Can undersized boiler work in a vapor/vacuum system?

vapor1

@PMJ
To PMJ
I read many of your posts as you suggested, and I'm really interested in your control system. However, our system has about 947 sq ft installed EDR vs 760 sq ft on the boiler tag. The house heats OK, but with variations room to room. The gauge on the boiler never sees over 1/2 psi even after a 2 hr burn (recovery). Except for the low water cut off, thermostat is in complete control. The main problem is that 3" to 4" of water exits the boiler from a cold start. It returns after the burner cuts off, but I figure it has to travel through about 180' of steam mains, and the level isn't fully restored for about 12 hours. This means we have to start with the level pretty high, about 1" from the top of the glass, which probably contributes to the water loss. The header arrangement is probably the biggest culprit - I'll attach pictures.

My plan is to have the header arrangement fixed. (The boiler is ~25 years old so I'm not sure the investment will have much time to pay off.) And I'd like to add back the stainless ball in the Webster 0023 vent trap - if I can find one. Then wouldn't we have a vacuum system? I don't know if it would improve efficiency, but it would stop the inrush of air through the vent on shut down. All that air can't be a good thing. Do you think it would make sense to make these changes, and should I consider your control system, either with a PLC or with just the sensors and timer?

STEAM DOCTOR

That piping is hard to look at. Hideous. Don't think that it makes sense to invest in a 25 year old boiler. Properly piped boiler won't lose as much water. Should not take 12 hours to return. Your return piping might be seriously clogged. Not a big fan of setbacks

vapor1

Thank you for the reply, @STEAM DOCTOR. I was thinking that most of the fugitive water was being thrown up into the supply main shown in the foreground next to the ceiling, then slowly making its way back through the loop (180') where it joins the wet section of the return line. If the culprit is instead the returns, do you think I could test by pouring water into the beginning of the dry returns and timing when it shows up back at the boiler?

Jamie Hall

Several points.

First, as @STEAM DOCTOR says, that header piping is really evil. Would I replace it on a 25 year old boiler? Dunno.

Second, your number one culprit on the slow return is most likely badly clogged wet returns. You could test them as you suggest, but... why not assume they are, and just flush them out on general principles?

Third, in answer to your question on "undersized" boiler on a vapour system -- yes it will work. You're not that far undersize. But, to make it really happy -- and you comfortable -- make sure all the traps and vents are working properly.

You won't need a fancy control system at all.

vapor1

Thank you, @Jamie Hall . The returns are dry until they are brought down at the boiler. The condensate pump was recently removed, and the wet piping to the boiler was flushed. Could there be a clog in the dry portion? I think it would be fairly easy to pour water into a trap once the cap is removed, and there is already a valve at the bottom of the the pipe where the dry returns drop into the wet return. I would just have to drain the boiler down to the Hartford loop.

There is only 1 vent, and I can hear it work twice on each burn (in and out). However, the vent stops exhaling after maybe 10 minutes of burn. I'm assuming that's because the traps seal, but I'm not certain . It looks like some of the traps have not been touched for a long time - maybe forever. A few are suspect - the pipes read ~207 F going into and coming from the trap. Looks like I need a good source for Warren Webster trap innards (712HB and T23).

PMJ

@vapor1 ,

One of the problems with downsizing boilers is that the normal "in process" water that is upstairs during operation becomes a higher percentage of the boiler capacity and drops its water level more. A smaller boiler has less water per vertical inch so the level will drop more for the same volume of water used. Mine drops about 1 to 1-1/2 inches so your drop doesn't sound crazy. This is just one of the things that gets closer to the edge of not working at all as a result of the choice to cut things closer on the boiler. The sum of what is given up going small seems way more to me than what is gained; but I'm clearly in the minority with that view here. Anyway, if you can put the waterline higher and don't shutoff on low water you can get away with it. Doing so might cause other problems, but we can worry about those later.

Natural vacuum needs boiler off time to work its magic. So bigger is better. But it is not an all or nothing proposition.... any off time with any vacuum is good time. Simply not sucking air at any time is a definite plus.

