Another discussion about steam boiler sizing

trivetman

Ive got thick plaster, no insulation,  and then around 14-16 inches of solid rock.  Its not exactly insulation,  but more like a heat sink.

Sylvain

As a home owner, If I were planing to change my boiler, (assuming I am happy with the present comfort achieved) I would make an evaluation of the heat losses based on the degree-days of a full heating season, the fuel usage during that season and the heating habit.

Before retirement, my house was kept, from monday to friday, at 22¨C from 17h to 22h and 17°C the rest of the time. That would give something like an "internal degree-day" of ¨((17*19) + (22*5))/24= 18,04 °C.
During the WE, 22°C from 08h to 22h which would give 19.91°C.
(If degree-day are only available for whole week, one can compute an average weekly internal temperature).

I would then have to make a correction to the degree-days to take into account my house temperature being slightly above the base temperature used for the determination of the degree-days and and this for the heating season and compute the heat transfer coefficient.
Being done for a complete season, it would include any wind and solar effect during that season. If one is using gas for cooking and hot water, one should see the average usage during non-heating season to subtract it from the global gas usage.

Now, the pick-up factor depends of the insulation, thermal inertia of the building/heating system and what is considered as acceptable for set-back recovery speed.

I guess many home owners could have the necessary data.

dabrakeman

Good source fo0r degreedays: https://degreedays.net/

EBEBRATT-Ed

Pick up is one thing, the amount of steam needed to bring the pipe, fittings and radiation up to 212 degrees. That is all it is....nothing else.

The BTUs or (lbs of steam) needed to do that is based on one thing and one thing only. The WEIGHT in lbs of the pipe valves and fittings and radiation and what material is is made from.

bburd

EBEBRATT-Ed said:

Pick up is one thing, the amount of steam needed to bring the pipe, fittings and radiation up to 212 degrees. That is all it is....nothing else. The BTUs or (lbs of steam) needed to do that is based on one thing and one thing only. The WEIGHT in lbs of the pipe valves and fittings and radiation and what material is is made from.

Yes… but the industry standard is a "piping and pickup factor". This includes the losses from the piping between the boiler and the radiation. In a house they may contribute to heating the building; in other occupancies they may not.

Another interpretation of "pickup" is reheating the building after a setback. The classic example is church sanctuaries that are only heated once or twice a week. They need enough capacity in boiler and radiation to raise the temperature in a reasonable amount of time, even in design conditions.

ChrisJ

EBEBRATT-Ed said:

Pick up is one thing, the amount of steam needed to bring the pipe, fittings and radiation up to 212 degrees. That is all it is....nothing else.

The BTUs or (lbs of steam) needed to do that is based on one thing and one thing only. The WEIGHT in lbs of the pipe valves and fittings and radiation and what material is is made from.

But that's not what it is.
As the link I posted multiple times shows, it was originally called the piping and pickup factor.
And it shows how they came up with the amount.

In my system starting from a cold start first the boiler heats, then once it starts producing steam it slowly creeps up the header heating all of that piping and then making it's way down the two mains. It then pushes out towards the radiators.

By the time even the first radiator valve gets hot, all of the header, mains and runouts are already at steam temperature and covered in insulation. Loss is minimal and there's no reason to have a bigger boiler for getting the piping hot. It all happens before any radiators get steam. In my case, that piping has a whole 104K to play with.


It then slowly heats each section of each radiator, one at a time working it's way across.

EBEBRATT-Ed

Pick up is the btus used to bring a system that is cold up to steaming temperature.. it is not extra btus to pull you out of nigh setback.

Sylvain

Thank you dabrakeman. That site is very interesting and the regression analysis allows to know what would be the part of the fuel usage for DHW or cooking and so on, without making a separate estimation during the non-heating season.
The explanations are better than mine.

ethicalpaul

EBEBRATT-Ed said:

Pick up is the btus used to bring a system that is cold up to steaming temperature.. it is not extra btus to pull you out of nigh setback.

But that value is meaningless in residential boiler sizing. What do you think of Chris’s description just above?

jesmed1

As I'm a newcomer to this forum and know nothing about steam heat except what I've read here, I did a little Googling to help me understand pickup factors for steam. And I found this:

https://forum.heatinghelp.com/discussion/149940/pickup-factor-help-me-understand

Several familiar names on that thread. Seems you guys have been debating this for 10 years now!

