Sizing a new boiler

georgede54

I'm trying to hire a contractor to install a new oil-fired steam boiler and one of the contractors, discussing what size boiler I would need, said that boilers come with 3, 4, or 5 sections. (He might have used another word other than sections, "panels" perhaps.) He knows that I have a two-family house in the northeast, and he said 3 would be too small and 5 would be too big, so he said the correct size for my boiler would be 4.

He is quite experienced and comes highly recommended, but this sounds like a strange way of sizing a boiler to me. The implication seems to be that the number of panels corresponds to certain BTU range, which he is reasonably certain applies to my boiler.

Would anyone care to comment?

Thanks.

Tom_133

What state in the Northeast? I am sure there is a couple of us near you to at least do a heat loss.

Intplm.

Sections is the correct term.

The way to get a proper steam boiler size is to have the "Equivalent Direct Radiation" or "EDR" measured throughout the building.
The near boiler piping is also crucial to proper system performance.

It's also a good idea to make sure all the radiators that are needed are in place, and have all of the pipes insulated.

KC_Jones

georgede54 said:

I'm trying to hire a contractor to install a new oil-fired steam boiler and one of the contractors, discussing what size boiler I would need, said that boilers come with 3, 4, or 5 sections. (He might have used another word other than sections, "panels" perhaps.) He knows that I have a two-family house in the northeast, and he said 3 would be too small and 5 would be too big, so he said the correct size for my boiler would be 4.

He is quite experienced and comes highly recommended, but this sounds like a strange way of sizing a boiler to me. The implication seems to be that the number of panels corresponds to certain BTU range, which he is reasonably certain applies to my boiler.

Would anyone care to comment?

Thanks.

Sure, I'll comment. If he didn't measure all the rads and come up with an EDR calculation he's guessing. Honestly I don't care if he claims it's an educated guess, it's a guess. There are ways to calculate proper boiler size, so for me, anyone who is guessing should be dismissed promptly.

If you want to calculate the proper boiler size, we can help you, and, with steam, it's really not that hard.

There are worksheets online available to calculate. If you want I can do it remotely for you. Just need pictures of a typical rad, height measurement (to the floor), and number of sections for each rad. EDR can be calculated and a boiler size chosen from that.

Intplm.

While your at it. It's a good idea to have the vents on the system updated too.

georgede54

Thanks to all who responded. I found this online and have been working with it:

https://www.weil-mclain.com/sites/default/files/field-file/Weil-McLain_BoilerReplacementGuide_WM1905-web.pdf

With this be an adequate way to figure out the BTU requirements for my system? As I have an oil fired steam boiler, I believe I need only deal with pages 8 and 9.

Finally, someone recommended I update the vents on the system. By that I believe the person was referring to the things on the ends of the radiators. Correct?

Thanks again to all.

KC_Jones

Start at the bottom of page 9 and all of page 10. If you have rads that don't match up with any that they show, post a picture here and someone should be able to help you.

To be clear all you need is the EDR calculation for your radiators, don't add any pickup factor or anything else. Once you have that number you compare that directly to the boiler ratings in their catalog.

For oil most everyone recommends the Burnham Megasteam as the best oil fired steam boiler on the market.

georgede54

Thanks for the advice!

John Mills_5

Here's the way to size a boiler. Stand across the street, hold your hand in front of your face. The number of fingers it takes to cover your house is the number of sections you need. Well, that's about as accurate as his guess. We did a steamer recently, old one was 175,000. Connected load said 100,000.

georgede54

I intend to follow the weil-mclain guide as best I can. It's going to be interesting to see how the old steamer compares with my computations. Thanks for commenting.

ChrisJ

georgede54 said:

I intend to follow the weil-mclain guide as best I can. It's going to be interesting to see how the old steamer compares with my computations. Thanks for commenting.

Just something to mull over for a bit, I'm running an EG-40 rated for 325sqft with 392 sqft of radiation. It's 94,080 btu/h worth of radiation with a boiler that technically has a gross output of 104,000 btu/h. That leaves me 10,000 for piping losses etc.

