PEX Pipe and Fittings

PEX is cross-linked polyethylene — a flexible plastic tubing that’s taken over residential plumbing. The tubing has replaced traditional copper and galvanized steel water supply lines, and it’s now used in over 60 percent of new construction residential water systems. The reason it caught on is simple. No soldering required, which can be dangerous and tricky, especially in tight spaces. Due to its flexibility, fewer fittings are needed, unlike metal piping which cannot bend. And water travels noiselessly through PEX, which is not always the case with metal plumbing.

For anyone building or repiping in cold country, here’s the part that matters most. PEX is more resistant to cracking due to freezing thanks to its ability to expand. That single property earns its keep through a Montana winter, especially in unheated crawlspaces and seasonal cabins where pipes see hard freezes. Unlike copper and steel pipes, PEX does not corrode, avoiding both water contamination and leaks.

The real decision isn’t whether to use PEX. It’s which type — A, B, or C — and which connection method you pair with it. Get that pairing wrong and your joints won’t hold. Get it right and you’ve got a system that outlasts the house.

Color coding keeps it straightforward on the jobsite. Red signifies a hot water line, blue is used for cold, and white or gray PEX can be used for either hot or cold water.

PEX-A vs PEX-B vs PEX-C

Here’s the thing most folks get backwards: the letter isn’t a grade. PEX stands for cross-linked polyethylene, and the letter that follows simply signifies the type of manufacturing method used to cross-link the polyethylene, not the grade of PEX. In fact, if you look in the international plumbing codes, you’ll only see references to PEX, not the different types — because by and large, all PEX pipes are very similar.

They share more than they differ. PEX is dimensionally the same across all three types as defined in ASTM F876 — they’re all copper tube size, or CTS. PEX-a and PEX-b both carry a material designation code of 5306.

Where they part ways is flexibility, freeze behavior, and chlorine resistance.

Type	Manufacturing method	Character
PEX-A	Peroxide (Engel) method	Most flexible; most resistant to cracking from freezing since it expands the most; more expensive than B or C
PEX-B	Moisture-cure (silane) method	Most common type; stiffer than A and tends to return to its coiled state; higher resistance to chlorine
PEX-C	Irradiation (cold) method	Stiffest and hardest to work with; prone to kinking; cheapest; best for small repairs that don’t require much bending

A few practical notes on the trade-offs. PEX-A has no major benefit over PEX-B besides its greater flexibility. On the B side, the higher chlorine resistance makes it a solid choice in regions where water contains higher chlorine levels. That stiffness in PEX-C cuts both ways — it’s prone to kinking and susceptible to cracks in freezing conditions. For a Montana crawlspace, that’s worth thinking about.

The material designation code on the pipe tells the whole story if you know how to read it. The first digit is chlorine resistance, where the highest rating is Class 5. The second digit is UV resistance, where the highest is Class 3, indicating six-month UV resistance. The last two digits are HDB — the same for all PEX sold in the U.S., reading “06,” which indicates a 630 HDB, or a pressure rating of 160 psi at 73°F. The highest code is PEX 5306.

Pressure and temperature ratings under ASTM F876 hold across types:

Temperature	Pressure rating
73.4°F	160 psi
180°F	100 psi
200°F	80 psi

Western Building Center carries PEX-B in the colors and sizes that cover most residential work — 1/2-inch and 3/4-inch in red and blue, both available in 10-foot sticks and 100-foot rolls, plus white in 5-foot and 10-foot lengths, and a 1-inch white run.

Connection Methods and Fitting Compatibility

This is where jobs go sideways. Not every fitting works with every type of PEX, and the wrong pairing is the most common failure point. Not all fitting systems are approved for use with PEX. To find out which fittings work with the tubing you choose, check the pipe — tubing is marked with the standard designations for the fitting systems approved for use with it. Read the print on the pipe before you commit to a tool.

Expansion (ASTM F1960). Works with PEX-A only. An expander tool stretches and widens the diameter of the tube before inserting the fitting; after about 10 minutes the tubing shrinks back down to create a seal. This method only works with PEX-A. Cold expansion fittings made with DZR brass and high-performance poly are corrosion and chlorine resistant, approved for use with PEX-A piping.

Crimp (copper ring). One of the most popular methods. You need copper crimping rings and a PEX crimping tool. The ring slides over the end of the tubing, a fitting is inserted, the ring is moved to the end over the fitting, and the tool crimps it snugly in place. Crimp fittings provide full, immediate strength upon installation, with 360-degree uniform pressure.

Clamp (stainless steel). A ratchet clamping tool tightens stainless steel rings around the connection. The ring slides over the tube before the fitting is inserted, then the tool squeezes a tab on the ring, tightening it around tube and fitting.

