If you're planning a plumbing project or replacing old pipes, you've likely
encountered PEX tubing. Its flexibility, cost-effectiveness, and ease of
installation have made it a popular choice for modern plumbing. But a critical
question often arises: Can you use PEX pipe for hot water? The short answer is a
resounding yes. PEX is fully approved for both hot and cold water distribution
systems. However, understanding the specifics—like temperature limits, material
types, and proper installation—is key to ensuring a long-lasting and reliable
system. Let's dive into the details.
Yes, PEX is Approved for Hot Water
PEX (cross-linked polyethylene) is specifically engineered to handle heated
water. Building codes throughout the United States and Canada recognize PEX as
suitable for residential hot water supply lines. Unlike older materials like
polybutylene (PB), which failed over time, PEX has a robust molecular structure
that can withstand the thermal expansion and contraction of hot water
cycles.
Understanding PEX Types and Temperature Ratings
Not all PEX is created exactly equal. There are three main types: PEX-A,
PEX-B, and PEX-C, differentiated by their manufacturing process. For hot water
applications, all three types are generally acceptable, but they have slightly
different properties.
PEX-A: Known for its superior flexibility and highest resistance to
cracking under freezing conditions. It typically has the highest chlorine
resistance, which is important given that public water contains chlorine that
can degrade plastics over time at high temperatures.
PEX-B: The most common and economical type. It is slightly stiffer than
PEX-A but is still highly durable for hot water use.
PEX-C: Less common and generally the stiffest of the three, making it more
susceptible to kinking.
Crucially, all PEX tubing must meet the same ASTM (American Society for
Testing and Materials) standards for heat performance. The standard temperature
rating for PEX water pipe is 200 degrees Fahrenheit (93 degrees Celsius) at 80
psi. Since most residential water heaters are set to a safe 120°F (49°C) to
140°F (60°C), PEX operates well within its safety margin.
The Color Code: Don't Be Fooled!
You may have seen PEX pipes in red, blue, and white. The red and blue
colors are for convenience only—red for hot water, blue for cold water. A white
PEX pipe can be used for either. The color is purely an identifier for
installers and homeowners and does not indicate a different material
formulation. A red PEX pipe has the exact same temperature rating as a white or
blue one from the same manufacturer.
Important Considerations for Hot Water Use with PEX
While PEX is excellent for hot water, a few factors require attention for
optimal performance:
Oxygen Barrier: In closed-loop heating systems (like radiant floor heat),
it's essential to use a special PEX-AL-PEX or Oxygen Barrier PEX. This type has
a layer that prevents oxygen from penetrating the tube walls, which can cause
corrosion in cast iron boilers and other ferrous components. For standard
domestic potable hot water lines, standard PEX is sufficient.
UV Resistance: PEX tubing is not resistant to ultraviolet light. Prolonged
exposure to sunlight can degrade the material, weakening it and reducing its
ability to handle pressure and heat. PEX should be stored indoors and installed
inside walls, floors, or ceilings.
Connection to Water Heaters: Most building codes require a short section
(12-18 inches) of metal pipe (copper or CSST) connected directly to the water
heater's hot outlet. This precaution is to protect the PEX from the extreme heat
that can be present right at the heater connection, especially if the thermostat
fails.
Chemical Compatibility: While PEX is highly resistant to scale and
corrosion, the quality of the water can affect its lifespan. If you have highly
chlorinated water, consulting with the PEX manufacturer about their product's
specific chlorine resistance is a wise step.
Advantages of Using PEX for Hot Water
Flexibility: PEX can bend around corners, reducing the number of fittings
needed and potential leak points.
Quieter Operation: The material absorbs the sound of water flow better than
copper, leading to quieter pipes.
Scale Resistance: PEX does not corrode or build up scale like metal pipes
can, maintaining water flow over decades.
Faster Heat Retention: Some argue that PEX water pipes may feel hotter to
the touch but also may lose heat slightly faster than copper in long runs.
Proper insulation on hot water lines is always recommended regardless of pipe
material.
Conclusion
So, can you use PEX pipe for hot water? Absolutely. PEX is a versatile,
reliable, and code-approved material for both hot and cold water supply lines in
your home. By choosing the right type of PEX, following manufacturer guidelines
and local building codes, and being mindful of installation details (like
keeping it away from direct sunlight), you can enjoy the benefits of a PEX
plumbing system for your hot water needs for years to come.
For any major plumbing project, always consult with a licensed professional
to ensure your system is safe, efficient, and up to code.