Looking at my installation manual I see my IBR rating is for my boiler is 1050sqft @362,000btu/hr output. On that same chart it is showing a model for 732sqft @240,000btu/hr output so your rating isn't matching quite. Perhaps they have changed since the 1950's. Others could speak to that. Yours seems pretty small to me. But the bottom line is if it heats the place on the coldest days it is big enough. It could be argued that I am getting it done with 180,000btu/hr.

About what percent of the total time does it need to run to heat on the coldest days you ever see? I need to burn about 50% of the total time on those days. This will give me the best idea of where you are so take a guess. Also, how many seasons is your experience with this system?

Jamie Hall

Good. There should be only one vent. If it closes, rather than just exhaling, however, tells me that at least one -- and probably several -- of your radiator or crossover traps is stuck open. You need to find it. A curious feature of vapour systems is that if they are working properly, the vent never closes.

And I quite agree with @PMJ -- which really shouldn't surprise him, and probably doesn't -- if you system is running properly with the water levels you describe, don't try to fix it. It ain't broke (other than the appalling near boiler piping...). Dry returns very rarely plug -- there's no standing water in them, or shouldn't be. On the other hand, there would be no objection to making sure there isn't crud built up where the returns drop to the boiler -- and that's where it would be, if anywhere.

vapor1

Gosh, @PMJ , that's a big difference. About 3 sqft/MBTUh for your chart vs about 5 sqft/MBTUH for the Utica boiler. Maybe the standards have slipped. Rare (oops, that's 4sqft/MBTUH, not 5)

With daytime outdoor temperatures in the 40's, the steam heat is used only in the morning for an hour burn or so to bring the inside temp up to 65 F from its overnight setback of 62 F. During most of the day when we are home, the library gas fireplace brings that room to nearly 80 F and provides lesser heat to most of the rest of the house. The boiler rests (and cools) for ~23 hours. In very cold weather and no fireplace, without monitoring it I would guess it fires 50% of the time.

We have lived with this system for about 15 years without paying much attention to it. This year, we noticed the high water level - well above the top of the glass! There may have been a leaky feed valve, and the automatic feed was called in whenever the system tripped on low water. We have since added a 90 second wait on the LWCO before invoking the automatic feed and throttled back the supply ball valve to the feed. This plus watching the system gets us by, but it's a delicate balance between flood and LWCO drought.

A local contractor figured the condensate pump was causing the slow return and removed it. Now we have another reason to keep the pressure low - limited "B" dimension.

vapor1

Jamie Hall said:

Good. There should be only one vent. If it closes, rather than just exhaling, however, tells me that at least one -- and probably several -- of your radiator or crossover traps is stuck open. You need to find it. A curious feature of vapour systems is that if they are working properly, the vent never closes.

And I quite agree with @PMJ -- which really shouldn't surprise him, and probably doesn't -- if you system is running properly with the water levels you describe, don't try to fix it. It ain't broke (other than the appalling near boiler piping...). Dry returns very rarely plug -- there's no standing water in them, or shouldn't be. On the other hand, there would be no objection to making sure there isn't crud built up where the returns drop to the boiler -- and that's where it would be, if anywhere.

Thank you, @Jamie Hall . The single vent is labeled "Webster Vent Trap 0023. It is now always open to the basement atmosphere, but I believe it originally had a stainless steel ball perched on top of a seat which let air out but not into the system. It is installed near the ends of the two dry return loops which are connected together. Two steam main loop ends are also joined to each other and then drop down to the wet return.
They are vented into a trap which vents into the dry returns (is this a crossover trap?) before the Vent Trap.

So the Vent Trap doesn't actually close - it just stops, or at least slows, exhaling after some period of burn. Then it inhales on shut down. (add: I don't think there is any thermostatic component.)

There is a third steam loop piped off a split from loop 1 and 2. This third loop ends in a trap (crossover?) which drains into the loop 2 dry return. This one is suspect.

There is a valve at the bottom of the return line drop. I drain about 1 gallon through it each month now.

Is my thought about water being shoved up into the steam mains and then taking a long time to return not probable?

Stay safe and well!

Jamie Hall

Your surmise about the Webster vent is correct -- that little ball was intended to seal when the system shut off and allow it to drop into a vacuum. It was supposed to -- and did -- increase efficiency some. How much? Good question.

