Stoker Coal Boiler that would best meet my needs

Northern Maine wrote:In other words our Outdoor boiler (in the outbuilding) constantly pumps water to each homes oil unit

This seems to me to be merely another potential source for heat loss that is unnecessary.

The cost of eliminating the oil units to a hot water holding vessel would be astronomical I think!

Northern Maine wrote:The cost of eliminating the oil units to a hot water holding vessel would be astronomical I think!

Got it! Then since the system is functioning pretty much exactly as I have described for an indirect hot water tank system, then just run with it.

As I see it (given the information I have seen, and the way I have interpreted it, which is always subject to error requiring correction) the AA-260 should be adequate for your three homes needs.

Im not the most articulate person on explanations in this realm...but, your answer does put me at ease....THANKS Larry!

Northern Maine wrote:

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.

What I meant to say here and for clarification the 3 to 5 degrees is total for all three homes combined! Sorry!

I was taken aback by this response and perhaps in reaction I responded in a quite knee jerk fashion. Now that I've pondered it more calmly and carefully, does this mean that each home is individually seeing water that is only 1 to 1-2/3 degrees lower in temperature when it enters the home vs. when it first left the boiler (in which case my knee jerk response/solution that led to the AA-260 being acceptable is correct), or is the boiler water entering each home via its own separate and individual underground pipeline from the boiler at somewhere between 3 to 5 degrees colder than when it first left the boiler (in which instance the case for the EFM 700 being acceptable is correct), or are the homes somehow actually plumbed in series with the boiler, with each home seeing 1 to 1-2/3 degree colder water upon entry than the temperature at which it departed the previous home (in which case the EFM 700 case is still the valid solution)?

In other words, just what do you mean by saying that for all 3 homes combined the underground passage loss totals to between 3 to 5 degrees?

This is really quite the show! Lets get right down to it. IF you are meeting all your heating needs comfortably with 22 cords of seasoned OAK, you did say Oak and not some less worthy hardwood, then the BTU equivalent would be in the range of 11 tons of coal per year. Maybe less if you were using green wood, or a wood with less BTU's. The real eye opener would be the realization that the would boiler you are talking about operates in the 45-50% efficiency range. Most coal boilers that are being mentioned operate around 80%. That brings the BTU equivalent load down to 7-8 tons of Pa's finest. All of a sudden, the adjustability of the EFM 520 or larger is the more practical choice. Oh, and how does burning 25 lbs of coal an hour end up giving a rating of 175K btu's. That is more like 250-300 k gross by my calculator.

Scottscoaled wrote:This is really quite the show! Lets get right down to it. IF you are meeting all your heating needs comfortably with 22 cords of seasoned OAK, you did say Oak and not some less worthy hardwood, then the BTU equivalent would be in the range of 11 tons of coal per year. Maybe less if you were using green wood, or a wood with less BTU's. The real eye opener would be the realization that the would boiler you are talking about operates in the 45-50% efficiency range. Most coal boilers that are being mentioned operate around 80%. That brings the BTU equivalent load down to 7-8 tons of Pa's finest. All of a sudden, the adjustability of the EFM 520 or larger is the more practical choice. Oh, and how does burning 25 lbs of coal an hour end up giving a rating of 175K btu's. That is more like 250-300 k gross by my calculator.

I'll grant that 175,000 BTU's at the output end was incorrect, but perhaps we are both wrong, though at roughly equal but opposite extremes of the truth. The EFM website says 25 lbs per hour yields 214,690 BTU's for the DF520. Are you willing to state without a real heat loss calculation that the 520 is going to be adequate for all of their needs clear down to sub zero weather? If the 214,000 BTU figure for the 520 refers to output then I will grant that this places the EFM 520 at virtually a BTU output dead heat tie with the AA and AHS 260's. My error here was in assuming 214,000 BTU's to be input, for which 175,000 BTU's of output sounds quite fair. Most heating appliances seem to be listed by their input BTU's, so I was only going with what I assumed to be the norm when I assumed the same for the DF520. It's rare to see a stove/furnace/boiler rated as to its true output BTU's. I commend EFM in doing so. The AA and AHS boilers are rated as to their input, not their output.

The 215k btu site info is IMHO, a way of covering their butts if poor quality coal is being used. Nobody wants to spend "bucku bucks"on any coal burner to find that it is undersized. From what my limited experience is, it is only 5 years of coal burning, most of the coal that is sold by name brand mines/breakers is considerable higher in Btu's than the 8600 Btu/lb. figure that is used to come up with the 215K btu. Every coal that I have tried in the last year with the exception of one poor excuse for coal was rated at least at 12800 btu's per lb. That alone make the 25 lb/hr. a a different story. One other factor to consider, that while the units you are championing are more efficient in the flat out burning like hell category, they are remarkable losers in the stand here and sit on the timer waiting for the heat call category. That category includes everything but the coldest part of the heating cycle. The other 9/10's. The March thru November time. You are right about the heat calculations though. But my simple formula for figuring it out somehow doesn't get the radiant fin to be more than the outside perimeter of the houses combined. There are doors there, You know!

On a dry basis anthracite is typically rated at about 13,350 BTU's per pound. But most coal in the real world is actually about 6% moisture by weight, so it actually yields up about 12,250 btu's per pound in the real world due to this. 12,250 BTU's x 80% efficiency = 9,800 BTU's.

25lbs. per hour consumed x 9,800 BTU's/Lb. = 245,000 BTU's of output

245,000 BTU's should be roughly the realistic output limit for 25 lbs. per hour burned on an output basis. That would make the DF520 noticeably larger in output measure than either the AA or AHS 260, and would agreeably also make it the better (and likely the best) choice in this application. 245,000 output BTU's adequately covers their baseboard plus underground loss needs (201,000 BTU), as well as their DHW needs (32,000 BTU) with some room to spare.

