Sizing New Gas Steam Boiler

JohnnyDebt

Hello everyone, I am getting ready to swap out an older oil boiler in a home I just moved into. I am currently looking for a professional to do the work but before I commit to someone I would like to do all the research into the new setup myself. This way I will feel completely competent when speaking with the professional. I have been going through the thought process of sizing the new gas steam boiler.



I understand from "Lost Art of Steam Heating" and other of Dan Holohan's books that in order to size a boiler for a steam system, one only needs to calculate the total EDR of radiators, or the total BTU output per hour on total radiation surface from radiators. I understand that when people calculate the EDR, they normally don't find an exact match of a boiler for their system so normally they would purchase a boiler that is 1 size larger. This is because having a boiler undersized won't heat the home as steam is turning back into water faster than steam can fill the system.

I have a total of 10 radiators, and they all resemble the Tube type in Dan Holohan's description in his books except for 1 radiator which appears to have thinner tubes than my other radiators. I used EDR per section based on tube radiators for all the radiators to calculate the total EDR. According to my calculation the total EDR of my system is exactly 325. The Weil McLain boiler EG-40 has a net IBR rating of 325 square feet. This boiler matches the exact requirements of my radiators.



Would it be advisable for me to decide on the EG-40 Weil McLain boiler? I am afraid the boiler may be undersized due to the following factors:



1) When sizing a boiler one calculates the total EDR and multiplies this number by 240 BTU to obtain the total heat output of BTU per hour. The 240 BTU is the amount of BTU that is radiated off one square feet of radiating surface per hour. In my case the total BTU output per hour on my radiators would be 325 x 240 = 78,000 BTU/Hr. However the 240 BTU figure is a measurement obtained at a temperature of 70 degrees Fahrenheit.



From my understanding of high school physics, heat transference should be greater when there is a bigger difference in temperatures between two mediums. So for instance if the home air temperature is 60 degrees Fahrenheit the 240 BTU may now be 250 BTU or even greater. In this case the boiler such as the EG-40 which has a net IBR rating of 78,000 BTU/Hr would be undersized as the total effective heat radiation from the radiators would be 325 x 250+ = 81,250+ BTU/Hr. In which case the boiler would be undersized until the home air temperature reaches 70 degrees Fahrenheit. When I am not home I usually turn down the heat under 70 degrees Fahrenheit to conserve on energy cost.



2) The difference between the DOE output (gross output) and the IBR Rating is 33% of the IBR rating. The 33% pick up factor is supposed to represent a rough estimate of radiating surface area before the radiators. The radiating surface area consist primarily of steam pipes connecting the radiator and I believe radiation from the boiler itself.

Can I calculate the amount radiating surface area by measuring the circumference of my steam pipes and multiplying that by the amount of feet of steam pipe I have? This can help me nail down if I’m under or over the 33% additional BTU output of the boiler. This will then ultimately help me figure out if the EG-40 Weil McLain is undersized or not based on the DOE output (gross output). The steam pipes are in rooms which are intended to be heated.



Do you guys think the EG-40 Weil McLain will be able to satisfy my heating needs?



Or do you think I should get the EG-45 Weil McLain instead?



Or do you guys think I’m entirely too anal about these calculations?



Can someone help me identify if the radiator picture I attached to this post is a tube type? And in calculating the total EDR of this radiator I should be referring to Dan's EDR figures for Tube type radiators?



Any help would be greatly appreciated.

Steamhead

Some questions

1- what make and model is your current boiler?



2- are all the steam pipes insulated?



3- regarding the rad in the pic, the chart in Lost Art does not cover it. How tall is this rad and how many sections does it have?



4- how long are your steam mains, and what pipe size? Do they have main vents, and if so what make and model?

JohnnyDebt

Answers

1) Current make and model is Peerless JOT-4-W oil boiler with a beckett burner. The sticker plating on the boiler shows an IBR Steam of 125,300 BTUs which appears to be considerably oversized (roughly 60% of required BTU for radiators). The current near boiler piping is not setup correctly, there is no steam header. The boiler is in the middle of the house and the two mains receive steam from 1 riser from the boiler straight to the ceiling then a 90 degree turn into the two mains connected by a Tee. This setup probably generates a ton of wet steam.



2) The steam pipes are insulated currently with fiberglass. But in the future I plan to remove the insulation as I plan to convert the basement to a family room and would want to have heat down there from the steam pipes.



3) The radiator is 26 inches in height with 30 sections. I calculated an EDR of 72 or 17,280 BTU/Hr



4) The house is approximately 46 feet long, so I assume that the steam mains would be that length as they run into the drywall on each side of the basement so I can't measure beyond that. They do not have any main vents, but I plan to add them during the installation of the new boiler.



