Undersized steam boiler?

Ori

Hello,

I suspect that my steam boiler is undersized because in colder days it can take more than 5 hours to raise the temp from 65 to 71. The Nest thermostat (set for ‘radiators’) is set at 71 degrees from 6:30AM, and 65 from 10:30PM.

The thermostat usually starts the boiler at 2:30AM in order to meet the 71 degrees target at 6:30AM, so normally 4 hours to raise 6 degrees. In colder days (say 12 degrees outside temp) even 6 hours aren’t enough, as the thermostat kicks in at 1:30AM and is finally satisfied at around 8:00AM, so 6.5 hours of continuous operation to raise from 65 to 71 . I should mention though that all radiators do get hot. The Nest History module indicates that the system worked between 10-15 hours daily, in the past 10 days during the month of January (Chicago area), with the longest heating cycle is early morning as mentioned above. I have not yet seen the boiler works constantly all day since I started monitoring it few months ago, but also we have not yet had any temp lower than about 10 degrees so far this season. I suspect that when it gets really cold (say below 0F) not only it will work nonstop, and won't be able to meet the demand for heat.

In addition, the pressure gauge doesn’t show any pressure by the boiler at all, even after hours of continuous operation (I monitor pressure gauge with a Nest camera). All gauge components are clean; the gauge itself (1- 3 psi) functions and moves when I blow air in it, pig tail and pipes are clean. Near boiler piping are correct (was verified by a steam pro few years ago), return lines are clean, boiler is clean (water is maintained with PH 8-10), and the water in the middle of the sight-glass doesn’t move much during a heating cycle, indicating that radiating and condensing are in balance. The meter on the water feeder device (VXT-24) doesn’t indicate on a steam leak; it drew only 1 gallon in the past 2 months of operation (and drew it in only one episode, not sporadically).

Further, even though there’s no pressure by the boiler, it seems that the rads on the 3rd floor apartment do get pressure as their air vents are hissing (some loud), and I also remember that when I removed the No 4 orifice of Made-O-Mist to replace it with No 6, the entire rad got hot very quickly, so it is interesting that there seem to be pressure on the 3rd floor apartment, but not an indication of it on the boiler pressure gauge (and also not apparent pressure on the 1st floor apartment, even though the rads there do get hot too). Does that sound normal that there is no pressure by boiler (or 1st floor) but there is on the 3rd floor apartment?

This is a one pipe steam system, installed in a 125 year-old 3-story building.
The boiler serves 2 units: there are radiators only on the 1st and 3rd floors (2nd floor rads had been removed by previous owner so they now have only forced air).
The boiler is located in basement the middle of the building and its main line splits into two branches/loops that go in opposite direction; one loop main is of 3” in diameter, and the other 2’.
The main horizontal lines in the basement are insulated with 1/2” fiberglass (actually, because there is an apartment in half of the basement, the 3” loop goes through that newly renovated well-insulated apartment, and still has the 1/2” fiberglass insulation on it). There are 2 Gorton No 2 air eliminators on each end on a loop (on the return lines), for a total a 4.

The steam boiler is Weil McClain EG-50-SPDN Series 4, Input btu/hour 175,000, DOE capacity 142,000, Steam Sqft 446, Net IBR output 107mbh.
There is a total of 530 EDR in the two apartment, not including piping and pick up: there are 8 radiators of various sizes in 1st floor with 241 EDR, and 8 radiators on 3rd floor with 289 EDR. So on face value it seems that the boiler is undersized as it provides only 446 EDR for actual 530 EDR demand. If I calculate it correctly that’s about 16% undersized. Is that large enough of a gap to explain the (what seem to me) abnormally long heating times? And do you think it will carry the load in the coldest day of the year?
Thank you for your help.

SteamingatMohawk

When is the last time you had the fire side of the boiler cleaned? Have you done the gas flow estimate?

Jamie Hall

Well, the boiler is a little small, perhaps -- but if your mains are insulated, it actually isn't (that EDR rating includes a pickup factor to handle uninsulated piping). And it does not explain the long time to warm up.