Based on this new (to me at least) insight the EFM 700 must be a monster.

Guys,

We are all trying to calculate his heat loss for him. He needs to do this on his own. He already said he heats with 22 cords of wood. But only has 1 place at 45*, another at 66* and finally 1 at 70*. Now we all know that once hooked to coal, he will be raising his thermostat.

He needs to do this heat loss calculation based on Sq. footage, baseboard length, windows, etc. I'm sure some programs have Maine's upper county's heat requirements figured in.

We are all guessing and estimating. We need some cold hard facts that only he can provide. Lets not over analyze this.......................




Rick

lsayre wrote:On a dry basis anthracite is typically rated at about 13,350 BTU's per pound. But most coal in the real world is actually about 6% moisture by weight, so it actually yields up about 12,250 btu's per pound in the real world due to this. 12,250 BTU's x 80% efficiency = 9,800 BTU's.

25lbs. per hour consumed x 9,800 BTU's/Lb. = 245,000 BTU's of output

245,000 BTU's should be roughly the realistic output limit for 25 lbs. per hour burned on an output basis. That would make the DF520 noticeably larger in output measure than either the AA or AHS 260, and would agreeably also make it the better (and likely the best) choice in this application. 245,000 output BTU's adequately covers their baseboard plus underground loss needs (201,000 BTU), as well as their DHW needs (32,000 BTU) with some room to spare.

Based on this new (to me at least) insight the EFM 700 must be a monster.

I agree on the 12,250, but I think there are 2 additional things that need to be taken into account. First, I think an S-20 may have trouble achieving an orderly burn of 25 lb/hr using rice as called for in the manual. The old spec sheet I'm looking at recommends 20 lb/hr (which happens to be the max feed rate using buck). The auger will feed rice at a faster rate than that, but it may not get enough air to burn. I haven't seen many people claim they run at 10 teeth on rice.

Second, the old school literature points out that in an optimal burn (counter-intuitively) 10 to as much as 20 percent of the coal will go unburned. A percentage lower than that indicates the fire is getting too much air.

So the reasonably achievable gross output of a 520 would be something like 12,250 x 20 x 0.8 x 0.875 = 171,500 btu/hr. That's pretty close to EFM's current claim of 171,750 btu/hr at 8 teeth (20 lb/hr). In the old days, I think they used more like 15% unburned, and claimed 166,400 btu/hr gross output at 20lb/hr.

Using the same approach a 700 would be 12,250 x 30 x 0.8 x 0.875 = 257,520 and a 900 would be 12,250 x 35 x 0.8 x 0.875 = 300,125. I think in practice the 900 may achieve greater efficiency relative to the 700 due to its greater heat exchange area.

The 520 is still a powerful machine, but I wouldn't count on it to carry anything close to that estimate of the load. The 700 and 900 are more powerful machines, and - depending upon the actual load - look like better candidates.

Mike

We are back to the most likely candidates being the AA-260 or the EFM 700, but they really need to do a heat loss analysis.

As to how much coal they might burn during an average winter season:

If they burn a nominal 22 cords per winter at 45% efficiency.

22 x 20,000,000 x .45 = 198,000,000 output BTU's

Despite my AHS S130 burning at a maximum efficiency of around 81% at the peak of firing, it exhibits an overall winter season efficiency closer to 65%, as can be seen from a previous post of mine to a different topic. I will use this as the ballpark system efficiency of any of the coal boilers being considered here.

198,000,000 / 0.65 = 305,000,000 input BTU's required

305,000,000 / 12,250 BTU's/Lb. = 25,000 lbs. of coal

25,000 / 2000 = 12.5 tons

lsayre wrote:

Northern Maine wrote:

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.

What I meant to say here and for clarification the 3 to 5 degrees is total for all three homes combined! Sorry!

I was taken aback by this response and perhaps in reaction I responded in a quite knee jerk fashion. Now that I've pondered it more calmly and carefully, does this mean that each home is individually seeing water that is only 1 to 1-2/3 degrees lower in temperature when it enters the home vs. when it first left the boiler (in which case my knee jerk response/solution that led to the AA-260 being acceptable is correct), or is the boiler water entering each home via its own separate and individual underground pipeline from the boiler at somewhere between 3 to 5 degrees colder than when it first left the boiler (in which instance the case for the EFM 700 being acceptable is correct), or are the homes somehow actually plumbed in series with the boiler, with each home seeing 1 to 1-2/3 degree colder water upon entry than the temperature at which it departed the previous home (in which case the EFM 700 case is still the valid solution)?

In other words, just what do you mean by saying that for all 3 homes combined the underground passage loss totals to between 3 to 5 degrees?

each home is individually seeing water that is only 1 to 1-2/3 degrees lower in temperature when it enters the home

Good morning all...each and every one of the posts on this thread has been very helpful in my gaining knowledge to my eventual install of a coal boiler...thanks to all of you! Keep them coming! Further, if I was rich, I would purchase one each of all of the boilers mentioned and try them out! I have read and watched videos on several of the aformentioned coal boilers and I like them all. The each have some very neat and unique features and atop that I love watching heating machinery work! When I retire...I would love to refurbish and work on any of these units....I like them and the cause they support that much!

Can you explain the system that distributes the heated water to each house?

If it is pex tubing, what size?
How long is it?
Heat exchangers?
Circulator size?

You can have the biggest boiler in the state of Maine, but your distribution system can only move so many btu's.