Cross-linked polyethylene, also known as PEX, is a lightweight and durable polyethylene thermoplastic with cross-links. This tubing is typically used for domestic or building service pipes, hydronic systems, and insulation for electrical cables. Nowadays, PEX tubing is quickly replacing traditional copper and galvanized steel pipes and is an exceptional option for underground piping.
PEX tubing is approved for direct burial outdoors. PEX has a life expectancy of 40-50 years, made possible by its durable and non-corrosive materials. Burial also reduces sun exposure, which would otherwise degrade the piping. Additionally, PEX tubing materials allow for expansion, making them resistant to freezing/cracking underground.
My brother-in-law and I have used PEX tubing in our last three homes including buried line to the underground water main. There’s a few key things you need to understand so let’s dig into PEX tubing and fittings in terms of what type works best underground.
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What Type of PEX Can be Buried?
Although you can generally bury PEX tubing, some tubing types will have a longer lifespan than others underground, especially when used to transport water in freezing conditions (source).
PEX-B is the first choice for burying due to its higher bursting pressure and reduced issues with leached chemicals.
Some individuals are wary of using any type of PEX tubing outdoors because it degrades under UV light. This means that if the tubing is exposed to the sun, it will break down much faster. Since PEX tubing isn’t the cheapest pipe option, costing anywhere between $1.75 and $7.50, a severely shortened lifespan is not ideal.
Luckily, because the PEX tubing is being buried in this scenario, it won’t degrade from UV light as long as you limit its exposure to the sun prior to installation. Embedding the tubing in the sand once it is buried can help prevent damage from rocks and soil. Bury the tubing below the frost line to prevent water from freezing in the pipes.
That being said, here are the three types of PEX tubing, two of which are ideal options for underground systems.
PEX-A
Compared to the other two PEX tubing options, PEX-A is manufactured using peroxide, and it is the most flexible and softest tubing with the highest degree of cross-linking for the strongest chemical bond. This is the second-best PEX tubing option for burial, behind PEX-B.
The benefits of using PEX-A tubing in this scenario are that it is a non-corrosive tubing as opposed to more common materials, such as copper or steel, which inhibits the likelihood of the PEX tubing leaking or contaminating the water supply.
Purchase PEX-A tubing online (link to Amazon).
However, PEX-A tubing is more likely to leech chemicals from the manufacturing process into the water supply than PEX-B, so be aware there is still some level of risk with this product (source).
PEX-A tubing is suitable for burial because its flexibility allows the tubing to expand, particularly when subjected to freezing water allowing a high degree of resistance to cracking in frigid temperatures.
Although the PEX-B tubing is not as flexible as PEX-A, it has a higher bursting pressure, which means, when exposed to colder temperatures, it will withstand these temperatures longer without bursting than the PEX-A.
Ultimately, PEX-A is much easier to work with and can moderately withstand freezing conditions when buried, but it is not the best choice for burial over the PEX-B tubing.
PEX-A tubing typically costs quite a bit more than PEX-B tubing at an average cost of $3.50 to $7.50 per 10-foot piece.
PEX-B
If you are truly set on burying a length of PEX tubing, you should opt for the PEX-B tubing as your primary choice. Not only is this the most affordable PEX tubing option with an average cost of $2.50 to $5.50 per 10-foot piece, but it also has all the benefits of the PEX-A tubing and few drawbacks.
We’ve already mentioned that the PEX-B tubing has a higher bursting pressure than PEX-A, which is optimal when burying tubing that might be subjected to freezing temperatures. In addition to its non-corrosive material and reduced chances of chemical leeching, this feature makes PEX-B a more suitable choice.
Purchase PEX-B tubing online (link to Amazon).
In terms of differences and drawbacks, PEX-B differs from PEX-A in that it is manufactured using a moisture-cure method. This tubing is much less flexible than PEX-A, rendering it more difficult to work with.
Additionally, if your PEX-B tubing gets a kink while underground, you will have to dig up the tubing, cut out the kinked section, and replace this section with additional tubing and fixtures.
With the PEX-A tubing, many people point out that you can skip this process by fixing the kink by applying heat although it’s not recommended due to the precise heating required (source).
Altogether, PEX-B tubing might be less flexible and has a lower cross-link ratio than PEX-A, for the purposes of burying the tubing, its increased bursting pressure and cost-effective pricing make it the best choice.
