A discussion about wet steam to not hijack anyone's thread

ethicalpaul · January 18

@Captain Who honorably didn't want to hijack a thread so I brought it here for folks who want to discuss wet steam.
I kind of don't usually continue to debate when someone clearly disregards most of what I say, and I don't want the OP to feel like this is about you and me and not him and disappear due to cringe, but I'll say this:
I didn't mean to disregard what you said. Your points might have been clearer to you than they were to me, I'll try again. If you don't like my replies below feel free to ignore them and ask me fresh questions or make fresh points.
Wet steam isn't "sub-visible" in problematic amounts—droplets are often visible as mist or spray in tests, and even trace wetness (1–3%) causes measurable efficiency loss (longer radiator heat-up, higher pressure drops).It's not "ceasing to exist BTUs"; it's
wasted sensible heat
evaporating the liquid instead of delivering latent heat in radiators.
I don't see how it can be wasted. It goes into the water in the boiler, it converts some water to steam, the steam goes into the pipes. If the sensible heat converts water to latent heat by evaporating it, all that heat energy is conserved and it is given back when the steam condenses. There are occasional visible drops that make it as high as the risers, but they don't take away any of the heat energy, they just travel a few inches until they hit the wall of the pipe. This we have observed in my videos.
Also, I think Dan Halohan would rightfully feel slighted by your comments. I mean, you are suggesting that he just conducted thought experiments and didn't do any research. I guess it is true that his writings aren't scientifically rigorous in the respect that he footnoted everything with references but come on! Some quick research online gave me this:
I don't know why he would feel slighted. I think he has stated he has never installed a boiler. I don't think he has measured the amount of liquid water in steam, or measured how it affects heating. I am indeed suggesting that he thought about steam, observed steam systems in action, read about, and thought about steam. Is there something negative about that?
The quotes below are words that someone wrote (I guess they are Dan's?). Some of them are fine and some of them don't mean very much. I'll address them since you listed them.
In articles like "Dry Steam Is The Goal" and "The Subtlety of Steam":
"If the steam goes too fast as it leaves the boiler, it will tornado-suck the liquid water right out of the boiler. That gives birth to wet steam, which is steam that contains more than 2% liquid water."
This is a strange one. How does steam go too fast as it leaves the boiler? When I constricted my steam supply pipe down to 1" what I saw was the opposite—the steam pressure built up in the boiler because of the bottleneck, which as we know causes the steam to be slower. It was faster in the bottleneck of course, but where the water is (in the sections), the velocity of the steam is slower.
So does that mean that by over-sizing the supply pipes that would increase carryover? I think @EzzyT who at least doubles the manufacturer recommendation for steam supplies on many boiler installs probably disagrees with this.
So I would disagree with the statement above.
"The slower the steam goes, the less boiler water it will take with it."
This is true I think, but not very useful since I have never seen steam take any boiler water with it (and I have repeatedly looked).
Larger headers slow velocity, giving carryover water time to drop back → "Drop headers leave the carryover water back in the boiler and the results are remarkable."
I would agree that larger headers and drop headers give carryover water time to drop back into the boiler. But again, the real issue is "what caused the carryover?" And I claim it is water quality and only water quality. As I have said recently, I don't believe in a thing called "wet steam" but I do believe in and have seen "carryover". You seem to agree with this as well because you have said that when your water is clean you don't have any trouble despite your bad piping. So it is clear that in your boiler, bad piping is not causing carryover, but water quality is. Correct me if I'm mis-remembering what you said.
Wet steam increases system pressure drop (water burdens the steam) → longer run times, higher fuel use.
The term used here is "wet steam" but are we really talking about carryover? Tiny droplets of water do not "burden the steam" nor do they stay steamborne very long. They hit the wall of the pipe and join the rest of the condensate that is forming there. But carryover into the main I could see where people would think it "burdens the steam". But I have to ask how could it cause higher fuel use? I return to what I said before, where do the BTUs supposedly go? The burners heat the water, the water makes steam and even if it is carrying over, all that heat is in the steam system, there's no other place for it to go.
Poor piping on replacements leads to callbacks: wet steam causes water hammer, uneven heating, high bills.

Carryover causes water hammer, but little droplets of water don't. Carryover could cause uneven heating by preventing steam from getting to some radiators, but tiny droplets of water don't. I don't know about high bills…I guess if a single radiator near the thermostat were being crippled due to carryover and being full of water, for example, that could potentially cause a little higher heating bills, but I don't think it would be noticeable — far more noticeable would be the water shooting out of the vents or the LWCO continually kicking in.

