PEX for 1 Pipe Steam returns

Kjmass1

Is there a technical or code reason why you can't use PEX as condensate return in a 1 pipe steam application? My existing returns are offset from the foundation almost 3 feet so would like to re-run to get them closer to foundation. They are rated at 80 psi @ 200F and I'm running .5 PSI if that.

Kevin

ethicalpaul

I think my returns must be about 212F-218F. I would fear the pex would start to deform. But I like the way you are thinking!

This document explains how the testing works, but says that pex shouldn't be used over 200F any time. But it looks like manufacturers could pass some testing that would show the tested material could last for a long time at wet return temps...I'm not quite scientific enough to know for sure: https://plasticpipe.org/pdf/tn-52-guide-pex-high-temp.pdf

Ironman

Pex on steam? Please, don't even consider this.

Kjmass1

ethicalpaul said:

I think my returns must be about 212F-218F. I would fear the pex would start to deform. But I like the way you are thinking!

This document explains how the testing works, but says that pex shouldn't be used over 200F any time. But it looks like manufacturers could pass some testing that would show the tested material could last for a long time at wet return temps...I'm not quite scientific enough to know for sure: https://plasticpipe.org/pdf/tn-52-guide-pex-high-temp.pdf

Your condensate is at 212F+? The highest I've seen my rad or supply pipe at the radiator is around 190, I can't imagine the return drips being anywhere close to that. Thanks for the document.

Kjmass1

Ironman said:

Pex on steam? Please, don't even consider this.

It's just an honest question and looking for reasons why not.

Jamie Hall

While I wouldn't recommend it, you could probably get away with PEX -- properly supported -- on wet returns; those which are solidly below the boiler water line.

Dry returns? Ah... no. Even if they are true dry returns, and not "dry returns" which are really extensions of steam mains, there is a possibility of live steam getting into them. You would be using the material in an application for which it is not intended, and for which it has not been tested. Never a good idea.

Also, even if they don't fail while you own the house, unless they are fully supported (not just hung from time to time, but supported in a trough) they will sag -- and since dry returns have to pass air, that will be blocked by the water trapped in the sags, leading to at best uneven heat and at worst no heat at all.

Kjmass1

Jamie Hall said:

While I wouldn't recommend it, you could probably get away with PEX -- properly supported -- on wet returns; those which are solidly below the boiler water line.

Dry returns? Ah... no. Even if they are true dry returns, and not "dry returns" which are really extensions of steam mains, there is a possibility of live steam getting into them. You would be using the material in an application for which it is not intended, and for which it has not been tested. Never a good idea.

Also, even if they don't fail while you own the house, unless they are fully supported (not just hung from time to time, but supported in a trough) they will sag -- and since dry returns have to pass air, that will be blocked by the water trapped in the sags, leading to at best uneven heat and at worst no heat at all.

Great explanation, thank you. It would be nice to have a cheap solution to this but doesn't seem like that is the case.

ethicalpaul

Kjmass1 said:

Your condensate is at 212F+? The highest I've seen my rad or supply pipe at the radiator is around 190, I can't imagine the return drips being anywhere close to that. Thanks for the document.

My thinking was that steam is in the main all the way to the wet return and the condensate would be just below steam temperature, which at pressure, could be as high as 218, especially with insulated main and return.

But I bet you are right that after the main vent shut off, the return would cool a bit. I'll have to measure it now.

Jamie Hall

Folks, don't forget that there are dry returns -- in two pipe systems, which are never intended to see steam, although they do get warm condensate (unless a trap fails...) -- and then there are "dry returns" in both one pipe and two pipe systems which are not truly dry returns at all, but are extensions of the steam main back to the boiler -- common enough in parallel flow one pipe systems.

They are not the same and they do not behave in the same way.

A "dry return" in the sense I use it above will see steam, whether it is vented or not Not much, granted, if it isn't vented -- but it will be there.

mikeg2015

IF a trap fails, it will melt the tubing. Just that simple.