And from that same year (2014) was this explanation from Dan Holohan, which included a discussion of piping losses and pickup factors:

https://heatinghelp.com/systems-help-center/boiler-ratings-explained/

Maybe Dan needs to be prevailed on to come out of retirement, however briefly, to settle the debate...

Intplm.

@jesmed1

This is a great walk down memory lane. A very nice reminder of how to explain that good old boiler plate etc.
Thanks for reposting.

Intplm.

This has been an insightful discussion. Here and abroad.

Im wondering?
What should be a new pickup factor measurement?
In this, the era of todays green energy movement?

ChrisJ

jesmed1 said:

As I'm a newcomer to this forum and know nothing about steam heat except what I've read here, I did a little Googling to help me understand pickup factors for steam. And I found this:

https://forum.heatinghelp.com/discussion/149940/pickup-factor-help-me-understand

Several familiar names on that thread. Seems you guys have been debating this for 10 years now!

And from that same year (2014) was this explanation from Dan Holohan, which included a discussion of piping losses and pickup factors:

https://heatinghelp.com/systems-help-center/boiler-ratings-explained/

Maybe Dan needs to be prevailed on to come out of retirement, however briefly, to settle the debate...

There's a lot of things that have been debated a whole lot longer than 10 years.

EBEBRATT-Ed

@ethicalpaul

Hot water boiler have a pickup factor as well it's usually 1.15.

When you size a hot water boiler your supposed to go by the buildings heat loss

The you add 1.15 to the heat loss so the boiler can get off the ground. Steam has a larger 1.33 pick up because if the boiler water is less than 212 you have to get it to 212 before you get steam. Also with steam in most cases the radiation capacity exceeds the heat loss but you still have to heat most of the metal in the radiator especially with one pipe steam


The pickup factor is to get the boiler and piping and radiation to the operating temperature when the building heat loss is at design conditions. Once the piping is heated weather hot water or steam you don't need the pic up anymore.

All boiler manufacturers specify in their sizing that the manufacturer should be consulted if the piping is unusual or more extensive than a "normal" system.

Things that would affect the pickup are uninsulated pipe, extensive piping with long runs, oversized pipe pipe run through colder than normal spaces and piping run outdoors running a system with glycol which transfers less heat.

Most of the time these things can be ignored and on most residential jobs it can be. Besides how often is a boiler started up in design conditions? But there are jobs like heating a church where the building may have large setbacks, or the building is heated intermittently That is where you may get burned without a pickup factor.

Things that could reduce the PU factor are reducing the radiation to equal the buildings heat loss

ChrisJ

It doesn't matter if the piping is ice cold you literally have the entire boiler to heat it long before any radiator gets steam.

Are there properly balanced systems out there that do not behave this way?



You don't need to fill the radiators unless all of that radiation is required and the radiators take time to fill. 

Mine take roughly 30 minutes to fill if the system has been running recently.

jesmed1

ChrisJ said:

It doesn't matter if the piping is ice cold you literally have the entire boiler to heat it long before any radiator gets steam.

This is true, and it brings to my mind an interesting comparison with our high water volume, gravity conversion heating system. We have cold start boilers that are massively oversized for the actual heat loss of the building, but because we have so much water volume (in addition to the cast iron radiator and pipe mass), it takes maybe 20 minutes for the water to heat up enough just to start feeling any heat from the radiators, and typically another 20 minutes for the thermostats to satisfy.

If we were running steam from those same boilers, I wager we'd be getting heat from those same radiators in 10 minutes, and the thermostats would satisfy sooner too, because the boiler isn't heating 1000+ pounds of water now, it's heating maybe 100 pounds of water to much higher temperatures, and transferring that heat faster because the steam temperature is much higher than our 120-degree water.

So, following that logic, the pickup factor for our hot water system should be higher than for a similar steam system, contrary to the prevailing wisdom that says the opposite. And in fact, I'm guessing that one of the reasons our boilers are 3X oversized is that the previous installers looked at all the large-diameter piping and all the radiators and were more concerned about heating all that thermal mass than actually sizing the boilers properly for the building's heat loss.

If we had had a steam system, the previous installers wouldn't have had all that water volume to worry about, and maybe would (correctly) have installed smaller boilers. Or maybe not.

