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How to Connect PEX to PVC Underground

Cross-linked polyethylene pipe is suited for many different applications. Otherwise known as PEX, it is flexible, durable, and easy to install as well as affordable. It can also be run for long distances with fewer fittings. Running PEX pipe underground is possible, so long as you adhere to local building codes. Below, we will detail how to connect PEX to PVC underground, so your installation is safe, successful, and code-compliant.

Is PEX Suited for Underground Use?

A PEX pipe will hold up well underground. However, it’s not rated for use outdoors unless it’s properly insulated. If using a PEX pipe underground, bury it at least 12 to 18 inches below the frost line. The temperature is warmer just a few feet below the surface. In a cold region, the frost line may be three or feet down, so this is an important consideration. A PEX tube can freeze along with the water in it, although it will expand with ice and contract to its original shape when the ice melts.

Compared to metal, PVC offers high corrosion resistance and is long lasting. It also better withstands tree roots. Running a PEX line underground is beneficial because of the pipe’s flexibility, temperature resistance, and lack of a need for multiple connections along its length. In areas with aggressive soil or water conditions, plastic or brass PEX fittings are recommended.

And being a high-density polyethylene, PEX can also be buried in concrete. In fact, it’s often used for radiant heating under concrete floors.

Making an Underground PEX to PVC Connection

PEX pipe is available in red tubing for hot water lines and blue tubing for cold water lines. It can be connected to PVC pipe underground using threaded adapters. Once you have access to the water pipe or hose line you want to replace or install, you’ll need the proper fittings.

For the PEX line, use a fitting with female threads. For the PVC line, a socket solvent fitting with male threads should be used. It’s easier to accomplish a tighter fitting when the male end has plastic threads and the female fitting has metal threads. If the couplings need to be twisted together, connect both before finalizing the attachment of the fittings to the pipe ends.

There are various fittings used to connect PEX to PVC underground. Aside from threaded fittings, you may also want to use:

  • Push-to-Connect Fittings: Theses anchor to the pipe by pushing it over the end, and is sealed via an O-ring. You’ll also need to run a support liner through the pipe and add a locking component, such as a snap ring or twist collar. Each fitting must be matched with the type of pipe used (PEX-A, PEX-B, copper, brass, etc.). These “quick-connect” fittings aren’t always appropriate for use underground, depending on the product and local codes.
  • Metal Compression Sleeves: Requires a cold expansion method to expand the PEX pipe, with an expander tool, to fit it over an oversized fitting. Once the pipe returns to its normal size, the metal compression sleeve is fit over the connection. Make sure the sleeve product meets ASTM F 2080 standards.
  • PEX Reinforced Ring: The PEX ring is placed over the end of a PEX pipe; the tubing is then expanded before the fitting is inserted. A seal is formed when the pipe contracts to normal shape over the fitting. The reinforcing ring should comply with ASTM F-1960 guidelines.
  • Compression Fitting: Slide a brass nut and compression ring over the pipe, and place a metal sleeve into it. The fitting is then inserted. To compete the connection, tighten the nut and squeeze the compression ring.
  • Crimp Fitting: Slide the metal rings over the end of the pipe, insert the fitting, and tighten the ring over the pipe and fitting using a PEX crimping tool.
  • Clamp Fitting: Use a ratchet clamping tool to tighten the steel rings on the PEX pipe by compressing a side tab on the ring. While the fitting is placed at the end of the pipe, the ring goes over the fitting.

Best PEX Fittings for Use Underground

A stainless-steel clamp ring is well-suited for underground use because it’s corrosion resistant. Another good option is a brass push-to-connect fitting with an O-ring. However, copper crimps expand due to frozen water. When temperatures rise and the pipe shrinks back to normal size, the seal can break, resulting in a leak.

Contact Village Plumbing & Air for Help

If you need to know more about how to connect PEX to PVC underground, our skilled team can help. We use the latest equipment to provide plumbing and repiping services quickly and on budget. Whether installing PVC or PEX lines or connecting both, we handle permitting and other requirements and warranty parts and labor. Specials, coupons, and financing options are available to suit your budget. To learn more, schedule service online or call 713-678-0483.

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