Pex for steam return line

ScottSecor

Yes, I'm aware that the majority of pex manufacturers rate their products at 70psi for 200 degree applications.

We recently picked up an apartment house that has approximately twelve buildings and one low pressure steam boiler. This is a typical two pipe steam system that was installed in the early 1950's. The steam condensate returns all were run in the crawl spaces of each building and connect each building in an underground concrete chase. The end of the steel return pipe is leaking where it enters the chase (approximately four or five feet underground).

Like most people we prefer to use steel pipe for returns, or occasionally copper. Unfortunately, the longest length of pipe we could fit without digging up the outdoor "vault" (pipe chase) is about three feet. The total length that runs underground is approximately forty feet. Using steel (or copper) would require about thirteen or fourteen couplings and I bet there would be many sagging areas of the pipe. The underground chase is approximately twenty for inches wide and twenty four inches tall (interior, no idea of outside), and houses four or five pipes in total.

Another contractor suggested using pex to replace the rotted steel return line. It would likely be the easiest method, but I have never tried it. Some manufacturers claim their tubing can take 230 degrees, but for how long and how many times and what if the traps allow gobs of live steam into the returns

To make things worse, I immediately noticed the last contractor installed the "save the condensate receiver pump" master trap. I suspect there are (or at least were) a bunch of original F&T and radiator traps that failed and instead of addressing them, someone installed the dreaded master trap. I can say that someone recently replaced many of the traps, so perhaps they are no longer blowing live steam back to the condensate tank that is located in a pit approximately eight feet below the base of the cast iron boiler.

Please share your thoughts.
Thank you.

Jamie Hall

I really wouldn't like to see you use PEX. It might take the heat from live steam getting into it -- which in that big a project it might well do -- but it isn't rated for it (the strength loss with temperature isn't linear -- like all plastics, it falls off rapidly past a certain temperatue).

Can you get hold of 1inch flexible Type K or L copper? In a long enough roll? That sounds small, but the actual flow rate of condensate isn't that great (one quart per minute per 100,000 BTUh) so the head loss should be manageable...

ScottSecor

I should have mentioned this being the end of the condensate line is the largest diameter on the loop. It is 2.5" steel pipe now. For reference, current boiler is a Weil McLain 1188 that is oversized for the standing radiation.

@Jamie Hall Yes, I'm, pretty sure we could get 1" soft copper in a long enough roll and we might be able to snake from the last building to the boiler room. Unfortunately, I think this is much too small to carry the amounts of condensate in this system (especially on startup). The other issue I see with soft copper is that it tends to "tangle" with other pipes in the chase. I suspect it would have high spots (dams) that would be another concern.

mattmia2

I think you would want to fish a cable/rope/tape through the chase and use it to pull the soft copper rather than try to push it. Just bend and straighten enough to get it around the corner and pull to get it to move along the chase.

I'm sure there is a chart somewhere showing temp vs pressure for the PEX. Probably isn't approved under US codes unless you can get an engineer to sign off on it.

ScottSecor

@mattmia2 I like your idea of the rope with a fishtape. We happen to have an engineer on staff, but I'm not sure we want the liability.

Jamie Hall

The 1188 will produce around 12 gpm of condensate at rated power. That will produce about 25 feet of head loss in 1 inch Type L copper for your length of run, and that is a bit much -- although that does assume that all the condensate is concentrated at the far end.

I would note, though, that PEX of the same size will have almost the same head loss.

If you can go up to 1.5 inch, you would only have about 3.8 feet of head loss -- 1.7 psi more or less. Some of that will be compensate by the steam pressure, however -- so it is probably manageable. I'd have to look at the layout and elevations to be more specific.

mattmia2

You could always run more than one tube as well.

JUGHNE

Is this a "wet" return....always full of water or a dry return...passing only water and air?

ScottSecor

Condensate station is well below the boiler water line (about eleven feet below) in a pit in the boiler room. The crawl space in the last building in the system is about one foot higher or the same height as the condensate tank. Again, off the top of my head I think this roughly forty foot underwound run has about one foot of pitch. I imagine the pipe is filled with water in the off season and cycles during the heating season.

Jamie Hall

You should have enough head to spare for 1inch copper or two 1 inch lines

Edit: that should be one 1.5 inch or two 1 inch

EBEBRATT-Ed

I did that exact same thing at a high school. They were going to tear the building down but had to get 2 years out of the old one. Condensate line rotted out.

My boss wanted to use Pex but I wanted steam rated hose. I am not sure the hose he got me was steam rated but it was 1 1/2 or 2" and we pulled it in with no issue. It was a 40-50 foot run as I recall. Don't know how it held up

Larry Weingarten

Hi, Might this help? https://www.mcmaster.com/hose/for-use-with~steam/high-temperature-steam-hose-7/ Of course, you would want it to have no sags...

