Another discussion about steam boiler sizing

EBEBRATT-Ed

Some states (and CT is one I believe) want a heat loss etc on the permit application not that they probably check it.

I think this discussion we should decide if we are talking residential or something else.

The other issue (and this is my own issue) is IMHO you can fire gas boilers to their rating without issue. I used to find on oil that things stayed cleaner when you fired the boiler at 85% of its rating.

Jamie Hall

I think you're right on the calculation, @EBEBRATT-Ed -- but I haven't built anything in a long time!

trivetman

I'll echoe Jamie's comments about every system being different. I happened to test the boiler output against the system last night. I had a SteamMax 299 put in last spring. Rated for 771 Net EDR against my load of 737. Two pipe vapor-type system in a big house. Lots of piping in the basement never mind the risers. The 771 Net EDR on the boiler is with the implied pickup of 33%. The thermostat's call for heat has generally lasted 25-30 minutes with the pressure never going above 3 oz.

Last night I cranked the thermostat up to see if the pressure ever built. At somewhere between 40-60 minutes (I wasn't keeping that close an eye on it), it started cycling on pressure (12 oz vaporstat cutout).

Sized right? Probably? Would I have been crazy to go one size down to the 250 with Net rating of 646 (Gross rating of 860 EDR). Probably.

It sounds like we've got a couple samples in this post where the 'real' pickup factor is close to zero. And mine, where 33% might be right. So maybe the real question is what does it take to evaluate the 'correct' pickup?

trivetman

Ill also add…it sounds like KC’s experiment was based on the ability to adjust the firing rate.  Awesome, but the vast majority of homeowners don’t have the equipment nor expertise to do so.  It doesn’t work to start talking about changing the way sizing is done if a key component is a technique well beyond the homeowner (at least if we’re talking residential)

dko

Did every radiator manufacturer use the same methods and process for calculating EDR? Old and modern? The castrad post on the wall posts leads me to think, no. The lab they used also tested older radiators and admits with their method the EDR came out consistently less than what was advertised/written by the manufacturer.

What if the way EDR is calculated for radiators is also "wrong" and the numbers we see in those books are actually 33% over "real word" EDR.

If you used castrad's numbers and sized a boiler based on ten of their 40sf radiators. that's 400sf edr. But if you extrapolated from comparing similar old radiators it'd be closer to 60 sf, that would be 600sf. That's almost 2 boiler sections worth.

How accurate is a boiler's written numbers?

How sure are you that all your radiators are exactly the EDR's you used to size the boiler?

ChrisJ

KC's experiment wasn't about being able to adjust firing rate. His experiment had to do with what happens if you run an undersized boiler on a single pipe steam system. Does it cause all kinds of balancing issues etc.

For what it's worth my single pipe system normally runs between 1/8 oz and 1/2 oz.
If I do a 10 degree recovery it may see an ounce.

It's heated beautifully this way for roughly 10 years now and it's very consistent.

EBEBRATT-Ed

Every job is different. Take and old church where they heat the building intermittently and used large set backs. You going to need some pick up on a job like that. Smaller houses not so much.

I had a job once (and no one believes this story) where we put new boilers in a school and if I didn't see it with my own eyes I wouldn't have believed it either. It was public bid job and the engineer undersized the boilers.

On a cold start with all the pipe in the building cold the boilers would start to make steam and the water levels were going crazy bringing the feed pumps on an off-water levels bouncing. And the boiler were piped right and had been skimmed.

I went up the ladder and throttled the gate valve on the steam supply from the boiler and the water line calmed down. I didn't leave it that way just wanted to see what it would do.

What was happening is the boiler was putting steam into the system full of cold pipe. The steam was condensing so fast it was pulling water out of the boiler. Think about it . You have a 50 hp boiler putting out say 60hp. The steam in the system condensed faster than the boiler could supply steam and it was forming a vacuum in the system. As soon as it got the pipe warm all was good.

They had a steam pressure transducer on the steam main. As soon as that would read a +.02psi it was ok. The boiler could heat the school fine as long as you got past the pick up.

Some jobs need pickup

Most all steam boilers have a clause in the manual that says" consult mfg for pick up requirements in systems with unusual piping." or words to that effect,
.

