Stoker Coal Boiler that would best meet my needs

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.

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