Let's consider this a moment -- and it has nothing to do with the boiler. It takes a certain power -- BTUh -- to maintain a certain interior temperature. Those BTUh are from the radiation. The radiation is powered in turn by the boiler, but if the radiation is all up to temperature -- as you indicate it is -- then more boiler power isn't going to help at all. The radiation is putting out all that it can. Now. What happens if we ask the system to raise the interior temperature? It is going to take more power, just as -- to use a homely analogy -- if you are travelling down the road at 50 and want to go 60, you need to step on the gas. The fact that the system radiation can, in fact, raise the temperature indicates that at that particular temperature difference between inside and outside the radiation does have the ability to deliver more power than needed. The fact that it takes that long to do it, though, indicates that there isn't much extra power available.

Will there be enough power available from the radiation to maintain a steady interior temperature at a lower outside temperature? Probably, but honestly it looks as though it will be marginal. Will there be enough power to recover from a setback such as you are using? Frankly, probably not.

Your boiler is none too big, but it is big enough. Your radiation is marginal. To correct that, you either need to increase the amount of radiation available -- and the boiler size to match -- or decrease the heat loss. Better insulation, if possible. Better -- or some -- storm windows. Draught sealing.

Changing the boiler alone will accomplish exactly nothing.

If you want to reduce fuel usage with the present system, reduce or eliminate the setback. Your Nest is doing you no favours at all. Further, the colder it is outside the less setback you will be able to tolerate -- on very cold nights, defeat the setback entirely -- or you will find that the temperature never does get up to the setpoint, although it might well have held the setpoint if you had let it.

Do not concern yourself about no pressure showing at the boiler. If you are looking at the code required 0 to 30 pound gauge, you won't see it. If you have a low pressure gauge in addition, say a 0 to 3 psi or 0 to 5 psi -- you would probably see a few ounces per square inch, which is clearly all you need -- since your radiators are hot.

I hope this helps.

JUGHNE

How well did it work before the Nest was installed?
The Nest may not be constantly calling for heat and shut down without you knowing it.

Or worse yet you could have a hole in the boiler at or above the water line and steam is going out the chimney. Look for a lot of white smoke on a cold day.

EBEBRATT-Ed

You already answered you own question, Your EDR is 530 and the boiler will do 446. The 446 the boiler is doing includes a piping and pickup factor of 1.33 which amounts to 145 EDR. So adding the 145 to the 446 =591 EDR. Which is really what you have when your running non stop.So you are maxed out.

There has been and continues to be debates on this forum about the piping and pickup factor. The manufacturers use the industry standard of 1.33.

Some say this is too much and use 1.15 or another#. Some say 1.5 should be used if the piping is un insulated.

Make sure your venting is up to snuff. And don't worry about not building pressure you don't need any measurable pressure to heat the building.

The only other thing you can do is have the gas pressure checked on the burner manifold........the burner side of the gas valve to make sure the boiler is firing to capacity

Ori

SteamingatMohawk said:

When is the last time you had the fire side of the boiler cleaned? Have you done the gas flow estimate?

Never! Is it straightforward operation or need a pro for that? What is the right procedure for that? The I did clean though each of the (9 or 10) tubes that convey the gas that burns...
Also, we have 1" main line gas to that boiler. How to estimate the gas flow?
Thanks.

Ori

"The only other thing you can do is have the gas pressure checked on the burner manifold........the burner side of the gas valve to make sure the boiler is firing to capacity"
How to do that?

Ori

Jamie Hall said:

...If you want to reduce fuel usage with the present system, reduce or eliminate the setback.
I hope this helps.

What is the 'right' setback with steam system, are you suggesting that our gap between the 65 at night and 71 during the day is too wide? By how much shell I increase the night temp to so as to reduce fuel usage and reduce time to hit the 71 in the morning? (though it looks counterintuitive to me that increasing the night temp will reduce the fuel usage...:)

EBEBRATT-Ed

@Ori

If you check the boiler name plate or manual it will tell you what the burner manifold pressure should be. It's usually 3.5" water column. You measure it with a low pressure gauge that reads in " of water or you can use a manometer.

