Swimming pools are a significant investment, providing hours of relaxation, physical activity, and social enjoyment. But behind the leisurely scenes lies a well-engineered system of components that ensure your pool remains clean, safe, and functional. One of the most critical elements in this system is the main drain. If you’re planning to install a new pool or are considering upgrades to your existing one, a common question pops up: How many main drains should a pool have? This guide dives into the intricacies of pool drainage systems, helping you understand what’s best for your unique situation.
Understanding the Role of Main Drains in Pool Systems
Before determining the number of main drains your pool needs, it’s essential to understand their function. Main drains are located at the deepest part of the pool and serve as the primary means for water to exit into the filtration and circulation system. When the pump is running, water is drawn from these drains, circulated through the filter, heater (if applicable), and then returned to the pool via the return jets.
While skimmers handle surface water and debris, main drains are responsible for managing the turnover of deeper water. Their importance extends beyond basic hygiene—they also play a role in preventing entrapment hazards and promoting even water temperature and chemical distribution.
Pool Types and Their Drainage Requirements
The number of main drains you should install or maintain depends heavily on the type of pool you have.
1. Inground Pools
Inground pools are the most common type and typically require at least two main drains. This is a requirement under the Virginia Graeme Baker Pool and Spa Safety Act (VGB Act), which was enacted to prevent entrapment deaths due to suction from a single drain. Each drain must be spaced apart and connected to the pump in a way that eliminates the risk of strong suction from a single point.
2. Above Ground Pools
Above ground pools often have different drainage setups. Depending on their size and structure, some models may not come with main drains at all and rely solely on the skimmer for water circulation. However, if a main drain is offered by the manufacturer, it’s often a single drain due to structural limitations. The VGB Act may not apply to above ground pools in all cases, but safety should remain a priority.
3. Commercial Pools
Pools in commercial applications, such as hotels, water parks, and recreation centers, have stricter regulations. These facilities must adhere to state and local health department codes and may require multiple main drains proportional to the pool’s size and usage level.
Key Factors Influencing the Number of Main Drains Needed
Several variables contribute to determining how many drains your pool should have. These include:
1. Pool Size and Surface Area
The larger the pool, the more likely it is to require multiple main drains. Water turnover efficiency decreases with large volumes, and circulation from the pool’s bottom becomes increasingly important.
- Small pools (under 300 square feet): One main drain might suffice.
- Medium-sized pools (300–700 square feet): Typically require at least two drains.
- Large pools (over 700 square feet): May require two or more drains, depending on configuration.
2. Pool Geometry and Depth Variations
Rectangular, L-shaped, or kidney-shaped pools may have areas where water stagnates. Main drains strategically placed at the lowest points of each distinct section will improve flow efficiency and reduce sediment buildup.
3. Local Building and Safety Codes
Always check local codes before installing or modifying your pool’s plumbing. States such as California and Texas have stringent guidelines regarding multiple main drains in residential pools, while others may follow federal guidelines more closely.
4. Purpose of the Pool (Recreational vs. Competitive vs. Therapy)
Pools used for high-intensity activities—like lap swimming or hydrotherapy—often need enhanced circulation systems, which may include additional main drains along with specialized jets and filtration mechanisms.
The Science of Water Circulation and Drain Placement
Proper circulation is key to maintaining a clean and safe pool. A good circulation system ensures that all water, from surface to bottom, passes through the filter and chemical dispensers.
Hydrodynamics 101: How Water Flows in the Pool
Water doesn’t just sit still; it moves, circulates, and settles. The ideal system balances this to:
- Prevent stagnant zones.
- Suck debris downward into filters, not allowing it to float.
- Maintain even chemical distribution.
Main drains play a crucial role in this downward movement and should be positioned with a hydrodynamic engineer if the pool is particularly large or oddly shaped.
Optimal Drain Placement Strategies
Main drains should be positioned at the lowest point or points of the pool where water can collect debris and cool water settles. The drains must be spaced at least 3 feet (0.9 meters) apart to comply with VGB safety standards. The design should avoid proximity to steps, benches, or other features where a swimmer may sit or lay on the drain cover.