Captain Who · January 18

I said: "Wet steam isn't "sub-visible" in problematic amounts—droplets are often visible as mist or spray in tests, and even trace wetness (1–3%) causes measurable efficiency loss (longer radiator heat-up, higher pressure drops). It's not "ceasing to exist BTUs"; it's wasted sensible heat evaporating the liquid instead of delivering latent heat in radiators."

You said: "I don't see how it can be wasted. It goes into the water in the boiler, it converts some water to steam, the steam goes into the pipes. If the sensible heat converts water to latent heat by evaporating it, all that heat energy is conserved and it is given back when the steam condenses. There are occasional visible drops that make it as high as the risers, but they don't take away any of the heat energy, they just travel a few inches until they hit the wall of the pipe. This we have observed in my videos."

Let's take things one at a time Paul. This is a very basic concept, the one of phase change thermodynamics and heat transfer. Latent Heat of Vaporization, ie. latent heat is what we want to maximize in the radiator because it is the condensation of the steam within the boiler that transfers the heat to the room through the cast iron of the radiator. Any liquid water disrupts that by taking heat energy from that steam by changing phase from a liquid to a gas, that could've been transferred to the room. Therefore,,,,,,,,stick with me on this……….the boiler has to run longer to satisfy the thermostat. «« Very most important concept in steam heating!!

Condensation releases 970 times more heat per unit mass than cooling the resulting liquid by 1°F (970 BTU/lb vs. 1 BTU/lb). Even if you consider a larger temperature drop for the liquid (e.g., cooling to room temperature, say ~140°F drop from 212°F), it's still only ~140 BTU/lb—less than 15% of the latent heat from condensation.

Can you try to focus on this simple concept? Agree or Disagree?

Now, if there is a little bit of liquid water in that steam that enters the radiator that is one thing. Can you agree that if there is even more liquid water (mass percentage) present in that steam it is worse?

Agree or Disagree?

No offense, but if you won't agree to these two things I think I'm wasting my time.

ethicalpaul · January 18

Any liquid water disrupts that by taking heat energy from that steam by changing phase from a liquid to a gas, that could've been transferred to the room. Therefore,,,,,,,,stick with me on this……….the boiler has to run longer to satisfy the thermostat. «« Very most important concept in steam heating!!
Can you try to focus on this simple concept? Agree or Disagree?

Sorry but I disagree the way that is written.

The energy is put into the water in the boiler, it can't be lost. It is given up in the radiator and the pipes.

To focus,

Any liquid water disrupts that by taking heat energy from that steam by changing phase from a liquid to a gas, that could've been transferred to the room.

I'm not sure what you are getting at here, but to answer what you wrote, liquid water doesn't disrupt anything the way you have written it. If the steam has enough energy to convert more water into steam, then it does so, and that energy is conserved as latent heat and gives back heat when the water becomes liquid again.

Let me present it this way:

In every single pipe in all of our systems, there is liquid water. There are droplets of new condensate on the walls of the pipe, there is flowing condensate on the bottom of the pipe. The steam passes all this water and some of the liquid water becomes steam again, while some of it continues on its way back to the boiler.

Is that stealing heat from us?

I'll keep saying it: the BTUs are going into the system. If we are losing them, where are they going?

Captain Who · January 18

You are thinking conservation of energy instead of maximizing heat transfer to the room (to satisfy thermostat) for the least possible run time (least amount of gas burned) for the boiler.

Yes the heat is not destroyed, it is just not maximized in doing what we want, namely warming the room and satisfying the thermostat.

For the same mass of steam mixture entering the radiator:

Dry steam: Almost all mass condenses → delivers nearly full latent heat (~970 BTU/lb) directly to the room.
Wet steam (e.g., 3% liquid): Only ~97% of the mass condenses → the 3% liquid must evaporate first (absorbing ~29 BTU/lb from the system), so net heat output drops proportionally. The boiler runs longer to make up the difference, increasing fuel use.

ethicalpaul · January 18

It does go to the room. There's no other place for it to go. If you have insulated pipes in the basement, then very little goes into the basement. This is independent of how much water happens to be with the steam.

If you have uninsulated pipes, then more goes into the basement, but this is not related to how "wet" the steam is.

No matter how wet the steam is, the BTUs are going into the system.

Yes, we don't deliver heat directly to the room, it has to go through pipes, but that is completely a separate thing from how much water is in the steam.