Their net output includes 33% "extra" for piping losses, mistakes etc. Personally, I'd never go larger than that if it's avoidable.

georgede54

Thanks for posting. You're a little above me on all this stuff, but is this what you are saying. If my radiators need 100,00 BTUs to satisfy them, then the weil-mclain guide would compute my radiator needs as 133,000 to account for the 33% BTUs that I may lose as the steam goes from the boiler to the radiators.

If that is what the guide does, do you have any idea on how I might alter the guide's computations. I think 33% may be high, but it seems as though there would be some losses. Should I be measuring my pipes or something.

Thanks again.

George

ChrisJ

> @georgede54 said:
> Thanks for posting. You're a little above me on all this stuff, but is this what you are saying. If my radiators need 100,00 BTUs to satisfy them, then the weil-mclain guide would compute my radiator needs as 133,000 to account for the 33% BTUs that I may lose as the steam goes from the boiler to the radiators.
>
> If that is what the guide does, do you have any idea on how I might alter the guide's computations. I think 33% may be high, but it seems as though there would be some losses. Should I be measuring my pipes or something.
>
> Thanks again.
>
> George

In my opinion, yes. But most do not figure out piping losses.

To get a system like mine to work it takes a bit of experimenting with the radiator vents to get it balanced. Once you get it right, it's a beautiful thing though.

If you go 33% over it makes things easier and faster.

Figure out what your radiators are first and we'll go from there.

SeanBeans

One brand that has 3 sections may be too big while another that has 3 section may be perfect

georgede54

Sounds good. Thanks.

EBEBRATT-Ed

You contractors educated guess sounds about right but it's just a guess. Doing the calculations is the right way and your contractor should be doing that

mikeg2015

In my home “test lab” I’m experimenting with a undersized boiler on a vapor system. The biggest challenge is they no longer make really really slow vents smaller than a Gorton 4. Ventrites can sometimes go a little lower.

I do have 1/3 of the radiators on TRVs so when those are mostly closed it heats evenly, but if most are open I get 1 or 2 cold radiators.

A little more skimming (still surging a bit) and some more insulation on the main an near boiler piping might resolve it.

ChrisJ

mikeg2015 said:

In my home “test lab” I’m experimenting with a undersized boiler on a vapor system. The biggest challenge is they no longer make really really slow vents smaller than a Gorton 4. Ventrites can sometimes go a little lower.



I do have 1/3 of the radiators on TRVs so when those are mostly closed it heats evenly, but if most are open I get 1 or 2 cold radiators.



A little more skimming (still surging a bit) and some more insulation on the main an near boiler piping might resolve it.

How undersized are you?
I do not get cold radiators even if all TRVs are wide open and my slowest vents are G4s. I have some G6s and GC's as well.

pecmsg

Agreed Measuring the EDR is the way to size the boiler but have any changes been made to the envelope? New windows, doors, insulation, if yes then the present radiators may be oversized as well.

Best to have a room by room heat load loss calculation performed, find out what the requirements for each room are and see if the radiators can or do need to be downsized. Then size the boiler accordingly!

ChrisJ

pecmsg said:

Agreed Measuring the EDR is the way to size the boiler but have any changes been made to the envelope? New windows, doors, insulation, if yes then the present radiators may be oversized as well.

Best to have a room by room heat load loss calculation performed, find out what the requirements for each room are and see if the radiators can or do need to be downsized. Then size the boiler accordingly!

Do you generally modify radiators on steam boiler replacement jobs?

pecmsg

In 100 year old houses with substantial upgrades we gave them the option. at the least covers that reduce the output.

JUGHNE

If the existing rads are left in place and boiler down sized somewhat.......would then the rads not heat all the way across and would that be a problem considering less heat needed?

pecmsg

JUGHNE said:

If the existing rads are left in place and boiler down sized somewhat.......would then the rads not heat all the way across and would that be a problem considering less heat needed?

Exactly but you need a Load / Loss calculation 1st!

JUGHNE

So after the heat loss is done and replacement steam boiler based on the new heat loss would you still apply the 33% pick up factor?

Would this work the same for 1 or 2 pipe systems IYO?

pecmsg

A lot of variables...……………
How much has it changed, 5%, 10, 50%

Every job is unique. How much pick up factor was calculated in 100+ year old structures with windows slightly open to control the room temperature? That's why on older homes you need that base line!

ChrisJ

@pecmsg I like your methods.