Any help is greatly appreciated.

jonny88

edr

you got Steamheads attention which is very good for you.He just helped me out on a few details.I recommend you get Dans book EDR.I needed it for my specific job and got what I was looking for.Good luck with project but maybe pics of current boiler,venting etc will help you get great help here.

JohnnyDebt

Pictures

Thank you, I will look into Dan's book EDR. I am attaching pictures of my boiler, but I don't have any venting on the steam mains.



I am also attaching a picture of my other radiators other than the one I posted on my first post. Can someone confirm that this radiator is a tube type?



Any help would be greatly appreciated.

JohnnyDebt

Interesting Ideas & Solution to My Problem

Who decided that 33% of a radiator's output is steam main? The 33% pick up factor is a crapshoot. I rather not do things by chance. I think if we calculated the circumference of the steam pipe (my case is approximately 8inches for a 2 1/2 diameter pipe) and multiplied it by the length of steam pipe we will arrive at a good approximation of the square feet of radiation. Add the EDR of the radiators, we can then size by DOE (gross output).



The modulating flame is such an interesting idea that I can’t believe the boiler manufacturers have not thought of. You are going to setup your boiler with a modulating flame (60% or 100%). Its too bad you can’t tie the modulating variable flame (if you can adjust between 1-100% of fire) to your pressuretrol or vaporstat. I wonder if one can build a controller that can modulate the flame based on the pressure in the system, to keep it as close to 1 psi as possible without going over would be ideal. You probably want to size the boiler with 60% flame to be equal or greater than the EDR output of your radiators assuming your steam mains are fully insulated.



I’ve also thought that there would be a fan product that one can install on radiators to help increase output by drawing in air faster from the room. By drawing in cooler air into the radiator faster we increase the BTU output of the radiators thus letting the steam condense back to water faster. This will help the boiler continue to burn longer without hitting pressure limits and short cycle.



Anyway I think I solved my problem. I forgot to factor into my calculations on EDR for radiators the fact that some of my radiators are built into the wall with a grill in front. This effectively reduces the effectiveness of the radiators by 23% or 17% without the grill of those radiators. This means that the EG-40 is slightly oversized and will work for my system.

STEAM DOCTOR

pick up factor

Take a look at this attachment. Should give you all the info you need for making an exact calculation of piping heat loss. Courtesy of Mr. Gill's website.

SWEI

Two-stage gas valves

really should be a factory-provided option on small boilers.  Full modulation is even better, but requires major upgrades to both burners and controls.



Steam boilers are always rated in square feet along with the various flavors of BTUs.  Start with square feet and it's really quite simple.  You can always adjust up or down a few percent to account for specific conditions.

Jason_13

Steam boiler

First off never remove the insulation from the main piping. You end up with more water in the system and can cause water hammer or boiler flooding.

Heat the basement with a circulated water zone off the steam boiler.

Do not be concerned with the issues you discussed. The heat will increase as the radiator heat up and the only time it may be a problem on the coldest day. I doubt that as the home is probably over radiated anyway as most were plenty over radiated back when steam systems were installed.

JohnnyDebt

Bit Confused

Thanks for the comments. I am afraid I don't quite understand what you are saying. You mentioned that if I sized a boiler based on IT'S net output (IBR) which matches the EDR of radiator and EDR of piping that I would be undersized. Why would I be undersized? If my boiler's net output is equivalent to the radiator EDR plus the piping EDR, wouldn't I be woefully oversized? For example if I my EDR of Radiators is 78k btuh and exposed steam main is approximately 42k btuh and I decide to purchase a boiler which has a IBR rating of 130k btuh and doe output of 172.9k btuh, wouldn't I be grossly oversized?

JohnnyDebt

To confirm

Jason,



Are you suggesting that since I calculated the EDR of the my radiators to be 78k btuh that I should just find a boiler that matches this EDR IBR? I'm inclined to agree.

KC_Jones

Full modulation

Here is an interesting read if you haven't seen this already.

http://www.heatinghelp.com/forum-thread/146058/A-Steam-Odyssey-Part-2-Midco-Low-NOx-Burner

Just one of many posts Mark S has made on this topic.  Just to point out one thing though.  I have TRV controls on some of my radiators so the connected load on my system is variable so that is a case when full modulation would be beneficial.  If it could be done affordable my burner could modulate lower and lower based upon how pressure is building in the system (all TRV satisfied means less load and pressure would build faster).  So there is definitely a case for full modulation and almost every system is different so we all have different requirements.

ChrisJ

33%

The 33% increase if I recall came about sometime in the 1950s when some tests were done and it's mainly intended for recovery after a setback.  They found that was the amount that gave the fastest recovery without using insane amounts of fuel.  kinda like a happy medium.



I could be remembering wrong, but that is what I recall.