There is a common quote that "water kills steam" but it can't (I'm not talking about cold water lying in a sagged pipe). After all, the whole boiler is full of water, yet steam is created and escapes. There is water throughout all the pipes, but yet steam travels to the radiators.

If water was preventing steam from delivering heat to our rooms, those BTUs must be going somewhere. Where are you alleging they are going?

Captain Who · January 19

You said: "It does go to the room. There's no other place for it to go. If you have insulated pipes in the basement, then very little goes into the basement. This is independent of how much water happens to be with the steam."

Noooooo!!! It (the hot water in the steam plus water 2 phase mixture) mostly goes back to the boiler along with the rest of the condensate, ie. very little and inefficient heat transfer through the cast iron. The steam that condenses on the inner cast iron walls of the radiator is doing what we want because that is transferring the latent heat of vaporization of the steam to the metal and that conducts in the direction from hot to cool, ie. through the cast iron and then by convection heat transfer to the ambient air of the room. Basic Heat Transfer and Thermodynamics. The heat in the hot water isn't destroyed but it doesn't do what we want, ie. it doesn't help to satisfy the thermostat, yet it cost us money and fuel to create it and it took the place of some of the steam which we want because it has roughly 970x more heat transfer per lb.

ethicalpaul · January 19

Sorry, we must simply disagree there. I'm still waiting for an answer to my 3-time question: If the BTUs aren't going (via steam) to the radiators, then where are they going?

Captain Who · January 19

You said: "If water was preventing steam from delivering heat to our rooms, those BTUs must be going somewhere. Where are you alleging they are going?"

I just answered this above. It is basic basic basic steam heating stuff.

ChrisJ · January 19

https://forum.heatinghelp.com/discussion/comment/1882918#Comment_1882918

Respectfully I didn't see you answer it.

It would be good if everyone could remain respectful though. There's no reason not to be.

Captain Who · January 19

You said: "If water was preventing steam from delivering heat to our rooms, those BTUs must be going somewhere. Where are you alleging they are going?"

Water takes the place of some of the steam that we would have if it was totally dry steam. Steam, due to the latent heat of vaporization, has roughly 970x the heat transfer of the water (edit to add - actually less than this due to the enthalpy of the saturated liquid water but it was just to make a point). The BTUs that are not transferred to the room are not effective in doing what we want, which is satisfying the thermostat, and are returned to the boiler. The boiler has to run longer, ie. burn more fuel, to satisfy the thermostat with wet steam. The wetter the steam is the worse this is.

ethicalpaul · January 19

I thought of something you said earlier and how it might help you understand what I'm saying. See if this triggers anything for you.

You said:

The steam that condenses on the inner cast iron walls of the radiator is doing what we want

So freshly condensed liquid water is "good water" because it came from steam that delivered its heat. OK, so that must mean that carried-over or "wet steam" liquid water must be "bad water" (because you have said it doesn't help in transferring BTUs to the radiators (I think that's what you said).

But what exactly is the difference between the two? They are both liquid water that is just at the saturation temperature. Is the system able to tell the difference between them? Do they act differently in the system?

I would say no

Do know that I do not like carryover—but I can't see it hurting BTU transfer any more than water in the boiler does—there's nowhere else for those BTUs to go (I guess I'll keep saying it 🙂).

I do appreciate your time in this discussion also, thank you.

Captain Who · January 19

Here is some stuff to help you understand the science of dry steam heating value vs. wet steam heating value. It is actually enthalpy. The enthalpy of dry steam on a per lb basis at 1psig (reasonable for our boilers but pressure at radiators is probably less due to pressure drops especially with wet steam) is 1151 Btu/lb. The enthalpy of saturated water is 183 Btu/lb and the difference between the two is the Latent Heat of Vaporization and is 968 Btu/lb.

https://www.engineeringtoolbox.com/saturated-steam-properties-d_273.html

Here is what is involved with a dryness factor of 0.95. I'm betting we have nowhere near that dry of a steam quality as it enters our radiators. I KNOW I cannot with my dirty and poorly piped system. I copied and pasted this from here and it is in SI units but you get the idea. Note that the actual situation is much worse regarding heat transfer to the room because a lot of the droplets drop out into the condensate within the radiator and do not effectively transfer their heat through the walls of the radiator to the room:

https://www.engineeringtoolbox.com/wet-steam-quality-d_426.html

The steam dryness fraction is used to quantify the amount of water within steam.

