Boiler sizing

Peteys

I am a little skeptical. How would the Weil McLain SGO–4 boiler heat this five family house?  It is so tiny. 

Attached radiation is 415 ft.² with 17 radiators.  The SGO 4 is rated at 450 ft.².  I also have a Weil McLain aqua +85 indirect water heater and a small basement loop of baseboard of around 25 feet running off the boiler.

I presently have Weil McLain 968 boiler and it takes approximately a half hour to make heat and does not short cycle. Under firing it now with a 2 gallon nozzle and an a AFG burner.

I know everybody says just use the EDR but Will it really work?

Steam system is one pipe parallel flow with one, 50 foot main going to the front 2, two bedroom apartments and one, 10 foot main going to the back three, one bedroom apartments.

This is a picture of the back of the building with three one bedroom apartments and the basement.

Will I save money on oil?

Should I get an SG0-5 just to play it safe?

Much appreciate it and thank you

Jamie Hall

I'd double check your EDR sums, just to be safe -- but if they are correct, the SGO-4 should be just fine.

I'm a bit concerned, however, by your statement that your current boiler is running a 2 gph nozzle -- and doesn't seem to be quick. Does it build pressure and shut down? For reference, that 2 gph nozzle should be good for almost 1000 square feet of radiation, not just 415, so something, as they like to say, does not compute here.

Peteys

It runs for about 20,25 minutes before the steam gauge hits around 2 1/2 pounds and the pressuretrol shuts it down and then it comes back on about one and a half pounds, by then the thermostat is almost satisfied. Before that, though it takes a while for the pressure gauge to start moving up.    It only starts going up after about 10,15 minutes.  

I used to use a vaporstat, but it didn’t work effectively for me. Seeing that it takes almost 25 minutes to hit 2 1/2 pounds and it only cycles on and off once or twice at the very end, I didn’t think that was bad.

The 450 ft.² SGO4 should also accommodate the small amount of baseboard heat in the basement and the Weil McLain aqua +85?

EdTheHeaterMan

So your average radiator is about 24 SqFt of EDR. That sounds correct for a building full of small rooms. The charts are sometimes deseving to someone that is not in the trade. We see all shapes and sizes of radiators and can correctly select the radiator from the chart that Weil Mclain provides. Without the experience of other radiators I remember that one person selected column radiators when they actually had tube radiator and that was a very big difference in the EDR calculation.

Can you post a picture of a typical radiator and perhaps we can verify your EDR selection on that radiator. Also give dimensions of floor to top, depth, and the distance from one end to the other.

Did you use page 10 of this form?https://www.weil-mclain.com/sites/default/files/field-file/Weil-McLain_BoilerReplacementGuide_WM2012-web_0.pdf

Peteys

The apartments are kind of small, about 650 ft.² each

From the first picture to the last picture, I have

30 ft.² of radiation, 23 inches high by 7 inches wide, 4 tube, 12 sections

32 ft.² of radiation, 38 inches high by 7 1/2 inches wide, 2 column with eight sections

17.6 ft.² of radiation, 20 inches high by 7 inches wide 4 tube with eight sections

25.2 ft.² of radiation, 22 high x 4 1/2” wide, 4 tube with 14 sections

These are examples from two different apartments

Peteys

Still have a hard time believing a peanut 4 Section boiler will heat this building 😳 only one way to find out, put it in or go for the five section and play it safe, it’s only $500 more.

EdTheHeaterMan

Looks right to me. That 9 section 68 boiler was way over sized... your new 4 section boiler will be a real energy saver!

Insulate all the pipes you can get to, with 1" fiberglass pipe insulation, and you will see a big difference in your oil bill. Your oil dealer might think you are buying oil elsewhere.

dabrakeman

If you are building 2.5psi in just 20-25min then it seems to me you are oversized and/or main venting insufficient.

