Replacing Oversized Boiler with Properly Sized Boiler = Savings?

AdmiralYoda

I touched on this in a few other threads but we are planning a home remodel and it would be a very convenient time to replace the very functional 40 year old NG Peerless G461. We will be having some steam pipe work done anyways so the pro's will already be there.

So. How can one predict the fuel savings by replacing a 50% oversized boiler with one that is properly sized?

The house is 123 years old and has the original steam radiators and piping. It heats great and evenly but I'm sure the EDR is higher than it needs to be. This house has recently been insulated and had new windows installed and tightened up.

Would there be any savings by replacing the oversized short cycling boiler with a new one that is properly sized? I'm trying to anticipate the return on investment (if any).

I know its impossible to accurately predict due to the variability of the weather and other factors, but if we pretend all things equal....does it make financial sense?

Thoughts? It is a 1-pipe counterflow system.

pecmsg

Do you have the Fuel #’s over the last few years?

ethicalpaul

I would expect less than 5% reduction in fuel use, possibly less than 1%. Possibly 0%!

Even with an oversized steam boiler, when you burn fuel, you are getting about 80ish percent of that energy delivered as heat into your house. BTUs of heat energy into your house is what counts and the large boiler doesn't know it's oversized

Yes it's maybe cycling, but still, when it's running, you're getting around 80% efficiency, and when it's off you're not using any fuel at all.

With a new boiler when it's running, you're getting around 80% efficiency and when it's off you're not using any fuel of course.

Does the efficiency vary through a long heating cycle uninterrupted by pressure cutouts? Maybe a little. Maybe not even measurable.

Jamie Hall

I'd agree with @ethicalpaul . With a further note: people almost never properly account for either depreciation or the lost opportunity cost in these calculations. Now I agree there is a good reason for that -- it's kind of a crap shoot, particularly when inflation is considered -- but even if one looks at only the lost opportunity cost one has to be seeing a savings of between 7 and 10 percent of the capital and installation cost of the new boiler to break even. That in turn implies a very large gain in efficiency -- which just isn't going to happen.

Greybeard

Don't forget that the boiler should be sized to the EDR of the radiators, not the heat loss of the building. Keeping this in mind, are you sure your boiler is oversized? I'm sure you don't want to change your radiators to match the reduced heat loss due to insulation and window replacement.

EdTheHeaterMan

The short cycling will save on wear and tare of the parts that are cycling. The limit switch, the gas valve, the vent damper (if equipped). The off cycle losses are not significant if the cycle is very short. I have been told that an oil burner will not reach its steady state efficiency until the combustion chamber warms up in order to assist in the vaporization of the oil droplets. That can take up to 3 minutes on some equipment. After that the 82% or 84.7% ( or whatever) efficiency will be realized. There is also some unburned fuel (some smoke) at the shut off of the oil burner. So I always told students, customer and others that a 5 minute run cycle is a minimum for achieving peak operating efficiency. If you cycle 3 on and 6 off, then you are wasting 2 to 5% of your fuel.

Gas is a different story. Atmospheric Gas Burners (like the ones in most steamers) do not take as long to get to their maximum operating efficiency. Maybe less than a minute to a minute and a half. (I'm not sure on those gas burner numbers). But that said, if you have a hot steam boiler and the combustion area is left off for 2 to 3 minutes, and the flame comes right back on, then your "start-up to peak efficiency time" is much less on the subsequent on/off cycles. So the steady state efficiency is very similar on a 100,000 BTUh boiler that cycles 3 min. on and 3 min. off compared to a 50,000 BTUh boiler that does not cycle. There will be a saving, but you would need to put a lot of testing equipment in the home and install the big one for a year and install the correct size (of the same model) boiler for a year in the same home and compare the fuel usage (after adjusting for the difference in degree days from one year to the next)

If you would be interested in doing that @AdmiralYoda, we would all be so greatful to review your findings.

I guess I'm saying, If you want a new boiler, then buy one. If you want to keep your old boiler, then do that. If it were my house and you were paying for the new boiler, then I would most certainly go for the new boiler. LOL

Get the new boiler! Then you can forget about it for 20+ years (unless the casting is made on a Monday or a Friday).

AdmiralYoda

Thanks everyone! I tend to appreciate older mechanical devices and hate throwing them out if they are still in working order.