There is either a tapping on the burner manifold...down stream of the gas valve or a plug you can take out on the gas valve. They are usually 1/8 pipe thread.

The other way with all other gas appliances shut off is to get the boiler running and clock the gas meter with a stop watch

Jamie Hall

Ori said:

Jamie Hall said:

...If you want to reduce fuel usage with the present system, reduce or eliminate the setback.
I hope this helps.

What is the 'right' setback with steam system, are you suggesting that our gap between the 65 at night and 71 during the day is too wide? By how much shell I increase the night temp to so as to reduce fuel usage and reduce time to hit the 71 in the morning? (though it looks counterintuitive to me that increasing the night temp will reduce the fuel usage...:)

There's a fairly lively debate, actually, on what the "best" setback is -- but generally with a steam system, or hot water with radiators instead of baseboards, I'd suggest no more than 3 degrees -- and only do it once a day, at night. That way your boiler only has one long run in the morning.

Be sure that your Nest isn't trying to be intelligent and running setbacks during the day if it doesn't sense anyone around.

KC_Jones

Are all the radiators getting fully hot during this recovery period?  If they are, the boiler isn’t too small.

175k input, the efficiency on those is 82%, so you have 143500 available, which supports 597 sq ft, compared to your 530 systems gives you about 12.6% pickup factor.  @ChrisJ runs less pickup than that with zero issues.

I agree with the above you don’t want pressure, it serves essentially no purpose in a steam heating system.

JUGHNE

I would take the Nest out of the picture temporarily.

Shut off the boiler power.

How many wires are connected to the Nest?...take a picture of connections before unhooking anything.

Twist the R and W wires together, if any other wires, isolate them.

This will force the boiler to run without interruption from the Tstat.
The pressure control will then cycle the boiler if you build pressure.
Does the boiler have a Cycleguard control on the side?
Then you can see if any pressure builds with a long constant run.

Just about all of the thermostat problems presented here on this site are about Nest's.
Same for another heating website.

Also it is rare to find an undersized steam boiler IMO.

MilanD

EG 50 is hood vented boiler, if I'm not mistaken. There's nothing much to adjust on it but the gas pressure on the gas valve as far as burners go, and that's usually preset at the factory, at 3.5" WC. Installers should have checked that too, but you're probably safe to assume your pressure is fine. 1" gas supply pipe is also enough for the natural gas delivery of 196k btus if shorter than 40 ft, at 3.5" WC pressure at the gas valve. So, you're probably good there unless your supply line is longer than 40ft (add approx 5 ft per directional change fitting).

Chicago design temp is -1.6F, and with 10F outside you're getting close to the design. The colder it is outside, the greater is heat loss and more energy is needed to keep indoor temps as desired. Now, per your explanation you also have a bit less supply than the demand (edr of the boiler vs. attached rads), so when you do a set back, you are asking the system to not just keep, but raise the temp, while a lot more of that thermal energy is also being lost to greater temp differential to the outside, and you are giving it less than the design requirement. So, closer you are getting to the design temp outside (-1.6F), the longer it will take for the space to heat out of a set back, plus you are inputting a bit less edr than the radiators can radiate as the boiler is smaller than the attached rad edr. But, this may be a wash as one of the units has its own heat source.

So what to do?

Think of it like car fuel efficiency: highway driving gives you better efficiency at steady optimal speed, vs. stop-and-go city driving. The colder it gets outside, don't do any setbacks. It's like going up a hill on the highway: it's easier to climb it, and faster, if you have a greater speed going into that climb. In this case your "speed" is your indoor temperature. So, the colder it is, the more you want to think of your steam heating as needing highway driving condition. When it's cold, set the temp and don't change it while it's cold. Then, the warmer it gets outside, the more setback you can do, but generally no more than 3-4 degrees.

mattmia2

you can clock the meter to find out how much gas it is consuming, but if this is multifamily you really should have a good professional service the boiler every year to every couple years.

