Stoker Coal Boiler that would best meet my needs

I have an AA260 in an uninsulated outbuilding, heating a ~4000 sqft house and a 2400sqft polebarn shop.

I think an AA260 would do the job that the wood boiler is doing quite easily.. but a proper heat loss calculation is needed.. and an evaluation of heat loss in your underground piping to each building.

A LL110 could be powervented, but a chimney is best. Since you once heated your house with oil, the
LL110 with it's backup oil burner is a natural for your application.

What type of heating systems and square footage are the other buildings?

Greg L

One of the other two homes is 1200 sq ft and only heated to 45 degrees because my grandmother is away in the winter....the other home is about 1700 sq feet...all 3 homes are baseboard hot water heat

22 cords isn't all that much really (tell that to the guys handling it! ) when it comes to outdoor wood boilers. Your heat load isn't anywhere NEAR 500k btu's/hr, if it was you'd be burning a lot more wood. Since all of the homes have hot water baseboard heat, start by measuring the radiation. Once you get the total feet of baseboard installed, you at least know what the load is on that end. Underground losses are a mystery, so I'd allow a buffer for piping losses.

Speaking of pex tubing, do you know if your tubing has an oxygen barrier? I assume it is hooked up with heat exchangers in the houses?

Rob nailed it! Begin with the baseboards. I believe that the output rating is typically calculated at 550 BTU's per lineal foot for hot water baseboards, assuming a 20 degree drop from 180 degrees to 160 degrees. If that is accurate, then the three houses would need a combined total of a bit over 900 feet of baseboards in order to accept a full output of 500,000 BTU's.

That said, coal boilers fire at a peak of about 80% efficiency, so a boiler with an honest max input of 500K BTU's would have a maximum potential output of about 400K BTU's. That output level can be handled (delivered to the homes) by about 725 feet of hot water baseboards. That's still a whopper load of baseboards.

If you assume that each home actually needs only about 85,000 BTU's worth of furnace input, then an AA 260 or AHS S260 should be plenty big. 260,000/3 = ~87,000 available intput BTU's per home (assuming here for simplicity that all 3 are quite similarly sized).

87,000 x 80% = ~70,000 output BTU's per home for 3 houses. Each home would require an average of 127 feet of baseboards in this case (totaling to ~380 feet), and this seems far more realistic. As Rob stated above, the biggest unknown will be the underground heat loss. You will also need some appreciable reserve for DHW if the boiler also supplies each of the homes hot water for showers, laundry, etc... A heat loss calculation is the only sure means to calculate all of this.

On an average winter day/night, probably about 15-20% of maximum rated output suffices to keep a home warm. The maximum output is only "potentially" needed when it is sub zero outside.

We rarely loose elctric service! 2 or 3 times a year...mostly in the summer months due to thunderstorms!

Rick 386 wrote:

Northern Maine wrote:
Wondering if the unit you mentioned can be power vented like my current oil boiler?

Most people will use a power vent for the oil burner as a backup heat source and run their coal appliance directly into the chimney.

Now since you call yourself Northern Maine, how stable is your electric service up where you are ??

Any "stoker Boiler" will need constant electricity to power the under grate fan to keep the coal burning. In a power failure, most stokers go out within 15 minutes. However the larger coal boilers usually have a larger bed of coal burning and at idle use the natural draft of a chimney to keep the coal burning. Our AA 260 will go at least 24 hours without electric before starting to die down. Of course without electric, you will not be running circulator pumps either.


As was mentioned, you really need to do that heat loss calculation.....................




Rick

Rob R. wrote:22 cords isn't all that much really (tell that to the guys handling it! ) when it comes to outdoor wood boilers. Your heat load isn't anywhere NEAR 500k btu's/hr, if it was you'd be burning a lot more wood. Since all of the homes have hot water baseboard heat, start by measuring the radiation. Once you get the total feet of baseboard installed, you at least know what the load is on that end. Underground losses are a mystery, so I'd allow a buffer for piping losses.