The two steam mains joining and then going into a crossover trap (yes, that's what they are called) isn't correct. They should each have a separate crossover trap into the dry return. How does condensate get back to the boiler? Which way do the steam mains pitch? Back to the boiler? Or are the crossover traps arranged so that they handle condensate as well as air, and the dry returns are well below the steam mains (kind of rare)? There are, I take it, no wet returns?

PMJ

I'm getting a better picture. 15 years with no problems is quite good - you have a pretty good system for a foundation. I agree with the others that your piping is unfortunate. However, there is lots of ugly stuff running out there without issue. I wouldn't touch the 25 year old setup until you have to replace that boiler.
My boiler isn't piped right either. I have a bull head T in the header and no equalizer. But the header is so big it doesn't make any difference. The pipe is 4 inch and the T is more than 24 inches above the water line. No issues whatsoever.

I am surprised that size boiler can actually get 8 ounces in a 1000EDR system unless some rads have been removed or turned off. Sure that gauge is accurate? Honestly it would take mine an hour and a half from cold start to do that.

You should probably clean out the wet return. I'm guessing mine has never been cleaned in its lifetime and likely is a little slow. But then my boiler is easily big enough to make up for that (that darn big boiler advantage again). You might go ahead and make sure that yours is fully open. Doing so might get you farther from low water shutdown and be worth it.

It doesn't sound like you really use the boiler all that much. You mentioned uneven heating. I'm curious what kind of complaints you have about that. Is it upstairs/downstairs differences or certain radiators just never get near enough steam or what kind of issue? Seems overall you're pretty satisfied.

Anyway, I'm happy to push it further and have a comment about whether vacuum or control changes might really have anything to offer in your situation. Spacing out the recovery burn some will ease the condensate return problem giving more time. It will also delay the recovery some and I'm not sure that works for you. I spread out my setback recovery. Rads are always warm and no one notices.

Vacuum can do a simply amazing job of evening out the heat in a 2 pipe system. Let me know your interests. There are a few people out there who wish they had your 2 pipe system so they could try it.

vapor1

@Jamie Hall



Steam loop 2 is about 90' long and drops 5" from the start at the header. Steam loop 1 is about 182' long and drops 10". Except for the drop to the boiler, what you see in the picture is the lowest point. The pipe to the crossover trap taps into the top of
the elbow at the connection between the two steam mains. The trap is hidden behind the steam mains, but it taps into the dry return of loop 1 before it enters the Vent Trap.

The pipe labeled steam loop 1 turns down, joins the return, and enters the boiler through the Hartford loop, now by gravity.

The other crossover trap is at the end of a third loop which rises to the 2nd floor. The runner from the basement main is pitched back into loop 2, so it drains condensate from the 2nd floor riser. The third steam loop ends as it drops several feet to a trap, which must handle both condensate and air (and maybe some steam, too, unfortunately). This is the beginning of the loop 2 return.

No wet returns.

Hope all this is clear. If not, I can always take more pics.

Stay well

Jamie Hall

I think I'm just confused enough to be dangerous. Can you make a diagram, with relative elevations, and post it?

vapor1

PMJ said:

I'm getting a better picture. 15 years with no problems is quite good - you have a pretty good system for a foundation. I agree with the others that your piping is unfortunate. However, there is lots of ugly stuff running out there without issue. I wouldn't touch the 25 year old setup until you have to replace that boiler.
My boiler isn't piped right either. I have a bull head T in the header and no equalizer. But the header is so big it doesn't make any difference. The pipe is 4 inch and the T is more than 24 inches above the water line. No issues whatsoever.

I am surprised that size boiler can actually get 8 ounces in a 1000EDR system unless some rads have been removed or turned off. Sure that gauge is accurate? Honestly it would take mine an hour and a half from cold start to do that.

You should probably clean out the wet return. I'm guessing mine has never been cleaned in its lifetime and likely is a little slow. But then my boiler is easily big enough to make up for that (that darn big boiler advantage again). You might go ahead and make sure that yours is fully open. Doing so might get you farther from low water shutdown and be worth it.

