Pool Pumps and Filters: How They Work

Whether you’re interested in DIYing your pool or are simply curious about how your pre-existing pool’s circulation works, you will need to get familiar with pool pumps and filters.

Pool pumps suck water by creating a vacuum with electric power and push it against a filter panel. The small pores on the panel keep impurities out while letting the water move to the next stage of the circulation, where it gets heated before being chlorinated.

This article covers the entire circulation process, including how water is brought to the lowest point for pump suction, what happens to it after it gets filtered, and the effects on the water at each stage of the circulation.

What Do Pool Pumps Do?

Pool pumps serve one essential function and one secondary function. The important function is to circulate the water, and the secondary function could be to heat the water or clean it; there is no third function that the pool pump would serve. Pool building and pool maintenance community will often use the terms pool pump and pool filter interchangeably, though these two are separate things, where one is nested within the other.

The pool filter rests within the pool pump mechanism, so a pool pump can exist without a filter. You can have a heat pump, for example, that does not have any filtration system. However, it is more likely to have a pool pump that is simultaneously responsible for heating and filtration.

However, it is wiser for better cleanliness and heating to have two separate systems though it might be an additional burden on the electric bill. A single circulation system with two different control panels for heating and filtering is the hybrid that is overall the most efficient and the most used system. That’s why it will be the one we explore in this post.

Why Are There Two Pumps in a Pool?

Before we get into where each component is placed, let’s discuss why the system is designed the way it is intended. Having different systems for heating and filtering that you can control separately requires fewer replacements. Another advantage is that both have separate pumps, which means that your pool does not become entirely unfunctional if one system fails.

Imagine having a pool party, and the heating system fails. Still, your pool at least has filtered water, and you can have hot water brought in from the shower in a few buckets and maintain a small pool’s temperature. Alternatively, it is also possible that your pool’s filtration system fails, which would severely limit the time you can give your guests in the pool, but at least the heating would be working. Having two separate systems is good for keeping the party going.

How Do Pool Pumps and Filters Work?

With pool pumps and filters defined separately, let’s look at how the overall system works. All you have to do is add or subtract the heating depending on whether it is included in your specific pool. If your pool is in a sunny state, you may not have inline heating. Simply ignore the heat-pump portion of this post in that case.

Water Goes Through the Drain

The first stage of the process is the suction, which removes water from the pool and runs it through skimmers, then the filter panel. But to realize solely on electricity-powered suction of the filter pump would be to drive up your electricity bill. Instead, most pools rely on gravity to do most of the water removal work.

Drains are usually positioned strategically towards the end of the pool and at the lowest level, where water cannot help but go through the drain.h This is also the reason why most pool floors are built at a slight slope. 

Usually, the drain also has a grill that acts as the first-degree skimmer that holds the larger residue and debris. And as the water goes through the drain, most of the chunkier dirt and the unclean residue are caught and kept from going into the finer pipes, which would otherwise be clogged.

Water Reaches the Skimmers

There are also second-degree skimmers positioned behind such drains and grills. And these skimmers are responsible for removing even smaller dirt particles like tiny blobs of clay, broken-up dry leaves, and small pebbles.

Filter Panel Pulls Water up and Across the Filter

Finally, water reaches the lowest point outside the pool, and the pump suction comes into play. Once the water has reached a low enough level to be pushed through a filter panel, the filter pump gets to work by vacuuming it up and across the filter panel.

A filter panel is fine enough to take out the smallest visible impurities, including individual sand particles. And because it is that restrictive, gravity cannot be responsible for pushing water through it at a rapid enough pace. 

Think about water dripping through a tiny hole at the bottom of a plastic tumbler. While gravity will have the water moving through that pore, it will not go through that hole at a rapid enough speed to create the kind of stream that you witness in a swimming pool.

In other words, it would be impractical for a filtration or circulation system to rely solely on gravity to move water through a filter panel. That’s why a filter pump is essential. A filter pump is responsible for suction and exertion. Water is sucked from the lowest point and taken out of the swimming pool, and pumped through the filter panel until it reaches the other side of the filter.

Water Reaches the Heat Pump

Once the water has been passed through the filter, it is time to heat it. Some readers might wonder why the heating doesn’t happen before the water is filtered. If the heater was positioned before the filter, it would heat impurities, and impure water gets heated quicker, depending on how dirty or contaminated the water is.

Getting heated quickly isn’t the problem. The issue is that depending on how impure or clean the water is, the time it takes to reach a certain temperature can vary. This makes heating unclean water entirely unreliable. 

One cannot know how much the water temperature will depend on the settings of the water heater. The pool water would come out hotter or colder with the same heat settings just because it doesn’t have the same degree of cleanliness in each circulation.

To make water heating predictable, you need to only pump filtered water to the heater. As long as the water that goes through the heater is at a constant chemical and cleanliness composition, one can reliably predict the level of water heating required and the electricity needed for the same.

The water heater often has its pump. That way, the filter pump does not have to sustain the burden of pumping water through both the very restrictive filter panel and the heater. The further the water goes, the longer, the harder it becomes for a pump to keep pushing water. That’s why there are multiple pumps throughout the circulation system, depending on how elaborate your swimming pool’s plumbing is.

Having a filter pump followed by a heat pump within a single circulation system is the average home swimming pool plumbing set up for. The heater works in pretty much The same way as a water heater for your shower or bathroom. The only way it deviates is that water pressure is maintained through a pumping mechanism, which is usually absent in shower geysers.

Water Gets Heated

This is similar in that the water goes in cold and is heated with coils and hot air, after which it is sent out through the water outlet on The other end of the heating system. Most heating systems have remote control options as well as On-system control. 