Dry steam - all water molecules are in the gaseous state
Wet steam - a portion of the water molecules have lost their energy- latent heat - and condensed to tiny water droplets

To produce 100% dry steam in an boiler and keep the steam dry throughout the piping system is in general not possible. Droplets of water will escape from the boiler surface due to turbulence and splashing when bubbles of steam break through the water surface. The steam leaving the boiler space will contain a mixture of water droplets and steam.

In addition heat loss in the pipe lines condensates parts of the steam to droplets of water.

Steam - produced in a boiler where the heat is supplied to the water and where the steam is in contact with the water surface of the boiler - contains approximately 5% water by mass.

Dryness fraction of Wet Steam

If the water content in the steam is 5% by mass, then the steam is said to be 95% dry with a dryness fraction 0.95.

Dryness fraction can be expressed:

ζ= ws/(ww+ws) (1)

where

ζ=dryness fraction

ww=mass of water (kg, lb)

ws=mass of steam (kg, lb)

Enthalpy of Wet Steam

Actual enthalpy of wet steam can be calculated with the dryness fraction - ζ- and the specific enthalpy hs-of "dry" steam picked from steam tables. Wet steam will always have lower usable heat energy than "dry" steam.

ht=hsζ+ (1 - ζ) hw (2)

where

ht=enthalpy of wet steam (kJ/kg, Btu/lb)

hs=enthalpy of "dry" steam (kJ/kg, Btu/lb)

hw=enthalpy of saturated water or condensate (kJ/kg, Btu/lb)

Specific Volume of Wet Steam

The droplets of water in wet steam occupies a negligible space in the steam and the specific volume of wet steam will be reduced by the dryness fraction.

vt=vsζ (3)

where

vt=specific volume of wet steam (m3/kg,ft3/lb)

vs=specific volume of the dry steam (m3/kg,ft3/lb)

Example -Enthalpy and Specific Volume of Wet Steam

Steam with pressure5bar gauge (6 bar abs) has a dryness fraction of 0.95.From the steam table:

hs=2755.46 (kJ/kg)

hw=670.43 (kJ/kg)

The total enthalpy can be calculated:

ht=(2755.46 kJ/kg) 0.95 + (1 - 0.95) (670.43 kJ/kg)

=2651kJ/kg

Specific volume can be calculated:

v=(0.315 m3/kg)0.95

=0.299m3/kg

Captain Who · January 19

Read this. He doesn't go into the methodology of testing for steam dryness but they used to do it even for our small BTU output boilers but they stopped when boiler sections became smaller for better combustion efficiency but that hurt the dryness of steam to the point where they didn't want to test them any more.

Dan Holohan: Dry steam is the goal

https://www.pmmag.com/articles/104718-dan-holohan-dry-steam-is-the-goal

ethicalpaul · January 19

you are proving my point with that graph.

As I have been saying, all the steam we produce is wet steam.

It’s all at about 5% regardless of piping.

The piping can help if you have carryover to let that water fall back to the boiler, but that’s it

All the steam we produce has the same energy at typical and desirable operating pressure.

Still wondering where those lost BTUs go in your view, or the difference between “good” and “bad” water in our systems that you said exist.

ethicalpaul · January 19

this is why so many people have been confused by Dan’s discussions of wet steam. He himself seems to be confusing the liquid content of the steam as generated with carryover water. They are two completely different things, do you agree?

clammy · January 19

sensible heat , latent heat know the difference and realize that insulating steam main and piping help keep the latent heat from collapsing and giving up the 970 btus and turning backing into 212 degree condensate which does no work on a steam heating system except possible cause grooving in supply mains and causing leaks at the threads on joints . how do i know this well i have seen it on uninsulated mains which the boiler where poorly piped it s a go hand and hand sceneone results in the other . Dry steam has a higher latent heat value then wet steam .This is why some like to go a little over manufactures spec being the dryer the steam the more latent heat gets on and better performance over all occurs . You can go to any extent of discission but over all poor piped boiler produce poor quality of steam ,uninsulated headers and steam mains waste heat putting it where it not suppose to go and give off all of it latent heat to the basement instead of radiators . There's really no need to drag a dead cat unless thats what your into ,This is not brain surgery so why make it that if ya gotta think and mill bout it possibly its not in your fortay .no need to prove it w glass risers it common knowledge to those who do this every day for ions ok maybe 35 to 40 years that being said i also goes w caring about the work you do over just a paid wrench spinner for a boss who's more interested in $ then the overall quality and operation of the whole pic ,This is why some of us do not get the work because w do all this and more but are beat down by 1/2 jobs being done . As things stand being different and telling it like it is ain t what it used to be now you must be wrong or your ripping us off .I say ok its fine by me im really not the one who has to live w it and be uncomfortable and pay a higher fuel bill or better yet pay and switch to hot air w heat pump . I m sure there loads of companies more then willing .

peace and good luck clammy

ethicalpaul · January 19

Thanks for that clammy, but I already showed with no doubt that my boiler delivers its steam perfectly fine with a single 1" supply pipe, did you see the video here, it's short?