Personally, if I could do my system over again (which is exactly matched to the EDR + 33%) I would go for  0 to 10% over, not 33%  My system works fine, but if I do a decent sized recovery it will slowly start to build pressure.  Many guys say you need to heat all of the piping, which is why you need the 33% however I disagree.  If you look at how a system works, you heat all of the piping, and then heat the radiators, you don't do both at once.  Once the piping is hot, it uses very little steam to keep it hot.  Furthermore, you don't heat the radiators all at once either, they start at one end and work their way across.  If you vent your mains appropriately, and vent your radiators carefully and insulate all of your piping I see no reason why you even need a pickup factor at all. Fact is, most systems are like mine and have radiators that are already 50% too big for the rooms, so why oversize the boiler on top of it.  You will need to vent the radiators very slow with something like a Hoffman 40 or Gorton #4.  You can probably work up to #5s on some radiators but you will have to take your time.  The end result will be a silent, easy running efficient steam system.





Please keep in mind, I'm not a professional nor have I had the chance to experiment with this.  it's just what my opinion is right now.  Proceed accordingly.

ChrisJ

Completely disagree

bc3510, I completely disagree, please see my post at the bottom.  Before steam gets to the radiators every ounce of output goes to heating piping and in my case, there is no way I need 125,000 btus worth of input to heat my piping.  Maybe 10,000btu.

SWEI

A 33% pickup & piping factor

is already included in the boilers square foot rating.

ChrisJ

Yep

I think I can agree with most if not all of that.

Using what is considered to be an "undersized boiler" can be very tricky without a doubt.

ChrisJ

Yep

Because as I said, you heat the piping and then the radiators.

Sure, the less heat you put out the longer it takes to heat the piping, but I also don't buy into the "all energy used to heat the water before steaming is lost" theory.  I think much of what is lost through the boiler jacket ultimately ends up in the structure especially if it's in the basement below the building.  I also believe the majority of the heat lost through pipe insulation also ends up in the structure as well.



A high/low setup or modulating burner is certainly superior and gives the best of both worlds, fast heating and then a nice low burn, but the majority of people have fixed rate setups and in those situations I will always push for a slower system.



The majority of the heating season I get steam to my radiators in around 3 minutes.  Steam reaches every one at the same time.  From an ice cold start it can take up to 20 minutes but most of that is just getting the water boiling.

ChrisJ

Depends

For the last few months of the heating season I was running 2 cycles per hour so usually it was sitting for about 20 minutes before firing up again.  Before that, if the system sat for an hour or two it would take approx 5 minutes.  Again, a majority of this was getting the water up to boil.

My 3 minute figure is accurate from December to March.

I have 1" insulation on 98% of my piping though I'm still slacking on putting the fitting covers on. 

ChrisJ

Dead men

I believe the dead men typically set things up for super slow vents and a coal boiler.  Completely different world than we are in now.  I think the safer bet would be to have your lowest fire slightly under the total radiation amount.  This would allow the use of TRVs as well without causing problems.  Worst cast the boiler will go back to high fire and then drop down again and won't do it a lot unless you're really far off.   Also, the room temperatures effect how much steam a radiator can use as well, the colder the room the more steam it wants.



Keep in mind, I'm not a professional and I do not do this for a living.  I just have a lot of time on my hands to think about things.

ChrisJ

Time

Ah, you're working with Jstar?  You're in good hands!



I had the system trip at 1.5 PSI one time and it took 1 hour and 15 minutes.  I even have a video of it, though the camera's battery died just before the pressuretrol tripped.  I couldn't believe it.



https://www.facebook.com/photo.php?v=10150738669961253&l=4207134340361352597



Edit : sorry, apparently the memory card ran out according to my notes on the video.

ChrisJ

Fast?

I don't make pressure very fast.  In fact, my 3 PSI gauge practically never moves.  I vent my mains very fast for their size and I vent my radiators as fast as I can without causing problems.



By problems I mean stealing steam from another, or causing the steam to take a shortcut across the bottom.  Have a look at the link in my signature and there is a map of my system and the current vents in use.  My system heats fast because of my venting and insulation, not because of pressure.



Because you have very little time I highly recommend following whatever Joe recommends. 

ChrisJ

Kind of

Like you said, 1.5psi is pretty high.  I'd rather the system never see more than an ounce or two.

ChrisJ

Maybe

If only using a thermostat as a control on colder days it could cycle some yes.

SWEI

Just to recap

for those of us who got lost along the way.  Which boiler did Joe recommend, and do you still have 325 square feet of EDR to heat?

SWEI

Which 8-section boiler?

Just curious, and want to compare square feet so I can wrap my head around this.



thanks~

SWEI

Got it

Can't find a spec sheet on the Bryant, but the IOM is online.  262 MBH NG firing rate, 671 square feet.  I know Joe has been doing a lot of 2-stage firing lately and look forward to hearing more.