JUGHNE

I worked on a 1932 school 2 pipe. Rad trap elements (some original) were removed and orifices installed in inlet valves.
(about only 20% cost of new elements BTW).
Big Mouth vents were added to the ends of major steam supply branches.

Throw rocks now because I studied each room considering window reductions, upgrades and outside walls with wind and solar gain provided.
And then decided the orifice size by my best WAG method of Feng Shui meditation.
Sizing was from 30% to 80% of rad EDR.
I stayed on the smaller size knowing they could be drilled larger.

Last winter was typically nasty and as far as I know everyone was comfy. A dozen or so ladies will let you know pretty quickly if not. Perhaps the phone will ring this winter.

Existing boiler remained, might have 2 burners capped off.
Building may be abandoned in 2 years.

mikeg2015

> @ChrisJ said:
> (Quote)
> How undersized are you?
> I do not get cold radiators even if all TRVs are wide open and my slowest vents are G4s. I have some G6s and GC's as well.

EDR is around 700. Boiler is 200k (510 EDR with 33% pickup).

I clocked input it at 188 on the gas meter and the combustion chamber is running really hot so thinking I have some internal scale inhibiting heat transfer too. Boiler was salvaged and was Sitting drained for about 6 months. On 2nd round of boiler cleaner. No skim port so have to “skim” vertically out PRV per the manual. Might try removing gauge glass and use top port there as a better solution.

So boiler just matches full Radiation without pickup.

I think the issue isn’t that the radiators will never fully warm. It’s the lack of back pressure to control the steam flow. I have 17 radiators so even with the smallest vents It’s still an issue.

georgede54

Thanks for all the interest and input. My house was built around 1905 and was insulated in the 1980s. Otherwise the only change that I can remember is that storm windows were added after the house was constructed.

The idea of doing a heat loss calculation based on the changes to the house and then resizing the radiators is interesting, but I doubt my boiler will make it through winter, and I don't think I have the time, stamina, or money to go through all that.

Thus, I'm going to go with the present radiators and try to figure out their EDRs.

To that end, I'm going to try to post some pictures of the current radiators. There are certainly more radiators in the house, but I wanted to start with just a couple. My reason is that my pictures may not be adequate for you people to figure out the EDR of the radiators, so before I photograph them all, I'd like to get some feedback on what you people need in the way of pictures to be able to help me.

With any luck, there will be 2 pictures for each of the two radiators, taken from different angles. There is a yardstick in each picture to help with measurement. Also, I have named each picture according to the room it is in. The word "Up" before the room indicates that the radiator is located on the second floor of a 2 family house. There is a 2 next to the second picture of a radiator because I cannot use the same file name twice. If you can see the name of the file, the height of the radiator is listed after the room the radiator is in.

They seem to be all attached. Let me know whether these pictures are adequate for you to figure out the EDRs. I going to try to do the computations myself based on the Weil-mclain guide, but I'm quite interested to see what any and all of you come up with.

Thanks for all the help thus far. I think you people are incredible!

KC_Jones

Can't read the yard stick very well in those pictures so I am guessing a bit, but will indicate my guesses.

The tube type radiator is 4 tubes and appears to be ~26" tall, which would be 2.75 sq ft per section, you have 6 sections so that would be 16.5 sq ft EDR.

The column type radiator is 2 columns, also appears to be ~26" tall, which would be 2 2/3 sq ft per section, you have 11 sections so that would be 29 1/3 sq ft EDR.

ethicalpaul

I'm really glad you got here now rather than after this contractor's guess happened to you, George. It might be right on, but as KC said, it's so easy to know for sure, there's no excuse for not measuring and that makes me not trust your contractor.

georgede54

I have just posted the information and pictures necessary to compute the EDRs for my upstairs radiators in a new discussion titled "Computing the EDRs of My House Radiators for a New Oil-fired Steam Boiler." If you want to take a look and run the numbers, I'd appreciate your efforts. Thanks.

georgede54

I'm going to write some stuff, and you people can correct me whenever I go awry.