Theo_G

As an interesting side note, I have a 1997 Burnham IN4 which is on its way out. Hole above the water line. It is massively oversized for the system and has a copper "header" with bullhead tees both at the equalizer and connecting to the two steam mains. All of the copper exited the joints long ago. It feeds an ~1880s 1 pipe system of around 180 EDR with variously sized radiators, one so large that it requires a varivalve to even get most of the air out on a 30 min- 1 hr cycle. Because of the sorry condition of the boiler, and the piping being so bad it will suck all of the water out of the boiler even at less than 1 psi, it is downfired to only about 65000 BTU input. Even at 11 degrees, it can bring the house from 62 degrees to 70 degrees in about an hour and a half. Of course the piping is unusual in that there are two perimeter mains, one 8ft long, the other 20ft long. The 8ft main has the majority of the radiation connected. So a very compact piping system. All the original piping is wrought iron, not steel. Both mains are 2 inch diameter, with 1 inch dry returns. Venting on the 8ft main consists of a straight varivalve. 20ft main has two Hoffman 75s. The boiler can't be very efficient in this condition, yet it can still recover from a deep setback while only building around 2"WC of pressure. It's getting replaced this spring, but the EDR of the system is also changing with unit heaters being added to the basement. I am shooting for about a 10% pickup factor on the new boiler, maybe less. A bunch of changes will be taking place to correct issues with the system and add new radiation at the same time. But at this point even with the horrible boiler and piping, it works, with what must be negative pickup. Vents on radiators are mostly around Hoffman 40 and Dole 1933 size, with one varivalve on the giant radiator, and one Hoffman 1A set to setting 4 on another slow to heat radiator. 2 out of 3 risers have Gorton D riser vents.

KC_Jones

It takes a certain amount of BTU’s to heat the pipe, and it’s done with full boiler output. Once the pipes are hot and steam is entering the radiation, the pipes need essentially zero BTU’s if they are insulated, if they aren’t it takes a little more than zero BTU’s. I use zero as a reference because it’s going to be closer to zero than 33%. And again, that’s only if the pipes are uninsulated.

I’d also add, if the pipes aren’t insulated and being used to heat, say, a finished basement, then they should be counted in the EDR calculation and no pickup factor added, because you really don’t need it then. It is radiation at that point isn’t it? Those calculations are simple, I have a spreadsheet to automate those calculations.

Theo_G

KC_Jones said:

It takes a certain amount of BTU’s to heat the pipe, and it’s done with full boiler output. Once the pipes are hot and steam is entering the radiation, the pipes need essentially zero BTU’s if they are insulated, if they aren’t it takes a little more than zero BTU’s. I use zero as a reference because it’s going to be closer to zero than 33%. And again, that’s only if the pipes are uninsulated.

I’d also add, if the pipes aren’t insulated and being used to heat, say, a finished basement, then they should be counted in the EDR calculation and no pickup factor added, because you really don’t need it then. It is radiation at that point isn’t it? Those calculations are simple, I have a spreadsheet to automate those calculations.

See that's exactly the way I would think it would work. With my boiler in suboptimal condition and downfired, the steam distribution is very slow. I can walk alongside the pipes as they get hot. The mains have always gotten hot before the radiators, or even the run-outs to the radiators. Once the main vents close, the radiators start filling with steam. On my large Carman's radiator, I can feel the heat travel up each large tube, one at a time. Because the radiator is so large, it takes quite a while for it to push all of the air out. If the boiler runs for long enough, the steam will travel up the last tube to the vent and close it. It's the last vent to close in the entire system, even though it is the largest radiator vent (angle varivalve). Ironically the first vent to close is a Dole 1933 on the smallest radiator in the house, a 9 EDR HB Smith Princess upstairs. But the mains always get full before the radiators. The vented risers are next. Then the radiators themselves, with the largest being last. Most of my vents are alcohol mixture type, and I can hear them close in the order of the steam filling the radiators. So the question is, if the pickup factor is completely unnecessary, what is it there for? Uninsulated pipes? Mine are all insulated, although not that well and not on the fittings. That will change with the new boiler. If I can recover from an 8 degree setback in cold weather with the boiler in the condition that it is, how could it be necessary for any system? I can see maybe the previously mentioned church or school needing one, maybe, but I wonder if that's because the piping would exceed the EDR rating of the boiler without it. Those buildings often have quite extensive piping systems. Another thing I have to add relates to unit heaters/fan coils. Since their high EDRs are based on the fan being on, and the fan is usually turned on based on piping temperature or system pressure, then even in a system with a pickup factor, they shouldn't relate to the pickup factor at all because their EDR increases only when the piping is hot. They can be sized to the full output of the boiler. Without the fan being on, their EDR is very low. In my case the boiler replacement is going to coincide with adding either one large unit heater (36-40kbtu/150-175EDR), or two smaller ones (18kbtu/75EDR each). By sizing the unit heater plus the rest of the radiation to be close to the full output of the boiler, I can have a perfectly matched system. I'm going the power burner in an oil boiler route, rather than atmospheric, partially because I like power burners, and partially because I want the option of switching to B100 biofuel down the line just by changing the burner, putting a Roth tank outside, and the barometric damper. Partially this is because of how many issues I have had with the gas company, and partially because they want to move the meter outside and drill through a 5 ft thick, 200 year old rock and mortar wall to put in a new pipe, and I'd rather pay more for fuel and have my own infrastructure than risking them ruining my foundation somehow. Plus I like being on a non petroleum based fuel and like supporting companies that are putting effort into that field. We have one local to the next town over that delivers B100 for heating. If I somehow can't heat the house with the smaller size boiler, I can go up to the next size up by putting baffles in and raising the input. A conversion kit is available. The only reason I am leaning towards a 5-10% pickup is due to a huge radiator of uncertain EDR. It dates from the 1880s, and there are barely any records of it existing. From my measurements and educated guesses on EDR, it could be anywhere between 40 EDR and 90 EDR. So it's not really a pickup factor, but a fudge factor for the unknown EDR radiator. 