Jamie Hall

And get the pressure down. 1.5 psi is all you'll ever need. If the boiler hits that and cycles off, well and good -- all the extra pound is doing is burning oil and not heating the building,

If the heat is uneven at 1.5 psi, raising the pressure won't fix it. Changing the venting to better balance distribution will.

And those main vents aren't even remotely big enough.

Peteys

Very funny Ed. Any estimates on how much I’ll save?

Spending 10 to 12 K a year now at around 4.60 a gallon, about 2300 gallons.

Peteys

I have a lot of venting, Gordon’s #2.  I’ll try to reduce pressure to 1.5 pounds. It should be fine at 1.5. Takes a while to get to 2.5 pounds from start up but also takes a while to get to 1.5.

Jamie Hall

Don't worry about it taking time to get to 1.5 That's quite normal -- and good. The pressure will stay low for a long time while the radiators are filling -- when all the vents finally close, that's when the pressure will start to rise -- and when the boiler should take a rest to let the radiators catch up.

The Steam Whisperer

I'm in Chicago with a design day around 0F and for the brick multi-family buildings here I figure the heat load around 25 Btu/ sq. ft. Multifamily buildings are much more efficient than freestanding single family homes since they have less exposed walls and ceilings per sq ft of enclosed space. With basic thermal improvments like attic air sealing and attic insulation and good low E glass storms, that number probably will drop into the teens, making these old buildings more efficient than "high efficiency" new construction

EdTheHeaterMan

Peteys said:

Very funny Ed. Any estimates on how much I’ll save?

Spending 10 to 12 K a year now at around 4.60 a gallon, about 2300 gallons.

In order to get your business, I would guarantee you a 10% savings in writing and ask you if my competition would offer you that! I know you will save 10% because it looks like you will save much more! You would probably purchase from me even if my price was a bit higher than the others. You would get the feeling that I knew what I was doing and I would gain your trust.

Too bad I'm retired now. LOL

But I would not be surprised if the smaller boiler cut 20% off your gallons. The important thing is the pipe insulation all thru the building. Wherever I can reach a steam pipe. If it were inside an apartment, I would recommend you soffit or box in the pipes after the insulation was completed so tenants could not damage it. I would add that as an option on my contract. This way you have the option to do it yourself cheaper.

KC_Jones

You do understand you should only be running at an ounce or two of pressure and everything above that is excess.  I’d say on the high end 4 ounces.  What you are running is because someone who selected the current boiler was clueless.

The performance you describe shows tremendous waste, the vaporstat didn’t work for you because the boiler is so ridiculously oversized it actually needed pressure to keep running and heat the building.  Vaporstat most likely shut it down so often the furthest radiators didn’t heat properly, sound correct?

The pressurtrol is NOT an operating control, it’s a safety and you really don’t want it doing anything under normal circumstances.  The boiler should run to the thermostat and heat the building, minimal pressure.

EBEBRATT-Ed

Just make sure whomever installs the boiler follows the MFG piping diagram and includes skimming the boiler and stay away from copper tubing on the steam. It is ok for returns

Peteys

All great points!! 

I’ll definitely try putting the vaporstat back in with the new boiler as it will probably work better.  It didn’t work before because it was short cycling, from what I remember.

I may put that puny little four section boiler in as soon as this summer, as the current boiler is 32 years old.  I’ll have to ask Ed to come out of retirement to help.😁

All of you are just amazing. What a resource of experience and knowledge, helping people you don’t even know.  I want to thank all of you.  

KC_Jones

If the boiler is sized properly you shouldn’t need the vaporstat.

EBEBRATT-Ed

Wish I could come out of retirement. Miss working

pecmsg

EBEBRATT-Ed said:

Wish I could come out of retirement. Miss working

https://m.youtube.com/watch?v=YOvbUu0OlbQ

Mad Dog_2

So come on Ed...get on your overalls.  The industry needs you.....