All the steam our boilers create regardless of piping is the same wet steam with the same percentage of liquid water in it
Carryover is something different and although good piping can let the carryover fall back into the boiler, it is not caused by the piping, it is caused by the water quality (oil or solids causing carryover).
Regardless of #1 and #2, the BTUs are getting delivered into the system, into our houses, into the radiators because there simply is no other place for them to go so all discussions of boiler piping increasing efficiency are imaginary, until someone can tell me where those BTUs are going if not into my radiators.

Captain Who · January 19

https://forum.heatinghelp.com/discussion/comment/1882963#Comment_1882963

Dude you are way to quick to dismiss Dan Halohan. I see nothing confusing here. I believe I told you in your youtube video about this, unless it was one of my comments that you deleted (or hid). With wet steam, the wetter the steam is, the higher the return condensate will stack up where it drops from the main to the wet return, due to the higher boiler pressure needed to overcome the additional pressure drop created in the pipe due to the fact that you don't have dry steam. I believe, if IIRC, in your video with the extreme restriction at the boiler, you got the condensate going above the sight glass in you return. You couldn't measure it and didn't realize its significance and your sight glass wasn't long enough or tall enough to measure it anyway.

EdTheHeaterMan · January 19

Although I like debating @ethicalpaul on subjects like this I must agree with him on this @Captain Who.

This discussion of wet steam appears to overlook a fundamental principle of thermodynamics:

Energy can neither be created nor destroyed… Much of the argument implies that heat is somehow wasted, lost, or rendered ineffective depending on whether the steam quality is wet or dry. That implication assumes the sensible heat contained in the liquid water entrained in the steam is effectively lost.

If that assumption were correct, it would be difficult to explain how a boiler operating entirely in the liquid phase—without producing steam—can successfully heat a building. Hot-water heating systems rely exclusively on sensible heat transfer and are demonstrably effective.

If only the latent heat content (approximately 800 BTU/lb for example) of wet steam is considered useful, and the remaining ~212°F liquid water is assumed to contribute nothing to space heating, then that conclusion directly conflicts with the proven performance of hydronic systems. Sensible heat transfer is not only real, but is the sole heating mechanism in hot-water systems and clearly contributes to heating the space wherever that energy is released.

A BTU is a BTU—it is a measure of energy content in the water or steam within the heating system. The only meaningful loss of fuel energy between combustion and the water/steam is the portion that exits the system through the flue. All fuel BTUs that are successfully transferred to the water and leave the boiler will ultimately be released as heat somewhere in the building, regardless of whether the steam is wet or dry.

If that heat is released from piping located in an unconditioned space, such as a crawlspace or basement, the issue is not steam quality but pipe insulation. This is true for both steam systems and hot-water systems.

From an energy-balance perspective, it is difficult to argue that wet steam is inherently more or less efficient than dry steam. The primary reason to strive for dry steam is system performance and reliability, not energy efficiency. Dry steam reduces water carryover, improves distribution, and minimizes problems such as water hammer and excessive condensate in the piping. It is therefore desirable for operational reasons, not because it represents a fundamentally more efficient heat-transfer medium.

ethicalpaul · January 19

I don't dismiss Dan, but I can think about and recognize areas where he was mistaken. It took me years of thinking about the A dimension before I realized it was mythical and then proved it with a video, for example.

It took me years of thinking about wet steam, first learning how it's defined and discussed in The Lost Art, and then realizing that some things he wrote didn't make sense to me, and then finally being able to show what I'm talking about in these recent videos. So it was anything but dismissing on my part.

I have never deleted or hid any of your youtube comments on my videos.

With wet steam, the wetter the steam is, the higher the return condensate will stack up where it drops from the main to the wet return, due to the higher boiler pressure needed to overcome the additional pressure drop created in the pipe due to the fact that you don't have dry steam.

In my video I linked above to clammy my "A" dimension does go up, but this is only because I have dramatically constricted my steam supply out of the boiler. Both Peerless and Dan state that A dimension rises in normally piped boilers, either due to "pressure drop" or "wet steam" and that is completely mistaken.