ChrisJ

@Theo_G

When I had 33% over, which is the standard all of my piping still heated first.
In my experience steam will not travel through cold piping,or a cold radiator. It heats the pipe first and then moves on slowly working it's way thru the system heating it.

As far as my understanding the "Piping and pickup factor" was to account for extra piping losses, and then have extra boiler to warm buildings up as fast as practical without building excess pressure. You've got a school, or a church that's cold and needs to be warmed up quick, that 33% over will get you the most you can from that system without burning excessive fuel. They found by oversizing by roughly 33% they got the fastest recoveries in such systems without wasting fuel. Most of that 33% is to rapidly heat the system during a recovery.


That's my interpretation.

Jamie Hall

Sounds about right, @ChrisJ -- and it's a rule of thumb. And like most rules of thumb, it really isn't possible to explain it or defend it in any rigorous way. It works... well enough, most of the time... for most of the systems... are there systems where a smaller margin over the calculated load works better -- like yours and mine? Sure. But a good deal of effort has been put into those systems -- after installation -- to get them more closely matched. Which goes back to what i said earlier in the novel we are writing: if I were installing a system from scratch, and the equipment was available (it isn't always) I would size a boiler which had a maximum output accommodating the 33%, but which could be downfired to be right at the EDR. Then, having gotten the rest of the system nicely balanced and operating well, adjust the firing rate to match the real world. But that takes time, and I doubt that the average homeowner would be willing to pay for the time -- not be able to and have the equipment to fiddle with nozzles and pressures to get it "just right".

ethicalpaul

You don't really need "just right", we know this because even 33% pickup factor boilers perform OK. Even boilers way oversized plus the 33% can do OK.

From the massive evidence showing that 33% is ridiculous and that even negative sizing is fine, I'd aim for 0% to 5% "cushion"

This 33% is a cover-your-@ss number if I have ever seen one. The explanations to try to justify it make no sense and contradictory, even against each other.

EBEBRATT-Ed

As far as water pick up time and steam pick up time a BTU is a BTU weather it is from water or steam.

Water needs a lower pick up because water in a water system does not boil. Every btu the boiler makes goes to the water, up the flue or into the building from boiler jacket and pipe loss that is it.

With steam the boiler is initially firing but no steam is produced it is packing the btus into the water so it will boil. This increases jacket loss and you have a boiler at 212 versus 180ish for water.

Steam piping is usually steel copper is usually water. It takes more btus to heat the steel pipe versus the copper pipe. @jesmed1 converted gravity system is the exception

Steam has to boil the water first. For every lb of steam generated the boiler has to add 970 btus to the water to make steam from water at 212 deg. Those btus are hidden (latent heat)

You get the latent heat back when the steam condenses. When it condenses in the radiation that is good. When it condenses in the pipe not so good. Condensing in the pipe that heat is in the house (basement) and not upstairs in the radiation where you really want it. This is why basements are warmer with steam than they are with HW.

Matt_67

The thing is, it’s the manufacturers call to make. In the liability driven world we live in if a contractor puts in a boiler that isn’t rated for the amount of radiation in the system they totally own it. If a radiator doesn’t heat for any reason, the homeowner can point at the tag and say the boiler you picked is too small - even if that isn’t the root cause.

