When it comes to plumbing, one of the most common questions homeowners have is whether or not they can use PEX pipe for their water heater. PEX, or cross-linked polyethylene, is a flexible plastic piping that has become increasingly popular in recent years due to its low cost and easy installation. However, many people wonder if it is suitable for use with a water heater. The quick answer is yes, in most cases PEX pipe can be used to connect a water heater. However, there are some important factors to consider.
Page Contents
PEX Pipe Overview
PEX pipe was introduced in the 1960s but did not gain widespread use until the late 1990s. It is part of a class of plastics known as thermoplastics, which means it can be heated and reshaped. This makes it very flexible and able to bend around corners without kinking. PEX is also extremely durable and resistant to freeze-breakage, corrosion, and scale buildup. Additionally, it does not contain any toxic materials like some other plastics. This combination of flexibility, durability, and non-toxicity has made PEX a popular alternative to traditional metal pipes like copper.
Types of PEX
There are three main types of PEX pipe:
- PEX-A: This is the most flexible type of PEX. It is manufactured using the Engel method which uses peroxide to crosslink the polyethylene.
- PEX-B: This type is moderately flexible and is made using silane for crosslinking.
- PEX-C: This is the least flexible type of PEX. It is manufactured using electron beam processing to crosslink the polyethylene.
All three types of PEX are approved for potable water use. However, PEX-A is considered the highest quality pipe with the greatest flexibility and cold weather performance. PEX-B and PEX-C give up some cold weather performance for increased rigidity and heat resistance.
Advantages of Using PEX for Water Heaters
There are several reasons why using PEX pipe for a water heater connection makes sense:
- Flexibility – The flexible nature of PEX simplifies installation. PEX can make tight bends around joists and studs without kinking.
- Durability – PEX is highly durable and can last 30+ years with minimal maintenance.
- Freeze resistance – PEX expands when water freezes inside it, reducing the chance of bursting.
- Corrosion resistance – PEX does not corrode from water exposure.
- Scale resistance – PEX is less prone to mineral scale buildup compared to metal pipes.
- Non-toxic – PEX does not contain lead or other hazardous materials that could leach into the water.
This combination of beneficial properties makes PEX an ideal choice for water heater connections in most homes. The flexibility allows it to be easily snaked from the heater to the supply lines. The durability ensures the pipe will last as long as the water heater itself. And the scale and corrosion resistance help maintain water flow and prevent leaks.
Potential Drawbacks of PEX for Water Heaters
While PEX has many advantages, there are a few potential drawbacks to be aware of:
- High temperatures – PEX typically has a maximum service temperature between 180-200°F. Fluctuating high temps from some heaters may impact long term performance.
- UV light degradation – PEX breaks down over prolonged UV light exposure. Runs in sunlight should be minimized.
- Rodents – Rodents are attracted to the taste of PEX and may gnaw on exposed pipes.
- Difficult repairs – PEX is not as easy to repair as sectional metal or copper pipes. Entire runs may need replacement.
- Expense – PEX costs more than basic plastic or vinyl tubing, although it is generally cheaper than copper.
These potential issues do not mean PEX cannot or should not be used for water heaters. But they are factors to keep in mind during design and installation.
Hot Water Concerns
The biggest drawback to be aware of is the hot water temperature limitations. While PEX can handle pressures up to 100 psi at 180°F, temperatures above 180°F will accelerate the breakdown of PEX over time. Standard tank water heaters normally operate at 120-140°F. However, some conditions may expose PEX to higher temps:
- Faulty thermostats leading to excess tank temperatures.
- Long pipe runs allowing heat dissipation before the tap.
- Being located downstream from a recirculating loop or tankless heater which can supply 180°F+ water.
In these cases, a heat diffusion plate or mixer valve can be installed to prevent PEX being exposed to excessive heat. Alternately, flexible PEX connectors can be used for the final hookups rather than full PEX runs from the heater.
Installation Considerations
When installing PEX for a water heater, there are several guidelines to follow:
- Use PEX rated for at least 100 psi at 180°F. Higher temperature ratings are available up to 200°F.
- Minimize UV exposure by avoiding runs in direct sunlight.
- In areas prone to rodents, encase PEX in metal or rigid conduit.
- Allow extra length for expansion and contraction of the flexible PEX pipe.
- Use bend supports if PEX will have tight turns to prevent kinking.
- Ensure all fittings and crimp rings are compatible with the type of PEX used.
The installation configuration can also impact performance. The optimal setup is to have a short PEX run directly from the water heater using 45° elbows or sweeps for any turns. This minimizes heat loss and flow restrictions. For heaters prone to high output temperatures, a heat diffusion plate or mixing valve can be installed to reduce excess temperatures before the PEX.
Making Connections
There are a few options when it comes to making water-tight connections with PEX:
- Crimp fittings use a copper crimp ring to seal to the PEX.
- Compression sleeves slide over the PEX and bite into the pipe when tightened.
- Push-to-connect fittings use an internal grip ring or teeth to secure the PEX.
For a reliable water heater connection:
- Use fittings approved for potable water use.
- Ensure fittings match the specific type of PEX pipe being used.
- Avoid using saddle valve connections which can limit flow and develop leaks.
- Make sure crimp tools provide an even, consistent squeeze.
Choosing the Right PEX
With all PEX brands claiming to meet standards for potable water use, choosing the right product can be confusing. Here are a few top options to consider for water heater connections:
PEX Brand | Type | Temperature Rating | Special Features |
---|---|---|---|
Uponor AquaPEX | PEX-A | 180°F | ProPEX expansion fittings, excellent cold weather performance |
Zurn PEX | PEX-A | 200°F | Dual temperature ratings, 25-year warranty |
Rehau Everloc+ | PEX-A | 180°F | Stable fitting expansion, no metal crimp rings |
SharkBite PEX | PEX-A | 200°F | Push-to-connect fittings, speedy installation |
Viega PureFlow PEX | PEX-A | 180°F | Minimal expansion, complete systems available |
PEX-A is usually the ideal choice for water heater applications due to its maximum flexibility and cold weather performance. Brands like Uponor AquaPEX, Zurn PEX, and Rehau Everloc+ are industry leaders in PEX-A quality and reliability.
Conclusion
In most residential settings, PEX can be safely used as the pipe connecting a water heater to the home’s supply lines. Compared to copper or rigid plastic, PEX offers a combination of flexibility, durability, and heat resistance that makes installation simpler while still providing reliable performance. However, it is important to follow temperature limits, avoid UV exposure, make secure connections, and take precautions in situations prone to excessive heat. With proper installation and care, PEX should last the full lifespan of a typical water heater with minimal issues.