Thermal Products, Inc. Hydronic Heating and Solar Thermal Wholesaler

Not illegal…but a terrible idea

July 1st, 2010

I got a call from a contractor asking about proper practices and regulations regarding the use of Pex or Pex-al-Pex in a Solar Thermal System and figured this would be as good a time as any to weigh in on this controversial topic.


Pex pipe or other flexible piping is not rated for the types of temperatures or pressures that you can see in a solar thermal loop. You’re looking at typical maximum temperature and pressure ratings on the Pex tubing of 200 °F and 200 psi respectively and the latter (pressure rating) has a negative correlation to the temperature so it’s not REALLY 200 psi at those higher temps. All that being said, I have had a VERY difficult time finding information on and off the web that says in clear, plain english (or even unintelligible garbled english) that

Pex pipe should not be used for Solar Thermal applications because of the inherent temperature and pressure limitations of the material. Even in the Uniform Solar Energy Code for 2009 it doesn’t mention much useful info on this topic. On top of that, the SRCC had a committee vote and decided to ALLOW Pex and Pex-al-Pex in drainback, open loop (atmospheric pressure) systems as long as it meets certain requirements.

Read the Letter and see for yourself!

So until the regulatory bodies wise up and start working towards properly protecting the consumer, it’s up to us! Understand the limitations of Pex and the liability of the entire system to both you as the installer, and the consumer. Lastly, a system done right, always costs less in the long run than a system done cheap.

P.S.~ If ANYONE can send me a link to an official document of ANY kind calling out Pex as not suitable for Solar Hot Water, I would be very appreciative.

~Ryan Burgett

Thermal Products Head of Technology

© 2010 Thermal Products, Inc.