Mad Dog_2

I remember the URGE TO OVERSIZE was huge...when I was starting out, but Smart 🤓 freinds from Saratoga Mark Hunt and Darin Cooke of CHT would laugh when I always wanted to go to the next size EVEN after running the numbers and measurements three times!!  I never wanted to undersize a boiler...it IS an expensive mistake.  Run numbers multiple times and methods to feel more comfortable and then DIVE out of the plane...you'll be surprised how SMALL u CAN go!  Its scary. Ha ha. Mad 🐕 Dog 

EdTheHeaterMan

Mad Dog_2 said:

I remember the URGE TO OVERSIZE was huge...when I was starting out, but Smart 🤓 freinds from Saratoga Mark Hunt and Darin Cooke of CHT would laugh when I always wanted to go to the next size EVEN after running the numbers and measurements three times!!  I never wanted to undersize a boiler...it IS an expensive mistake.  Run numbers multiple times and methods to feel more comfortable and then DIVE out of the plane...you'll be surprised how SMALL u CAN go!  Its scary. Ha ha. Mad 🐕 Dog 

Do I remember those days way back then! The homeowner was sometimes SOOO Angry that we put this little suitcase of a heater in, to replace the behemoth of a boiler that we just removed. They were amazed how much heat one of those little suitcase sized castings could put into those old homes.

ChrisJ

Peteys said:

All great points!! 

I’ll definitely try putting the vaporstat back in with the new boiler as it will probably work better.  It didn’t work before because it was short cycling, from what I remember.

I may put that puny little four section boiler in as soon as this summer, as the current boiler is 32 years old.  I’ll have to ask Ed to come out of retirement to help.😁

All of you are just amazing. What a resource of experience and knowledge, helping people you don’t even know.  I want to thank all of you.  

There's nothing puny about a 4 section boiler for a small house like that.

It doesn't matter how big the boiler is if the radiation can only condense so much steam.... You're doing absolutely nothing but creating excess pressure to do no work.  Paying for no work is bad.

The idea is to condense all of the steam you pay money to create as fast as you create it.  No one wants workers standing around with nothing to do.

nde

Do you have option to switch fuel to natural gas? If so you can use either SGO wet base with ng gas buner or use dry aka atmospheric EG line. The SGO is a wet base boiler so it has more volume per section that the EG line. For example on the EG you would be using a 5 section and WM uses this same boiler as sg04/sgo5 equivalent the difference being the burner setup/trays are factory adjusted from either 175k to 200k input. This is roughly what you would see different on the sgo4 vs sgo5 input of 168k and 203k.

My point is you can use the sgo5 if you want without issue as not big enough difference to really matter. Who measured your rads? I see mix of fin vs column in one pic so might be higher than calculated if fin was use to calculate. The main pipe/risers being insulated or not can also matter as uninsulated should be give roughly 1.5 pickup vs factory 1.33 built into ratings. Might want to recheck, The fact you have a boiler almost double sized that only cycle on pressure after almost satisfying therm makes me think the measurements are off.

ChrisJ

Please DO NOT use a 1.5 pickup factor even with completely bare piping.

The amount of times I see guys on this forum say you shouldn't use mains for heating a space because of how little heat they radiate., but then say you need a huge pickup factor because of how much heat they radiate. It gives me a headache........

33% over is more than enough for most if not all residential systems even with bare piping.


This is in the same category as telling guys we need a big "Pick up" factor, which is literally intended to do recoveries, but then tell people not to do setbacks because it'll build excess pressure due to the pickup factor we didn't need in the first place.


Sorry for the rant.........

KC_Jones

nde said:

Do you have option to switch fuel to natural gas? If so you can use either SGO wet base with ng gas buner or use dry aka atmospheric EG line. The SGO is a wet base boiler so it has more volume per section that the EG line. For example on the EG you would be using a 5 section and WM uses this same boiler as sg04/sgo5 equivalent the difference being the burner setup/trays are factory adjusted from either 175k to 200k input. This is roughly what you would see different on the sgo4 vs sgo5 input of 168k and 203k.