That’s because if your pool is in-ground, the circulation system Is hard to access. Therefore, you need remote control. For above-ground pools, an attached control panel makes it easy For you to change the temperature.

Water Gets Treated

The final contraption in the water circulation system for a swimming pool is likely to be a chlorinator. You can also have a saltwater generator at this point in the circulation system. This is an optional step not because chlorine or salt aren’t essential in the water. It is optional only because automating this process leaves little room for error.

Chlorination via gadgets is not essential if you can be diligent and use pool chemicals and shock the pool manually, but it is better to have a chlorinator or a saltwater generator. That way, the water that keeps circulating also stays free of microbes. Remember that circulation, first of all, keeps the water from stagnating or making it attractive for insects to lay eggs. It discourages the propagation of Amoeba or Algae.

While circulation in itself is a safety measure, filtration improves water safety as it removes dirt and other impurities that make water more attractive for microscopic life forms to build colonies. However, water can still have microscopic life forms. Bacteria and fungi that aren’t visible are too small to be filtered by an average swimming pool filter panel. That’s why it is crucial to have chemicals that make the water organically inert.

In other words, no life form other than the individuals in the swimming pool gets to live. And for that, you need enough chlorine to overpower whatever potential invisible microscopic life form might be crawling around in the water.

The Underappreciated Components of Pool Circulation


When circulating water through a filtration and heating system, you must keep in mind that pressure can vary within each loop. You can have water held up in the heating loop, the filter panel, or the chlorinator. And depending on where the water is held up, its flow might get reversed. That’s where the unsung heroes of water circulation come in the form of check valves. Check valves are one-way valves that make sure that water only flows one way.

You do not want water to start flowing back through the drain just because a filter takes a lot longer to push water through. When water is pushed through a layer with fine pores, there is significant resistance and friction.

To understand resistance, you have to picture water being run through the filter panel, as it is pushed through a wall with tiny holes that lets water come out but keeps impurities even as small as individual sand particles from going through. You can visualize how such a wall could generate significant pushback.

Without the presence of check valves, this could easily lead to the water flowing back. Check valves are also important for leak tests and pressure adjustment. You have to realize that water circulation is not just a function of practicality but also a matter of enhancing the swimming pool experience. 

Most kids can relate to jumping into the pool and standing right by the water inlet to actually enjoy the artificial waves formed by pressured water coming back into the pool. Most specialized leisure pools have wavemakers for this very function, but good water pressure is only possible with valves turned to a specific degree.

The Skimmer Box and the Drain

Finally, we have a duo that is as essential as any other component: the skimmer box and the drain. Though water is fed through gravity to the filter pump, it goes through two inlets that merge into a single tube once they reach the filter pump. 

These two are the drain and the skimmer box. The drain has a grill that acts as a skimmer, whereas the skimmer box is more specialized towards skimming and is situated much higher. It also prevents the overflow of water.

These two inlets are initially separated because the skimmer box alone can’t do the job. It needs a certain level of water before it can start draining the rest. If the swimming pool’s water levels are too low, the skimmer box and the tube that leads the water from the skimmers to the filter inlet can run dry, which might damage your filtration system.

The drain on the other end does not run that risk. Once you are closing the pool for the year, you need to use antifreeze and apply it both in the skimmer box tube and the drains so that the pool is functional when the swimming season arrives. 

Usually, if you keep the water levels to at least half the height of a skimmer box, your circulation system will not run dry. However, if you fail to acknowledge that water levels go down due to harsh summer weather or low water supply, you might incur some filtration and circulation repair Costs.

Circulation System Installation and Operation Mistakes

Not Getting the Right-Sized Pump

When you install a water filtration system for your pool, you’re supposed to get the right-sized pump. If your pump is too big for your swimming pool, you will run up your electric bill while turning your swimming pool into a stormy home sea. You might have to use your check valves and other pressure adjustment devices to nerf the filter pump, but it will still cost more to run.

On the other hand, if you go too conservative and use a pump too small, it might not circulate the water at an optimal speed or the ideal quantity, which would, in turn, affect the water purity levels.

Therefore, consulting with a pool builder or even reading the instructions on the pool pump package would provide you with insights as to whether the pump is suitable for your pool or not. Most pool pump, packaging, and sales pages include information regarding the pool size for which the pump is appropriate.

Not Running the Pool Pump Enough

Once you get the right pool pump for your specific home pool, you will need to run it enough. If you do not run it enough, it doesn’t matter that your skimmers are receiving enough water; the pump will run dry. you need to run the pump regularly for the mechanism to keep working.

In fact, using a pool pump once or twice during the pool closing season is recommended for smaller pools because it is feasible. However, running water through a large pool’s circulation during closing season can’t be practically done when a pool is outdoors and closed.

Run pool water through the system once or twice a year during the non-swim season if you live in an area where the swimming season lasts only a few months. You need to run your pool pump so that water can go through it once or twice during the year just so the pool pump remains active. 

Of course, antifreeze and other freeze-fighting solutions also help, but nothing can replace water going through the pool pump and the fuel pump having to work. With the system that is as intricate and long as water filtration and heating systems in a swimming pool, there is a use it or lose it tendency.

Final Thoughts

When it comes to water circulation, pool pumps are essential though gravity is step one in removing water from most pools. It is the job of a pool pump to not only suck water out of circulation but also push it through the filter panel. Moreover, there is a heater attached on the other end, which can have its pump that forces the water out the other end, heated and ready to go through an auto-chlorinator.

Jed Arnold

Jed spent every year from the ages of 15 - 22 as a Lifeguard (Red Cross) and ages of 17 - 22 as a Certified Pool Operator (CPO). Between working for over a dozen facilities and owning a pool, he carries over a decade of pool experience.

Recent Posts