Can PEX be used on hot water heater?

When it comes to plumbing, one of the most common questions homeowners have is whether or not PEX tubing can be used on a hot water heater. PEX, or cross-linked polyethylene, is a flexible plastic tubing that has become widely popular in recent years for use in residential plumbing systems. Many homeowners are interested in using PEX because it is easy to install, resistant to corrosion and freezing, and often more affordable than copper or CPVC piping. However, there is some debate over whether or not it is appropriate to use PEX on a hot water heater.

The short answer

The short answer is yes, PEX can be used on a hot water heater in most situations. PEX tubing is rated for high temperatures, with some types rated for constant use up to 200°F. As most residential water heaters keep water between 120-140°F, PEX should be able to withstand these common water heater temperatures without any issues. However, there are a few caveats to be aware of when using PEX on a hot water heater which will be covered throughout this article.

PEX temperature and pressure ratings

One of the first things to understand when considering using PEX on a hot water heater is the specific temperature and pressure ratings of the tubing you plan to use. There are a few different types of PEX tubing available:

• PEX-a: Also called PEX-UNE, this type has the highest temperature rating at 200°F constant use and up to 230°F intermittent use. It is also pressure rated to 160 PSI at 73°F.
• PEX-b: This type has a slightly lower temperature rating of 180°F for constant use and 200°F for intermittent use. It has the same 160 PSI pressure rating as PEX-a.
• PEX-c: The lowest rated type, PEX-c tubing is approved for 140°F constant use and 200°F intermittent use. It shares the same pressure rating as PEX-a and PEX-b.

As you can see, all types of PEX tubing have temperature ratings well above the 120-140°F temperatures found in most residential water heaters. However, PEX-a provides the highest heat tolerance and safety margin.

Other performance factors

In addition to temperature ratings, there are a few other performance factors to keep in mind when using PEX on a hot water heater:

• Oxygen diffusion: Over time at high temperatures, oxygen can diffuse through PEX tubing and cause corrosion inside a tank water heater. Using an oxygen barrier PEX tubing and replacing anode rods regularly can help minimize corrosion.
• Thermal expansion: PEX is more flexible than copper or CPVC pipe. This flexibility allows the tubing to expand and contract with temperature changes. Properly securing PEX to prevent excessive movement is important.
• Pressure ratings: In general, PEX has a pressure rating of 100-160 PSI depending on type. This is suitable for many residential systems but high pressure demands should be verified.

Hot water heater type considerations

You also need to consider the type of water heater you plan to connect PEX tubing to. The main choices are:

• Tank style heaters: Most common type, compatible with PEX but higher risk of corrosion over time.
• Tankless heaters: Heater water on demand only, PEX is generally compatible.
• Electric heaters: Often have higher temperature settings that may exceed PEX ratings.

Tankless heaters that raise water temperature gradually are best suited for PEX. Always verify the actual system temperatures before installing PEX tubing.

Installation and transition considerations

When installing PEX on a hot water heater, there are also some important installation and transition details to address:

• Use the correct PEX fittings and crimp/clamp connections rated for the application.
• Properly anchor PEX tubing to prevent excessive movement.
• Provide thermal expansion allowances and flexibility.
• Use suitable splice connectors when transitioning from PEX to copper or other piping.

Paying close attention to the manufacturer’s instructions for proper PEX installations is always recommended.

Conclusion

In most typical residential installations, PEX tubing can be used on a hot water heater as long as you choose a high temperature rated PEX product, such as PEX-a 200°F tubing. However, you need to be aware of the temperature and pressure capabilities of the specific PEX tubing used, as well as factor in performance considerations such as oxygen diffusion, thermal expansion, and proper installation techniques. Consulting with a professional plumber is the best way to ensure your system is designed and installed properly for compatibility and safety when using PEX on a hot water heater.

Frequently Asked Questions

What are the main advantages of using PEX tubing on a water heater?

