Unsure on which way to go-stoker or handfired?-steam boiler

1. You get steam when your boiler water gets to 212 deg and then absorbs the "latent heat of vaporization". If you add a DHW load when the boiler is trying to make steam, those btu's come pretty much entirely from steam production. Put another way, with a steam system, if the DHW load pushes your boiler water to 211 deg, you get 0 steam into your radiators. With a hot water system, even if the DHW load pushes down your boiler water temp, you'll still get some heat from your radiators.

I really don't know where you are getting all this from, hope not from experience. Who is to say my DHW is going to push my temps to 211? If it does and the thermostat is not happy, guess what, the boiler turns on. What if my steam is 220? I drop to 219 all is well. You are trying to argue some point which i have no idea what it is. If you are running hot water and your DHW drops your water temp to below the low setting, your pumps don;''t run either, Ha ha. I can get steam at 211, or even less. Can you guess how?


2. My point is that any boiler, including an AA, if run without its original jacket basically can't make steam per its original specs. If they have any future scenario that would involve running a coal boiler without a jacket, they need to factor that in when they compare it to the performance they get from their current oil-fired boiler.

Like i said, show me a AA with a jacket, you won't find one. How do you know the original spec had a jacket on? Please post the spec. Did you work there or something 50 years ago? I can show you a spec from AA that says btu output on steam is only 97,500. Therefore, with your thinking, my house could not possibly be heated last winter because the oil boiler i took out was rated at 165,000. I also have no jacket so that brings it down to 80,000 btu output, so no way could it even begin to heat 9 radiators. I told you it hardly runs, i have a good draft, fire burns hot, makes some steam at idle with timer running 2 minutes each half hour.

3. As far as I know it's not a big trick to add hydronic heating zones to a steam boiler (without converting the existing steam radiation to hot water) and several forum members have done so. My last house had a hydronic loop and my current house has an indirect water heater; both use water from steam boilers.

If the original poster had stated a little more about his steam system, we would have more to go on. He is scared away never to return. It could be a 1 pipe or if the original owners of his house had money, they might have installed a 2 pipe steam system.

4. If you burn 20 lb/hr in a boiler with a given heat exchange area, and I burn 20 lb/hr in a boiler with, say, a 25% larger heat exchange area, all else equal I'm pretty sure more of my btu's are going to end up in the water. A given boiler may work most efficiently near its maximum output, but that doesn't tell you anything about how it compares to the efficiency of other boilers with larger hear exchange areas.

Where are the the other btus going then? We are talking steam ,unless you are talking something else again to try to get some point across i still haven't figured out. They are being used as heat, yes in the basement or heating the floor. 20/lb/hr only gives off so many btus. If you can get more btus out of a lb i will ask one of the moderators to lock this thread. I can put a heat reclaimer on the top of my chimney also but......(don't steal my idea)......then i can claim more btu's per pound of coal. A AA260 with hardly any load is a waste of coal. I don't know the difference between a 520,700,900 but i'm sure it's SIZE. No matter what i am still sticking with my guess that a AA130 would heat his house. Measuring the 13 radiators as suggested would be a great start.

Of course, if you find you have an underpowered steam system you can always shut off radiators, manage the timing of your DHW consumption, insulate the boiler and live with cold floors, etc. To me, that misses half the point of the cheap btu's you get from coal - you can choose to have a quality of life that involves greater comfort in - and even expansion of - the habitable area of your home, as well as prodigious amounts of DHW, all while saving a large percentage of the cost. Especially with steam, I just don't see the point of cutting it too close on capacity.

In that respect, economically speaking, he installs, better yet, he pays to have a AA260 installed. Maybe $6000. He got a good deal. All is good. Steam works all 13 rads, all the way across if needed. He doesn't remodel the basement because it is scary down there, the kids don't live in the attic because of the bats. So now, few years go by, say 2 -3 years. He adds some insulation on top of the bat guano,installs a few cheap windows from Lowes, etc.etc. This may be a true story, it has happened before. People insulate and upgrade the windows all the time. All of a sudden the AA260 is spitting out unburned coal. Such a waste. Solution, remove the oversized boiler, install smaller coal boiler, AA130, spend more money on new install. He currently has 2 coal stoves. They can supplement the small boiler, while he insulates,if needed. Maybe on the other hand he should just forget the coal until he gets the house all snugged up and r-96 insulated.
Mike

P.S. Mozz, how many sf are you heating to what temperature, and what is your annual coal consumption? Thanks.[/quote]

Mozz -

This is getting kind of bulky, so I'll try to "boil" it down:

1. My original concerns were expressed in response to your proposal that a 130 (rated for 540 sf of steam) be substituted for an oil boiler rated for 742 sf of steam.
2. My first post initially referenced the possibility that the 130 "wouldn't fill the radiators under the best of circumstances". I assume everybody can agree that filling the radiators is important, and jimd described how to check that.
3. I described 3 specific further concerns related to the potential need for additional boiler capacity in the situation at hand. First was DHW. I assume everyone can agree that if the boiler is expected to produce DHW, some kind of allowance for that is needed above the capacity required by the installed radiation. I further asserted that DHW can have a bigger impact on the production of steam than it does on hot water. While this was based on about 25 years of experience with steam systems (and a little coursework in thermodynamics) you can see the same thing on your stovetop. If you have a pot of boiling water and you add even a small amount of water below the boiling point, the water in the pot generally stops boiling for a while even though the burner is still running. The water in the pot may still be scalding to the touch (as it would be in a hot water radiator), but introducing the need to heat additional water temporarily takes away the ability to make steam. Your comments about whether steam is formed above or below precisely 212 deg due to the presence of positive pressure or a vacuum doesn't change the fact that adding load diverts energy from vaporization.
4. I also expressed a concern about the effect of running a coal boiler with the jacket off on its ability to produce steam. You seem to agree that the coal boiler is likely to be operated without a jacket, but your comments about whether boilers were tested with or without jackets miss the point. At best, if boiler ratings are developed without jackets, you need to make sure that the Peerless boiler is running without a jacket; otherwise, you're comparing a 130 with an oil boiler that has steam-producing capabilities above the rated capacity on the nameplate.
5. I expressed further concern about possible future capacity expansion needs. To me, it is reasonable to expect a growing family in a house that has undeveloped space may try to make use of that space. I still have the modines we intended to install in unheated areas of our last house. You seem to want to assume they'll never want to add a basement playroom or a 3rd floor teenager hangout or even a 3rd floor master bedroom, and that they'll be happy to just shut off radiators if their boiler selection is inadequate. I wouldn't want to make a decision on boiler sizing without having these considerations on the table up front.
6. I concluded by observing that bigger boilers may have efficiency advantages over smaller boilers if the bigger boilers have larger heat exchange areas that enable them to better capture the btu's generated by a given rate of coal burning. I don't understand the relevance of your comments about losing heat into the basement, since I thought we were talking about heat being captured by the boiler vs. going up the flue. Your comment about adding a heat reclaimer to the flue of the smaller boiler gets back to what I was talking about, but you ignore the part about "all else equal". Even if you hold aside the possibility of using a heat reclaimer with the bigger boiler, if you're saying you'd use a heat reclaimer with the smaller boiler to achieve the efficiency of the larger boiler, I think you've agreed with my original point.

Maybe some of our differences stem from differences between the makes of boilers that we're discussing. My experience with EFM's has been that they generally run pretty efficiently over a wide range of output below their maximum capacities. If your boiler doesn't do that, I can see how you might have a different view of the issues associated with running a bigger boiler.

Mike