Most pool owners can tell you exactly what equipment they have — the pump brand, the filter type, whether they’re running a saltwater system or a heater. But ask about pipe sizes and most people go quiet. It’s one of those behind-the-scenes details that rarely gets discussed — until something goes wrong, or until it’s time to upgrade equipment and you realize the pipe running underground doesn’t match what you’re trying to connect.
For gunite pool owners, especially, understanding your pool’s plumbing is worth the time. Gunite pools are permanent, custom-built structures — and the plumbing installed during construction is encased in concrete and buried underground. There’s no pulling it out and starting over without a major renovation. Getting it right from the beginning matters enormously, and knowing what’s in the ground helps you make smarter decisions for every equipment upgrade, repair, and renovation down the road.
How Pool Plumbing Works
Your pool’s plumbing system has two sides: the suction side and the return side.
Suction lines carry water away from the pool — pulling from the skimmers at the surface and the main drains at the floor — and deliver it to the pump. The pump draws the water through and pushes it into the filter, heater, salt cell, or any other inline equipment.
Return lines carry that cleaned, treated water back to the pool through the return jets in the walls. Return jets create circulation patterns that prevent dead spots where algae loves to grow. Sublime Pools
Everything in the system depends on these two pipe networks being properly sized. The movement of water to and from your swimming pool depends more on pipe size than pump size — you can put a larger pump on a pool with larger pipe, but you can’t put a larger pump on a pool with smaller pipe.
What Size PVC Pipe Is Used in Gunite Pools?
Inground pools are typically plumbed with either 1.5″ or 2.0″ PVC pipe — and it’s not uncommon to find both sizes used in the same system. In a well-built custom gunite pool, the sizing is intentional and different for each side of the system. In the Swim
Suction lines (skimmers and main drains): 2″ PVC
Suction lines carry the heaviest volume of water and are the most demanding part of the system. Using 2″ on suction lines allows the pump to pull water from a single line without cavitation occurring. Cavitation happens when the pump isn’t getting enough water due to an undersized pipe — it strains the pump, reduces efficiency, and shortens equipment life significantly.
Return lines: 1.5″ PVC
Return lines are plumbed with 1.5″ PVC to ensure proper water pressure back to the pool. The slightly smaller diameter on the return side actually helps maintain the pressure needed to push water through the jets effectively. Landi Pools & Games
Equipment pad plumbing: 2″ PVC
Filter systems are plumbed with 2″ PVC to increase flow rate through the system and provide maximum pressure. 2″ plumbing eliminates back pressure that can cause pump and filter issues. Landi Pools & Games
For larger or more complex custom gunite pools — those with spas, water features, tanning ledges, deck jets, or in-floor cleaning systems — additional pipe runs in smaller diameters (¾” or 1″) are common for those dedicated lines.
Why Pipe Size Matters More Than Most People Think
This is where a lot of pools — even expensive ones — get quietly shortchanged. An undersized plumbing system can’t be fixed by upgrading the pump. In fact, putting a more powerful pump on undersized pipe makes things worse.
At water velocities above approximately six feet per second, there is a sharp increase in system efficiency loss. The water begins to swirl and create vortices and turbulence, all of which counteract smooth flow. Friction especially is a concern, measured as friction losses in a plumbing system — as water velocity increases, friction and losses within the system increase. Swimming Pool Steve
For reference, maximum flow efficiency at 6 fps by pipe size breaks down as follows: 1.5″ handles up to 38 GPM, 2″ handles up to 63 GPM, and 2.5″ handles up to 90 GPM. A pool with too little pipe diameter for its pump simply can’t move water efficiently — no matter how much horsepower is behind it.
You would be better off with 2.5″ plumbing and a ¾ HP pump than 1.5″ pipe and a 1.5 HP pump. That’s how much pipe size matters relative to pump size.
What Type of PVC Is Used?
Most inground pools use white Schedule 40 PVC pipe, Type 1, Grade 1. Schedule 40 is the standard for pool plumbing and is suitable for nearly all residential applications. In the Swim
Rigid Schedule 40 PVC pipe is capable of a lifespan of over 75 years when properly installed — which matters enormously in a gunite pool where the pipes are encased in concrete and not accessible without major work. In the Swim
One important note for pools with heaters: standard Schedule 40 PVC is not resistant to high water temperatures. Some pool plumbers prefer to use CPVC pipe for heater and pump connections, which withstands water temperatures up to 200°F and can prevent warped or deformed pipes from heaters repeatedly shutting down before a proper cool-down period.
How Plumbing Is Installed in a Gunite Pool
In a gunite pool, plumbing is installed before the shell is shot — which means the pipe layout is planned and placed during the steel phase, before concrete is ever applied. All suction and return lines are run from the pool structure out to the equipment pad, tested for pressure, and then locked in place when the gunite is applied.
This is one of the reasons the quality of your pool builder’s plumbing plan matters so much. Installing plumbing lines directly in the gunite shell protects them, reduces the chance of unforeseen damage, and increases flow rate by allowing a more direct route from pool to filter with fewer fittings and less total pipe. Every additional fitting — every elbow, tee, and valve — adds friction and reduces flow. A well-designed plumbing layout minimizes those losses from the start.
What to Know When Upgrading Equipment
If you’re replacing a pump, adding a heater, or installing a salt chlorine generator on an existing gunite pool, understanding your pipe size is essential before you buy anything.
For your pool to achieve proper water circulation, the pump and filter unions must match the connecting pool pipe size. Mismatched connections create leaks, reduce efficiency, and can damage new equipment. In the Swim
If you’re not sure what size pipe your pool has, a pool professional can assess your equipment pad connections and, in most cases, identify the pipe size without any excavation. It’s a quick diagnostic step that can save you from buying equipment that won’t work correctly with your existing system.
PEC Builds Gunite Pools With Properly Sized Plumbing From the Start
At Pinnacle Exterior Construction, we design and build custom gunite pools throughout Baton Rouge and the surrounding area — and the plumbing plan is one of the first things we get right. Every pool we build is sized specifically for its volume, features, and equipment, so you’re not inheriting an undersized system or a plumbing layout that limits what you can add later.
If you’re planning a new pool or working through a plumbing issue on an existing one, our team is happy to walk you through it.
Contact PEC today or explore our pool construction process to see how we build.