If you’ve ever peered into a pool skimmer, you might have noticed something peculiar—two small holes at the bottom. It’s easy to dismiss these as drainage points or remnants of manufacturing. But the truth behind their purpose is far more fascinating and essential to the efficient operation of your pool. In this article, we’ll explore the functional importance of the dual openings in a pool skimmer, how they work in tandem with your pool’s filtration system, and why understanding this can lead to better pool maintenance and energy savings.
The Basic Function of a Pool Skimmer
Before diving into the significance of the two holes, let’s first establish the role of a pool skimmer. A skimmer is a critical component of a swimming pool’s circulation and filtration system. Installed at the edge of the pool and partially submerged just below the water surface, the skimmer’s primary purpose is to draw in water from the surface, along with floating debris—like leaves, bugs, and oil from swimmers—to prevent them from settling and contaminating the pool.
The skimmer includes a removable basket that catches larger debris before the water moves deeper into the filtration system. This helps reduce strain on the pump and filter while keeping the water cleaner at the surface.
The Mystery of the Two Holes
Now, back to the main question: why are there two holes in the bottom of a pool skimmer?
There are two primary holes located at the bottom of the skimmer. One is significantly larger and serves as the main water inlet, connecting directly to the pool’s pump. The other is a much smaller hole—usually no more than an inch in diameter. At first glance, this tiny orifice might seem unimportant, even ornamental, but it plays a crucial role in the skimmer’s operation and safety.
The Main Water Inlet
The first—and typically larger—hole is the main water intake for the skimmer. Water drawn in from the surface passes through the basket and then out this opening into the plumbing lines that lead to the pump and filter. This hole is directly connected to the pump’s suction line and works continuously when the pump is running, helping to circulate the pool water and maintain cleanliness.
Proper skimming action via this hole ensures that contaminants on the surface are removed before they have a chance to sink and contribute to cloudy water or algae growth.
The Equalizer Hole (or Auxiliary Hole)
The second and smaller hole is commonly known as the equalizer hole or auxiliary hole. While it looks minor, its role in the pool system is anything but negligible. The equalizer hole serves multiple purposes:
- To prevent the pool pump from running dry if the water level drops too low.
- To facilitate smooth and uninterrupted water flow from the skimmer, even when the water level fluctuates.
- To protect the pump motor from damage due to airlocks or cavitation.
Let’s explore each of these points in more detail.
The Protective Role of the Equalizer Hole
The equalizer hole is a safety feature designed to prevent a potentially catastrophic scenario: the pump running dry. When the water level in the pool falls below the skimmer’s intake—either due to evaporation, splash-out, or a leak—the skimmer could potentially pull only air through the main suction line.
This can lead to several issues:
Airlocks and Loss of Prime
Pool pumps need to be primed, meaning they must be filled with water to create the necessary suction. If the skimmer begins drawing air instead of water, the pump may lose its prime, resulting in reduced efficiency or a complete cessation of water flow through the system.
Pump Damage and Overheating
When a pump runs dry, it lacks the water needed to cool the motor’s internal components, particularly the shaft seal. This can cause the seal to overheat, wear out prematurely, or fail completely. Replacing a burnt-out pump or seal can be both costly and inconvenient.
This is where the equalizer hole comes in.
How the Equalizer Hole Works
When the water level in the pool drops below the skimmer’s mouth, the equalizer hole—which is positioned lower than the main skimmer intake—remains submerged. It connects to the pool’s main drain line or sometimes opens directly into the pool body below the skimmer lid.
This low-positioned hole allows water to continue feeding the pump even when the main skimmer intake isn’t submerged. Essentially, it ensures a steady supply of water to the pump to avoid airlocks and motor damage. It acts like a backup water source during water level fluctuations.
Think of it as the pool system’s built-in failsafe. The equalizer hole keeps your system running longer and more efficiently, even during minor water level drops.
Technical Details and Variations
Different pool designs and skimmer models may influence how the equalizer hole is implemented, but the fundamental concept remains the same.
Connections and Plumbing Paths
In many pool setups, the equalizer hole connects to the main drain via the pool’s return line. In some configurations, it may connect directly to the pump’s suction line. This connection allows water to be drawn from a lower point when the skimmer mouth is out of reach of the water line.
Importance in Closed-Loop Systems
Pools with more than one skimmer often rely on the interplay between skimmers and equalizer holes to maintain system performance. In a multi-skimmer system, if one skimmer becomes air-bound, the other can still function and potentially draw water through the auxiliary openings, maintaining functionality.
Design Variations Across Brands
While most skimmers will include a dual-hole setup, some manufacturers offer adjustable or modifiable auxiliary systems. For example, some skimmers come with a threaded plug or valve that allows pool owners to control the amount of water drawn through the equalizer hole, which can be beneficial in fine-tuning the balance of water return and pump safety.
However, the vast majority retain the standard two-hole design with the smaller one serving specifically as the equalizer opening.
