PEX Plumbing: Types, Connections, and Installation for DIY Repipes
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PEX (cross-linked polyethylene) has largely replaced copper for residential water supply lines in new construction. It costs less, installs faster, resists freezing better, and does not corrode. The flexible tubing routes through walls and floors with fewer fittings than rigid pipe, reducing potential leak points. If you are repiping an older home or adding a new fixture, PEX is almost certainly the right material unless your local code says otherwise. This guide covers the different PEX types, connection methods, layout strategies, and installation best practices for residential water supply work.
PEX Types: A, B, and C
PEX-A is manufactured using the Engel method (peroxide cross-linking). It is the most flexible of the three types and has the best freeze resistance. PEX-A can be expanded with a specialized expansion tool and then returns to its original diameter, which is the basis for expansion-style connections. The flexibility makes it easier to route through tight spaces, around corners, and through floor joists without as many fittings. PEX-A typically costs 15 to 30 percent more per foot than PEX-B. Common brands include Uponor (formerly Wirsbo) and Mr. PEX.
PEX-B is manufactured using the silane method (moisture cross-linking). It is slightly stiffer than PEX-A but still far more flexible than copper or CPVC. PEX-B works with copper crimp rings or stainless steel cinch clamps. It is the most common type for residential plumbing across the country, balancing cost and performance well. PEX-B actually has a slightly higher burst pressure rating than PEX-A at the same temperature, though both exceed any residential water pressure by a wide margin. Common brands include Viega and SharkBite.
PEX-C is manufactured using the irradiation method (electron beam cross-linking). It is the stiffest of the three types and the least commonly used in residential plumbing. PEX-C accepts the same crimp and cinch connections as PEX-B, but it is more prone to kinking during installation, especially in cold weather. Most professional plumbers avoid PEX-C for water supply lines because the stiffness makes routing more difficult without adding practical advantages.
Color coding in PEX is simple: red tubing carries hot water, blue carries cold water, and white carries either. The color is purely for identification at a glance during installation and future service. The material itself is chemically identical regardless of color. You can use white PEX for everything if you prefer a consistent look in exposed areas like a mechanical room or basement ceiling, though separating hot and cold by color makes troubleshooting and future work easier for whoever comes after you.
Connection Methods
Crimp connections are the most common and least expensive method. Slide a copper crimp ring over the PEX tubing, insert a brass fitting into the tube end, position the copper ring over the barbed section of the fitting (about 1/8 to 1/4 inch from the end of the tubing), and compress the ring with a crimp tool. The tool squeezes the ring evenly around its circumference, creating a permanent seal. After each crimp, verify it with a go/no-go gauge. A properly crimped ring passes the go side of the gauge (slides over easily) and does not pass the no-go side (catches on the compressed ring). Crimp tools are available for $30 to $80, and the copper rings cost pennies each.
Cinch clamp connections work similarly to crimp but use stainless steel cinch clamps instead of copper rings. The clamp has an ear that gets compressed with a ratcheting cinch tool, pulling the band tight around the PEX and fitting. Cinch clamps are slightly easier to install in tight spaces because the tool grips from one side only, unlike a crimp tool that must fit around the full circumference of the ring. The tradeoff is that cinch clamp tools cost slightly more, and the clamps themselves are a few cents more expensive than copper crimp rings. In practice, both methods produce equally reliable connections.
Expansion connections work only with PEX-A tubing. An expansion tool enlarges the end of the PEX tube, you slide it over a fitting, and the PEX contracts back to its original diameter over the next few seconds, gripping the fitting tightly. No metal ring is required. The key advantage of expansion fittings is flow: they have a larger interior bore than crimp or cinch fittings because the fitting sits inside the expanded tube rather than inside the tube at its original diameter. This means less flow restriction, which is a real advantage on 3/8-inch and 1/2-inch lines where every fraction of an inch matters. Expansion tools are more expensive ($200 to $400 for a manual tool, $300 to $600 for battery-powered) but worth it for larger projects.
Push-fit connections from brands like SharkBite work with all PEX types, as well as copper and CPVC pipe. No special tools are needed. Cut the PEX square, mark the insertion depth on the tube, and push it into the fitting until it clicks. Push-fits are the most expensive per connection ($5 to $15 per fitting versus pennies for crimp rings) but are extremely useful for quick repairs, transitions between PEX and copper, or situations where you need one or two connections and do not want to buy a crimp tool for the job.
Layout: Home Run vs Trunk-and-Branch
Trunk-and-branch mimics a traditional copper plumbing layout. A main line (the trunk, typically 3/4-inch) runs through the house, and smaller branch lines (1/2-inch) tee off to individual fixtures. This layout uses less total pipe but requires more fittings, since every branch point needs a tee. Each fitting is a potential leak point and creates a small flow restriction. The trunk-and-branch approach works fine and has been standard practice for decades, but PEX opens up a better option.
Home-run (manifold) layout uses a central manifold with individual dedicated PEX lines running from the manifold to each fixture. Every fixture gets its own uninterrupted run of PEX from the manifold, with zero fittings between the manifold and the fixture. This dramatically reduces the number of hidden fittings inside walls and ceilings. Each line can also be shut off independently at the manifold, so you can isolate a single fixture for repair without turning off water to the entire house or even an entire bathroom.