I was involved in another job where they were having problems with the boilers. Turns out they were over firing the boilers. Where they really over firing the boilers? Yes & No The condensate was too hot.

Think about that. If the condensate is too hot and you fire it to the name plate you are over firing the boiler because you causing it to produce more steam than it is rated for. Hotter condensate =more BTUs

You have to find out from the mFG how they rate the boiler at what temperature condensate.

Jamie Hall

All of which points out something I used to tell students, decades ago when I had students. That calculator is all very fine, but don't just go by the numbers with your head down. Think about what's happening -- or might happen. If you don't understand at least intuitively, don't do it until you do.

ChrisJ

@EBEBRATT-Ed

I think schools and churches are what the so called pickup was actually intended for.

But these aren't residential systems.

@Jamie Hall did you have time to read that report?

ethicalpaul

Every job is different yet every job should have 30% pickup factor, as determined by net sq ft rating on boiler? Logic fail

BobC

@Jamie Hall I learned electronics in the early 60's using a slide rule, we spent a week learning that and that gave me a leg up when using a calculator or spreadsheet because i don't accept their answer as gospel. When you use a slide rule you already know about what the answer is because you have to reduce everything with scientific notation. That requires you to pay attention.

I may be broke but not so much I can't pay attention. i still use the sliderule on the bench both to keep in practice and because the batterues never run down.

Bob

EBEBRATT-Ed

It's like installing ac in the northern states. People here don't run ac 24/7 and set the temp and leave it alone. They put in oversized units because they run them as intermittent operation. So they put a 3 ton on a 2 ton load.

Down south it is hotter people put them on and leave them alone. If you need two tons in the south you get 2 tons and it works.

It's not just the equipment size it is how it is used.

dabrakeman

I wouldn't generalize too much and assume one always knows how a prospective homeowner is going to use their "Residential System". Maybe they do leave the home 3-5 days out of 7 day week for work or something and thus are repeatedly doing huge setback and recoveries (as they should).

trivetman

But even if you do know how a system will be used,  thats a dynamic variable.  Household patterns change.  A system is installed with long lasting footprint.  My heating system was installed in 1910 and has been owned by at least a dozen people, each with very different behaviors.  You can tailor a system for niche usage but if the usage is way outside the norm,  its going to give someone fits down the road.  

ethicalpaul

Do the sizing calculations have a section where you ask the homeowner how they are going to use the system?

ChrisJ

My system with an undersized boiler can do a recovery no problem, but a "proper" sized boiler cannot because it'll build excessive pressure and we tell people they can't do it.

So I'm really confused......


If your radiation can only condense X amount it doesn't matter if the boiler can exceed that or not you're not putting more than that into the house.

My boiler does roughly 104k out and the radiators can allegedly do 94k. 

EBEBRATT-Ed

@ethicalpaul
How the system is used makes a huge impact on the system and how it heats

Do you turn a HW radiant floor system on and off?

Homes are a different story when it comes to steam. Pick up factors in the average house are small or nonexistent. But what about a 1900 Victorian with no insulation and 3 floors?

And how you run the system. Makes a huge difference. Size a boiler for the edr don't include any pick up factors and the homeowner does 10 degree set backs at design conditions. Can you guarantee they will be happy?

My sister used to complain her AC would not keep up. In hot weather she would keep the house closed up windows, curtains and blinds closed to "keep the heat out" then at 2 or 3 pm when the house was starting to boil she fired up the ac and complained it couldn't cool the house. Heating and AC is a lot more than air temp. It's humidity, it's infiltration its the building material. When the sun shines on an 18" thick brick building how long before that heat gets to the inside of the building. Do the heat gain and find out you will be in for a surprise.

If you have never done a heat loss or heat gain calculation the long way with a pencil (forget the fancy software) you need to do one because if you don't you will not know how a building works.

ChrisJ

@EBEBRATT-Ed
I've never known anyone that used central air that way.

But as I said before I'm confused.  We can't do recoveries with a "properly sized steam boiler" but can with undersized.



My house is an 1860s with two floors and no insulation.

ethicalpaul

Pick up factors in the average house are small or nonexistent.

OK now we’re getting somewhere! The average house needs no pickup factor! We agree!!