Example Placement in a Rectangular Pool
| Pool Size | Recommended Number of Main Drains | Ideal Placement | Notes |
|———–|———————————-|——————|——-|
| Up to 15,000 gallons | 1 | Single deep end | Only for small above-ground pools |
| 15,000 – 20,000 gallons | 2 | Both deep ends, or diagonally from one | VGB-compliant |
| Over 20,000 gallons | 3 or more | Multiple deep or bottom points | Commercial-grade consideration |
Safety Considerations with Main Drains
The importance of safety cannot be overstated. The horrific incident involving Virginia Graeme Baker in 2002, where she was entrapped by a hot tub’s powerful suction, led to life-changing legislation.
VGB Compliance and Its Implications
The VGB Act requires that all public and private pools must have:
- At least two main drains (unless the suction outlet cover meets performance standards designed for single-drain setups and is vacuum release system compliant).
- Drain covers that meet ASME/ANSI A112.19.8 performance standards.
- A safety vacuum release system (SVRS) or other entrapment prevention devices.
Entrapment Hazards and How to Prevent Them
There are several types of entrapment:
- Body entrapment: A body part or the entire person is trapped by drain suction.
- Hairstyle entrapment: Hair gets caught in the drain.
- Limbs entrapment: Arms or legs get stuck.
Using multiple drains in different parts of the pool reduces the risk of strong localized suction. Installing VGB-compliant covers and automatic safety shut-offs further reduces danger.
Maintenance and Inspection of Main Drains
Drains may be out of sight, but they shouldn’t be out of mind. Regular inspection and maintenance are critical to ensuring that drains continue to function correctly and safely.
Signs of Drain Issues
- Reduced pump performance or pressure.
- Visible hair or debris trapped under drain covers.
- Cracks, chips, or dislodged grates.
- A “gurgling” sound when the pump runs.
How Often Should You Inspect Drains?
- Visually inspect drain covers monthly.
- Hire a professional to clean and check all components every 3–6 months.
- Replace covers every 5–7 years or immediately if damaged.
Upgrading Your Drain System: When and Why
Sometimes, modifications or upgrades are necessary to improve safety, efficiency, or compliance.
When to Consider Adding Additional Drains
- When converting a small in-ground pool into a larger one.
- If building or rebuilding with outdated drain systems.
- If you add features like benches or deep ends not originally planned.
Retrofitting Older Pools
If your pool was built before the VGB Act (2008), you may be non-compliant with current safety standards.
Retrofitting Options Include
- Installing a second drain.
- Replacing old drain covers with VGB-compliant models.
- Adding an SVRS (Safety Vacuum Release System) or pump monitoring device.
Choosing the Right Drain Covers
The type of drain cover you use matters just as much as the number.
Types of Drain Covers
- Dome-style covers: Rounded and reduce the risk of entrapment by minimizing direct contact with body parts.
- Flat covers: Commonly used, especially in older pools, but may be less safe if not VGB-compliant.
- Anti-entrapment covers: Designed specifically under VGB standards to evenly distribute suction.
Material and Durability
Choose covers made of durable, non-corrosive materials like:
- Stainless steel
- ABS plastic
- Fiberglass-reinforced resin
Durability reduces the need for replacements and increases long-term safety.
Common Mistakes Pool Owners Make with Main Drains
Avoiding these mistakes will keep your pool functioning optimally and safely.
Mistake #1: Overlooking VGB Standards
Some assume that if their pump runs well, drains must be safe. However, compliance and safety are not optional, especially with multiple occupants or families with children.
Mistake #2: Wrong Placement
Drains installed directly under return jets or near seating areas can create dead spots in circulation or entrapment zones.
Mistake #3: Neglecting Covers
Old or cracked drain covers can compromise safety even if the system is otherwise compliant.
Conclusion: Pool Main Drains — More Than Just Plumbing
Knowing how many main drains your swimming pool should have isn’t just a matter of plumbing codes — it’s about making an intelligent, safe, and long-lasting investment. Whether you’re building a new pool or retrofitting an existing one, the key point to remember is that a minimum of two main drains is generally recommended and required by law under the VGB Act for inground pools. Considerations like pool size, local codes, safety standards, and maintenance strategies should all guide your decision-making process.
By ensuring that your pool’s drainage system is optimized, you contribute to:
- Enhanced filtration and water clarity.
- Reduced chemical consumption.
- Lower maintenance costs.
- Greatest safety for all swimmers.
Proper planning and regular attention to pool drains will extend the life of your equipment, prevent dangerous incidents, and ensure your swim space remains clean, safe, and enjoyable for years to come.