As I understand matters, boilers come with a number of ratings. The one I seem to be gravitating towards is the DOE Heating Capacity, sometimes referred to as the Gross Output Rating.
To me, the DOE Heating Capacity is the amount of steam the boiler is putting into the system. And my system is made up of the pipes and the radiators. So, let us say, the radiators come out to 70,000 BTU/ hour and the pipes come out to 15,000 BTU/hour, I should be looking to get a boiler with a DOE rating of 85,000 BTU/hour.

I'm guessing that the DOE rating will be standardized across companies and boilers because the Department of Energy has probably defined what the DOE Heating Capacity is and mandated that it be somewhere in the literature for the boiler.
The measurement for the radiators is reasonably straight forward.

But I keep thinking about the piping in the middle of the night. And when I say piping, I mean both the basement pipes and the pipes connecting the first and second floor radiators, of which there are four.

Now, I understand that uninsulated pipe within the apartment does not represent lost heat - because it is going into the room - but as I see it, the volume of the pipes in the apartment, and of course in the basement, would still be relevant because the boiler still has to make enough steam to fill those pipes, just as it has to make enough steam to fill the radiators.

I have read a reasonable amount of stuff and have found ways to calculate radiator requirements, but the literature on the piping has been a lot less specific.

I have a lot of pipes in my basement. Most of them are insulated, I believe to 1", but I will check, and I intend to insulate the gaps that have somehow evolved. (I'm away from home now, but I will send pictures upon my return.}

Now when I get home, I intend to measure the volume of the pipes in the basement. I intend to do this by measuring the circumference of the pipe (at an uninsulated spot). Having the circumference, I can compute the radius. I then multiply pi x the radius squared and multiply that by the length of the pipes, and that would give me the volume of the pipes.

But from there, I'm lost, for three reasons.

First of all, my measurement will give me a volume in cubic feet. But when the literature measures radiators, the result is listed in square feet. So I'm not sure we'd be talking about the same thing here.

Second, there is the issue of insulation. How does insulation affect the number I come up with?

Third, how do I treat pipes within the living space?

Apparently, there is something called a "pick-up" factor that is somehow built into rating of the boiler. I believe it is 1.33 for steam boilers, and it is supposed to account for the piping. But how do I know that number is correct for my house?

If the 1.33 produces a boiler with too many BTUs, my boiler may short cycle, create water hammer, and end up with a shorter life span.

If the 1.33 produces a boiler with too few BTUs, my boiler will not produce enough steam to heat the radiators that are furthest from the boiler.

So is there any way to come up with a more precise number for the amount of direct radiation in my pipes?

Thanks again for the help.

Jamie Hall

Well, yes there is a way to come up with the radiation from the pipes -- but it's normally completely irrelevant. What you really want to do is to make sure that the EDR rating of the boiler is the same as, or very slightly less (preferably) or very slightly more than the EDR total of all your radiators. The pickup factor to which you refer is normally more than adequate; in fact some of us feel that 1.1 to 1.2 is more like it. But the 1.33 works.

Do NOT go by either the gross input or net or gross output DOE BTUh figures. Use the EDR. It's there for a reason. Don't overthink it.

Now you can compute the equivalent direct radiation from the pipes: it is the total surface area of the pipes -- not the volume. So you would take the diameter of the pipe (not the insulation if any) and multiply by pi, convert to feet and multiply by the length of the pie and there your are. For example, a 50 foot 2 inch diameter pipe will have an effective EDR of about 25 -- if there is no insulation. If there is insulation, the effective EDR will be much less.

You still need some pickup factor, however, as that is there not only to account for the radiation from the pipes, if it is significant, but to account for heating all the metal up.

If your pipes are insulated, which they should be, you will need slightly less pickup factor -- so as I said above, if you can't match the radiation exactly to the boiler, err on the side of the boiler a bit smaller rather than larger.

If the boiler is much too large, it will short cycle, and that, as you note, you do not want. SIZE THE BOILER BY THE EDR.

Water hammer is steam systems is not caused by an oversized boiler. There are two fundamental causes -- in older houses, pipes sometimes sag and trap water. Easily fixed. Unfortunately, the other cause is poor installation of the boiler and the near boiler piping. This is all too common (but gives us on The Wall lots of things to talk about). Boiler installation isn't rocket science -- but it has to be done correctly.

georgede54

Thanks for a really great answer, which I'm certain I will read at least a few more times. But there is one important point that still puzzles me. How do I match up the EDR of my radiators to a number on a manufacturer's brochure?