This YouTube video from Williams Plumbing and Heating gives an outstanding overview of the differences of PEX-A and PEX-B as well as covering the key advantages and disadvantages of each:
PEX A vs PEX B: Pros and Cons 🤔
PEX-C
PEX-C is manufactured using an irradiation method and is ultimately not suitable for burial. It is, by far, the most difficult PEX tubing to work with because it is incredibly stiff. This means the tubing is more prone to kinking and cracking when exposed to freezing conditions.
Since the goal is to bury the tubing, using PEX-C would most likely require frequent repairs due to damage and bursting.
The sole benefit of PEX-C tubing is that it is the cheapest option, with an average cost of $1.75 to $3.50 per 10-foot piece. However, the amount you would spend on repairs if you used this tubing would significantly outweigh what you saved purchasing PEX-C over PEX-B.
Ultimately, if you want to use PEX-C, it is best suited for short repairs where you need a straight and sturdy pipe, not for lengthy underground piping.
| PEX-A | PEX-B | PEX-C | |
|---|---|---|---|
| Pro | Highest Flexibility | Highest bursting pressure | Most environmentally friendly |
| Con | Potential for chemical leaching | Stiff and prone to coil memory | Prone to cracks |
| Suitable for Underground | Yes | Yes | No |
Can PEX Crimp Fittings be Used Underground?
PEX-A and PEX-B tubing are both exceptional options for underground piping. However, these pipes’ effectiveness means very little if the fittings used cannot withstand the same conditions.
Crimp fittings are a popular option when installing piping, but they are not optimal for underground piping.
There are two common PEX fittings, clamps and crimps. The PEX crimps are often made of copper, which is the primary reason they are not conducive to burial.
The biggest concern when burying tubing and fittings is how extreme temperatures, particularly freezing conditions, affect their overall functionality.
In the case of copper PEX crimps, a common occurrence when exposed to freezing water is that it will cause the ring to expand, and then, over time as temperatures rise, this expansion will result in a leak.
Alternatively, the best PEX fitting for underground use is the stainless-steel clamp ring resistant to corrosion and more suitable for direct burial applications.
My brother-in-law likes to plan out this process and prevent any joints underground that we can, thereby reducing the potential for issues.
Always remember that anywhere you are joining pipe with fittings you are introducing a potential point of failure. Keeping those to a minimum in buried runs will reduce the opportunity for issues.
Can Sharkbite Fittings be Used Underground?
As opposed to PEX crimp fittings, Sharkbite fittings are suitable for burial as professed by the company and supported by The International Association of Plumbing and Mechanical Officials (source).
SharkBite uses a lead-free brass push-to-connect fitting with an EPDM O-ring and a stainless steel 316 grab ring. These materials ensure the fitting is durable, long-lasting, and won’t contaminate your water supply. The fitting is also compatible with a series of pipes, including PEX (source).
Although the material make-up of the fitting is beneficial to underground conditions, the real reason Sharkbite fittings are conducive to burial is that they are wrapped in silicone tape. Sharkbite guarantees the silicone tape won’t break down, and the fittings are wrapped in this material for two reasons.
- Protect the fitting from chemicals and soil contaminants.
- Helps ensure the company’s 25-year warranty.
The quality materials of the lead-free brass fitting and the added insurance of the silicone tape render these fittings an exceptional choice to accompany underground PEX tubing.
This YouTube video is a great overview of using Sharkbite fittings for buried PEX connections.
PEX to PVC: Sharkbite Fittings and Silicone Wrap..
Final Thoughts
Initially, the PEX company had a bit of a rocky start with frequent product leakage complaints. Now, after significant product improvements, you can find PEX products in over 60 % of new construction residential water supply systems (source).
Both PEX-A and PEX-B tubing are exceptional choices for underground work and can be supported with stainless steel PEX clamps or Sharkbite Fittings.
The significant lifespan of PEX tubing ranging from 40-50 years in addition to its 25-year warranty (an offer that also applies to Sharkbite fittings) enhances the benefits of choosing these products over more traditional pipes for underground systems.
FAQs
What type of PEX can be buried? ›
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.
Can PEX fittings be buried underground? ›Direct Burial Underground Method
All types of PEX piping could be installed underground, nonetheless, it's better for you to research which type will last longer in this condition. As a general rule, PEX B can withstand freezing temperatures for a longer time than PEX A due to its high bursting pressure.