Captain Who · January 19

OK Ed. No offense but you aren't just going against my opinion, but all the experts including the boiler manufacturers, Hydronic Institute testing engineers, and Dan Halohan et al. Did you read his article?

Can you pay me for my gas bill last month which was crazy high with my wet steam due to the fact that I didn't drain and flush my boiler and returns this year due to having to replace a 16 ft steam main myself that rusted out? I'd appreciate the help. My canary in the coal mine radiator was barely heating and that was just the tip of the iceberg illustrating how much more my boiler was having to burn to satisfy my thermostat. You need to understand the basics involved in system efficiency between a Btu going to heat my leaky basement and a Btu going to heat my living space.

And Paul, maybe I'll post a picture of how my boiler was piped when the previous owner rushed to do an install due to the fact that inspection revealed a leaking boiler. Then you can duplicate it on your system to see what happens. I'll get a kick out of hearing you report on the results. You say you appreciate the time but what, did it take you all of 30 secs to post two quick dismissive replies to what took me over an hour to find and relate to you? And it is totally hysterical the way your video proved you had wet steam going into your mains resulting in higher condensate stacking in the returns yet you looked at your second sight glass going up from your drop header and pronounced that wet steam in residential boilers was a myth because it looked good to your eyes.

ethicalpaul · January 19

I am not dismissive, I replied with reasoning and even referred to both articles that you linked. You though have repeatedly dismissed my question "where are the BTUs going that you claim are lost to wet steam?" 🙂

Your boiler seems to have issues when the water quality gets bad—this is carryover (as you are describing it). You have the same self-reported bad near boiler piping, and yet sometimes the steam is "dry" and sometimes it is "wet" (to use your definitions of those—which I consider misleading). This is what I've been saying—carryover is caused by bad water, not bad piping.

I think instead of these misleading terms you might consider saying that sometimes it has carryover and sometimes it doesn't.

Carryover can't prevent the BTUs from getting into your house, but I could see how it might change which radiators get steam which could result in longer running times for you. But the heat is indeed going into your house regardless. Carryover is definitely undesirable as @EdTheHeaterMan mentioned above.

Your recent carryover was no doubt caused by the oils from your new piping. You should consider skimming. If your gauge glass level is dropping while steaming, that is definitely carryover—not "wet steam"

Captain Who · January 19

Carryover is relative, just like the term wet steam is relative. There are spectrums from mild to bad in both. They should be taken as synonymous. It's semantics. Mechanical carryover/wet steam is real as is the type caused by bad water quality. I think I have taken this discussion further than I intended to when I initially told you that if you disagreed I'd not waste my time.

Edit to add - You are mistaken that my steam main installation added any oils whatsoever to my boiler. Since I did the work myself I cleaned all the pipes and fittings prior to installation, and everything was fine as far as I could tell for about a month and a half after installation. And don't take this as an insult but I think you should learn the basic science involved in steam heating before you go on to teach people about it.

ethicalpaul · January 19

OK as you wish. We definitely disagree. I'm sorry to see you go, but for others I will summarize my thinking about wet steam:

"Wet steam" is steam that is simply created by boiling water, without any additional heating. This is the scientific and industrial definition.
Therefore, every bit of steam ever created by every residential (and many many commercial) boilers is "wet steam"
"Wet steam" can't be reduced by proper near boiler piping—a few turns of pipe cannot change the water content in the steam—only the introduction of additional heat can change that.
"Carryover" is different from "wet steam" and is a common problem in residential boilers, caused primarily by oil on the water, or also from other solids or substances in the water. It is large quantities of water getting thrown out of the boiler (similar to what we see in a coffee percolator—or in my videos). It can be indicated on most systems by a dramatic drop in the gauge glass level.
neither "Wet steam" nor "Carryover" can "kill" or "remove" BTUs from the heating system. Even though carryover is not desirable, it does not cause inefficiency — all the BTUs go into the home regardless.

jesmed1 · January 19

As a neutral observer/mechanical engineer who does not have firsthand experience with steam systems, but who did learn something about steam in engineering classes and has learned more from Dan's books and the good people on HH, I offer a few comments.

It's obvious that the term "wet steam" causes a lot of semantic confusion in both steam neophytes and professionals alike. The particle size of water in "wet" steam can be less than 1 micron, or a thousandth of a millimeter, far smaller than the visible size of a half-millimeter raindrop, for example. And Paul's sight glass experiments demonstrate that the "wet" steam coming from his boiler has no visible droplets, even though he knows and says clearly that the steam is in fact "wet."

