These photos depict the proper way to plumb a spa, or other curvy layout. Using flex tubing, a common shortcut to this kind of careful installation, should be avoided when encased in concrete.
The elastic properties of flex tubing, which make it ideal for plumbing portable aboveground spas and pools, cause failures when embedded in concrete. It's a shortcut you shouldn't take.
There are a number of reasons why flexible tubing should not be used to plumb concrete pools. Here's an even dozen of the main issues:
- The elastic nature of the tubing's side walls allows it to flex. This expansion and contraction will cause glue joints to fail.
- The exterior dimensions are irregular, and properly glued joints are virtually impossible to achieve.
- The additives in the tubing gradually degrade over time, leading to failures.
- Flexible tubing is not rated for hot water applications. The application of heat softens the tubing, weakening joints and promoting joint and tubing failure.
- Flexible tubing does not have an NSF-61 rating for potable water.
- Flexible tubing cannot handle pressure exceeding 60 PSI. Periodic water hammer can cause joints to fail.
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- It is not resistant to insects. It is not uncommon for termites to bore into flexible tubing.
- It is not abrasion resistant. Water hammer will cause flexible tubing to move, expand and flex. If back filled with rock or sharp objects, holes can develop.
- Dimensionally, it does not meet the standard for Schedule 40 PVC pipe, though it does fit inside Schedule 40 fittings. By code definition, it is classified as a "hose," not a pipe.
- PVC tubing and hose are not approved for plumbing in-ground pools (IAPMO 311.1-311.3). Numerous organizations also have published opinion papers against such uses (Genesis Position Statement #3, section 3.3).
- Flexible tubing can collapse under vacuum pressure.
- Flexible tubing moves around during the shotcrete process, creating voids and cavities (which allow it to move, flex and expand under pressure).
With all of these reasons not to use flexible tubing, why would you? Why would you proudly promote that you use it?
Heat bending rigid Schedule 40 with a pipe oven or heat blanket is the correct way to plumb circular or irregularly shaped vessels.
On a related note: Running an air line under the pool will prevent the removal of the water used for pressurization. Many linear feet of water will be trapped in the pipe under the pool. Blowers are ineffective against so much back pressure. Air lines should be installed as high as possible around the entire project, unless there is a means to drain the trapped water.