Normally, you would bury your underground insulated PEX pipe 2 feet deep (24 inches). This is the right depth for burial for most ground types. Just be diligent enough to backfill it with soil that is not rocky or preferably sand.
What is the code for PEX A pipe? ›F876 is the Standard Specification for Crosslinked Polyethylene (PEX) Tubing and F877 is the Standard Specification for Crosslinked Polyethylene (PEX) Tubing Hot and Cold-Water Distribution. Following this, the ASTM codes for approved fitting systems listed.
Does PEX need to be sleeved underground? ›Use sleeving over PEX where it runs through an expansion joint/crack. A b, crack-resistant poly piping is preferred and should cover (sleeve over) the PEX pipe at least 1-1.5ft on both sides of the joint. For 1/2" or 5/8" PEX, 3-4ft long pieces of 1" PEX can be used for sleeving.
What is the best pipe to use for underground water line? ›What is the best pipe to use for an underground water line? You can use both PVC and PEX pipes for an underground water line. Both are able to be buried and can withstand high pressure. They are also resistant to rusting and corrosion.
How long does PEX pipe last underground? ›PEX: Due to its flexibility and durability, PEX piping should last at least 50 years. PVC / CPVC: Under typical conditions, these pipes should last up to 100 years.
Are SharkBite fittings approved for underground? ›Pros often ask: Can SharkBite push-to-connect fittings be used underground? The answer is yes. All SharkBite fittings are tested and approved for underground use.
Where is PEX not allowed? ›PEX cannot be taken anywhere outside the house where it is directly exposed to UV for a long period. The synthetic material of the pipes can slowly disintegrate due to the light of the sun. Even light bulbs have been known to affect the lifespan of PEX water lines.
Can PEX freeze and burst? ›Don't Believe the Myth of Freeze-Proof Pipes
Whether you're working with copper, CPVC or PEX – you are not automatically protected from frozen and burst pipes. All of these materials can and will burst when frozen, under the right conditions.
Is PVC or PEX better for underground? ›
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.
What is the difference between PEX A and PEX B tubing? ›Again, the main distinction lies in the manufacturing method, which is what assigns an A, B or C to PEX. PEX A is made using the Peroxide, or Engel, method. PEX B is formed using Silane, or Moisture Cure, method. This is the most common PEX pipe type out there.
What are the rules for running PEX? ›Run the PEX tubing: PEX needs to be supported a minimum of every 32 inches when running horizontally. If running vertically, it should be supported every 4 to 6 feet. (These supports are critical.) The straps should be plastic or metal that is designed to work for plastic pipe.
Do you have to use color coded PEX? ›Color-Coded: Red PEX pipes can be used for hot water supply lines, blue PEX for cold water supply, and white for either hot or cold. These colors are just for your convenience. Plumbing code does not require the pipe color to match the type of water supply.
How long should PEX hold air pressure? ›This pressure shall be held for not less than 15 minutes. The water used for tests shall be obtained from a potable water source.
Can PEX be buried under slab? ›Can PEX be used under a concrete slab? Yes, PEX pipe can be installed under a concrete slab. Since PEX pipe is supplied in coils, installation can be completed in one continuous length without the need for extra fittings. PEX pipe can also be encased within a slab, which is commonly used for radiant floor heating.
Can you run PEX through PVC? ›And fortunately, connecting PVC to PEX is easy to do. Whether you're looking to repair or expand your plumbing, adding PEX to your existing system is accomplished using a threaded fitting. In general, a fitting comes with one half to attach to existing pipe, and another half that fits on the PEX pipe.
How far apart should PEX tubing be in concrete? ›As a general rule, place PEX tubing at approximately 3” from what will be concrete slab edge and 12” apart. PEX Installation TIP: Divide the total area by the number of loops to be used. Space the tubing as required, filling that area with the loop serving it.
Is PEX better than copper underground? ›PEX pipe is not only cheaper than copper but more durable too. PEX is immune to corrosion and mineral build-up, and it's not affected by electrolysis, which can cause small pinhole leaks in copper piping. Copper pipes can last anywhere from six months to the life of a building.