After it has been off a while, how long does it take for the radiator to get fully hot? as @JUGHNE said, it is unusual for older steam systems to not be oversized unless someone has removed some radiators.

pecmsg

6° is a lot when at design conditions. Its huge if the wind is blowing.
It is much cheaper and you'll get a much higher return on investment tightening the envelope then installing a larger boiler.

I agree take the NEST out and try a different stat.

ethicalpaul

Everyone is making sense on this thread. Related question: When the industry sizes a heating system per design day temp vs heat loss of a home, that is not including any setbacks, right? Said another way, a properly sized system on design day should run 24 hours that day. If there's a setback, it's not going to get there.

If the recovery from setback is making you uncomfortable (in temperature or in thought), then just don't have a setback

Personally, when I had an actual undersized system (it was a ground-source water to air heat pump), I was thrilled when it couldn't quite keep up on the coldest day of the year. That made me know that I sized it correctly. I put a sweater on that day and smiled.

EBEBRATT-Ed

@ethicalpaul

True. But as with any heat loss calc there is always some "guesstimating" and the tendency is to build in a little fudge. The you select the equipment which seldom exactly matches the heat loss so you go up to the next size

Ori

Thank you all very much for the advise -- I understand that the main problem I have is that of a too large of a setbeck; a gap between 65 degrees at night and 71 during the day is too large and should be smaller, like 3-4 degrees max, for steam system. Understood.

Just to clarify one more thing, are you suggesting that:
1) a boiler that is correctly sized should work 24 hours on the design set day (-1.6F in Chicago) to keep 70-71 degrees inside (,and that assuming no setbacks at all)?
2) and if so, should I expect the boiler NOT to meet demand (that is to keep the temp 70 degrees steady) if the outside temp falls significantly below the design temp, say falls to -10F ?

Separately, I have one radiator that its air vent keeps filling with dirty brown droplets, which sometimes reduces the vent ability to properly vent the air; it's not stuck on open or close position and there's no debris per se, but still gets filled dirty water. Replacing that valve doesn't solve that as it happens again on the replacement too. The rad is on the 1st floor. What do you think can cause it?
Thanks again!

AdmiralYoda

Setbacks are real tricky when it comes to steam.  In theory you could save fuel but if the boiler cycles over and over trying to recover from a setback your probably wasting more fuel than you saved.

I haven't found any difference in my gas bill from using a 3 degree setback vs just keeping the boiler at 70 all the time.  The only difference is the boiler works harder and cycles alot when using a setback....which is a big negative for me as my boiler is 38 years old and I want it's life to be as easy as possible.

I have a 40% oversized boiler which compounds the problem but even with a properly sized boiler that won't cycle on pressure will waste lots of fuel during a setback.  Once the radiators are full and hot....the boiler continuing to run is just wasting fuel.

In this case you need to outsmart your boiler and start playing with delay timers and logic controllers.  Not for everyone.

Unless your system venting/sizing/etc is perfectly set up you'll find it's cheaper and easier to just set it and forget it.

Jamie Hall

Well, yes. If the boiler for hot water heat is exactly sized to the heat loss on a design day, it will run all day and hold the temperature. It won't be able to raise the temperature (no recovery from setback) and, as you expect, while it will be able to maintain the same temperature differential on a colder than design day, that means the the interior temperature will drop, too.

There is an inherent conflict here between economy of installation and operation, on the one hand, and the ability to meet unexpected demands which are greater than design. There is a great emphasis these days on the former aspect. The customer demands that money be saved, and both the customer and society demand efficiency. Therefore the tendency is to design and install things right at the limit.

Indeed, I myself have often said that for hot water (and forced air, as it happens) it is recommended to determine the heat loss on the design day and design and size for that. I have to admit, though, that there is a bit of "do as I say, not as I do" to that -- if I were doing such a thing for myself, or for an understanding client, I would oversize on that. Not much, perhaps -- but enough to give myself and them a safety factor. It's a balance: you don't want to go too far overboard, but you don't want to cut it too close, either.

ethicalpaul

Separately, I have one radiator that its air vent keeps filling with dirty brown droplets, which sometimes reduces the vent ability to properly vent the air; it's not stuck on open or close position and there's no debris per se, but still gets filled dirty water. Replacing that valve doesn't solve that as it happens again on the replacement too. The rad is on the 1st floor. What do you think can cause it?