Are the (for example) 1 micron water droplets in "wet" steam causing problems? Probably not. Yes, those droplets reduce the overall heat transfer to the radiators because they're already condensed and thus have no latent heat to sacrifice. So while in a perfect world we'd all like 100% dry steam, as Paul has already said, all residential boilers produce "wet" steam. Does this mean all residential boilers must therefore have problems with water hammer, etc? Obviously not. If piped correctly and the water quality maintained, all residential boilers can be made to operate without such problems, despite the <100% quality steam.

But with poor quality water, water droplet size increases, and at some point quite large "slugs" of water can get thrown up into the header. Is that also "wet" steam, or is it carryover? Well, it's both, because now the droplet size has increased, and there are large slugs of water being carried along by the steam.

Now, how do you separate the water out before it causes problems? I think Paul's point is that the typical droplet size of water in "wet" steam with no carryover is so small as to be (1) not problematic, and (2) carried along by even low-velocity steam, so that the elbows, etc, of properly designed headers aren't going to remove them. It's only when the droplet size gets big enough to have a significant amount of inertia relative to the propulsive force of the steam that they're going to drop out.

So how big does the droplet need to be in order to be "separable" from the steam flow in the header? Do we even know? The rules of thumb that Dan talks about in his books were developed 100+ years ago. On page 43 of LAOSH, Dan talks about two different "rules of thumb" velocities: (1) 15 fps max to prevent carryover, and (2) 23-32 fps max (depending on pipe size) to allow condensate drainback. But note, neither of these has anything to do with micron-sized droplet separation from "wet" steam. Has anyone ever done an experiment to see how large the droplets need to be to actually separate out in a typical header? It doesn't sound like it. All any expert can reasonably say from experience is that things like drop headers work to separate carryover and condensate, but no one seems to have any experimental data showing that a drop header also separates out micron-sized droplets in typical "wet" steam. And I think Paul was making this point.

So all residential boilers make "wet" steam, but can operate well as long as there's no carryover. Then some homeowner comes to HH and complains that they're having problems from "wet" steam. Well, no, they're having problems from carryover. And I think Paul made this point earlier too. The problem is a semantic one. They don't understand that all residential steam is "wet," but not all residential steam has carryover. Then a long thread ensues discussing the difference between wet steam and carryover, and here we are again…

ARobertson13 · January 19

I have read this discussion with concern. I was before I retired an instructor. As I tried to explain in another discussion you have to understand what is going on in your heating system. So I will make this simple. It is true that the heat generated by the burner does go someplace [conservation of energy]. It goes up the stack [chimney] , into the boiler where some leaves the boiler in the form of steam, water droplets, carryover ect.. There are also jacket losses conduction and convection. If you increase the amount of water transmitted through the pipes [mains and risers], this water does not transfer heat as well as steam does. The water will just travel back down along with the steam condensate into the the return lines which will also give off heat into the basement. So it will take longer to heat up the radiators in the apartments and more heat will be lost to other parts of the system.

Also, I stated on the other discussion that "Wet steam" is not a good term. Because it refers to a mixture of water droplets and steam.

ethicalpaul · January 19

the basement pipes can only give off so much heat. The rest goes back into the boiler and is not wasted.

Carryover will put a tiny bit more heat into the basement because the returns are hotter but you’d never see that on a fuel bill

ChrisJ · January 19

https://forum.heatinghelp.com/discussion/comment/1882992#Comment_1882992

Most of my returns are insulated with 1" fiberglass.

I do have a section, maybe 10' long that isn't.

EBEBRATT-Ed · January 19

My $.02.

All steam is saturated unless it is superheated which doesn't exist in a residential or commercial steam system.

Saturated steam is wet steam but there are degrees of saturation or wetness. The drier the better I think we can all agree with the above.

Can wet steam cause issues? Not so much on a residential job but there are situations with process steam that the steam quality is very important. Condensate collected in a sagging pipe will cause water hammer. It will make some of the steam coming down the main to condense when it contacts the cooler condensate. The resulting pressure drop from collapsing steam causes more steam to rush in to fill the vacuum and cause hammer. This is more of a piping problem than a wet steam problem.

Does the steam coming down the main reboil the cooled condensate? I guess it might after some time.

That's one of my questions.

This is the way I think about wet steam flow.

I am sure some of you know what a low loss stack is. I used to look at these for years and wondered how they work.

Picture an exhaust fan vented through the roof with 6" round pipe. They put a sleeve of 8" round pipe over the 6" pipe with a 1" air space between the two. The pipes have to overlap for 6' or so.

The top of the pipe has no cap on it.