Half of me says if it ain't broke don't fix it, but the other half is saying that Murphy's Law will apply if I don't replace it during the remodel and when the steam pro's are already there.

Hap_Hazzard

Greybeard said:

Don't forget that the boiler should be sized to the EDR of the radiators, not the heat loss of the building. Keeping this in mind, are you sure your boiler is oversized? I'm sure you don't want to change your radiators to match the reduced heat loss due to insulation and window replacement.

100%

I might be all wet, but the way I look at it, adding insulation, weather-stripping and energy star windows won't make your boiler oversized or make it short cycle (as in multiple cycles on pressure during each heating cycle), it will just satisfy the thermostat quicker and take longer between cycles, kinda like it does when it's not so cold outside.

Jamie Hall

Um.... sort of. On a two pipe system, yes you can run undersized. However, what is perhaps not obvious in the "simply a matter of utilizing suitable orifices" comment is that that is by no means simple, as if the power supply -- the boiler -- is sufficiently undersized that it cannot, in fact, power at least some if not all of the radiators completely, then every radiator must be orificed, and there is -- unhappily -- no way other than cut and try to do that. Further, the system differential pressure becomes even more critical than it is in even a normal vapour system, never mind a plain vanilla two pipe steam system.

Can it be done? Yes it can. Should it be done, other than being able to boast about how your system operates on this or that boiler? I'm not so sure. But keep in mind that I am an engineer, and engineers avoid systems or designs with no safety margin if they possibly can.

EBEBRATT-Ed

Keep in mind that all steam boilers if the radiation load is calculated and the boiler is sized in accordance with that radiation load the boiler will be 33% oversized especially when the piping is hot as the 1.33 piping and pick up factor is built in

AdmiralYoda

My calculated EDR is 218. My 40 year old Peerless G461can provide 308 sq.ft. of steam. So my memory was actually a little incorrect....it is 30% oversized, not 45%.

I haven't done a heat loss calculation on my house....but it certainly is better than than it was in 1899.

If I replace this boiler it will probably be a Peerless 63-03L which can provide 233sqft of steam. After adding a couple small radiators due to the remodel my new EDR will be around 240sqft.

That means my existing boiler would then be 22% oversized and the Peerless 63-03L would be about 3% undersized.

Jamie Hall

Perhaps referring to the men and women on the Wall as idiots isn't quite the best way to persuade people of your ideas? Just sayin'...

I think, @BC_20 (with all of 5 posts), you might pay a bit more attention. Many of the folks on the Wall have a good deal of experience sizing and installing steam systems, and I believe I would be correct in saying that as a rule they prefer to slightly undersize the boiler, based on EDR ratings. Some systems more than others. I think it is also reasonable to suppose that if the client is willing to pay for adjusting all the radiation appropriately they might be willing to undertake that, too, and install a smaller boiler.

However, I think in regards to heat loss you have a major problem common not only to steam systems, but all heating systems: the heat loss -- even the most meticulous Manual J -- has two inescapable characteristics: first, it is, of necessity, based on a design temperature differential -- that between the "design day" exterior temperature and the desired indoor temperature. The latter may be mandated at a certain minimum by local building code. The former may also be code specified, or may be derived -- more or less accurately -- from weather records. In addition, again of necessity, some approximations and assumptions must be made about the building envelope, and -- if one is prudent -- degradation of that envelope with time. If it is new construction, one can be much tighter in terms of these assumptions than if one is dealing with an existing structure -- but even for new construction, these are assumptions.

Even the best Manual J, then, can only be an approximation as to the actual power required to heat the structure on a specific day. The prudent designer and installer will at least meet that Manual J power requirement, if only because while one may be attacked legally for perceived problems with a heating system, one has a good defence if one can show that one did one's work -- and no defence at all if one can't.

The second problem with heat loss actually makes most of the discussion silly. The design heat loss will occur on only a very small fraction of the days -- depending on the source of the design day temperature, with somewhere around a 1 in 100 probability and a 3 in 100 probability on any given day. On any other day the power of the heating system will, indeed, be oversized. Perhaps ludicrously oversized, as on a day when it is 60 F out.

