of a pump.

The following steps are a simple guide on how to do this:

Step 1:

Calculate the volume of your pool.

Volume/m 3 = Length/m x Width/m x Depth/m

If the pool is not all the same depth, you can use the average depth.

Same Depth: Different Depths:

How to select the correct filter size for your swimming pool

Average Depth = (shallow depth +deep depth)/2

Please note these images are for a rectangular pool.

If your pool is circular, you can calculate the volume using the formula:

V=π r²h

Worked Example for Rectangular Pool (same depth):

If you had a 20m pool, which was 8m wide and 1m deep, the Volume would be:

V= 20m x 8m x 1m = 160m 3

Step 2:

From step 1 you will be left with a value in metres cubed. This should be converted to litres.

1m 3 = 1000 litres.

Therefore, multiply your volume by 1000 to give the figure in litres.

For the worked example, this would be:

160m 3 x1000 = 160,000 litres

Step 3:

Calculate the required flow rate to circulate the pool in 8 hours.

As the water must all be circulated in 8 hours, you must divide the figure by 8 to give you the litres per hour figure.

For the worked example, this would be:

160,000L ÷ 8hours = 20000 L/h

Step 4:

Our pumps are rated in litres per minute, so the above figure must then be divided by 60 to give the litres per minute rate which can then be matched with one of our pumps, from either the SMP or SWIMM range.

For the worked example, this would be:

20000 L/h ÷ /60 mins = 333.3 L/m

You now should have a figure which is the flow rate required in litres per minute. Our swimming pool pumps have this figure detailed.

Step 5:

Select a pool pump from our range of swimming pool pumps which matches your requirements. Ensure the pump has an adequate head for your system.

For the worked example, from the SWIMM range, the SWIMM 1000 would be suitable with a flow rate of 350 Ltr/min:

How to select the correct filter size for your swimming pool

Please note:

The size of your pool filter is directly related to the size of your pump. If the filter is too small, this will put additional strain on the pump as it tries to force water through the filter and meets obstruction, causing friction. This may eventually cause the pump to burn out.

Most filters have a maximum flow rating. Ensure the pump does not exceed this. For example, if your pump output is 250 litres per minute, you should not pair this with a filter that has a maximum rating of 200 litres per minute.

Avoid downsizing the pipe for the pump as you run the risk of the pump running hot as it is starved of water.

Both our SWIMM and SMP range of swimming pool pumps are reliable and come with a 2 year warranty from the manufacturer. As always if you need any further assistance please feel free to call our UK helpdesk on 0115 987 0358.