Yours, Larry

ChrisJ

I'll be honest.
If I was going to try such a thing I'd probably go with polyethylene pipe.

You'll see it's only rated up to 150F, but technically I think pex only claims 180's? And they're both essentially the same material as far as temperature IMO.

I think you could have sags @Larry Weingarten as long as there's a way to wash the piping out with pressure.


But........I don't know.
I doubt I'd do it in my house, long and often run times could easily bring that over 200F.

ScottSecor

Thank you for all the ideas. Not sure I ever saw flexible hose for steam, but I have seen braided hose used on high pressure steam kettles used in cooking (kettles were on wheels). I will be suggesting this hose to the client.

mattmia2

If you dig in to the literature for hepex it is rated at 200 f and 80 psi but there might be a standard that doesn't exist in the US for that.

ScottSecor

Found something yesterday called Rovanco Pexgol. Not sure how available it is or how hard it would be to snake (or should I say sneak) it into the chase with the other pipes in the way. They claim it is rated for 230 degrees and mention condensate n their literature. I think the steam hose would be much easier to intstall.

EBEBRATT-Ed

@ScottSecor

I only worked with Rovanco 1 time. Never again. It's only flexible if you consider a rock flexible. I think the hose @Larry Weingarten pointed to is the answer

JUGHNE

I worked on a school (2 pipe system with rad traps) that had "dry" returns leaking under the floor, the floor was cut open and the piping replaced in the middle of winter. This was before I had ever been there.

I believe the piping was not laid with slope to drain correctly to the cond pump, that is I believe it had sags containing water that would prevent the air from venting thru the cond pump.
In effect it was almost a "wet" return.

Air vents were added to the end of mains for air removal.
This worked well and the steam got to the end of the piping quickly without the air having to struggle thru water pockets of the return.

If you go with a flexible return you may have the same issue.

EBEBRATT-Ed

Steam hose that is flexible laying in a pipe should be fine. Especially on a commercial job with probably higher pressure.

the alternative could be a condensate pump pumping through the new pex or hose

hot_rod

There was a time when Onix was rated at 250F. Maybe the attorneys made them back off that temperature, available in 1".
I know this because they wanted to promote it as a solar tubing needing 250- 275 rating.

The corrugated stainless tube we used as a solar tube could certainly handle the temperature. Not sure how the corrugations would bother flow. It does have a high pressure drop. CSST gas tubing without a jacket is all it was.

hot_rod

While not listed for above 200F pex can certainly run much hotter, here is one of the tests. Other tests run up to 248F for a period of time. Temperature and pressure relationship, of course.

Ironman

If you’re worried about black iron sagging with couplings every four feet, how does pex or any flexible tubing compare with that?

mattmia2

I want to see appendix A

Solid_Fuel_Man

What do they have for emitters? CI rads? Could it be converted to water? Most likely the boiler could. Then you can run PEX, copper, or whatever you want. 

Flame suit on!

Steamhead

Solid_Fuel_Man said:

What do they have for emitters? CI rads? Could it be converted to water?..... Flame suit on!

For a 12-building apartment complex?

ChrisJ

Solid_Fuel_Man said:

What do they have for emitters? CI rads? Could it be converted to water? Most likely the boiler could. Then you can run PEX, copper, or whatever you want. 

Flame suit on!

Solid_Fuel_Man

Steamhead said:

What do they have for emitters? CI rads? Could it be converted to water?..... Flame suit on!

For a 12-building apartment complex?

Maybe? Elevation would be the problem? 

I'm popping popcorn 🍿  as I type!

WMno57

Silicon heater hose.
350 F and 83 psi.
https://ph.parker.com/us/en/silicone-high-temperature-heater-hose-standard-wall-series-6722

WMno57

410 F, 261 psi, 2 inch ID, available in 40 meter rolls.

https://ph.parker.com/us/en/vigor-en-iso-6134-type-2-a-hot-water-steam-transfer-hose/ih36801706-40

I Wonder how much? Specs are similar to the hose from McMaster that @Larry Weingarten posted.

Long Beach Ed

We've used PEX for return lines on a (vacuum) Paul system we created. The steam risers were exposed and we ran clear PEX right down the backs of them. No problems at all. Sags in the horozontal runs fine because only air was handled as there is a thermostatic trap on each radiator. Any water vapor gets sucked out by the vacuum.

gerry gill

EBEBRATT-Ed said:

@ScottSecor

I only worked with Rovanco 1 time. Never again. It's only flexible if you consider a rock flexible. I think the hose @Larry Weingarten pointed to is the answer

We used steam hose to connect the ships boilers to the pier risers when in port (Navy). They held up quite well.

lenrempe

While everyone is concerned with the temperature there is Thermal Expansion to contend with. At least 150* temperature changes on each call for heat. Probably 6 inches. 