My point is you can use the sgo5 if you want without issue as not big enough difference to really matter. Who measured your rads? I see mix of fin vs column in one pic so might be higher than calculated if fin was use to calculate. The main pipe/risers being insulated or not can also matter as uninsulated should be give roughly 1.5 pickup vs factory 1.33 built into ratings. Might want to recheck, The fact you have a boiler almost double sized that only cycle on pressure after almost satisfying therm makes me think the measurements are off.

Please, please, please don't use 1.5. I know people around here advocate for it on occasion, but if you actually run the numbers on how much uninsulated pipe a 1.33 pick up will support your eyes would bug out of your head.

I'll use my little EG-40 as an example.
Gross input is 125,000 BTU
Gross output is 103,000 BTU
With the 1.33 they rate it for 77,000 BTU
That give 26,000 BTU for piping
26,000/240=108 ft² radiation
2" pipe is .622 ft² per foot
108/.622=173' of 2" pipe, I have 40'. That is a ton of pipe for a system that uses a boiler that size. 1.5 would be nuts.

Jamie Hall

I suppose it's called a pickup factor as that sounds more professional somehow that "fudge factor". Which is, pretty much, what it is.

There are a number of rather mysterious problems which can arise from seriously undersizing a boiler, particularly on one pipe steam systems. Serously undersizing is not something we see very often.

The boiler size as given by the manufacturer in square feet includes that fudge factor, and so the boiler should be no bigger than the calculated EDR of the system. Just compare the two numbers. Can it be smaller? Indeed it can. Several people have noted systems where the boiler real output is matched to the system very closely, or with only perhaps 10% over. So what's a person to do? You have a system EDR. Pick a boiler the EDR rating for which is not more than that. Two choices, neither of which match, one is somewhat bigger, one somewhat smaller? I'd go for the smaller one in almost all cases.

What about the argument that a bigger boiler will help the system heat up faster? Not really. The timing for when steam gets to the radiators from a cold start is mostly dependent on the insulation of the steam mains and their lengths, and somewhat less on the venting. From a hot start -- say the boiler is oversize and cycling on pressure (system pressure never drops to zero) -- there will be almost no delay, regardless of venting or insulation. The in between case -- the system is basically hot, but the system pressure has dropped to zero during the off cycle -- the timing is almost entirely dependent on venting. More boiler power is not a factor in any case.

ChrisJ

@Jamie Hall It was originally called "The Piping and pickup factor".

nde

I think you should factor in if it is all 3 or even 4 floors? You own the whole building right? could be quite a bit of pipe. One theory on using slightly oversize boiler and downfire 10% is to help with thinner castings on more modern boiler. I run sgo5 with 175k input on 425+- sf and it works nicely. The installer specifically talked about the thinner casting issue over the 35+ years he has been working with WM. Burhams Independence issues were thin casting stress more than water quality imo. Hence the new upper thickness/non pin on the steam max.

ChrisJ

nde said:

I think you should factor in if it is all 3 or even 4 floors? You own the whole building right? could be quite a bit of pipe. One theory on using slightly oversize boiler and downfire 10% is to help with thinner castings on more modern boiler. I run sgo5 with 175k input on 425+- sf and it works nicely. The installer specifically talked about the thinner casting issue over the 35+ years he has been working with WM. Burhams Independence issues were thin casting stress more than water quality imo. Hence the new upper thickness/non pin on the steam max.

The op's system has 100,000 btu/h worth of radiation and the 1.33% gives 33,000 btu/h for exposed piping which to me already seems excessive.

Of course the piping should be looked at, but I wouldn't just guess and add another 17,000 btu/h just because.

Peteys

Yes, the building is three floors. All the mains are insulated in the basement but the vertical risers from the basement to the apartments are uninsulated and in walls.  so now you have me thinking, maybe the SGO-5 would be better. I’ve never heard of thin castings before.