EBEBRATT-Ed

@ChrisJ most people in the north run their ac that way. They don't want to pay the electric bill so the run it on the hot days and off on the cooler days. They think they are saving money just like big setbacks when heating.

delcrossv

EBEBRATT-Ed said:

@ChrisJ most people in the north run their ac that way. They don't want to pay the electric bill so the run it on the hot days and off on the cooler days. They think they are saving money just like big setbacks when heating.

We do that. For most of summer it's the whole house fan, but if we're going to get a hot spell the AC goes on in the cool of the evening before the heat comes the next day. Else, the AC is trying to cool off an already heated house.

ChrisJ

EBEBRATT-Ed said:

@ChrisJ most people in the north run their ac that way. They don't want to pay the electric bill so the run it on the hot days and off on the cooler days. They think they are saving money just like big setbacks when heating.

I'm in Northern NJ.  Does that count as the North?

jumper

Here is some experience from way back. I may remember incorrectly.
In the seventies big boilers in multi unit residences were often replaced with a "train" of small units. A strategy to save gas was to fire only one small boiler during day and night. Only for mornings and afternoon/evening was the whole train going. Presumably the train was sized for zero °F or less? Most days in Toronto the single boiler, 33% or less of design capacity, adequately heated the building. And I would think that cycling was minimized?

We sometimes hear stories about steamers being installed in HHW houses. If the boiler is small enough one can conceive that all steam condenses in radiators and the crazy kludge works. How economical is a different question.

My inclination is that under size is a good idea. One can use a space heater in an occupied cold room. But I've read that over sizing for pick up saves gas.

dabrakeman

As far as AC many are now going to time of use electricity plans. AC is off 3-7PM and then cranking at 7PM. Often cooling an extra degree or two before 3PM.

ChrisJ

@jumper the only way you could save gas is if the system is out of balance and a radiator by the thermostat is being starved.

LRCCBJ

KC_Jones said:

Intplm. said:

Intplm. said:

Gee, I don't know?
EDR? Well always have done it this way with steam. And a proper heat loss calculation when sizing for hot water.
I do not want to tinker with these proven methods.
They have never let me down.

I haven't had an installation problem since I have become a student of Dans books. Not one that has had a customer uncomfortable.

While I read into this post, Im trying to relate to its purpose/learn something helpful.

So the only criteria is callbacks? If that's so there is no point in sizing any equipment properly. You could throw any oversized thing on almost any system and not get callbacks.

We are currently exploring if that 33% makes sense. Just because something has been done for years, doesn't mean it's the only way, and honestly, doesn't mean it correct either. We should always be learning and experimenting...always.

Kenneth,

Your analysis as an engineer is totally correct. You have analyzed your own system to death and you have concluded that you can operate it at a 0% pickup factor. This is commendable.

However, there are a multitude of systems out there with extended runouts that are of miserable size that will demand an additional supply of steam and will also demand a bit more than three ounces of pressure.

Sure, if you spend 100-200 hours on such a system, you MAY be able to balance it with venting, but that is not a certainty. What is a certainty is that with a 33% pickup factor, the installer has a bit of leeway in attempting to get such a radiator to heat properly. Changing vents will definitely work for him.

As a contractor, one cannot take the risk (unless they are extraordinarily knowledgeable about every single building they walk into) that they cannot heat one or two radiators in the building. THIS is why the steam boiler manufacturers use a 33% pickup factor. Is it excessive in MOST cases? Absolutely.

However, you simply cannot make a case for reducing the pickup factor to zero for every possible installation out there.

One variable that greatly affects your calculations is heatloss versus EDR. IF, by some miracle, the heatloss equals the EDR, and you proceed with a 0% pickup factor, you are walking into a guaranteed failure in that installation. Of course, if the heatloss is 65% of the EDR, this allows you great leeway with the pickup factor and still be able to be successful. Sadly, the industry is totally ignorant of the heatloss on steam installations and simply calculates the boiler size via the EDR and adds 30%. Heatloss is never a factor..............but, for a successful installation with a 0% pickup factor, it is absolutely relevant.