Is HDPE the same as PEX? ›PEX pipe is made from high density polyethylene (HDPE), PEX is the term for the cross-linking process that improves the chemical and temperature performance of the polymer and provides flexibility and additional strength.
How deep does a water pipe need to be buried? ›
Avoid freezing pipes
According to 'The Department of the Environment', they recommend that pipes should be buried at least 600mm (two feet) underground. At this depth, the soil acts as a natural insulator and prevents them freezing.
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.
Mice and rats will chew through anything they can, including plastic, so PEX tubing is at just as much risk as the plastic-coated wiring in a car or an HVAC unit. While all rodent damage can be expensive, if rodents chew through a home's PEX water pipes, the result can be disastrous.
What causes pinholes in PEX pipe? ›Poly b piping will start to leak due to the molecular bonds in the piping starting to decay. Over time the bonds start to shake apart, this separation is what causes the pinhole leaks to start.
Why are plumbers against SharkBite fittings? ›A SharkBite fitting contains a rubber O-ring, which is not best for permanent connections. We don't recommend using a SharkBite fitting outside because sunlight can dry out the rubber O-ring and cause it to crack or split.
How long will a SharkBite last underground? ›SharkBite fittings last a long time. In fact, SharkBite warrants the fittings for 25 years when used with SharkBite tubing.
Do shark bites meet plumbing code? ›Approved by the Uniform Plumbing Code, International Plumbing Code, and National Plumbing Code of Canada, properly installed SharkBite fittings offer permanent connections, says Product Manager Michael Kornegay.
What is the lifespan of PEX? ›In most cases, PEX is extremely durable and lasts up to 50 years or more. PEX piping is also less likely to crack or break than metal pipe because it does not expand and contract as much when heated and cooled.
Does all PEX have an oxygen barrier? ›All three types of tubing are PEX (Poly Ethylene X-Linked) but some have extra features built in. The "barrier" referred to in PEX tubing is actually an oxygen barrier. This extra layer in your tubing will assure that no oxygen gets into your heating system.
Does PEX leach into water? ›One of the most recent studies, conducted in 2021, tested water from eight different types of PEX pipe brands. They found that 62 chemicals leached into the water, with half of those organic compounds leached considered toxicological but not carcinogenic.
Is it better to crimp or clamp PEX? ›
Pinch Clamp Tools Work Better in Tight Spaces
Especially when your PEX is pressed up against a wall—or there is just otherwise very little wiggle room to work—crimp tools can become a much bigger hassle. The larger jaw of the tool means you need ample room behind your PEX to be able to make a proper connection.
The plastic pipe manufacturers like this provision. If a water distribution system is designed for a maximum flow rate of 8 ft./sec., you will never need a water hammer arrestor for CPVC or PEX tubing. So, if you only install CPVC or PEX tubing, you don't have to read any further.
Do I need to winterize PEX? ›Cold temperatures don't affect the strength of PEX pipe either — except in extreme temperatures. However, freeze-resistant pipes are not freezeproof. So it's important to insulate pipe exposed to freezing temperatures during installation.
What lasts longer PEX or PVC? ›PVC has a predicted lifespan of 50-70 years or more, compared with 40-50 years for PEX. - Lower cost. PVC is less expensive to purchase than PEX, although it usually will cost you more in labor.
Which PEX pipe is better A or B? ›Bottom line, PEX A is more resistant to burst pressure than PEX B. PEX A's expansive material can handle up to 500 PSI, which makes it reliable in extremely cold temperatures. Since PEX B is a more rigid material, it will not hold up as well in similar situations.
Does PEX a leach more than PEX B? ›PEX-A is the most flexible of all PEX tubing types, one important downsides to this type is high rate of chemical leaching, which is much higher than PEX-B.
Can you bury PEX tubing? ›PEX tubing is approved for direct burial outdoors, a practice most often necessary when running a water supply line to a house. PEX, since it can expand, resists freezing more effectively than rigid pipe, but PEX can still burst if water freezes in a line.
Which is better PEX A or PEX C? ›One of the most apparent differences is that PEX A is very flexible and doesn't show any coil memory. So, as a user, you can repair any kinks simply with a heat gun. On the other PEX C is manufactured via the Electronic irradiation or cold method of cross-linking. PEX C is also more vulnerable to kinks and damage.
