Does PEX Freeze and Burst? What Every Outdoor Boiler Owner Should Know

When winter sets in and temperatures drop, outdoor boiler owners have to be extra alert at protecting their systems. We often see this question during the cold season – “Does PEX freeze and burst?” That is a very pertinent issue for those of us which use PEX tubing in our outdoor boiler systems. In this in depth guide we will get to the bottom of the issue, the characteristics of PEX and what it does under freezing conditions as well as how you can protect your investment from the cold.

What Is PEX Tubing?

Before we look at whether PEX freezes and bursts we will first define what PEX is.

PEX, as explained in this article, stands for cross-linked polyethylene which is a type of plastic tubing that has come to be a very popular alternative to copper and PVC in home and commercial plumbing. It is also very much at home in hydronic heating systems, radiant floor heating and outdoor boiler set ups due to its durability, flexibility and resistance to scale and chlorine.

Benefits of PEX:

• Flexible and easy to install

• Resistant to corrosion and scaling

• Lower cost than copper

• Expands under pressure

But although it is very strong PEX is not invincible – in particular when it comes to extreme cold.

Does PEX Freeze?

Yes PEX can freeze if the water in it reaches freezing point. As is the case with any pipe, if water is still in a PEX tube and the environment around it drops low enough the water will turn to ice.

How Cold Does It Have to Be for PEX to Freeze?

Water freezes at 32°F (0°C). PEX does not insulate the water within it so if the tubing is out in the elements and left without proper insulation or movement for a while it can freeze. The real issue is what happens once it does.

Does PEX Burst When It Freezes?

The good news is that PEX is more freeze resistant than copper or PVC. Due to its flexibility PEX tubing is able to expand a little when water in it turns to ice and then go back to its original shape once the ice melts.

That said it is not freeze proof. In very cold or very long term freeze events, or in repeated freeze and thaw cycles the tubing’s structure will break down over time. In some rare cases PEX may still crack or split at connection points.

Factors That Increase the Risk of PEX Bursting:

1. Poor insulation of the tubing

2. Extended power outages which stop water flow

3. Water filled PEX lines that are not in use

4. Improper install or faulty fittings

Why Is This Important for Outdoor Boiler Owners?

Outdoor boilers depend on constant water flow to transfer heat from the boiler to your home’s heating system. If the water flow stops – due to a pump failure, power outage or some other issue, any exposed pipe, including PEX, is at risk of freezing.

Key Points for Boiler Owners:

• A frozen pipe will shut down your whole system

• A broken pipe will cause water damage and you’ll be looking at expensive repairs

• Frozen water in the system also reduces efficiency and may damage other components

How to Protect PEX Tubing from Freezing

Now that we know PEX can freeze and may burst under certain conditions, here are practical steps every outdoor boiler owner should take:

1. Insulate PEX Tubing Thoroughly

Use high-quality pipe insulation rated for outdoor use. Insulate both the supply and return lines—especially any section that runs above ground or is exposed to air.

2. Bury the Tubing Below the Frost Line

When installing new PEX lines, bury them deep enough to avoid exposure to freezing air temperatures. Check your local frost line depth to determine the correct burial depth.

3. Use an Insulated Underground Pipe System

Consider investing in pre-insulated underground pipe systems designed for outdoor boilers. These systems often include multiple layers of insulation, vapor barriers, and protective sheaths.

4. Maintain Continuous Circulation

Water that’s constantly moving is less likely to freeze. Make sure your system is designed to keep water circulating even when the indoor thermostat is not calling for heat.

5. Install a Backup Power Supply

Power outages are a leading cause of system failure and frozen lines. Installing a generator or battery backup system can keep your pump running during outages.

6. Drain Idle Lines

If you anticipate long periods of inactivity, drain the water from unused PEX lines to prevent freezing.

7. Regular Maintenance and Monitoring

Frequently inspect insulation, pumps, fittings, and temperature gauges to catch potential problems early.

Can Heat Tape Be Used on PEX?

Yes, certain types of heat tape are safe for use with PEX, but it’s important to choose the right product. Look for:

• Low-temperature, self-regulating heat tape

• UL-listed for plastic pipes

• Tape that does not exceed the temperature rating of PEX tubing (generally 180°F)

Always follow the manufacturer’s installation guidelines to avoid overheating or damaging the tubing.

What Happens If Your PEX Tubing Freezes?

If you suspect your PEX has frozen:

1. Turn off your boiler to prevent further pressure buildup

2. Try to identify the frozen section by feeling for cold or rigid areas

3. Thaw carefully using a heat gun, warm towels, or heated tape—never use an open flame

4. Check for leaks after thawing, especially at fittings and joints

If damage is found, replace the affected section immediately and inspect your system for vulnerabilities.

FAQs: PEX and Freezing

Q: Is PEX better than copper for freezing conditions?

A: Yes. PEX is more flexible and is also less prone to breaking when frozen in comparison to rigid copper pipes.

Q: Can I leave my outdoor boiler off in winter?

A: Not advised. By stopping the circulation you increase the risk of freezing and system damage.

Q: How long does it take for PEX to freeze?

A: That is based on ambient temperature, insulation, and water movement. Uninsulated still moving lines may freeze in just a few hours at 32°F.

Q: What temperature should I maintain to avoid freezing?

A: Keep water temp above 40°F and run circulation for best results.

Final Thoughts: Is PEX Safe for Outdoor Boilers in Cold Climates?

Yes, PEX is a great and very reliable option for outdoor boiler systems which do well in cold climates – but do require proper installation, insulation and maintenance. While it does offer better freeze resistance then metal pipes it is not totally immune to freezing and bursting.

By the time you understand how PEX performs at very low temps and put in place protective measures for your system you can have trouble free heating all winter long.

Looking for high quality insulated piping systems for your outdoor boiler? Visit OutdoorBoiler.com to see our wide range of cold weather ready solutions that will keep your system safe year round.