Bobsredtrucks

I have used Mega Press steel fittings designed for steam. You use steel pipe and once the Mega Press coupling is tightened the pipe will stay straight and strong. I've used Mega press fittings on many steam repairs, the amount of time saved almost pays for the tool. The fittings are not cheap but what a time saver. I've done repairs which would have taken at least 20 hours to do and my crew of 2 men were done in less then 8 hours.
Good Luck,
Bob Cermignano

LMacNevin

PEX is high density polyethylene that is crosslinked during manufacturing to improve its properties. PEX can withstand higher temperatures than HDPE and has other improved properties as well. PPI TN-17 has this information https://plasticpipe.org/common/Uploaded files/Technical/TN-17.pdf

PEX tubing is not intended or recommended for steam condensate.

All PEX tubing is rated for continuous operation of 100 psi @ 180F and many brands of PEX are also rated for 80 psi @ 200F. Hot Rod is correct that when PEX is tested for chlorine resistance, it is exposed to continuous pressure at up to 248F for hundreds or a few thousand hours, until it fails. But PEX is not rated for operation about 200F. Continuous exposure to temperatures above 200F could eventually damage the tubing and cause embrittlement. It might take 15-25 years for this to happen, depending on many factors, but it is still not recommended.

See PPI TN-52 for details about High Temperature Applications of PEX https://plasticpipe.org/common/Uploaded files/Technical/TN-52.pdf

This PPI webpage includes many details about PEX, in general https://plasticpipe.org/BuildingConstruction/BuildingConstruction/PEX.aspx

PEXGOL is a brand of PEX pipe produced by Golan Plastics in various diameters for use in many types of industrial applications. https://www.pexgol.com/

Finally, for sizing PEX or other plastic pressure pipes, check out the Plastic Pipe Design Calculator at http://www.plasticpipecalculator.com/. Thanks

JoeEngineer

This is a stretch, a total left turn; I do not have enough to make it as an informed suggestion: downsizing the whole system; how much does heating cost running an oversized boiler to feed oversized radiators; if this complex has been improved over the years with insulation, thermal windows, etc. AND it was originally sized to meet the "open window" heating load, maybe such a radical solution might make sense, especially with all the energy incentives out there.

Luv'nsteam

Why not use high temp silicone hose?  It does cost more than PEX, but some of it can handle up to 550* and comes in many ID's. 

Brian Tober

Can you pull through the old 2.5" steel pipe? Maybe 2 or 3  1" dia oxygen barrier pex lines would fit. Or the other types of pipe or hose mentioned. Use lots of liquid soap to lube it.

HEATSPEC

No, I don't think PEX would work; even in an ideal world the return water temp would still exceed 200 deg F, above the safe working limit. In addition, those of us who've worked with PEX know how "curly" it is; there would be water trapped all over the place as a straight, evenly graded run would be impossible.

I do like the CSST idea, however: it would certainly handle any temp/pressure thrown at it. It would still be difficult to get a straight, graded run, but probably doable whereas the PEX would be impossible. You could probably use gas fittings on either end and get away with it.

I also like the idea of re-examining the building itself and seeing if any of the radiators could be done away with; trouble is, downsizing would still involve keeping the existing radiators, as replacements are likely to be VERY expensive.

But, hey, anyone considered the elephant in the room? Converting the G*****n thing to a HYDRONIC system would mean you could use PEX just about anywhere you wanted; and, for the price of a circulator pump[s], you could permanently dispose of [expensive] steam traps, air vents, etc. No more "Tales of Hoffman"!

ChrisJ

I guess this forum is changing from pro steam to pro heat pumps and referring to steam systems as "G*****n things".


That's just grand, isn't it?

JohnNY

Can you install a "condensing" type radiator/fint-tube/holding tank setup to cool the condensate before it gets to your problem area? Then go to PEX or whatever you decide to use downstream of that?

Steamhead

HEATSPEC said:

But, hey, anyone considered the elephant in the room? Converting the G*****n thing to a HYDRONIC system would mean you could use PEX just about anywhere you wanted; and, for the price of a circulator pump[s], you could permanently dispose of [expensive] steam traps, air vents, etc. No more "Tales of Hoffman"!

Like some others, you have conveniently forgotten two basic facts:

1- A hot-water system runs with at least ten times the pressure of steam. This WILL cause leaks if there are any weak points in the pipes or radiators.

2- A hot-water radiator can only emit roughly 2/3 the heat of the same radiator on steam. This would probably result in under-heated rooms.

This topic comes up every so often. See:

https://forum.heatinghelp.com/discussion/145002/actual-savings-over-steam-heating