It doesn't sound like you really use the boiler all that much. You mentioned uneven heating. I'm curious what kind of complaints you have about that. Is it upstairs/downstairs differences or certain radiators just never get near enough steam or what kind of issue? Seems overall you're pretty satisfied.

Anyway, I'm happy to push it further and have a comment about whether vacuum or control changes might really have anything to offer in your situation. Spacing out the recovery burn some will ease the condensate return problem giving more time. It will also delay the recovery some and I'm not sure that works for you. I spread out my setback recovery. Rads are always warm and no one notices.

Vacuum can do a simply amazing job of evening out the heat in a 2 pipe system. Let me know your interests. There are a few people out there who wish they had your 2 pipe system so they could try it.

Thank you again, @PMJ .

One thing I didn't note on the boiler picture is that all that riser piping is 2". When the 2 risers join, the full 182,300 BTU/HR is trying to flow through one 2" pipe ( steam velocity >50 ft. per sec.) so that any water that makes it above the first tee would probably be shot up into the header and then up into the main.

I'm sure you're right about the 8 oz pressure. I'm using an old vacuum/pressure gauge which shows 30 psi either side of "0".
I see roughly 1/2 the deflection from 0 to 1.

I appreciate your comments and counsel.

Stay safe and well

Jamie Hall

I didn't comment on pressure -- I was concerned about other things -- but for a Webster system the pressure should be kept well under 8 ounces -- 4 to 6 would be much better. Which, unless you are uncommonly fortunate, either means a vapourstat or one of @PMJ 's interesting -- if more complex -- approaches (it's one of the few areas on which he and I often actually debate!).

Either way, you are going to need a low pressure gauge in addition to the insurance company's 30 pounder. They are worth getting. If you are using the vapourstat approach, it's easy to set once you get one. As the boiler starts, you will see perhaps an ounce or two of pressure build. Then it may get up to 3 to 4 ounces -- often less -- and pretty well stay put at about that pressure for a while. Then, when all the radiation is taking about all the steam it can handle, you may see the pressure start to rise significantly -- and that's when you want either you vapourstat or timer to shut off. If you are using a vapourstat, set the differential to about half the cutout; chances are that if there is a post purge or pre purge (or both) on your burner, the boiler will cut back in as soon as it can. If you are using a timer, it gets a little more interesting (!) (and that's the area where @PMJ and I tend to part company -- what is the ideal off time?).

PMJ

It is an ongoing debate @Jamie Hall and I have on this and I think a healthy and friendly one. To continue it in that spirit I add the following:

All I am saying is that pressure even in ounces in these systems is an indication that far more steam is already in the radiation than is needed to satisfy the conditions on a continuous basis and is therefore by that point raising the temperature in the space quickly. When the tstat or vaporstat does finally stop the boiler, a longer wait time is required while the radiation fills with air and cools down a lot by the time the next cut in temp is reached. The result is a temperature roller coaster that while may be very tolerable is not required and easily avoided with very simple burn time management. I also do believe the extra burn time on every cycle required both to remove the air and to reheat the delivery piping is quite wasteful. It surely is less comfortable. Few have lived with the same system in both conditions (and paid the gas bills) to know the difference as I have. Not sort of, not maybe, not close.

Sorry Jamie, couldn't resist a poke.

ChrisJ

PMJ said:

It is an ongoing debate @Jamie Hall and I have on this and I think a healthy and friendly one. To continue it in that spirit I add the following:

All I am saying is that pressure even in ounces in these systems is an indication that far more steam is already in the radiation than is needed to satisfy the conditions on a continuous basis and is therefore by that point raising the temperature in the space quickly. When the tstat or vaporstat does finally stop the boiler, a longer wait time is required while the radiation fills with air and cools down a lot by the time the next cut in temp is reached. The result is a temperature roller coaster that while may be very tolerable is not required and easily avoided with very simple burn time management. I also do believe the extra burn time on every cycle required both to remove the air and to reheat the delivery piping is quite wasteful. It surely is less comfortable. Few have lived with the same system in both conditions (and paid the gas bills) to know the difference as I have. Not sort of, not maybe, not close.

Sorry Jamie, couldn't resist a poke.

So 8 oz max is an absolute maximum, not a "recommended range".