Can you use SharkBite on PEX? ›SharkBite brass push-to-connect fittings are compatible with PEX, copper, CPVC and HDPE pipe. They come with a PEX stiffener pre-loaded into the fitting for PEX and HDPE, and the stiffener doesn't need to be removed for copper or CPVC applications.
What PEX pipe can be buried? ›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.
Should you run PEX through I joists? ›
The Advantages of PEX
You can snake long runs through joists and studs. Second, PEX doesn't sweat under high humidity conditions, and it's also resistant to bursting, even if the lines freeze solid. Third, joints are easier.
It has also been overtaking copper and CPVC because of its flexibility compared to copper and although PEX might freeze, unlike PVC, it would not burst. In general, PEX would freeze when surrounding temperatures reach 20 degrees Fahrenheit—especially if the water line is uninsulated.
Does PEX need Teflon tape? ›For example, if you're working on PVC, copper or PEX pipes, these use alternate bonding methods and Teflon tape isn't necessary.
What happens if you don't use oxygen barrier PEX? ›PEX without an oxygen barrier actually allows oxygen from the air to permeate it. This happens even if the PEX is embedded in concrete. Cast iron circulator pumps will rust when oxygen is present in the water. Bronze or stainless steel circulators are necessary when this is the case.
Is Blue PEX A or B? ›Blue PEX-B Pipe (Coils)
What PSI should you test PEX at? ›The test pressure is recommended to be at least equal to the expected working pressure of the system, not less than 50 psi (345 kPa)5 and not greater than 160 psi at 73 °F (1,103 kPa at 23 °C), or as recommended by the tubing manufacturer.
How much psi can 3/4 PEX handle? ›PEX. PEX tubing comes in nominal sizes ranging from 1/4 to 3 in. copper tube size (CTS), and pipe sizes in both inch and metric sizes. PEX tubing is SDR9 with standard hydrostatic pressure ratings of 160 psi at 73°F (1105 kPa at 23°C) and 100 psi at 180°F (690 kPa at 82°C).
Does PEX leak over time? ›As with any other pipes, PEX is not prone to leaking. Nearly all of the plumbing leaks occur at joints (connection spots) and most of them are due to incorrect installation. Much like installing PEX tubing, repairing it is also an easy process.
Can SharkBite PEX be used underground? ›Pros often ask: Can SharkBite push-to-connect fittings be used underground? The answer is yes. All SharkBite fittings are tested and approved for underground use.
What is the difference between PEX A and PEX B? ›Again, the main distinction lies in the manufacturing method, which is what assigns an A, B or C to PEX. PEX A is made using the Peroxide, or Engel, method. PEX B is formed using Silane, or Moisture Cure, method. This is the most common PEX pipe type out there.
Which is better PEX A or PEX B? ›
Bottom line, PEX A is more resistant to burst pressure than PEX B. PEX A's expansive material can handle up to 500 PSI, which makes it reliable in extremely cold temperatures. Since PEX B is a more rigid material, it will not hold up as well in similar situations.
Can I use blue PEX for hot water? ›Color-Coded: Red PEX pipes can be used for hot water supply lines, blue PEX for cold water supply, and white for either hot or cold. These colors are just for your convenience. Plumbing code does not require the pipe color to match the type of water supply.
Is PEX expansion or crimp better? ›PEX crimp equipment is a lot more affordable than the expansion kits. However, despite the pricing and form shortcomings, most plumbers prefer to work with expansion because installation is more efficient. There are fewer leaks, and it also seems to be more durable against extreme colds and frozen pipes, etc.
Do you crimp PEX A or B? ›The PEX-A side will require an expansion ring while the PEX-B side requires the crimp ring. This method will also require using pipe dope and tape to ensure the seal is good.
Can you use copper crimp rings on PEX-A? ›Both copper crimp rings and stainless pinch clamps are great for making connections onto ASTM-F1807 PEX fittings.
Are plastic or metal PEX fittings better? ›If you are considering purchasing a good fitting for your pipe, it is better to make use of the plastic PEX fitting as it doesn't easily corrode, it can be used for any water condition and doesn't have fake products like the brass.
How do you keep PEX from freezing underground? ›You can prevent your PEX pipes from freezing and getting damaged by adding insulation to your basements, garages, attics, walls, windows, door cracks, and others. We also recommend insulating the parts of your pipe that are often exposed to extreme temperatures.