Crimp and clamp are the versatile pair. Crimp fittings can be used with standard copper PEX crimp rings, copper rings with positioning caps, and stainless steel clamps — approved for use with both PEX-A and PEX-B piping. A crimp and clamp system works with any type of PEX and is certified for use in potable water and hydronic heating applications; depending on pipe size, water temperature, and pressure rating needs, you choose between brass or poly fittings.

Push-to-connect. The quickest method — special fittings pop onto the end of the tubing, creating a seal. No tools are needed, although a specific removal ring is necessary to take them off once connected. Check the tubing for the right marking. All SharkBite PEX tubing, for example, is marked with ASSE 1061, the standard for push-to-connect fittings.

Compression. A threaded brass nut slips over the tube, a tapered plastic compression ring slides in place, and a hollow brass tube is inserted into the end of the tubing. All of it goes into a threaded fitting, and the nut squeezes the ring against the brass fitting to create a seal as it tightens.

One firm rule: PEX is joined mechanically, never chemically. Don’t reach for solvent cement or heat fusion — those belong to other piping systems.

Sizes, Applications, and Installation Basics

PEX covers a wide range. It’s available in 3/8- to 1-inch diameters, and it’s a good idea to install 1/2-inch or 3/4-inch PEX for main lines for adequate water flow. The Jones Stephens dimension data runs the full span from 1/4-inch up through 2-inch in copper tube size. Length options match the job — from convenient 10-foot sections, perfect for small repairs or hose bib installs, to 500-foot rolls used for building a home’s entire water supply system.

Beyond potable hot and cold distribution, PEX handles radiant floor heating and hydronic loops. The oxygen-barrier pipe is the one to know for closed-loop heating. PEX-A is offered for both potable water and oxygen barrier applications, with PEX-B for potable water. For buried service lines, the same tubing carries the relevant approvals — a complete PEX system covers potable water and oxygen barrier uses with both expansion and crimp fittings.

On layout, there are three main layout options: trunk and branch, parallel, and zoned (zone and multi-port tee). Which one fits depends on the floor plan and fixture demand.

A handful of handling rules protect the system:

• Keep it out of the sun. Ultraviolet rays from the sun cause PEX to break down quickly, making it unsuitable for outdoor use. Where exposure can’t be avoided, sleeve it.
• Mind the bend radius and minimize joints. Run continuous coils where you can to cut down on fittings and pressure drops.
• Support it properly. Horizontal and vertical runs each have support requirements, and the tubing needs protection from mechanical damage.
• Test and disinfect. Pressure test the system and disinfect potable lines, and remember that any manufacturer’s guide is intended as a guide only — it does not supersede local plumbing codes.

The freeze story matters here too. PEX resists cracking better than copper because it expands, and if a line does freeze, it can be thawed — installation guides include thawing procedures, which is useful for the unheated crawlspaces and cold seasonal cabins common across Montana. There’s a repair difference worth knowing between the types: a kink in PEX-A can often be reformed with heat, while a bad kink in stiffer PEX generally means cutting out the damaged section.

Frequently Asked Questions

What does PEX stand for? PEX is short for cross-linked polyethylene, a flexible plastic used for plumbing. The letter that follows — A, B, or C — signifies the manufacturing method used to cross-link the polyethylene, not the grade.

Which PEX type is best for freezing conditions? PEX-A. It’s the most flexible and the most resistant to cracking from freezing, as it can expand the most. By contrast, PEX-C is prone to kinking and susceptible to cracks in freezing conditions.

Do all fittings work with all PEX? No. Not all fitting systems are approved for use with PEX. Expansion fittings work with PEX-A only, while crimp fittings are approved for use with both PEX-A and PEX-B piping. Always check the pipe — tubing is marked with the standard designations for the fitting systems approved for use with it.

What size PEX should I use for main lines? It’s a good idea to install 1/2-inch or 3/4-inch PEX for main lines for adequate water flow. When replacing old supply lines, the standard is to use the same size, though you can transition from 3/4-inch to 1/2-inch with an adapter.

What’s the difference between PEX-A and PEX-B? PEX-A is manufactured using peroxide; PEX-B uses a moisture-cure method and has a higher resistance to chlorine. PEX-A is more expensive than B and has no major benefit over it besides greater flexibility. PEX-B is the most common type out there.

Can PEX be used outdoors? Not exposed. Ultraviolet rays from the sun cause PEX to break down quickly, making it unsuitable for outdoor use. Protect it with UV-blocking sleeves where it can’t be hidden.

How long has PEX been around? Industry professionals have used PEX piping for over 40 years, because of its durability, easy installation, and resistance to corrosion.