Stoker Coal Boiler That Would Best Meet My Needs

Northern Maine wrote:CORRECT STATEMENT/ADVICE! Thanks! How about two aa130 in tandem...would that work?!

From the perspective of summer/winter efficiency that solution seems like it might even be better. And particularly in the summer, since only one boiler would be required to run during the summer months. Others who have done this sort of thing will have far better insight here than I would though. If whistlenut says he recommends one AA-260 boiler, I would take his advice for sure.

Center Farms Coal would be my coal dealer....Only 5 miles from my house...$280 at ton

I was just thinking that if you had two 130K BTU boilers perhaps you could set up boiler #1 to initiate fire (turn on the fan motor) at a water temp of 170 degrees and shut off (the fan motor) at 180 degrees, and boiler #2 to fire at 160 degrees and shut off at 170 degrees. That way under lighter loads only boiler #1 would fire, but under heavier loads both boilers would be firing. Just thinking with my finger tips here. No real knowledge regarding multiple boiler installs or how to squeeze maximum efficiency out of them, as I stated previously.

Boiler #2 would for sure need a hold fire timer, as there would be some long intervals under which it would not be firing otherwise.

lsayre wrote:I was just thinking that if you had two 130K BTU boilers perhaps you could set up boiler #1 to initiate fire (turn on the fan motor) at a water temp of 170 degrees and shut off (the fan motor) at 180 degrees, and boiler #2 to fire at 160 degrees and shut off at 170 degrees. That way under lighter loads only boiler #1 would fire, but under heavier loads both boilers would be firing. Just thinking with my finger tips here. No real knowledge regarding multiple boiler installs, as I stated previously.

Im no genius at this either...I did set up/install my Outdoor wood boiler by myself, so I'm a little "handy" with straight forward stuff...but your idea sounds good in theory..Thanks! Im sure others will "chime" in on this as well and give input...that's what I like about this FORUM...Glad I found it!

I think the previous posts have touched on some of the good reasons for generous sizing of boiler capacity in this situation, including heat losses from the 3 buildings, potential DHW loads from 3 buildings (figure it takes at least 40k btu/hr of boiler output for each GPM of continuous DHW load), underground piping losses and losses from the outbuilding itself (whether or not it is insulated). To those I would add:

- if the wind and temperature conditions in northern Maine in the dead of winter happen to be worse than the hidden assumptions in the heat loss calculator you use, an undersized boiler could leave you cold even if the calculator says you should be fine;

- fly ash accumulation acts as an insulator on heat exchange surfaces. A January night when it's -30 deg and the wind is howling is not a good time to be reminded that you haven't yet done your mid-year cleaning;

- if you happen to get a marginal batch of coal, your boiler may not perform as planned;

- running hard with red ash coal can produce clinkers that with some stokers can interfere with coal feed and combustion efficiency;

- under the best of conditions, some coal boilers do not achieve proper combustion when operated at or near the input ratings claimed by manufacturers;

- if your fuel/air adjustments aren't optimal you may have either excess (cooling) air entering the combustion chamber or unburned coal, either of which compromises boiler output; and last but not least,

- an oversized boiler (with a larger heat exchange area) running easy can often satisfy a given BTU load with less coal than can a smaller boiler running hard.

For these types of reasons, and probably a few more that have been lost to the ages, most coal equipment installed during the age of coal heating looks like it is oversized by modern standards. The Dead Men didn't skimp on boiler sizing, and I think it's with good reasons that are especially important in the situation addressed in this thread.

Mike

P.S. I'll have to disagree with the idea that an EFM 520 running hard would provide the most efficient approach here. People are reinstalling EFM Highboys that have been out of production for over 50 years largely because their larger heat exchange area provides greater efficiency compared to a regular 520. I'd second Scott's view that the situation described calls for one of the bigger EFM's.

I agree with much of this. If it was me and I could not afford both a 260 K boiler (or 2 x 130K boilers) and the undertaking of a reliable heat loss calculation I would lean toward the EFM 700 for its comfort margin of surplus BTU's in this application. But a heat loss calculation may agree more closely with 260K, as the houses are not overly large.

In my opinion, even for an expert, calculating the potential and real underground BTU losses will be quite difficult to do properly. I would however imagine an EFM 900 or an AHS S500 to be overkill to an excess that is not required.

Thanks Mike! I Definitely DONT WANT TO UNDERSIZE! and As others have mentioned someday the needs of the three home will change. At this point in time my brother and I live in the two larger homes full time and my grandmother only from June to September...eventually her place will be a rental and much LATER the other two homes will be passed to another generation...SO I TOTALLY AGREE! Prior Planning Prevents Piss Poor Performance...that what my Senior Chief P.O. used to tell me when I was in the Navy!

One thing to me is fairly certain, and that is that if you have only 340 feet of total hot water baseboards, you will not be utilizing more than perhaps at best 200K BTU's of boiler output via the baseboards alone. And to achieve 200K of utilized boiler output through the HW baseboards alone you would presumably need to be running measurably higher than a nominal 180 degree supply water. That cuts down on the margin for safety and pressure relief.