Speaking of pex tubing, do you know if your tubing has an oxygen barrier? I assume it is hooked up with heat exchangers in the houses?

YES...Cutting log length wood and splitting it is a big chore...plus when we installled our current unit we got our wood for $50 a cord...that has nearly tripled...so, the work plus the price increase is the true reason for our need to switch!

I don't know the actual rated input/output BTU figures for the EFM 700, but that would also seem to be a great choice here. It is probably a bit higher in output than an AA or AHS 260. Perhaps about 300K BTU's would be my first guess.

Rob & Larry,

according to measurements of baseboards in all three homes we have just about enough. Heat loss from the outdoor unit to each home varies from 3 to 5 degrees.

Northern Maine wrote:Rob & Larry,

according to measurements of baseboards in all three homes we have just about enough. Heat loss from the outdoor unit to each home varies from 3 to 5 degrees.

How many total feet of baseboards did you find? The temperature drop of 180 degrees to 160 degrees is for the boiler water, and it assumes that it leaves the boiler at 180 degrees and returns to the boiler at 160 degrees. For that specific case (considered to be the norm) you are getting an average of about 550 BTU's per hour out of each foot of HW baseboard.

Larry,

340 ft

340 feet of baseboard x 550 BTU's per foot = 187,000 boiler output BTU's per hour required. The AA 260 and AHS 260 should be plenty large. They are capable of delivering about 208,000 output BTU's per hour.

An EFM 700 would also work, and would have a bit more reserve to overcome the underground heat loss and provide plenty of reserve BTU's for DHW on those sub zero degree days.

An EFM 520 might even be all you need, particularly if you are only using the coal to heat the homes and not for domestic hot water (DHW for showers, laundry, etc...). At maximum output it should be capable of delivering 170,000 BTU's per hour. Though with your inevitable underground BTU losses this option seems the most iffy.

Overall efficiency should slightly favor the AA or AHS over the EFM 700. But if you can eek by with the smaller EFM 520 that route would seem to be the efficiency champ for this application. I would be hesitant of choosing the EFM 520 without first getting a professional heat loss calculation.

My initial guess is that you will need to burn about 12 tons of anthracite annually. Add perhaps 2 additional tons to this if you are also making the three homes hot water for showers, etc... via the boiler, and you are therefore firing the boiler year round instead of only during the winter months.

On an average heating season day you may find that you only need about 40,000 BTU's of boiler output per hour.

No DMH use in the 1200 sq ft home and that home is only kept at 45 degrees. 1600 sq ft home is only kept at 66 degrees and has DMH twice daily for showers. 1700 sq ft home is kept at 70 degrees and DMH use is 4 showers daily and a load of laundry daily.

Northern Maine wrote:No DMH use in the 1200 sq ft home and that home is only kept at 45 degrees. 1600 sq ft home is only kept at 66 degrees and has DMH twice daily for showers. 1700 sq ft home is kept at 70 degrees and DMH use is 4 showers daily and a load of laundry daily.

Some day you (or someone) will likely want to keep all 3 homes at a cozy 70-75 degrees. You will perhaps someday also want to provide all of the DHW for all 3 homes via coal. I would plan accordingly.

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

I'd opt for a single AA 260, especially since your uncle has one close by. You already know the reputation of these powerhouse boilers, and you could share parts if you ever needed any. I would not be afraid of either an AHS 260, any EFM product, Leisure line or Keystoker product. Arnie has new and rebuilt Van Wert boilers out in central, NY......They are outstanding machines also.
I am assuming you would buy a rebuilt one over a new one. Some of us know where there are any number of rebuilt units, or have the ability to get a brand new unit to your door......waaaaaaaaay up near the top of Maine.

Nice country that you live in......almost another world....Is pea coal affordable up there? Oak Farms are the guys aren't they?

Sending you a PM right now with a couple ideas.