I'm curious where did that number come from? Why 8 oz?

Jamie Hall

Actually that maximum depends on the system. Hoffman Equipped Systems -- the ones I know best -- are limited to an 8 ounce (actually usually slightly less) differential between the steam main at the boiler and the dry returns at the boiler, by the geometry of the Hoffman Differential Loop. Anything over that and the Loop trips, reducing the differential to that figure -- so there's no point in raising the gauge pressure further. Other vapour systems had similar hard wired, if you will, gadgetry which did much the same sort of thing, but in different ways.

PMJ

I think we all know that 8 ounces continuously at the header in our systems would roast everyone so obviously that isn't what was happening back in the coal days. This is my whole point. The continuous requirement is far lower than that....well below what a vaporstat can help with.So I just don't see the reason ever to go up in that range at all. Doing so results in a roller coaster environment to an extent that really isn't necessary.

Jamie Hall

I quite agree. Running 8 ounces continuously would be ridiculous. Exactly how many ounces continuous... really depends a lot on what the heat loss from the spaces is, and what friction losses there are in the pipes (usually pretty darn small!).

I still say -- and I think @PMJ would agree -- that the ideal would be some way to modulate the firing rate to match the heat loss, in a system which was in a naturally induced vacuum so that the condensing temperature was right for the heat loss.

While keeping the efficiency up to something reasonable on the burners...

PMJ

Jamie Hall said:

I quite agree. Running 8 ounces continuously would be ridiculous. Exactly how many ounces continuous... really depends a lot on what the heat loss from the spaces is, and what friction losses there are in the pipes (usually pretty darn small!).

I still say -- and I think @PMJ would agree -- that the ideal would be some way to modulate the firing rate to match the heat loss, in a system which was in a naturally induced vacuum so that the condensing temperature was right for the heat loss.

While keeping the efficiency up to something reasonable on the burners...

I do agree @Jamie Hall. Such a burner would produce the same boiler output the coal fired setup did...barely steaming a whole lot of the time at very low header pressures and basically slight vacuum in the rads.

What puzzles me is what I will call pretty fierce resistance here to even considering just breaking the burns of an on/off boiler into smaller pieces to eliminate the pressure altogether and produce a more even result. It is as if cycles were the worst thing that could happen to a boiler. I have ended up at just over 2 cycles per hour during calls for heat which I try to make as long as possible. I do that because the length of the call proves how even the heat is. You want the boiler to run less each hour and satisfaction of the call to take a long time if you want even heat. Coal fired "calls" were endless. If nothing else coal fired heat was even because nothing could change quickly.

vapor1

Jamie Hall said:

I think I'm just confused enough to be dangerous. Can you make a diagram, with relative elevations, and post it?

@Jamie Hall , Wish I knew how to describe this better. Here are some more pics. Hope they help.

Jamie Hall

I think I see a little better -- and now I'm a little worried. At the end of loop 3 you have the comment "drops 3 feet into crossover traps and dry return". Which return, presumably, continues on towards the ends of loops 1 and 2 and then goes into the boiler?

And there is a dark line paralleling the red lines which are the mains? And most of those dark lines are just slightly below the red lines? Except the one from the end of loop 3 to the boiler, which is 3 feet below?

Is there -- are there -- any other vertical pipes down from the steam mains or the dry returns (I'm trying to see how condensate gets out of those pipes back to the boiler).

I have a suspicion that that pipe 3 feet down may have been meant to actually be wet at some time in the distant past, but the newer boiler have a lower water line...

Loops 1 and 2 really seem to be one continuous loop -- which is fine for two pipe steam (before someone faints...).

PMJ

@Jamie Hall what is the point of the crossover traps?

I actually have a very similar setup - except that the main and the dry returns simply join to themselves after completing their loops around the house and then drop down to a joining point below the water line in the wet return. There were vents on both at the drop point which I determined weren't needed at all and removed them. I found that once you decide not to let the air back in it makes little difference where on the dry return you let it out so I moved the exhaust point to the garage.

Anyway, help me understand what the original idea was. It surely is something else to go wrong that my 2 pipe doesn't have.