Another question that needs to be proven is economy. We need actual data that proves it is more economical to run with zero pickup. I’m not saying it is or isn’t, just that anecdotal evidence isn’t enough.

ethicalpaul

Yes and it's not even the manufacturers, there is the IBR or whatever it is and other ratings agencies/organizations that the boiler manufacturers have to follow (that is my naive understanding anyway).

But gosh golly gee-willakers, it's just totally fine for a boiler to be twice the size it should be, you have to laugh to keep from crying

jesmed1

EBEBRATT-Ed said:

Condensing in the pipe that heat is in the house (basement) and not upstairs in the radiation where you really want it. This is why basements are warmer with steam than they are with HW.

@EBEBRATT-Ed Steam would actually be good for us in that respect, because our basement is cold from three different flue penetrations in the chimney (2 oil boilers and one gas hot water heater). That cold air in the basement cools the uninsulated ceiling, which happens to be the floor of my condo unit. So both first-floor condo units have built-in convective cooling systems in the floors.

The hot water heat we have is nice though because it's low temperature water that releases heat evenly for a long time after the boiler stops firing.

jumper

If steam plant and radiators can keep a building habitable @10° below zero then they're obviously over sized when outside is 40°. So perhaps it make sense to downsize boiler & radiation and use supplementary heaters for cold days?

ChrisJ

jumper said:

If steam plant and radiators can keep a building habitable @10° below zero then they're obviously over sized when outside is 40°. So perhaps it make sense to downsize boiler & radiation and use supplementary heaters for cold days?

Mine can not only keep the building habitable, it can keep it at 72F down to -39F due to grossly oversized radiation according to the heatloss calculations I've done.. And only a 10% "pickup factor".

I would not recommend supplementary heaters. They seem to cause more problems than they're worth for a lot of people.

These systems steam can all, or, almost all be made to work silently and quite efficiently all winter long. More than efficient enough that the primary upgrades people need to look at are insulation, windows and tightening up drafts.

jumper

New tighter windows: then original size is even more over sized?

ChrisJ said:

jumper said:

If steam plant and radiators can keep a building habitable @10° below zero then they're obviously over sized when outside is 40°. So perhaps it make sense to downsize boiler & radiation and use supplementary heaters for cold days?

Mine can not only keep the building habitable, it can keep it at 72F down to -39F due to grossly oversized radiation according to the heatloss calculations I've done.. And only a 10% "pickup factor".

I would not recommend supplementary heaters. They seem to cause more problems than they're worth for a lot of people.

These systems steam can all, or, almost all be made to work silently and quite efficiently all winter long. More than efficient enough that the primary upgrades people need to look at are insulation, windows and tightening up drafts.

ChrisJ

@jumper

Less heat loss means less fuel consumed, period.

It doesn't matter what the heating system is.

Sylvain

Wiki: "One square foot of EDR is able to liberate 240 BTU per hour when surrounded by 70 °F (21 °C) air and filled with steam of approximately 215 °F (102 °C) temperature and 1 psi of pressure."

So, 240 Btu is the heat losses of a radiator of 1sqft of edr when the temperature difference ( steam-room)= 145°F.

Somebody may have the right formula or a table giving a correction factor for inside temperatures other than 70°F.

Just for illustrating the idea, let us use a linear relationship,

What about starting to heat a building whose inside temperature has dropped to 40°F.
Now the difference between steam and room is 175°F.
The EDR of the installed radiators (and pipes) would now be multiplied by 175/145= 1.20 at the start of the recovery.

Without a pick-up factor (or a way to throttle the steam), one will face the problem of the school which EBEBBRATT has spoken of hereabove.

What to do if the inside temperature has dropped so much without the possibility of throttling?
Maybe close 20% of the radiators when starting the recovery to lower the EDR?

The condensate temperature will also be lower then in normal operation for some time.

Sylvain

I have found a formula and a table in this document:
https://estudijas.lbtu.lv/customfiles/2017.08.14.Metodika_KP_Arturs_Lesinskis/radiators CHAPTER 36. HYDRONIC HEAT-DISTRIBUTING UNITS AND RADIATORS.pdf
It is not linear.
q=c* [(Ts-Tr) exp n]
Temperatures in °C and q in watt.
Where n is >1 and depends of the type of radiator
n=1.2 for cast iron radiators.
So the effect of a lower room temperature is greater than with a linear equation.
The EDR multiplication factor for 15°C (59°F) for a CI radiator is already 1.15 (steam at 105°C/221°F)

Jamie Hall

There are times...

