#109 – CPVC vs. PEX: What’s the Best Choice for Home Fire Sprinkler Systems?

CPVC or PEX in home fire sprinklers: which thermoplastic is the winner?

Schedule 40 steel used to be the material of choice for fire sprinkler pipes until the mid-1970s, followed by thinner steel pipe and a push toward copper. 1985 saw the introduction of a non-metallic material that is still widely used today: Chlorinated polyvinyl chloride (CPVC). A thermoplastic that had been used in water distribution systems since 1959, it was able to do the job because of its strength, pressure tolerance, and heat resistance.

In the decades since, it has been joined by cross-linked polyethylene (PEX). First used in water distribution systems in the 1970s, PEX has “has quickly grown to be the most-installed piping product for potable plumbing systems in residential applications nationwide, more than copper and CPVC combined.” CPVC remains the most commonly-used material in home fire sprinkler installations, though PEX is quickly gaining ground, especially in multipurpose sprinkler systems that are integrated with a home’s overall plumbing.

Both are explicitly approved for use in “wet” home fire sprinklers by the National Fire Protection Association (NFPA). And both have numerous advantages over metallic pipe, with fewer disadvantages. The materials are less expensive, installation is easier and quicker, and thermoplastic pipes allow water to flow through them with less friction and much less chance of corrosion.

But which is better?

If you’re simply looking to buy parts for your home fire sprinklers, check out QRFS’ selection of residential system components or use the search bar at the top of the page to find what you’re looking for. Otherwise, let’s get to the match-up:

A look at CPVC in home fire sprinklers

CPVC is manufactured by taking standard polyvinyl chloride (PVC) and “adding chlorine … in a water slurry or fluidized bed chlorination process” which is “initiated by ultraviolet light.” Adding this element gives the material much better resistance to corrosion and the ability to withstand higher temperatures than PVC. It is “is available in nominal sizes from 1/2″ to 24″ and is approved in all model plumbing and mechanical codes across the United States and Canada.”

The benefits of CPVC

• Water flows through a pipe made of CPVC more easily than metal alternatives. “The Hazen-Williams C factor is used to describe the amount of friction loss that is encountered when water flows through a pipe. Steel pipe has a C factor of 120 compared to the 150 C factor of CPVC pipe. This higher C value indicates that CPVC pipe has less friction loss, which often allows for pipe downsizing of at least one size smaller in diameter than steel.”
• It’s resistant to the corrosion that happens in metallic pipe, meaning less chance of leakage and the build-up of sediment that blocks water flow. This also means that the system will continue to perform as designed (maintaining the same Hazen-Williams C factor), which is one of the reasons it tends to last longer than metallic pipe; a properly installed CPVC network can last 30 years.
• It’s easier to install than metallic pipe. It’s lighter; installers can make flexible new cuts without the aid of heavy, loud tools; the joints are assembled via hand using a compound that chemically welds them together (no torch required); and because it has better flow characteristics, fewer sprinkler heads may be necessary based on the hydraulic calculations of the system.
• It is considered a “sustainable” material compared to steel, based on an “ISO-compliant, peer-reviewed LCA conducted by Environmental Resources Management Ltd. (ERM).”
• With “a flash-ignition temperature of 900-degrees F,” it will not sustain burning. Neither will metallic pipes, of course.
• Both because the material is cheaper and the installation is easier, it costs less than installing metallic pipe. Installation labor costs are up to 50 percent less than metallic options.