KC_Jones

LRCCBJ said:

Gee, I don't know? EDR? Well always have done it this way with steam. And a proper heat loss calculation when sizing for hot water. I do not want to tinker with these proven methods. They have never let me down.

I haven't had an installation problem since I have become a student of Dans books. Not one that has had a customer uncomfortable. While I read into this post, Im trying to relate to its purpose/learn something helpful.

So the only criteria is callbacks? If that's so there is no point in sizing any equipment properly. You could throw any oversized thing on almost any system and not get callbacks. We are currently exploring if that 33% makes sense. Just because something has been done for years, doesn't mean it's the only way, and honestly, doesn't mean it correct either. We should always be learning and experimenting...always.

Kenneth, Your analysis as an engineer is totally correct. You have analyzed your own system to death and you have concluded that you can operate it at a 0% pickup factor. This is commendable. However, there are a multitude of systems out there with extended runouts that are of miserable size that will demand an additional supply of steam and will also demand a bit more than three ounces of pressure. Sure, if you spend 100-200 hours on such a system, you MAY be able to balance it with venting, but that is not a certainty. What is a certainty is that with a 33% pickup factor, the installer has a bit of leeway in attempting to get such a radiator to heat properly. Changing vents will definitely work for him. As a contractor, one cannot take the risk (unless they are extraordinarily knowledgeable about every single building they walk into) that they cannot heat one or two radiators in the building. THIS is why the steam boiler manufacturers use a 33% pickup factor. Is it excessive in MOST cases? Absolutely. However, you simply cannot make a case for reducing the pickup factor to zero for every possible installation out there. One variable that greatly affects your calculations is heatloss versus EDR. IF, by some miracle, the heatloss equals the EDR, and you proceed with a 0% pickup factor, you are walking into a guaranteed failure in that installation. Of course, if the heatloss is 65% of the EDR, this allows you great leeway with the pickup factor and still be able to be successful. Sadly, the industry is totally ignorant of the heatloss on steam installations and simply calculates the boiler size via the EDR and adds 30%. Heatloss is never a factor..............but, for a successful installation with a 0% pickup factor, it is absolutely relevant.

A multitude of things here.

First, Kenneth? I don’t have that name posted publicly anywhere that I’m aware of, so, sir, who are you? And why, without my permission, are you posting that? I don’t have an issue with someone looking around at my online presence, but I do have a problem with people posting as you did. At least have the manners to ask me privately if I’m ok with you posting my real name. At the bare minimum, what you did makes you a jerk.

I’m not an engineer of any kind in fact I’ve never even graduated from college at any level. My understanding is, essentially, all hands on.

But since you seem to be so interested in my personal life, let’s get actual reality on the table and not your ASSumptions (which you made many) about me or what I’ve done. I work for Evapco as a Senior Lead Designer. You can check out Evapco’s website for what we do, since you obviously like researching so much. I generally like my work to speak for me so I’m not going to get into my credentials, or experience level, as frankly I view that as the mark of a hack.

Second, I haven’t spent 100-200 hours on my system, including replacing the entire boiler. I’ve spent maybe an hour on my venting, 9 years ago. Basically all your assumptions are completely wrong and off base, I won’t assume anything bout your motivation for all your speculation, I’ll simply state I don’t understand people who assume. I love my steam system, but if the pros on here think us DIY are spending that kind of time on things you’re nuts. I have 100 other things in my life and literally don’t have that kind of time to spend on it.

And finally, you need to read much more carefully if you’re going to make posts like this. My system does have an EDR that is close to the heatloss, as I already stated at the beginning of this. First I’ve done heat loss on the house, but also I’ve lived here long enough to see this system run with all, completely hot radiators, all day long. Information any contractor can acquire by talking to a homeowner, if they even care to ask. So, again I am the case you are claiming won’t work, yet it does, and works amazingly well. So, without question, it is not a failure, no amount of your conjecture can make it a failure. It works, you’re wrong.