Probably 60 feet of insulated mains pipe running through the basement and maybe 200 feet of 1 1/4” vertical risers direct to Radiators which are uninsulated.  There are around 5 take offs at different locations along the length of mains going vertically to supply radiators in different rooms and apartments.  Plus 80 gallon indirect water heater and 25 feet of baseboard in basement running off boiler.

ChrisJ

Peteys said:

Yes, the building is three floors. All the mains are insulated in the basement but the vertical risers from the basement to the apartments are uninsulated and in walls.  so now you have me thinking, maybe the SGO-5 would be better. I’ve never heard of thin castings before.

Probably 60 feet of insulated mains pipe running through the basement and maybe 200 feet of 1 1/4” vertical risers direct to Radiators which are uninsulated.  There are 4 take offs at different locations along the mains going vertically to supply radiators in different rooms and apartments.  Plus 80 gallon indirect water heater and 25 feet of baseboard in basement running off boiler.

So,
You've calculated the size you need, with extra on top of it, likely a good 33% extra.
And, you still feel a need to go bigger.


Ultimately it is your decision obviously but you'll live with it.

From what I read in this thread, the castings are no thinner on an SGO4 than an SGO5.

Peteys

I think what NDE meant was that the castings are thinner on the newer boilers compared to the old ones. Never heard of that and not sure if that’s true or it would affect the performance or longevity.  

I’d prefer to go with the SGO-4

ChrisJ

Peteys said:

I think what NDE meant was that the castings are thinner on the newer boilers compared to the old ones. Never heard of that and not sure if that’s true or it would affect the performance or longevity.  

I’d prefer to go with the SGO-4

I'm sure they are but I think that started in the 70s.

Go with the 4.

Long Beach Ed

If you really want to calculate real-life piping pickup factor for a particular system, Jake Myron's Steam - The Perfect Fluid for Heating and Some of the Problems book sheds some light on how to do it. It's a pretty technical textbook.

The Steam Whisperer

It looks like you have many lower mass and low steam volume large tube type radiators... which translates into less pick up load.

Peteys

I was thinking about pick up factor and trying to understand it. 

The SGO-4 has a steam square foot rating of 450. Assuming the pick up factor would be around 1/3, that would be around 150 ft.², correct?

Hypothetically, If this boiler was connected to one, very large, 600 square-foot radiator coming out the top of the header, would this boiler be sufficient for that one, 600 square foot radiator, to produce steam sufficiently?

In other words, a 450 square-foot boiler really produces 600 ft.² of steam?

pecmsg

The pick up factor is already calculated in why add it again?

ChrisJ

Peteys said:

I was thinking about pick up factor and trying to understand it. 

The SGO-4 has a steam square foot rating of 450. Assuming the pick up factor would be around 1/3, that would be around 150 ft.², correct?

Hypothetically, If this boiler was connected to one, very large, 600 square-foot radiator coming out the top of the header, would this boiler be sufficient for that one, 600 square foot radiator, to produce steam sufficiently?

In other words, a 450 square-foot boiler really produces 600 ft.² of steam?

It was originally called a "Piping and pickup factor".
I.E. a fudge factor for piping losses, but also, an amount they found sometime in the 1940s they could oversize a boiler without building too much excess pressure, in order to rapidly recover from a big setback. For example in schools, churches etc. In modern day uses in homes etc, all you really need is the piping losses so in most cases that built in 33% is already way too much.

That's why it's annoying to see guys recommending 33%, but then tell people not to do setbacks because the system will build too much pressure and short cycle. Personally, I had a boiler with exactly 33% over and I reduced it after a few years to only 10% and it's wonderful.

But yes,
an SGO4 should be able to feed 600sqft of radiation.
Chances are it'll do 500-540 just fine in most situations.

Peteys

Wow, very interesting insight.  Thank you, Chris.