Drawbacks or special considerations for CPVC

• If antifreeze is used in a system, it cannot be comprised of glycol, though glycerin can be used. Glycol is absorbed into the pipe and causes “environmental stress cracking.”
• The performance of CPVC depends on how it is manufactured and stored; for example, unpainted CPVC can degrade with extended exposure to UV light. These are not major concerns when purchasing it from a reliable manufacturer and using a professional installer, however.
• It is not compatible with certain “hydrocarbon- or petroleum-based materials used in the installation of building systems,” which can cause chemical stress fractures. “Examples of this incompatibility include the installation of CPVC pipe downstream of steel pipe that has been protected with antimicrobial coatings, and CPVC pipe that has come in contact with oils used for cutting steel pipe.” Following manufacturer instructions during installation should avoid this issue.
• Like metal pipes, it is susceptible to freeze damage. If the water in a wet system freezes and expands, it can crack or completely rupture the pipes, causing extensive damage and system failure. CPVC pipes should be placed in consistently warm or climate-controlled environments, or be sufficiently insulated from falling temperatures.
• CPVC has a higher thermal expansion coefficient than metal, meaning it expands as temperatures rise. Designers must account for this expansion when hydraulically designing a system.
• CPVC must be protected/separated from areas that could be exposed to a fire – with a few exceptions. Common protection measures are “3/8-inch minimum thickness of gypsum wallboard and 1/2-inch minimum thickness plywood or lay-in ceiling tiles having a minimum weight of 0.35 pounds per square foot.” CPVC can be exposed in certain areas, such as unfinished basements or under special conditions subject to the approval of the authority having jurisdiction (AHJ; the local government authority that approves a sprinkler system).
• It must be joined correctly. Metal pipes are fitted together with heat and PEX is joined via pressure or mechanical crimping. CPVC is put together with a special compound that chemically welds the fittings.An installer who uses too little or too much adhesive, joins it “at ambient temperatures below the manufacturer’s listed minimums,” or doesn’t give it enough time to dry could compromise the fitting. In addition, there is the potential for an installer to place in a dry fitting while laying out the network, which would result in a massive leak once the system activates or undergoes hydrostatic testing.Again, the solution to this is to hire a qualified installer who knows what he or she is doing and follows manufacturer instructions. Below is a video tutorial on properly joining CPVC pipe:

The verdict on CPVC

CPVC is an easier, more economical, and higher performing solution than metallic pipe in a home fire sprinkler system. It has a decades-long history of safety and durability in both plumbing and fire safety applications and it is explicitly approved by NFPA for the latter. And disadvantages or considerations can be minimized or avoided altogether with proper system design and installation.

A look at PEX in home fire sprinklers

PEX is made by chemically crosslinking polymer chains of polyethylene molecules, which makes the original substance stronger and more resistant to chemicals, abrasion, and heat. PEX tubes vary in size from about 3/8” to 4”. This thermoplastic was initially only approved by NFPA for use in multipurpose, residential wet pipe sprinkler systems because of high-pressure-tolerance requirements but this was changed – if a system meets some additional requirements (emphasis added):

From the 2016 Edition of NFPA 13D

5.2.2.4 Nonmetallic pipe used in wet pipe sprinkler systems not equipped with a fire department connection and provided with a pressure-reducing valve set no higher than 80 psi (5.5 bar) shall be designed to withstand a working pressure of not less than 130 psi (9 bar) at 120°F (49°C) and 100 psi (6.9 bar) at 180°F (82°C).

5.2.2.4.1 If the maximum static pressure from the water supply is less than or equal to 80 psi (5.5 bar), pipe designed to withstand a working pressure of not less than 130 psi (9 bar) at 120°F (49°C) and 100 psi (6.9 bar) at 180°F (82°C) shall be permitted to be used without a pressure-reducing valve.

5.2.2.4.2 If a pressure-reducing valve is used to comply with 5.2.2.4, an automatic means of pressure relief shall be installed on the sprinkler system side of the pressure-reducing valve.

Basically, this means that PEX or any other listed nonmetallic material can now be used in a standalone wet fire sprinkler system “if the maximum static pressure from the water supply does not exceed 80 psi” – or a pressure release valve and an automatic means of pressure release is used when the pressure from the water supply is higher than this limit.

