Pex tubing temp/pressure limits

George Webster said:

Does anyone out there know what the safe limits are to run pex tubing at? I am using 1" pex to "communicate" with my storage tank. The tank is not pressureized, so the pex sees very low pressure (circulators). I'd like to run the supply up a bit hotter to reduce the charge time, or maybe increase the storage temp. I am at 180 right now. I'd like to get closer to 186 for supply to get my tank into the low 180's.

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It should be stamped right on the tube, often it is something like 200Fat 80psi, 180F at 100 psi, and 73F at 160psi, from an old Wirsbo Design Manual.

Rumor has it PEX can run higher temperatures, at lower pressures but the manufacturers legal team may have a say in the ratings.

The PEX folks have had a fair share of legal claims over the years and I expect they are very conservative. I expect the tubing has a much higher pressure rating than the connections.

While it will take temps above 200, the pressure curve slopes downward with the same trajectory as a pregnant elephant diving off the Empire State building.

Every year we hear about a mishap involving someone who connected pex directly to the back of their boiler.

heaterman said:

While it will take temps above 200, the pressure curve slopes downward with the same trajectory as a pregnant elephant diving off the Empire State building.

Every year we hear about a mishap involving someone who connected pex directly to the back of their boiler.

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And it gets incredibly soft at temperatures above 180F, almost like a spaghetti noodle. It needs plenty of supports, especially at fittings where the tube hangs, for elevated temperature use. Do as with swimming pool heaters do and run a section of steel or copper, then transition to pex for a bit of temperature relief.

I cringe when I see pex crimped right onto the back of OWF, it's just a matter of time...

,,, with the same trajectory as a pregnant elephant diving off the Empire State building.

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The person who did the physical research study on that trajectory so that she could see the elephant take the dive was suddenly unable to complete her work.

Your PEX is on the other side of a heat exchanger from the boiler, so it should be somewhat safer from unintended high temperature excursion. Still, it gets a lot softer and a lot longer (if it can). Depending on how it's supported, that could lead to really interesting sags, bends, and kinks. I need to look up the coefficient of thermal expansion for PEX - I wonder if it's linear?

Sometimes increasing efficiency is like climbing a tree: At first, it's relatively easy and fun. You can smugly look down on all the folks who didn't have the initiative or cleverness that you have. As you get higher, though, the branches get thinner......