What PEX is and where it fits
PEX stands for cross-linked polyethylene. It carries pressurized water, and it is color coded, with red for hot, blue for cold and white for either. Common sizes are 3/8, 1/2, 3/4 and 1 inch.
Plumbers use it for new bathrooms, kitchens, basements and whole-house supply replacements. It is not approved for drains, and most codes limit it indoors because ultraviolet light weakens it within weeks of direct sun exposure.
| Feature | PEX | Copper |
|---|---|---|
| Joining | Crimp, clamp or expansion fittings | Soldered or press fittings |
| Bends | Flexes around corners with fewer fittings | Needs elbows and joints |
| Freeze tolerance | Expands and often survives a freeze | Splits when water freezes |
| Sunlight | Degrades with direct UV | Not affected |
| Noise | Quieter, with less water hammer | Can ring and knock |
| Fire and heat | Plastic, so keep away from flues | Handles high heat |
Home run, trunk and branch, and manifolds
Two layouts are common. A trunk and branch system uses a main line with branches to each fixture, similar to copper. A home run system runs a separate line from a central manifold to each fixture.
A manifold lets you shut off any single fixture without losing water to the whole house. It also helps with pressure when two fixtures run at once, since each has its own line. The trade-off is more pipe and a good location for the manifold, usually near the water heater.
- Trunk and branch uses less pipe and fewer holes.
- Home run gives per-fixture shutoffs and steadier pressure.
- Mixed layouts are common in older homes where walls limit access.
Cold weather in Hazelwood and what it means for PEX
The City of Hazelwood publishes a frost depth of 30 inches and a winter design temperature of 2 degrees F. For PEX, that matters in unheated spaces such as crawl spaces, garages and exterior walls. PEX tolerates freezing better than copper, but it can still split at a fitting, so insulation and heat matter.
In January 2024, Missouri American Water crews responded to 16 main breaks in one day, and one local plumber reported more than 180 calls. Pipes burst as things thaw, so know where your shutoff is. A PEX manifold with labeled valves makes that faster, since you can isolate one branch and keep the rest running.
PEX tubing is made to ASTM F876, PEX systems are covered by ASTM F877, and drinking water pipe should be certified to NSF/ANSI 61. Look for those markings printed on the tubing itself before it goes into a wall.
Fittings, tools and the details that matter
PEX is easy to cut but not forgiving about joints. Crimp rings, clamp rings and cold-expansion fittings each need the matching tool and the matching pipe type. Mixing parts from different systems can leave a slow leak that shows up weeks later.
Brass fittings can be a restriction point because they reduce the inside diameter of the pipe. Expansion fittings, which stretch the pipe, keep a larger bore and flow better, which is useful for long runs or a large tub. Ask your plumber which system they use and why.
- Plan the layout. Mark fixtures, the manifold and the main shutoff before cutting pipe.
- Cut square and clean. A crooked cut or a nick in the pipe makes a weak joint.
- Make each joint with the right tool. Use the ring and tool made for that system.
- Support the pipe. Fasten it at the spacing in the manufacturer's instructions so it does not sag or rattle.
- Pressure test. Bring the system up to pressure and watch it before covering.
What affects PEX project pricing
We do not publish a PEX repipe price because the scope varies. A plumber needs to see the walls, floors and access points before giving a clear price.
A water heater swap is a good time to update the lines near it. See the notes on water heater replacement if yours is nearing the end of its life.
Rules for using PEX in a Hazelwood home
PEX must be installed following the manufacturer's instructions and the plumbing code in force. Do not run PEX within a set distance of a flue, recessed light or gas water heater vent. Many installers use metal pipe for the first stretch off a water heater.
Hazelwood contracts with St. Louis County for plumbing permits and inspections, and plumbing work is done under a county license. Ask your plumber to confirm permit steps for a repipe. Florissant's code shows owners may pull a homeowner permit for their own work but not for slab-enclosed piping, so verify your own rules.
When to call a plumber
A new PEX branch to a single fixture is within reach of a handy owner, but a whole-house job or anything that ties into the main is not. Leaks inside walls from a bad fitting are expensive to chase.
Call if you see unexplained water use, low pressure after a repipe, or a spot of moisture near a fitting. Our leak detection page explains how hidden leaks are found. For a full replacement project, see repiping, and for new rooms see plumbing installation. We serve Black Jack and Maryland Heights along with Hazelwood.
Frequently asked questions
For water supply, PEX is widely used and performs well. It resists freezing damage better than copper and installs faster, though it can be damaged by sunlight and heat.
It can, though it often survives better than copper. The city lists a 30 inch frost depth and a 2 degree F winter design temperature, so insulate PEX in unheated spaces.
PEX used for potable water is listed to standards for drinking water, and most homeowners use it without issue. Ask your plumber for the listing and flush new lines before use.
Yes, with transition fittings such as a push-fit or a crimp-to-sweat adapter. A plumber will choose the correct type for your pipe and water pressure.
Plumbing permits in Hazelwood go through St. Louis County via the city. Confirm with Hazelwood Inspections and Permits at 314-513-5034 before starting.
Missouri American Water crews responded to 16 main breaks in one day, and a local plumber reported over 180 calls. Know where your shutoff is before cold weather.
Questions about your situation? A licensed plumber is on the line any hour.
Call (855) 575-2890