No. For one thing, a heating system is just that: a system. It is not a thrown together jumble of parts, or at least it shouldn't be, but each part should be designed to match the rest of the system and work together. It doesn't matter whether it is forced air, hot water, steam, radiant floors -- that is irrelevant. What matters is that each part of the system (in a steam system, for instance, the boiler, the piping both near and distribution, the radiation, and indeed the building) is correctly related to all of the other parts. For another thing, no craftsman or engineer will ever design something, never mind build it, which knowingly will not meet the maximum reasonable load it is expected to carry. There are good economic reasons not to overbuild, obviously, so one avoids that -- but the consequences of underbuilding are, even with something like a heating system, much more serious (or at least some people think so): damage to reputation at the very least.

JUGHNE

I am applying the principles of "The Steam Whisperer" and that of Henry Gifford by utilizing inlet offices in a two pipe system.
This is a school that has been a "pet hobby" project for the last 10 years.
Took out a vastly oversized boiler and installed a PB 63-4L and 63-5L to feed this 2 pipe system.

The boilers together can only feed 80% of the connected EDR.

So far with 2 mornings of -6 degrees we are maintaining temp of 67 inside with only the 5L at 2-3 ounces. Christmas (not winter) break....we can say that out here.

Bringing the idle 63-4L on line will get pressure up to maybe 1.5? PSI and raise temp to the needed 72 inside.....need more gauges at this point.

School starts back today.

This has been a great lesson in pipe insulation. Asbestos was abated 2 years ago.
Not a problem for the 1.3 million boiler to overcome.
But with baby boilers the steam would only get thru maybe 2/3 of the main before "running out of steam" so to say.

So as fortune had it, a needy collage student grand son was home on "winter" break, (he goes to the state University...no Christmas there).

So after 350 feet of tunnel crawling he (mostly) and I got all piping insulated, checking pipe slope and hangers along the way.
Now heat gets to the end of the system.

BobC

Thank God for poor college kids willing to work for a little scratch.

Bob

ChrisJ

The sizing of steam boilers as well as controls for them needs a lot of attention I suspect it'll never get and it'll just die off completely.

For some reason sizing hot water systems as well as the controls have been updated a lot but steam we just keep doing the same old thing. Oversize the boiler, slap a T87 on it with the anticipator disabled (set to 1.2) and that's called "proper",

Oversize a hot water boiler or an air conditioner and you're called all kinds of names.
Oversize a steam boiler and it's called normal.

Installing boilers that constantly bounce off of the high limit because the system cannot accept all of the heat being created and then say it has to be this way is, I don't know........

Jamie Hall

My, my, @ChrisJ . Well, except that Cedric is not oversized... (he rarely, like very rarely, gets over 4 ounces), your second paragraph up there is a pretty good description of my home system...

Guess I'm just an old fogy who hasn't a clue what he's doing and is hopelessly stuck in the past.

ChrisJ

Jamie Hall said:

My, my, @ChrisJ . Well, except that Cedric is not oversized... (he rarely, like very rarely, gets over 4 ounces), your second paragraph up there is a pretty good description of my home system...

Guess I'm just an old fogy who hasn't a clue what he's doing and is hopelessly stuck in the past.

You are an old fogy.

But that's a whole other subject.
Steam deserves updates, not abandonment.

While we're on the subject, why can't a 2 pipe system just be throttled with the supply valves rather than orifices?

Jamie Hall

ChrisJ said:

Jamie Hall said:

My, my, @ChrisJ . Well, except that Cedric is not oversized... (he rarely, like very rarely, gets over 4 ounces), your second paragraph up there is a pretty good description of my home system...

Guess I'm just an old fogy who hasn't a clue what he's doing and is hopelessly stuck in the past.

You are an old fogy.

But that's a whole other subject.
Steam deserves updates, not abandonment.

While we're on the subject, why can't a 2 pipe system just be throttled with the supply valves rather than orifices?

It can. And often is. That's the whole point behind the Hoffman (and some other makes) adjustable valves. Much simpler than juggling with orifices!

One of the secrets to Cedric is that all the radiation does have Hoffman valves, and they are all set to around 80% fill for the radiators. Which results in nice even heat -- and perhaps more interesting, all of the traps are original to the 1930 installation and are still working.

ethicalpaul

AdmiralYoda said:

My calculated EDR is 218. My 40 year old Peerless G461can provide 308 sq.ft. of steam. So my memory was actually a little incorrect....it is 30% oversized, not 45%.