Real-World Implications: Why This Matters for Pool Owners
Understanding the dual functionality of the skimmer’s bottom holes isn’t just an academic exercise—it has real implications for the longevity and performance of your pool system.
Efficient Water Circulation
The two-hole design ensures that surface water—and its load of oils, pollen, and other floatables—is consistently removed, contributing to better circulation and more effective use of filtration.
By preventing sudden disruptions in suction, the skimmer keeps water moving through the system without unnecessary strain, which results in clearer, healthier water over time.
Energy and Cost Savings
When a pool pump runs inefficiently, it draws more power, increases energy bills, and wears down faster. The equalizer hole helps maintain consistent suction, optimizing pump performance and reducing long-term energy consumption.
This simple hole prevents potential downtime in your filter cycle, allowing your pool to remain clean without unnecessary manual intervention.
Safety and Maintenance
From a safety standpoint, the equalizer hole is like a miniature insurance policy for your pump. You’re less likely to encounter sudden failures caused by air entrapment, and that means fewer service calls, fewer replacements, and a longer-lasting system.
Moreover, having this extra pathway helps pool maintenance professionals assess system flow. A blocked equalizer hole can be a sign of plumbing issues or buildup, making it a useful diagnostic point.
Common Problems and How to Address Them
Despite its utility, the equalizer hole can—on occasion—cause or indicate problems. Let’s walk through a few of the more common issues related to the two skimmer holes.
Blockage in the Equalizer Line
If debris or scale buildup blocks the pathway from the equalizer hole to the pump or drain line, the backup function can fail. Signs of this include:
- Increased air bubbles in the pump basket.
- Inconsistent water flow from the skimmer.
- Overheating and vibration in the pump motor.
You can help prevent these issues by routinely checking both the skimmer basket and the small inlet opening for debris. Some pool owners flush the line behind the equalizer hole during maintenance to ensure full flow.
Improper Water Level
One of the biggest contributors to skimmer inefficiency is incorrect water level. If the water sits too low, not only does the main skimmer stop functioning, but the equalizer line may not provide enough suction to make up the difference.
The ideal water level is typically one-third to half the way up the skimmer mouth. This ensures both the main skimmer line and the equalizer line have sufficient water access and work together optimally.
Corrosion or Damage to the Hole
Over time, especially in pools using aggressive chemicals or in coastal environments, the skimmer and its components can corrode. The equalizer hole may narrow or rust over, especially if made of metal, compromising its effectiveness.
In such cases, a replacement skimmer lid or housing is recommended.
Myth: Two Holes Cause Water Loss
Some pool owners mistakenly believe that the secondary hole “wastes water” or increases evaporation. This is a misconception—the equalizer hole is not open to the air; it’s a sealed plumbing connection. It allows water to pass only when the system is actively pulling from it. Under normal conditions, it has no impact on water loss or chemical consumption.
Best Practices for Maintaining the Skimmer and Its Holes
To get the most out of your pool skimmer and its dual functions, consider these maintenance tips:
Regular Inspection of Skimmer Holes
Check the equalizer hole during routine maintenance. If using a non-transparent lid, you can remove it and visually inspect the small orifice for build-up or blockage.
Keep the Water Line Consistent
Make it a habit to check and adjust your pool water level weekly, especially during dry or hot seasons. A pool cover can reduce water loss and help maintain optimal level.
Annual Plumbing Inspection
Have a professional inspect your plumbing lines annually, including the connections and pathways used by the equalizer hole. This can detect issues such as leaks or blockages early.
Replace Damaged Skimmer Lids or Housing
If you notice cracks, warping, or deterioration in your skimmer components, replace them. A compromised lid can lead to reduced performance, and a damaged equalizer tube can affect pump function.
Conclusion: A Small Hole That Makes a Big Difference
The dual-bottom hole design of a pool skimmer isn’t just an engineering artifact—it’s a carefully considered feature that contributes to the overall efficiency, safety, and longevity of your swimming pool system. The main water inlet ensures surface-level debris removal, while the equalizer hole safeguards the pump and ensures continued operation even under less-than-ideal water conditions.
Understanding this design gives pool owners and service professionals alike a deeper appreciation for how each small component works in harmony to maintain a clean and functional swimming environment. By respecting and maintaining these small features, you’re taking a crucial step toward a longer-lasting, trouble-free pool system.
So next time you peer into your skimmer, don’t overlook those two unassuming holes at the bottom. They’re more important than they look—and your pump will thank you for it.
Why are there two holes in the bottom of a pool skimmer?
The two holes at the bottom of a pool skimmer serve specific and important functions in maintaining the overall efficiency of the pool’s circulation and filtration system. One hole is connected directly to the pool pump, creating a primary suction point that pulls water and surface debris into the skimmer. This ensures the skimmer can effectively draw in floating debris such as leaves, insects, and oils before they sink to the pool floor or clog the filter.
The second hole, commonly referred to as the “equalizer” or “backup” line, is positioned slightly lower and is designed to prevent the pump from drawing air if the water level in the pool drops below the skimmer’s main opening. By allowing water to enter from a lower point, the equalizer line helps maintain prime in the pump system, preventing damage that could be caused by airlocks or dry running. This dual-hole design is a safety feature that helps protect both the pump and the filtration system.