The benefits of PEX

• As with CPVC, water flows more easily through PEX than metallic pipe since it has a higher Hazen-Williams C factor.
• Also similar to CPVC, it is more corrosion-resistant than metal, and therefore likelier to last longer and with better performance.
• A huge benefit of PEX is that it can bend, which makes installation easier and (literally and figuratively) more flexible. This flexibility enables different designs for the network of pipes and means that an installer will have to use far fewer joints; fewer joints mean less installation time, fewer potential leak spots, and potentially lower expense.
• Also like CPVC, adaptations are easier than metal; simply cut a new length of the tubing and join it by hand.
• PEX is also considered a more sustainable material than metal.
• It is less susceptible than CPVC “to environmental stress-cracking when in contact with common construction materials, such as leak detectors, thread sealants, pipe wraps, lubricants and caulks.” It is sensitive to UV-light degradation, however, so it shouldn’t be stored in the sun.
• It uses mechanical-type joints, obviating the need for any chemical or heat welding.
• Another benefit of PEX is its resistance to freeze-related damage. While it will develop weaknesses with repeated expansion, “PEX can expand up to three times the pipe’s outside diameter.” That said, PEX pipes should still be winterized to avoid freezing.Check out this demonstration of how PEX holds up under freezing:

Drawbacks or special considerations for PEX

• Like CPVC, PEX has a higher thermal expansion coefficient than metal – it expands 1 inch per 10°F per 100 ft. length. This should be compensated for in system design.
• Also like CPVC, PEX must be protected from the room where a fire may take place, though at least one form of PEX tubing, Uponor’s AquaSAFE™, has been listed for exposed use “in unfinished basements with dimensional lumber, engineered wood or wood I-joists.”Where CPVC and PEX differ is that PEX has a lower “limiting oxygen index” (LOI), which is “the percentage of oxygen that has to be present to support combustion of the plastic.” Thus, PEX is less combustion-resistant than CPVC (and of course, metal). Common fire protection methods include installing the same gypsum/plywood or tile barriers as CPVC.
• If PEX is used, especially in a multipurpose system where potable water is supplied, it may run into issues involving the leaching of chemicals into the water supply. This is really dependent on the quality of the water supply to your home, with the most common issue being over-chlorinated water.Steps to mitigate/evaluate any leaching include testing the water supply to make sure the pH is at or above 6.5 and chlorine is less than 4.0 parts per million, and/or installing a home water filter. The system should ideally also be flushed after installation.
• PEX pipes must be joined correctly. The tubes are joined via a mechanical process – no chemical or heat required – that can include copper crimping, stainless steel clamps, a push-to-connect method, and cold expansion with PEX-reinforcing rings. An installation can run into trouble if not done properly. For examples, an improperly calibrated tool can screw up the crimping/clamping method, and some common mistakes with push fittings are covered here.That said, this Uponor demonstration shows that joining tubes via the cold expansion with PEX-reinforcing rings method is fairly simple:

The verdict on PEX

PEX is also an easier, more economical solution than using metallic pipe in a home fire sprinkler system. Like CPVC, it has a decades-long history of safety and durability in both plumbing and fire sprinkler applications (though a much shorter run in the latter), and it is explicitly approved by NFPA. And disadvantages or special considerations can be minimized or avoided altogether with proper system design and installation – as well as an evaluation of the quality of the water supply and the use of a water filtration system in a multipurpose system.

So, which is better?

Opinions may vary, but it’s basically a push. A homeowner can’t go wrong with either material in a fire sprinkler system.

Multipurpose systems with PEX may require slightly less maintenance and fewer components (like a backflow preventer that stops water from moving back into the potable supply), and PEX also has better resistance to freeze damage. On the other hand, CPVC tends to be a bit more flame resistant. But both materials are excellent options.

If you need to buy parts for your home fire sprinklers, check out QRFS’ selection of residential system components or use the search bar at the top of the page to find what you’re looking for. If you have any other questions about residential fire sprinkler pipe materials or need help finding an item, add a comment below, give us a call at 888.361.6662, or fill out our contact form and we’d be happy to help.