Jamie Hall

Nice to have things that can't go wrong! The crossover traps essentially vent the air in the mains into the dry returns, whence it goes to the main (and only) vent. Their venting capacity is huge (hence the popularity of "BigMouth vents -- which are just traps which go to the atmosphere, after all) so the main vent controls things.

Condensate was taken by a drip to a wet return, if the mains were parallel flow -- which most of them were. Condensate and air from the radiators went into the dry returns (which were often counterflow) and the condensate dripped to the wet return also -- which is one reason why one has to be a bit cautious about boiler water levels: the wet return where the drips come in has to be well and truly below the water line, otherwise steam happily goes down the drip from the main, around a couple of corners and back up the other drip into the dry return. Not helpful.

If there even is one. Some earlier vapour installations just vented the dry returns to the atmosphere -- often through the chimney -- with nothing in the way. In others, the single main vent acts in combination with some widget or other to limit the differential pressure as I mentioned earlier. In systems with vacuum vents -- such as Hoffman and Webster -- that main vent sealed on a vacuum and the whole system dropped into a natural vacuum -- which, if there were no leaks, could be remarkably deep (hence the combination gauges found on such systems)(If someone gave me three Hoffman #76 vents, I'd happily put them on Cedric!)

PMJ

Thanks. Take it a little further for me though.

I have found that in a cold start there is plenty of time (and capacity) for all the air to go out of the mains through the radiators and through a very small vent anywhere in the dry return in a 2 pipe system. Now I can see why open vented in an already hot system why more venting might be helpful when an intermittent boiler fires on high into it full of air. But in the original system after what would have been a very slow cold start with coal wouldn't the mains always have steam in them? I'm not seeing any ongoing venting issue in the original design. Please advise.

vapor1

Correct, @Jamie Hall . The pipe on the right in this picture is the end of steam loop #3. The pipe on the left serves as return for 3 convectors on the 2nd floor and then drops down to the basement ceiling, catching the crossover trap along the way, to continue servicing 1st and 2nd floor convectors on its way back to the boiler. It is named "return from loop 2" in my last set of pictures (IMG_5889paint.jpg), and it ends by the boiler as it joins the return from loop 1.

And yes, the red lines are the steam mains (the innermost lines), and the the next lines, actually green but hard to see color, are the returns. The outermost pencil lines represent the perimeter of the house and the division from the garage.

Return loop 1 starts near the garage and drops 14.5" on its 160' path back to the boiler. Return loop 2 starts with the drop shown in the picture above to a point just below the basement ceiling, and from there drops another 2" over its 30' path back to the boiler.

Back at the boiler, the two returns enter the Vent Trap and drop to a wet return into the boiler. (There are 44" from the return lines to the boiler water level.) The end of steam mains does the same.

Please let me know if more pictures would help. And thank you for your comments.

Jamie Hall

@PMJ -- Yes, in the original coal fired systems (if they were -- the system Cedric fires has always been oil; many were) the steam mains would always have vapour in them. The dry returns would never have vapour in them. Everything just sort of sat there and wandered along.

Until some idiot overfired the boiler.

That's what the gadgets got invented for -- the Hoffman Differential Loop, for instance, was advertised as "The Watchman of the Water Line", and the whole idea was to keep the pressure differential low, so the water wouldn't back out of the boiler if the coal fire got out of hand -- which they did (and yes, it works -- if the system has no leaks, the Loop will keep the water line where it belongs, even if the burner goes bonkers. Been there, done that).

It has been my experience that these systems don't need anywhere near the venting that some folks suggest -- for the simple reason that while you are pushing air out of the mains, at the same time steam is going into the radiators. Cedric, for instance, at some 385,000 BTUh, gets on just fine (about an ounce) with one Hoffman #75 and one Gorton #2, and there is less than 2 or 3 minutes time difference between the first radiator to heat (practically on top of Cedric) and the last one (about 70 feet away). Works for me...

And @vapor1 -- that all should work pretty well. I do wonder, though, if that lower bit of return -- that "drops 3 feet" one -- wasn't wet once upon a time. Can you very carefully measure the height difference between it and the current boiler water line for me?