Most PEX installations in practice use a hybrid approach: a manifold for the main distribution with short trunk-and-branch runs where routing individual lines would be impractical (for instance, a bathroom cluster where three fixtures are within a few feet of each other). The manifold typically mounts in the mechanical room near the water heater, where it is accessible for future shutoffs and maintenance.
For a full repipe of an older home, the home-run manifold approach is worth the extra pipe cost. You will use more linear feet of PEX, but the material is cheap. A 100-foot coil of 1/2-inch PEX-B runs $25 to $40. The labor savings from fewer fittings and the reliability benefits of fewer hidden connections more than offset the additional tubing cost. The ability to shut off individual fixtures at the manifold without affecting anything else in the house is also a significant practical advantage that homeowners appreciate for years after the install.
Installation Best Practices
Support PEX every 32 inches on horizontal runs and every 4 to 6 feet on vertical runs. Use plastic hangers, padded clamps, or purpose-made PEX clips. Never use unpadded metal clamps or copper wire to support PEX. Metal edges can cut into the tubing over time, especially as the PEX expands and contracts with temperature changes. Leave a slight curve or bow in each run to accommodate thermal movement. A perfectly straight, tightly strapped PEX line has no room to expand when hot water flows through it, which can stress fittings at each end.
Protect PEX from UV exposure. PEX degrades quickly in direct sunlight. Most manufacturers specify a maximum UV exposure of 30 to 60 days before the warranty is voided, and damage begins well before that point. UV exposure weakens the molecular cross-links that give PEX its strength and flexibility. Cover any exposed PEX with pipe insulation, UV-rated sleeve, or opaque conduit where it passes through unconditioned spaces with potential sun exposure, such as attics with skylights or garages with windows.
Do not install PEX within 18 inches of a water heater or any heat source that exceeds 200 degrees F. The transition from the water heater to the PEX system should use copper stub-outs. Solder or thread copper pipe to the water heater connections, extend it at least 18 inches, and then transition to PEX using a push-fit coupling, a threaded adapter, or a dielectric union (which also prevents galvanic corrosion between dissimilar metals). This rule applies to both the hot and cold sides of the water heater.
Check the manufacturer's temperature and pressure ratings before installing PEX in any application. Most residential PEX is rated for 160 degrees F at 100 PSI, or 73 degrees F at 160 PSI. These ratings are adequate for standard residential hot water systems but not for high-temperature applications like radiant heating loops connected to boilers that operate above 180 degrees. For those applications, use PEX specifically rated for radiant heating, which has different specifications.
PEX vs Copper: When Each Makes Sense
PEX wins on cost (40 to 60 percent less per linear foot than copper, with even greater savings when you factor in labor and fittings), installation speed (flexible tubing routes through framing without as many cuts and fittings), freeze resistance (PEX can expand up to three times its diameter without bursting in most freeze events, while copper splits), corrosion resistance (PEX is unaffected by acidic water, mineral buildup, or aggressive soil chemistry that eats copper from the outside), and noise (PEX absorbs water hammer naturally and does not transmit pipe noise the way rigid copper does).
Copper wins on UV resistance (copper is fine for outdoor exposed runs indefinitely), code acceptance in certain jurisdictions (some areas still require copper for specific applications, though this is increasingly rare), rodent resistance (mice and rats can chew through PEX tubing but cannot damage copper), and long-term track record (copper plumbing systems have lasted 50 years and beyond, while PEX has been in widespread residential use since the 1990s and shows no signs of premature failure, but does not yet have a 50-year real-world track record).
Use copper for the first 18 inches from a water heater, for outdoor exposed runs where UV exposure is unavoidable, for connections to gas appliances (PEX cannot carry gas), and in any jurisdiction where PEX is not code-approved for the specific application you have in mind. Use PEX for everything else in a residential water supply system. The cost savings, faster installation, and reduced leak risk from fewer fittings in a manifold layout make it the clear choice for most residential plumbing work.
Frequently Asked Questions
Can I Connect PEX Directly to My Existing Copper System?
Yes. The simplest method is a push-fit coupling like SharkBite. Cut the copper pipe square, deburr the cut end, mark the insertion depth on the pipe, and push the fitting onto the copper on one side and the PEX on the other. No tools, no solder, no torch. For a more permanent and lower-cost transition on a larger project, solder a female threaded adapter onto the copper and thread a male PEX adapter into it. Both approaches are code-approved in all major jurisdictions. The push-fit method is faster; the solder-and-thread method costs less per connection.
Does PEX Affect Water Taste or Quality?
New PEX can give water a slight plastic taste for the first few weeks after installation. This is most noticeable on hot water lines. Flushing the system by running water for several minutes at each fixture after installation removes this. The taste dissipates entirely within a few weeks of normal use. All PEX sold for potable water in the US is NSF/ANSI 61 certified, meaning it has been tested for leaching of chemicals into drinking water and meets established safety standards. The initial plastic taste is temporary and not a health concern.
Can Rodents Chew Through PEX?
Yes. Mice and rats can and do chew through PEX tubing, usually in search of water. This is PEX's one significant vulnerability compared to copper. In areas with known rodent activity (crawlspaces, attics, unfinished basements, older homes with gaps in the foundation), protect exposed PEX runs with rigid PVC conduit, galvanized wire mesh sleeve, or keep the area rodent-free through exclusion by sealing all entry points larger than 1/4 inch. Buried PEX for outdoor supply lines should always be run inside a protective sleeve for this reason.