Do whatever you want. I can only present information I can’t understand it for you.

ethicalpaul

No residential system needs more than 3oz. There is no noticeable pressure drop in a residential system.

retiredguy

I love reading these stories of guys that will experiment with their heating systems just to see what they can do or what they can accomplish. Since the company I worked only did schools, hospitals and industrial steam, with pressures to 300 psi and inputs up to 30,000,000 btu's I have little experience working or sizing residential systems. That said, I can tell you guys what an undersized steam boiler will do in a large building like a nursing home that has no control valves on the radiation. The job consisted of 2 low pressure steam boilers that the heating engineer undersized due to his stupidity. I started these 2 units and adjusted the input to 100%. With the outside temp at 30F, 1 boiler running all day would not heat all the building. All the radiation on the outside perimeter of the building and being the furthest from the boiler never even got warm and the radiation closest to the boiler room overheated. The steam only heated the radiators until it was exhausted and condensed with no more steam for the rest of the radiation. The only way that building would get warm was to run both boilers all the time or at least until they caught up with the steam load. Of course, there is much more to my story but you get the picture.

EBEBRATT-Ed

Commercial and Industrial steam compared to residential steam is like comparing warm air to hot water heat. They obviously share some of the same basics but are almost more different than they are alike.

jesmed1

As a homeowner running two hot water boilers in a 4-unit 100-yr old condo building, we're not in the steam business, but the general principles of doing a heat load analysis and sizing the boiler properly are similar.

I would suggest that a fundamental, underlying issue is how to make equipment sizing and design decisions in situations where the level of knowledge (eg of a given building's heat loss, etc) may vary greatly, and the time available (and incentive structure) for analysis and decision making varies greatly.

In the case of us homeowners who have perhaps lived with and observed our systems for many years, we've had time to assess very accurately the actual heat loss of the building, observe the venting behavior of steam systems, observe boiler cycle times, etc. Sometimes we conclude that our systems are perfectly sized. More often we find that our boilers have been massively oversized.

Which then leads us to consider the position of the contractor who installed the boiler, probably based on very limited time (or none) doing a heat loss calculation or calculating EDR's, and whose fallback method is either to install a boiler of the same size as the previous one, or to use a "rule of thumb" BTU per sq ft, both of which usually result in oversizing.

Why? Because (1) the contractor's time is money, so he feels pressure to move faster than perhaps is in the customer's best interests, (2) the contractor knows that whatever heat loss calculation he does is going to have some unknown degree of error, so the incentive is to err on the side of conservatism, and (3) for residential jobs, the marginal cost of oversizing the equipment is relatively minor, so in his mind, there's little downside in oversizing the equipment just so he can be sure not to get an angry phone call when the temperature outside drops to zero.

So in my case, we ended up with two 175,000 BTU DOE output boilers totalling 350,000 BTU in a building with a heat loss of 90,000 BTU/hr. It took the contractor maybe 10 minutes to size those, probably based on total square footage multiplied by a 50 BTU/hr/sq ft "rule of thumb." Those boilers didn't cost that much more than boilers half their size, which would have been more appropriate. But the contractor is happy because no one ever called him to complain about lack of heat, and the previous condo owners who paid for those oversize boilers were happy in their ignorance, as long as they stayed warm.

So I guess I see both sides of the coin. We homeowners have the time to observe our systems at work and collect the data that, if the contractor had had, he might have been able (and willing) to size the system more accurately. On the other hand, the contractor has time and cost pressures that work against doing careful, thorough sizing analyses, and is working within a framework of asymmetric cost/benefit factors that are usually going to favor oversizing the equipment, with minimal marginal cost penalty, at least in residential systems. The result is that he falls back on received wisdom about pickup factors and BTU/sq ft rules-of-thumb that, basically, operate similarly to factors of safety in structural design, to ensure adequate margin in the face of uncertainty.

ethicalpaul

retiredguy said:

The job consisted of 2 low pressure steam boilers that the heating engineer undersized due to his stupidity. I started these 2 units and adjusted the input to 100%. With the outside temp at 30F, 1 boiler running all day would not heat all the building. 

Thanks @retireredguy!

i wonder a couple things:

- how undersized was the one boiler vs the radiation?

- there were two boilers but you described only firing one. Were they designed to run in tandem, or was one a backup?

EBEBRATT-Ed

@jesmed1 said

"In the case of us homeowners who have perhaps lived with and observed our systems for many years, we've had time to assess very accurately the actual heat loss of the building, observe the venting behavior of steam systems, observe boiler cycle times, etc. Sometimes we conclude that our systems are perfectly sized. More often we find that our boilers have been massively oversized.