Jamie Hall

Oh and a PS for @PMJ -- the reason the sole vent is at the boiler on these things is that the idea is that if the thing does get carried away, the widget works by putting live steam direct from the boiler into the dry returns -- promptly closing the vent and pressurizing the dry returns. If the vent was off in la la land somewhere, that wouldn't work.

vapor1

@Jamie Hall
And @vapor1 -- that all should work pretty well. I do wonder, though, if that lower bit of return -- that "drops 3 feet" one -- wasn't wet once upon a time. Can you very carefully measure the height difference between it and the current boiler water line for me?

The last pic I posted is located in the garage. The "drops 3 feet" actually starts from the space between the 2nd story floor and the garage ceiling, so that the crossover trap shown is about 8' over the remaining portion of return loop 2 and nearly 12' over the boiler water level. Hope that helps. Thanks again for your comments.

PMJ

@Jamie Hall , I see that about the diff loop, but the crossover trap is only there to assist getting air out of the main faster right?
Anyway, @vapor1 , it that were my system the crossover traps would be gone and I'd try finding a ball for the vent. I'd be about getting the system to hold vacuum.

And while the subject is still up... we have agreed that the perfect setup would be a partially filled radiator continuously condensing just enough steam to satisfy current demand. That steam would be produced by a modulating burner providing just the right amount and adjusting in real time to the conditions. But we all have on/off boilers. My point here is that if on/off boilers are allowed to run long enough to produce measurable pressure in these vapor systems the radiators will then oscillate through a very wide range of fullness and temperature every cycle. They will fill every cycle way past what would be the needed "continuous" fill level. A longer wait would then be required while all that heat dissipated. The radiator would end up much closer to room temperature when the next call arrived. While there may be some folks who desire this swing every cycle; I doubt that it is most of us. It is not even heat. Yes, yes, Jamie the old anticipator was in fact pretty good at helping with this...I did have one. But it is not as good as what I will describe now.

All I am doing is using a remote temperature sensor and two timers inside a PLC to target a fill level that would get the job done on a cold day if it were continuous and then dramatically reduce the temperature oscillation of the radiators. Every burn makes the remote sensor when steam arrives and I burn a set time after that. Every new burn starts after that sensor opens again plus a set time. I haven't changed the times this season. In this way the calls go on a long time and the swing in radiator temperature is dramatically reduced. Coupled with vacuum it is really even heat.
It has produced on the average day burns of 7-8 minutes and waits of 18-20 minutes. Of course cold starts in mild weather will take 20+ minutes to satisfy the remote sensor that first time. The net burn/wait times change gradually as the conditions do.

This is not a complicated control. But it is inexpensive and highly effective.

vapor1

@PMJ asked:
It doesn't sound like you really use the boiler all that much. You mentioned uneven heating. I'm curious what kind of complaints you have about that. Is it upstairs/downstairs differences or certain radiators just never get near enough steam or what kind of issue? Seems overall you're pretty satisfied.

Yes, pretty satisfied except for the delicate balance between flood and drought. In general, does working with low pressure require better tuning of the resistance or thirst of each individual convector? The second station on steam loop 1 is a large bay window convector (153 sqft EDR, 38% of the downstairs radiation). It seems to take a long time for steam to progress beyond this point, possibly 10 minutes on cold start. Would an orifice on the supply help? Or perhaps there would be a way to reduce the amount of air the trap passes. Convectors at the end of loop 1 might take 45 minutes to heat on cold start.

Jamie Hall

What kind of valves are on the inlets to your radiators? Can you identify them -- or take a picture of them? In many cases or older vapour systems, the valves can be used quite successfully to modulate the steam going in -- unlike one pipe systems. Try just closing the valves on that king size radiator a bit -- oddly enough.

PMJ

This is 2 pipe so I am assuming you have a control valve at the inlet of every convector right? You use those to slow some down. No on the low pressure question as it should never require any pressure to get steam anywhere on start up in two pipe. If it does, then it is because air can't get out from somewhere.

45 minutes is way too much of a difference for getting steam between areas. You need to do some real investigating as to where and why the hold up is. Are you sure none of the crossover traps are stuck open? That would cause real problems.