Need help determining how many main drains are best for your specific pool design? Contact a certified pool professional or local technician. Remember, your pool’s safety and efficiency begin at the bottom — literally.
How many main drains should a pool have?
The number of main drains a pool should have primarily depends on the pool’s size and surface area. According to the U.S. Consumer Product Safety Commission (CPSC) and the Virginia Graeme Baker Pool and Spa Safety Act (VGB Act), any pool with a bottom drain must have at least two main drains. These requirements are in place to prevent dangerous suction entrapment hazards.
For larger pools, it is recommended to have additional drains based on local codes, generally allowing one main drain per 400 square feet of pool surface area. Proper drain placement and the use of anti-entrapment covers are also important factors in ensuring swimmer safety and balanced water circulation throughout the pool.
Why are multiple main drains important for pool safety?
Multiple main drains reduce the risk of dangerous suction entrapment by distributing the suction force more evenly. If a single drain is blocked, such as by a swimmer’s body part, hair, or clothing, the suction force can become strong enough to trap the individual. Having at least two drains significantly lowers this risk because each drain divides the suction pressure.
Furthermore, modern pool safety standards require that dual drains be spaced far apart and equipped with anti-entrapment covers that meet VGB certification. These dual systems are designed to ensure that if one drain is obstructed, the remaining drain can still function, avoiding the potential for life-threatening entrapment situations.
What are the differences between main drains and other types of pool drains?
Main drains are located at the deepest part of the pool and are designed primarily to draw water toward the pump for circulation and filtration. They are essential components of a pool’s circulation system and are particularly important during pool draining or major maintenance. Main drains should not be confused with skimmers, which are located at the water’s surface and are used to catch floating debris.
Additionally, some pools have secondary drains or emergency drains that are used under specific circumstances such as hydrostatic pressure relief or during drainage procedures. These drains serve different purposes than main drains and are often not part of the filtration system’s routine operation. Understanding the role of each drain type is key for proper pool maintenance and safety compliance.
How does pool size affect the number of main drains needed?
Larger pools require more main drains to maintain safe and efficient circulation. As per industry guidelines, one main drain should be installed for every 400 square feet of pool surface area. This ensures that water is drawn evenly from the pool floor, reducing the risk of improper flow and dangerous suction at any individual drain.
In smaller pools or spas that are less than 400 square feet, at least two drains are still required for safety reasons, even if the flow rate doesn’t strictly require it. The dual drain requirement is a fundamental safety measure that addresses potential suction entrapment dangers, regardless of the pool’s size. Local regulations may vary, so consulting local codes is also essential.
Can I install only one drain if my pool is small?
While it might seem logical that a small pool only needs one drain, current safety standards require at least two main drains regardless of the pool’s size. This provision is part of the VGB Act and is based on safety concerns related to suction entrapment. Even in small pools, having only a single drain can pose serious risks if the drain cover becomes blocked.
Although a small pool may not require the additional water flow provided by multiple drains, the safety benefits of a second drain outweigh the minimal extra cost and effort of installation. Pool owners must follow these requirements to meet legal safety standards and reduce the chance of injury or drowning incidents related to drain entrapment.
What should I consider when placing main drains in my pool?
Proper placement of main drains is critical for safety and functionality. Drains should be spaced sufficiently apart so that a person cannot block both with the same body part at the same time. The CPSC recommends that dual drains be placed at least 3 feet apart, although local building codes may specify greater distances depending on the region.
Additionally, it is important to ensure that main drains are installed at the deepest point or points of the pool to effectively collect debris and water for circulation. The slope and design of the pool floor should direct water toward the drains. Drain covers must also be VGB-compliant and inspected regularly to ensure they are in good condition and free of damage.
What are the consequences of not having enough main drains?
Having insufficient main drains can lead to several serious issues, including the risk of suction entrapment. This can cause injuries or fatalities, particularly to children who might be more vulnerable to the powerful suction of a single blocked drain. In addition to the safety hazard, inadequate drainage can compromise the pool’s circulation system.
Poor circulation due to too few or improperly spaced main drains can result in stagnant areas where water does not circulate effectively, leading to algae growth and water chemistry imbalances. Pools that do not meet the VGB Act’s requirements may also be in violation of local or national safety regulations, which can result in fines, liability in the event of an incident, or difficulties when selling the property.