The main unknowns seem to be the heat loss due to the underground piping, and the DHW requirements, along with the actual requirements for each of the three houses. Presumably the existing hot water baseboards have worked to maintain sufficient comfort regardless of the outside weather conditions in the past, and also with supply water starting at a nominal 180 degrees, so 187,000 BTU's of maximum boiler output has for the past umpteen years been sufficient (or perhaps even overkill) in this regard. Realistically, a trustworthy heat loss calculation may even point to the EFM 520. No one can know by guessing.

The only way we have determined the heat loss below ground to each home is through an in line temperature gauge at each home as it enters. We've written down the temps and compared to the boiler temp and thats how we cam up with the loss. Right now we are only running our current unit at 150 low and 160 high...Out side temp teens at night high twenties durning the day. In decemeber we bump up the high to 175 and low to 160. Jan., Feb. and March High 185 and low 175.

At to efficiency, a boiler idles at down to only about 20-25% efficiency (which is what you will see if you run one all summer), and it fires at perhaps 75-82% efficiency, so to me it seems logical to desire for the boiler to be firing more often and idling or just lumbering along less often. I could be wrong.

I'm willing to speculate that the result of most "honest" heat loss calculations is the discovery for less BTU need, vs. for more BTU need. Then again, I can imagine an unscrupulous HVAC outfit making a discovery that despite decades of past history and comfort, ones current system is not sized large enough to accomplish the task at hand. I actually saw this happen once, whereby a fellow employee where I work was instructed to replace his existing furnace with a larger one (and did). Bigger furnaces typically cost more and have larger profit margins.

AxemanAndersons and AHS boilers are self cleaning, they don't need mid season 'flyash cleaning'' . Their flu pipes may need mid season cleanings, mine does.
I would not recommend two 130's, the standby losses of a second boiler only coming online to make heat every couple of days would negate
any efficiency gains of one larger boiler. more coal used, more heat lost to the uninsulated building.
The only way I'd use two 130s woud be one in the larger well heated house, and one in the shed feeding the two other houses.

How many square feet is your father's AA260 heating ??

I'd keep an eye out for another AA 260, you can share spare parts, share knowledge and share coal stockpiles.

Keep in mind that the larger EFM's are not in production so only used and refurbished units are available the EFM 520 is still being made. to

Do you have space to add a large coal hopper for an AA or EFM to feed from??

Greg L

LsFarm wrote:AxemanAndersons and AHS boilers are self cleaning, they don't need mid season 'flyash cleaning'' . Their flu pipes may need mid season cleanings, mine does.
I would not recommend two 130's, the standby losses of a second boiler only coming online to make heat every couple of days would negate
any efficiency gains of one larger boiler. more coal used, more heat lost to the uninsulated building.
The only way I'd use two 130s woud be one in the larger well heated house, and one in the shed feeding the two other houses.

How many square feet is your father's AA260 heating ??

I'd keep an eye out for another AA 260, you can share spare parts, share knowledge and share coal stockpiles.

Keep in mind that the larger EFM's are not in production so only used and refurbished units are available the EFM 520 is still being made. to

Do you have space to add a large coal hopper for an AA or EFM to feed from??

Greg L

My Uncle has the AA260...heats and old farmhouse of about 5000 square feet....not well insulated, but some newer windows and he burns about 12 ton a year. Our current Outdoor wood boiler is in the outbuilding and is 16 X 26...it holds most of our 22 cords with some of it stacked and tarped outside of the building. I could insulate this building easily...I have the insulation to do it...but have not had the need too. Our coal supplier is only 5 miles from our house and delivers in bulk and thats how I would go...

Man, you are lucky to have Center Farms in your area. They are a class act, and don't take advantage of the special relationship they have with shipping. A win-win situation! I still say an AA 260 will be a cost effective investment. I have a little bit of experience with them, and they are all still running all these 40 years later, producing heat and hot water affordably and reliably. LS Farm isn't any fool, and he burns with one.....and he is more than a 'tank' away from Pennsylvania! I've seen more in Maine basements than most other states, and most are smart enough to keep them out of the water. Several I know of sit in a basement all hooked up, mothballed for the day oil goes nuts.......problem the owners have is that when they were installed in the 80's, they were in better shape and more coal dealer were around locally. Now in their 60's and 70's, winter is somewhere south of you....waaaay south.

Oh, I wouldn't worry about windows and insulation much in your situation....even the shop. It's always 82 in mine, and it does not care how cold it is outside.

LsFarm wrote: Keep in mind that the larger EFM's are not in production so only used and refurbished units are available the EFM 520 is still being made.

As far as I know EFM stopped making the bigger units in the mid-1980's, but I believe that new replacement parts for 900's are readily available from Mark's Supply. There also seems to be reasonable availability of good used components.

It probably should be noted that these units are built like industrial equipment, and have very long life expectancies with minimal maintenance. The "littlest" of the stokers on the bigger units - the S30 on a 700 - by itself weighs 375 lb, which is 160 lb more than the very substantial S-20 stoker on a 520. For most of the time since early February 2004 I have been relying year-round for heat and DHW on EFM equipment that is 50+ years old and so far have had to replace 2 shear pins. It's prudent to keep a few spare parts around, but most people don't need them very often.

Mike

ALL I CAN SAY IS THIS: We will be switching to coal....Handling 22 cords of wood every year after 8 years is Definitely getting old....Plus the wood is getting harder to find because so many people are in and out of that business so quick up here...not very reliable....and with Center Farms just across town I have no worries with getting coal! Anyone got any ballpark figures on some used units?