I am also worrying again about your boiler size. That is a lot of iron to get heated up from a cold start.

clammy

I m just going to comment on 1 or 2 issues . 1 being your boilers near boiler piping is terrible and without correcting it there no sense in wasting any time trying to resolve other issue that basically may be nothing when supply w dry steam from the correctly designed and installed near boiler piping . Some may not believe but the installation of a oversized header using both boiler trappings and system connection properly taken off are vitally important to proper operation of the system as a whole . After thats out of the equation you can isolate what other issues are and straighten them out . As for sizing if this is a 2 pipe system then according to your system edr you should be ok being the boiler should be about 20 % less then the connective load being the rads should only fill to about 80 % . You have to do something about air elimination to return to vapor vacuume you should replace the main vents w Hoffmann 67 vacuume vents possible replace the crosssover trap I would not remove it . The installation of a low pressure gauge like a 0 -60 rated Hg .possibly a vaporstat but in some case you can get by without at least I ve seen a few system w a standard pa404 that worked flawlessly . Your comments about the water level dropping on start up is caused by that nbp for sure it will always rear it ugly head on start from a cold .Last but not least are your pipe insulated if not do it and use mim1 wall fiberglass for best results uninsulated pipes cause issue and are a waste of putting heat where it was designed to go otherwise be prepared to deal w the issues .. Peace and good luck clammy

vapor1

@Jamie Hall and @PMJ , Thank you for the replies. There are 3 cast iron radiators with Warren Webster valves.



Two valves are shut and the third in the garage is frozen open.
Then there are 28 finned convectors. I don't see any throttles on them other than the dampers on the grills mounted in the walls above the convectors.

I do suspect the crossover at the end of loop 3 loop because when things get hot, the pipes on both sides of the trap read ~ 207 F and the return downstream from the trap heats, but incrementally cools over the 30' distance back to the boiler in spite of the other returns joining the flow.

add on: However, if any of the traps (including crossovers) were leaking steam, wouldn't it be coming out the single vent? After the startup (which passes cold air), maybe 10 min, the vent goes still until shutdown.

Jamie Hall

Crossover on loop 3 sounds stuck open -- that should be repaired. Not that hard to do.

The Warren Webster valves are very adjustable. With gentle persuasion and some WD-40 or PB Blaster the stuck one may relent. Patience.

I'm rather surprised that there aren't valves on the finned convectors. I presume there are traps, though?

As @PM said, 45 minutes difference in heating from one point to another is way off. You have more research to do -- trace the flow of steam in the mains and see what is -- or isn't -- happening. Something (or somethings!) is amiss.

vapor1

Thank you for your suggestions, @clammy . In that the boiler is 25+ yrs old, I'm trying to avoid investing in near boiler piping till I have to do it during replacement. I'm hoping to make the system as good as possible until then.
There is only one vent. It is at the end of the dry returns.
I will install a low pressure gauge.
Thanks again.
Stay safe

Jamie Hall

That one vent is where it belongs. Don't let some Happy Harry persuade you to move it or to add others!

vapor1

Jamie Hall said:

Crossover on loop 3 sounds stuck open -- that should be repaired. Not that hard to do.

The Warren Webster valves are very adjustable. With gentle persuasion and some WD-40 or PB Blaster the stuck one may relent. Patience.

I'm rather surprised that there aren't valves on the finned convectors. I presume there are traps, though?

As @PM said, 45 minutes difference in heating from one point to another is way off. You have more research to do -- trace the flow of steam in the mains and see what is -- or isn't -- happening. Something (or somethings!) is amiss.

Thank you @Jamie Hall . Is there packing inside those valves I might screw up with WD-40 or Blaster? I assume hand force only? Yes, all the convectors and radiators are trapped.

Jamie Hall

I don't think there is any packing in there. There isn't in Hoffman valves, anyway.


The procedure I've found to free those things is to zap them -- and let them sit a bit. Then zap again. Then try moving them -- even just a tiny bit at first -- and see if you can get them to move both ways. Hand force may not be enough, though you don't want to be a gorilla either. No impact, though. I use a vise grips, arranged to be able to put some force (in one direction or the other) on the handle, reacting against the top of the valve (not just holding the handle) and try one way and then the other... it can be frustrating. When you get bored or frustrated... zap it again and go away for a while!