It sounds to me like water is being pushed into the radiator. There is of course always water in every working radiator...that's what the steam condenses to. But condensation shouldn't cause rusty pieces to get lodged in your vents, so we have to think "what could be doing this?"

Here are some ideas:
- "wet steam" (actually large amounts of water) being carried into your mains and into your radiator (often caused by improper near boiler piping, quite common)
- incorrect pitch on radiator causing water to back up into radiator
- faulty or partially-closed radiator valve causing water to back up into radiator
- A sagging section of horizontal supply pipe in the floor below the radiator causing a water trap that might result in water being carried into the radiator (not likely if the radiator is otherwise heating normally)
- high pressure of steam system causing water to get pushed out the return side of the boiler, all the way up to the first floor radiators (it doesn't take much pressure to do this...the water level can raise about 27" for every 1 PSI) -- this would normally be indicated by water "shooting" out of the vent and is usually quite noticable

MilanD

Here's one kicker: your radiators may in fact be sized to the post 1918-20 pandemic heat loss practice, of heating 70F indoors with windows open, aka "fresh air movement". So, in reality, design day for your system with closed Windows may mean temps way below -1.6 F. If on those days boiler runs 24h, op. pressure stays at 0 psi, and during a cold snap it keeps up, than great. If not, then you'll know. But I still wouldn't do setbacks on very cold days. One way to find out for sure if your total rad edr is actually heat loss or open windows heat loss is to actually do a heat loss calculation.

Now, I think that in either case, with a 33% pick up factor, once the system is hot and stays hot, there is that 33% pick up capacity that won't be used completely bc the pipes are all hot and will take way a marginal amount out of btus (esp if mains are insulated), and that you'll probably still see the boiler cycling some and still may be having a hard time keeping up due to a set heating edr output of a sum of all radiators. But, if at this point you're to raise the operating pressure (assuming you see normal op pressure raising), say to 3 psi (too high for normal operation), you will in fact give the system extra 4btu/lb of saturated steam. This would mean that your 10 edr rad will emit 2440 btus and not 2400, extra 40 btus. On a 600edr system, that's 2400btus. Is this enough? Probably not, but your heat loss calculation can tell, as can finding out whether or not your whole system is sized for extra heat with open windows.

So all this being said, a sweater or a space heater might be a better choice.

Ori

JUGHNE said:

“Or worse yet you could have a hole in the boiler at or above the water line and steam is going out the chimney. Look for a lot of white smoke on a cold day.

Ho dear! I now see white smoke coming out of the chimney! Only today was I able to observe it as finally the outside temp is about 0°F in Chicago. Is that an indication of a leak at or above the water line in the steam boiler itself? How can I locate the crack/leak in the boiler? Do I have to remove the chimney vent where it connects to the boiler and fire it up and try to see where in the boiler the steam is coming from? And if identified, is it fixable? How? That might explain why I never see pressure builds at the boiler. Never, even today when it was working for hours continuously. And also might explain the relative high bills, and also the long time it takes to heat. BUT, on the other hand I don’t see that the water feeder device (VXT-24) draws water to compensate for that (again, I have the one that counts gallons). Mind you, I see similar ‘white smoke’ coming out of the chimney in my different property, where it has hot water radiators system (also over 100 years old building). Is that normal for hot water boiler to see that white smoke, or it’s also an indication of a leak in the boiler. Both boilers (steam and hot water) are operated by natural gas. Please see attached video of the ‘white smoke’ I observed this morning coming from the chimney of the steam boiler (if I find how to load it...). Thanks!

Ori

JUGHNE

Compare the white smoke to other chimneys you see.
If your water fill counter is working as you say, you may not be loosing water.

Did you try operation by by passing the Nest?

You need a pro in there....check "Find a Contractor" section.
Maybe "The Steam Whisper" is near you.