It's 41.28% oversized

218 * 1.4128 = 307.99

JUGHNE

I have tried to throttle 2 pipe convectors with the supply valves.
They would "walk" themselves more open with expansion thru steam cycles.
Also in a school house they could be messed with by anyone.

The basic generic replacement valves are too course for permanent adjustment.
Really good vapor valves are pricy.

No one messes with a $10 orifice.
Traps are not necessary if set up right and low pressure is maintained.

Hap_Hazzard

Jamie Hall

I find no need to comment... It think -- I hope -- that I am finally learning not to attempt to debate with someone who has all the answers. Not worth my time.

The Steam Whisperer

JUGHNE said:

I am applying the principles of "The Steam Whisperer" and that of Henry Gifford by utilizing inlet offices in a two pipe system.
This is a school that has been a "pet hobby" project for the last 10 years.
Took out a vastly oversized boiler and installed a PB 63-4L and 63-5L to feed this 2 pipe system.

The boilers together can only feed 80% of the connected EDR.

So far with 2 mornings of -6 degrees we are maintaining temp of 67 inside with only the 5L at 2-3 ounces. Christmas (not winter) break....we can say that out here.

Bringing the idle 63-4L on line will get pressure up to maybe 1.5? PSI and raise temp to the needed 72 inside.....need more gauges at this point.

School starts back today.

This has been a great lesson in pipe insulation. Asbestos was abated 2 years ago.
Not a problem for the 1.3 million boiler to overcome.
But with baby boilers the steam would only get thru maybe 2/3 of the main before "running out of steam" so to say.

So as fortune had it, a needy collage student grand son was home on "winter" break, (he goes to the state University...no Christmas there).

So after 350 feet of tunnel crawling he (mostly) and I got all piping insulated, checking pipe slope and hangers along the way.
Now heat gets to the end of the system.

I am glad to hear that is working out so well for you. It's really amazing to watch a tiny little boiler heating a big system and maintain temperature through out the building. The total EDR for my church system was around 5800 EDR powered by a 2,100,000 input boiler (a little undersized for the radiation load). Now more than half that was in a steam to hot water heat exchanger powering a 1950's slab radiant system. I sized the orifice capacity @ 2 psi. The heat exchanger supply was throttled with a steam cock to provide the correct btu's needed for the heat loss of the radiant heated structure. About 1400 EDR heating the sanctuary and social hall was orificed to full convector/radiator capacity to meet the design heat loss. The balance was restricted down below full capacity to match the radiation to the heat loss. The traps are all in place on the radiation because we need to run more capacity during Sunday morning ramps ups, so steam will make it all the way through the convectors. However, nearly all the rest of the time, the traps sit there unused.
Last winter a single 345,000 btu/hr steam boiler ( net 867 EDR) heated the 5800 EDR, 15,000 sq ft building down to about 0F outdoor over multiple windy cloudy days, holding the building in setback of 45F to 50F. A small supplemental hot water boiler added a little extra bit to the hot water loops so more steam was available to the main system when temperature dropped down to around -7F.
Orifices do the job quite well. The big vapor system manufactureres had figured that out by the 1930's, so if you look at alot of the later vapor systems, they came with orifices or adjustable orifice radiator valves that were set by the installers.
Some systems do require an extra punch at cold start up to heat evenly, but then the btu's can be backed down to the current heat loss of the building most of the year.


I have an efficiency curve published by the National Bureau of Standard for atmospheric hot water boilers that plots the seasonal efficiency versus steady state efficiency. You'll see that curve published in information by Burnham with thier staged boiler designs.
Using Bin Data Analysis, I arrived at the efficiencies of boilers at various amounts of oversizing versus the design heat loss (coldest design day, not radiation load).
The seasonal efficiency of an 80% steady state efficiency atmospheric boiler with no stack damper sized to design load is about 70%. This agrees with older AFUE data on residential boilers when stack dampers were optional and both ratings were published. At 2 x design heat loss, the seasonal efficiency is about 60%, at 3x, 56%.
I've used this data for many years to predict potential fuel savings of properly sized boilers and it seems to work quite well.