I have a two family house, with radiators on the 1st and 2nd floors. The boiler and a lot of insulated pipes are in the cellar. (I'm away from home, so I can't give you pictures of the piping right now.) I have computed the EDRs and come out with an EDR of 286 for the radiators of both floors.

In a piece on this site titled, "Steam Boiler Ratings Explained," Dan Holohan discussed the various ratings that come on manufactures' catalogs. Those ratings were "Input," "DOE Heating Capacity," and "Net."

He didn't mention that there would be a number on a manufacturer's brochure that corresponded to the EDR of the radiators, so I figure I have to go from my EDR to either the "Input," "DOE Heating Capacity," or "Net." Does a manufacturer list an EDR rating somewhere?

To make this a bit more concrete, I looked up a boiler. I'm not sure whether I would be allowed to list the make and model on this site, so I'll just give you the numbers. It had three numbers: Input .75 GPH, DOE 92,000, and Net I=B=R 69,000.

I guess I have to multiply the EDR of 286 x 240, which brings me to 68,640. Now I have a lot of pipes in the basement and most of them are insulated and I intend to insulate the rest.

My guess is the EDR of 286 turns into 68, 640 BTU, but because of the pipes, this boiler at 69,000 is not going to be quite big enough. Or is it? If 69,000 is not the number, what number should I be looking for?

I know it's hard to go from radiators to boiler size without more information on the pipes, but anything you tell me, if you tell me what your assumption is on the pipes, would certainly be helpful.

Thanks again.

STEAM DOCTOR

That boiler would be a perfect match. The EDRx240= Net I =B=R. The piping is factored in. The boiler will give you 33% more then the IBR. That is to cover the pipes and valves....

KC_Jones

The boiler manufacturers give you a sq ft rating for each boiler, you take your EDR number without adding anything to it and compare to their rating. You want to get as close as possible, no need to add extra. See picture for example.

georgede54

In selecting a new boiler, everyone agrees that it is important to select one of a proper size.

There are, however, other considerations, such as making sure the new boiler has a correct water level, making sure the new boiler has adequate steaming capabilities, and making sure the new boiler has a low steam (exit?) velocity. (There may be others that I have not come upon.)

My instincts are telling me that I am not going to find any boiler that is just right for all these characteristics; compromise will become necessary.

But proper size, if not the most important, is certainly quite important. But I also doubt that I'm going to find a boiler that is exactly the number of BTUs that my system requires, regardless of other considerations. So there must be some range of BTU boiler sizes within which my system can operate in a trouble free manner.

To make this concrete, if I have measured correctly, the amount of BTUs required for my radiators would be 68,740. How far can I deviate from that number, up or down, before problems arise?

Would 75,000 be too much? Would 60,000 be too little? Is too small better than too big, or vice-versa? And finally, would one compute, or guess, the acceptable range, by adding or subtracting a number of BTUs to the ideal or by increasing or decreasing the ideal BTU size by fixed percentages?

Thanks again.

Jamie Hall

Proper boiler sizing is paramount. However, that said, the acceptable range is surprisingly large -- anywhere from 10% small to 5% over will probably work very well. Also, many boilers have a range of acceptable firing rates, using different nozzles, which a good steam man can use to match even more closely. This is somewhat empirical, though, as the actual system heat loss from such things as uninsulated risers is hard to compute, and the exact radiation characteristics of the radiators is also not accurately known.

That said, stop bothering your head with BTUh. Use the rated EDR figures and compare them with you calculated EDR figures. Much simpler, and just as reliable.

As to the engineering that goes into the boiler itself -- not a factor. Any of the more reliable makes will have taken steaming capacity and exit velocity into consideration in the design, and will perform correctly if the manufacturer's near steam piping "suggestions" are followed -- or better. The best boiler in the world will be hopelessly compromised by incorrect near boiler piping.

Correct water level is quite important when retrofitting a boiler. Easy enough to do, though. If the existing system is operating correctly, just match the old working water line and the new one. If the existing system isn't, it may well be that the existing boiler's water line is incorrect, and you will have to do some work on the system to determine whether it is too high (rare) or too low (dismayingly common) and set the new boiler accordingly.