How much rain water comes into the exhaust fan?

None. Rain water doesn't fall straight down. In a 6' section of 8" pipe all the rainwater will hit the sides of the 8" pipe and drip out the space between the 6" and 8" pipe.

I think wet steam does something similar.

Wet steam carryover whatever leaving the boiler has to go through several elbows to get to the main. The steam/water crashing into elbows makes the water drop out of the steam similar to the LL stack above …..if the velocity is not too high. The higher the velocity the more chances that wet steam gets into the main. The condensate gets drained out hopefully through the equalizer

I think of the steam/water issue like this

A pond can be frozen at 32 degrees. A pond can be all water at 32 degrees. A pond can be water with ice floating in it at 32 degrees.

So steam/water is similar to water/ice they can exist in the same area.

so wet steam/carryover isn't as much of a problem till it becomes a problem.

Can you run a boiler without an equalizer? Yes, but producing wet steam or carryover will make you wish you installed one

ChrisJ · January 19

@EBEBRATT-Ed

Could one superheat steam slightly by closing their king valves a hair and building a little pressure in the boiler? I.E. when the steam leaves the header it should be slightly above it's boiling point, no? I.E let's say 2 psi in the boiler and 1/4 psi in the system.

I doubt there'd be any benefit, but just curious.

ethicalpaul · January 20

@ChrisJ I think I saw this in my videos where I constricted the supply pipe. The pressure went up to about 1/2 psi in my boiler and it was much lower in the header and main. The condensate produced by the supply pipes (glass and metal) never would go over a certain amount. I believe the slightly superheated steam was able to evaporate (re-steam) the condensate that formed in the supply as it was formed.

The problem is you can only go so high because the boiler will push water out the back.

ChrisJ · January 20

https://forum.heatinghelp.com/discussion/comment/1883043#Comment_1883043

But with the restriction at the main(s) you have the equalizer keeping the water in the boiler, and the steam going out the correct way, no? Allegedly.

ethicalpaul · January 20

Haha, no. Just for those who missed that whole thing, I will state that the equalizer does nothing to keep water in the boiler unless your wet return suddenly gets a quarter-sized hole in it, in which case it will break a syphon that would result.

EBEBRATT-Ed · January 20

Superheated steam you would think is very hot just by the name, but it actually doesn't heat much. You need the latent heat to do that

EdTheHeaterMan · January 20

https://forum.heatinghelp.com/discussion/comment/1883014#Comment_1883014

Closing the king valve to allow pressure to build will not produce superheated steam. Superheated steam can only exist when steam is completely separated from liquid water. If a boiler contains water and steam under pressure above the water line, the steam remains in direct contact with the water. By definition, steam in contact with liquid water is saturated steam, not superheated steam, regardless of the pressure.

If, by chance, you do cause all the water in the boiler to become superheated steam, the boiler would have no water in it. That would be a problem for the boiler that is not covered under the manufacturer's warranty.

ChrisJ · January 20

https://forum.heatinghelp.com/discussion/comment/1883060#Comment_1883060

I was saying the steam becomes superheated after passing through the valves to the lower pressure side. It would be whatever temperature above its boiling point at that point.

ChrisJ · January 20

https://forum.heatinghelp.com/discussion/comment/1883053#Comment_1883053

I just think of the same thing we deal with in refrigeration. Evaporator superheat isn't hot but it is superheat.

I guess a wet return is sub cooling.

EdTheHeaterMan · January 20

I was saying the steam becomes superheated after passing through the valves to the lower pressure side. It would be whatever temperature above its boiling point at that point.

That makes sense. It is just like getting superheated refrigerant after the TXV or orifice metering device. Yeah, that makes sense. But why would you do that in a heating system when you can heat the home with saturated steam for less money/energy/flame, then getting the steam up to a higher pressure/temperature, just to get a lower temperature/pressure on the other side of the valve. But I see your point. @ChrisJ

ChrisJ · January 20

https://forum.heatinghelp.com/discussion/comment/1883066#Comment_1883066

Dunno. I guess just useless ideas.

I find sometimes thinking about ridiculous stuff creates a useful idea. Not usually, but sometimes.

Eastman · January 20

What would happen if the water in the boiler was being circulated by a pump to agitate it? Do you think this would improve the boil? When you stir a pot of boiling water on the stove it seems to do something.

ethicalpaul · January 20

I don’t think it would affect much. There is already some circulation from the wet return (and in my case the hot water loop circulator pump adds more)

A discussion about wet steam to not hijack anyone's thread

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