Some of the main advantages of using PEX tubing on a water heater installation include:

• Flexibility – PEX tubing is far more flexible than rigid copper pipes or CPVC tubing.
• Easier installation – PEX does not require soldering and has fewer connections.
• Corrosion resistance – PEX tubing itself does not corrode.
• Cost – PEX is often a more affordable option compared to copper.

What are the downsides to using PEX on a water heater?

Potential downsides to using PEX tubing on a water heater include:

• Oxygen diffusion – Oxygen can seep into the tank and cause corrosion.
• Thermal expansion – PEX will expand more than rigid pipe when heated.
• Plastic fittings – PEX fittings may be more prone to failure over time.
• High temperatures – PEX may not be rated for extremely high temp electric heaters.

What is the maximum temperature PEX tubing can withstand?

The maximum temperature depends on the specific type of PEX tubing:

• PEX-a can handle 200°F constant, 230°F intermittent
• PEX-b can handle 180°F constant, 200°F intermittent
• PEX-c can handle 140°F constant, 200°F intermittent

So PEX-a has the highest temperature rating for residential water heater applications.

Does PEX tubing require special installation techniques on a water heater?

PEX tubing does require some special care during installation on a water heater:

• Use proper hangers and clamps to anchor the tubing and prevent excessive movement.
• Allow for thermal expansion and contraction of the flexible PEX tubing.
• Use the approved PEX fittings and crimping tools for connections.
• Make proper transitions if connecting to dissimilar tubing materials.
• Follow manufacturer instructions for securing PEX tubing.

What is the expected lifespan of PEX tubing on a water heater?

With proper installation, PEX tubing can have a long service life on a water heater. Most manufacturers indicate an expected lifespan of 50+ years for PEX tubing itself when used in standard hot and cold potable water applications. However, factors like UV exposure, excessive temperatures, or aggressive water chemistry may shorten its usable life.

PEX Compatibility with Water Heater Types

Here is a table looking at how compatible different types of PEX tubing are with common water heater types:

Water Heater Type	PEX-a	PEX-b	PEX-c
Tank (Gas/Electric)	Excellent	Good	Fair
Tankless	Excellent	Good	Good
Electric (High Temp)	Good	Fair	Poor

As you can see PEX-a provides the highest level of compatibility across common residential water heater types due to its high temperature tolerance. PEX-b also works well for most installs, while lower rated PEX-c may not be ideal for high temperature electric water heaters.

Typical Residential Hot Water Usage

To size a hot water system appropriately, it is helpful to understand typical residential hot water usage. Here is a table showing estimated hot water usage for common residential plumbing fixtures:

Fixture	Typical Usage (Gallons)
Shower	10-25 gallons
Bath	30-50 gallons
Sink	4-8 gallons
Dishwasher	6-12 gallons
Washing machine	15-40 gallons

Understanding the number of bathrooms, showers, sinks, and other hot water appliances can help in properly sizing a water heater system. This is important when selecting a tank size and heating capacity.

Water Heater Replacement Costs

When budgeting for a water heater replacement or installation project, the costs for different types of heaters should be considered. Here are typical price ranges:

Water Heater Type	Typical Cost (Installed)
Gas storage tank	$500 – $1,500
Electric tank	$500 – $1,100
Tankless gas	$900 – $3,500
Tankless electric	$500 – $1,100

As you can see, traditional tank style units tend to be the most budget friendly options for most homes. Tankless heaters provide an endless hot water supply but at a higher upfront cost. Considering your family’s needs and hot water usage can help determine the right water heater choice.

Conclusion

In summary, PEX tubing can be a great option for connecting a hot water heater in many residential installations due to its flexibility, corrosion resistance, and low cost versus metal piping. While PEX tubing itself can withstand typical water heater temperatures, care must be taken to choose an appropriate PEX product rated for the expected temperatures. PEX-a provides the highest heat ratings. Properly anchoring the tubing, allowing for thermal expansion, and using suitable PEX connectors is also important when installing PEX on a hot water heater system. With some basic precautions, PEX offers a durable and easy-to-install piping solution for most homes and water heaters.