When I think calculators and computers should be prohibited. It's not that hard, folks. First place, none of your input numbers (EDR, total EDR, building heat loss, boiler output power (BTUh) are likely to be known within plus or minus 10% Nor do you have any way of knowing which way the error is on any given number.

While it then becomes lots of fun to play with those numbers on your calculator or whatever, the answer you come up with also has an error range of 10%, and if any of those numbers has an error greater than that, so does you answer.

Don't fuss it. You aren't trying to land on the moon, or even the back 40 paddock. If you are in the design phase, give yourself some wiggle room and, once in operation, adjust as needed. If you are in the operating phase, ask -- is it working? Yes? Fine. No? What can I tweak to make it better.

Then sit back and relax.

Sylvain

I was not trying to find exact numbers.
The Dead Men made a good work by trial and error but there is satisfaction in finding a justification for the pick-up factor.
I would not have looked at this without EBEBBRATT experience in a school mentionned hereabove.

My question to those running a boiler with no pickup factor:
What do you experience in case of recovery?
What do you experience in case of really cold start?

ChrisJ

Sylvain said:

I was not trying to find exact numbers.
The Dead Men made a good work by trial and error but there is satisfaction in finding a justification for the pick-up factor.
I would not have looked at this without EBEBBRATT experience in a school mentionned hereabove.

My question to those running a boiler with no pickup factor:
What do you experience in case of recovery?
What do you experience in case of really cold start?

I have an alleged 10% pickup.
I've done multiple 10 degree recoveries without building excessive pressure or any balance issues.

Define really cold start, but what's the worse that will happen?
The system will start, worse case is slightly out of balance and will warm the house enough that the next start won't be really cold.

Jamie Hall

Cedric seems to be around 10%, too, on a rather big system, and sems to work just fine.

Sylvain

ChrisJ said:

Define really cold start, but what's the worse that will happen?
The system will start, worse case is slightly out of balance and will warm the house enough that the next start won't be really cold.

Really cold start would be for a house whose temperature would have dropped to a few degree above freezing.

If I understand what EBEBRATT-D has described, the water was not coming back fast enough to the boiler, the feed pumps could not keep the water level. The boiler was under some vacuum because the (cold) EDR of the whole system was too high, and thus vaporising water quicker than the used boiler rating. Apparently a pick-up factor would also be needed for the feed pumps.
Now of course feed pumps are for big systems.
But one might experience low water shut-off.

I guess your are right for the subsequent starts.

ethicalpaul

Regarding the situation described in the post just previous, no matter how cold or big a system is, there is no way for a system to generate a vacuum on startup like this...the system has to fill (at least partially) with steam then have the steam collapse to create a vacuum. As the boiler starts to create steam in a cold system, yes, the cold pipes will collapse the steam that reaches them, but the boiler is pumping out its rated steam volume and no system vacuum can occur.

Correct me if I'm wrong!

And the entire BTU output of the boiler is going to be heating pipes and only pipes and that is not a lot of load (relative to the entire EDR of the system). The pipes will get hot in a timely fashion.

EBEBRATT-Ed

@ethicalpaul

Sorry but I don't agree.

I will be the first to admit that what I saw is extremely rare and the only time in 46 years that I saw it happen. If I did not see it with my own eyes, I wouldn't have believed it myself. The pressure transducer that was piped to the steam main had an electronic readout and when start-up was occurring, I saw the reading in a vacuum.

But what about when a boiler is steaming at full output and you have a sagging steam main (a very common occurrence) and the steam is collapsing due to condensate in the main and starts hammering. That also is caused by a vacuum.

ChrisJ

When my system starts cold the steam slowly works it's way down the mains.
But, it's not a steady flow.

You'll see a slight positive pressure followed by a slight vacuum over and over.
My opinion is this is the steam advancing and then condensing in the cooler section of pipe creating a vacuum. Once that area is warm it advances again and then condenses again. This is the interesting part of steam, as you attempt to cool it, it pulls more in behind it. It's relentless.


One thing I am curious about is I do have a runout in the past that was pitched wrong enough it held too much water and wouldn't allow the radiator to heat and hammered. But that was a single runout.

If a steam main is holding water and hammering, and we assume it's the only steam main on the system, how long will this go on for? What will happen over time if that puddle is sucking up 100% of the boiler's output? I don't see anyway that length of 2" pipe could dissipate 80,000+ btu/h? I guess it'll hammer and complain until the water gets hot enough to boil out? But there's a supply feeding it fresh water......