What happens if a pool skimmer only has one hole?
If a pool skimmer only had one hole, the system could run into several issues, especially related to pump performance and skimming efficiency. The main hole is connected to the pump, and without a secondary equalizer hole, a drop in water level could expose the skimmer’s primary inlet, allowing air to be sucked into the pump. This air intake can cause the pump to lose prime, reducing filtration efficiency and potentially damaging the pump motor due to overheating or cavitation.
Additionally, the absence of an equalizer line might reduce the effectiveness of debris collection. In the event that the skimmer basket becomes clogged or the water level drops slightly, the continued flow of water could be compromised. The second hole ensures a consistent water flow to the pump, maintaining a steady turnover rate, which is essential for keeping the pool clean and chemically balanced. For these reasons, a skimmer with only one hole would be incomplete and functionally inadequate in most pool systems.
What is the purpose of the equalizer line in a skimmer?
The equalizer line, or the second hole in the bottom of a pool skimmer, is primarily designed to maintain consistent water flow to the pool pump, especially during fluctuations in the pool’s water level. Situated lower than the main skimmer opening, this line allows water to continue entering the system even when the main skimmer weir (the flap that opens and closes with the water flow) is not submerged. This feature helps prevent the pump from drawing air, which can cause operational issues such as loss of prime or equipment damage.
Beyond protecting the pump, the equalizer line serves a secondary filtration function. By providing an alternative inlet, it enhances the ability of the system to circulate water when the pool’s surface is disturbed, such as during windy or rainy conditions. Although the equalizer doesn’t actively skim surface debris, it plays a supportive role in ensuring water is consistently moving through the system, contributing to overall pool cleanliness and helping maintain balanced chemical distribution.
Can both skimmer holes be used simultaneously?
Yes, both skimmer holes can and often do work simultaneously, especially when the water level in the pool is balanced and the system is functioning correctly. The main skimmer hole, which is higher, is responsible for capturing surface debris, while the lower hole (the equalizer line) draws in water from a lower point. When the water level is optimal, both lines contribute to the overall suction and flow of water toward the pump.
However, there are situations where the equalizer line becomes more active, such as when the water level drops slightly or when surface turbulence increases. In these cases, the equalizer line ensures the pump doesn’t pull air, which would disrupt the system. While both lines operate together under normal conditions, they are designed to complement each other and maintain system stability, even when water levels fluctuate, preventing system inefficiencies and protecting pool equipment.
Is it safe to block the second hole in a pool skimmer?
Blocking the second hole in a pool skimmer is generally not recommended because it eliminates an important safeguard for the pool’s circulation system. This second hole serves as a backup inlet that keeps water flowing to the pump in case the pool’s water level drops below the main skimmer opening. If this equalizer line is blocked, the pump could start pulling air, which may cause it to lose prime or suffer mechanical damage over time due to overheating or cavitation.
While some pool owners may consider blocking the second hole to increase suction power at the main skimmer, the trade-off can lead to more serious issues. Any minor improvement in skimming performance would not outweigh the risk of potential pump damage. Moreover, inconsistent circulation can lead to dead zones in the pool where water doesn’t circulate properly, increasing the risk of algae growth and chemical imbalance. Maintaining both holes ensures the pool system functions efficiently and safely.
How does the skimmer’s second hole help protect the pool pump?
The second hole in a pool skimmer, known as the equalizer line, helps protect the pool pump by providing a secondary source of water in case the water level in the pool drops below the main skimmer opening. This hole is positioned lower in the skimmer and isn’t affected as quickly by minor fluctuations in pool water levels. As a result, even if the main skimming port becomes exposed, water can still be drawn into the system through this second hole, preventing the pump from sucking air and potentially losing prime.
Losing prime can cause the pump to run dry, which may lead to seal damage or motor overheating. The equalizer line acts as a failsafe, ensuring that water continues to flow and maintain the prime in the pump system. This is particularly important during periods of heavy evaporation, splashing, or when the pool is being used frequently. By keeping water flowing, the second hole supports the longevity of the pump and the overall functionality of the pool’s circulation system.
Does the second hole in the skimmer affect skimming performance?
The second hole in the pool skimmer, while essential for system stability and pump protection, does not significantly contribute to active debris skimming. Located below the main skimmer opening, this equalizer line primarily serves as a backup water source to maintain suction and prevent the pump from drawing air. Because it sits lower and is not directly under the pool surface, it doesn’t draw in floating debris like the main skimmer hole does.
However, the equalizer line can have an indirect effect on skimming performance by ensuring more consistent water flow through the system. If water flow is disrupted, the pool’s turnover rate decreases, which means debris may not be collected as efficiently. Maintaining both holes ensures that the pump runs smoothly and the skimmer can continue to function optimally. So while the second hole doesn’t actively skim, it helps sustain the conditions necessary for effective skimming and overall pool maintenance.