Which then leads us to consider the position of the contractor who installed the boiler, probably based on very limited time (or none) doing a heat loss calculation or calculating EDR's, and whose fallback method is either to install a boiler of the same size as the previous one, or to use a "rule of thumb" BTU per sq ft, both of which usually result in oversizing.

Why? Because (1) the contractor's time is money, so he feels pressure to move faster than perhaps is in the customer's best interests, (2) the contractor knows that whatever heat loss calculation he does is going to have some unknown degree of error, so the incentive is to err on the side of conservatism, and (3) for residential jobs, the marginal cost of oversizing the equipment is relatively minor, so in his mind, there's little downside in oversizing the equipment just so he can be sure not to get an angry phone call when the temperature outside drops to zero.


This is exactly 100% correct IMHO

Contractors would go broke if they spent the time that homeowners spend analyzing their system and they can't work for free. If they do they go out of business and most homeowners will refuse to pay the higher price.

If you run around doing "free" estimates all the time and you don't get paid for it that is lost time which you can't recover.

How many jobs to you ahe to quote to get one job/

Jamie Hall

Completely agree with @jesmed1 and @EBEBRATT-Ed above. When I was a practicing engineer, i faced much the same problem. How much "free' work can you do to prepare an estimate or a bid? It's bad enough with private individuals or corporations, who can and often will take the time to compare two or three bids for quality, but government work? Low bid takes it all. So I never did do government work.

ChrisJ

Should contractors do an EDR survey and a basic heatloss when sizing a replacement hot water boiler?

Matt_67

@KC_Jones - could you get us a diagram of the house with pipe sizes and lengths? Just curious what your system is like.

Intplm.

Many moons ago when I was in trade school in order to graduate I had to do a full heat loss calculation.
I had to do it manually. No computers no computer programs of any kind.

It really opened my eyes to how important sizing was
.
I remember when I was an apprentice having conversations over the years about sizing for hot water and steam. Both hydronic but two different animals in the same family.
As an apprentice I discovered the Epiphany that is EDR. ( Equivalent Direct Radiation )
What a concept. Didn't get a lot of that till I was on the job working for a living.

These methods of sizing with the help of the pick-up factor/safety factor and dare I say fudge factor left in place for all of the different systems and installed over the years for the reason of replacing a steam boiler.
Differentiating between the system...being the piping and rads. And the boiler being the heat plant.

Wether its the way it's always been done or not. Sometimes you can't argue with success until you show a proven better method to replace the method(s) that is being used.

Accommodating the system of pipes and radiators/heating elements to install the best Heating plant ie. boiler.
Well, all of these factors must be considered to do the right thing in good faith.

EBEBRATT-Ed

@Intplm.

Same for me we used the manual "J" over 50 years ago now and I still have my original copy. One of our projects was to do a complete heat loss and heat gain on the house we lived in.

Its why I say everyone should know how to do a manual heat loss. You get to understand how a building works and with software you don't get that experience.

@ChrisJ

Yes, a heat loss should be done for hot water. But in the real world I have gone into houses and asked them "how does the house heat"? If it works ok and they are happy the way it heats I will add up the baseboard footage and calculate the btu off that. I plead guilty. If they have issues, then I do a heat loss.

The heat loss issue comes down to how much insulation is in the walls which is an unknown. Anything built in the 50s and later is usually half decent it is the older homes that have been added to and remolded that are an issue.

I have seen older houses where they took down the old plaster for a gut job and the wall were insulated with crumpled up newspaper.

ChrisJ

@EBEBRATT-Ed

Mine is 1860s and if you look in the walls they're empty and you see the back of clapboard. No sheathing.

Heat loss is 72k @ -8f in 1600sqft but wind plays a roll in that here and I cannot say what the wind speed was on that night.

Crumpled up news paper would be a bonus 

Jamie Hall

On the other hand, it's surprising just how little the heat loss is, relatively speaking, with heavy plaster (three coat job) on wood lathe on the inside, and then 1 inch board sheathing, tar paper, cedar clapboards, and asbestor shingles on the outside...