Looking for the best Coal stoker for my applicatiton.

I'm not sure where you guys are getting your efficiency numbers from, the Harman boiler I saw ran the flue gas cool enough to lay your hand on the pipe. If you purchase the oil gun option, Harman rates the efficiency as 84-85% with a 300deg flue temp, not too bad in my book.

I would also price in the options on the AHS unit, the belt drive blower option, the thermoash monitor and the hot water coil added almost $1000 to the price when I looked. My boiler with the hot water coil came in right around $4200 without tax.

FAX Jeff an order and follow up with a deposit check. Too good a deal to let go.

With the AHS or likely any boiler or furnace that uses a combustion blower all this concern about keeping the chimney warm is meaningless. It's forced draft. Why does the chimney need to stay warm? When the blower is not running you are not asking for Btu output and you don't need much draft at all. In fact if you have two much draft you use a barometric damper to get rid of it. Someone explain why a hot fuel applies to coal (NOT wood) burning. Remember all this insulated fuel chimney liner business is to solve a problem with WOOD appliances. Build the best, a masonry clay lined chimney.

Highlander wrote:I'm not sure where you guys are getting your efficiency numbers from, the Harman boiler I saw ran the flue gas cool enough to lay your hand on the pipe. If you purchase the oil gun option, Harman rates the efficiency as 84-85% with a 300deg flue temp, not too bad in my book.

Is that combustion efficiency for oil or coal? Is that temperature measured on the flue pipe exterior or in it's center? All important details. The A-A boiler in the two year study published by the Bureau of Mines in 1952 had the following temperature ranges: Boiler water 150-225 deg F. with corresponding center flue gas temperatures of 150-450 deg F. The AHS boiler because it's virtual clone would be very similar. If the Hartman has 84-85% combustion efficiency I'd like to know how they do it with only 300 deg. F flue gas temperature. Perhaps it's an average flue gas temperature.

Coal stokers still require draft to operate even though they have a forced air draft. A coal stoker operates on positive draft and requires a drafting chimney or power vent to operate. For a chimney to draft effectively the flue gas temperature at the top of the chimney must be higher than the ambient air temperature. Yes a stoker requires less draft to operate than a hand fired appliance does but it can't operate with no draft like a pellet appliance which uses a exhaust blower which creates its own draft. that being said an external masonary chimney can be insulated as well and would be mroe effective and draft better than a metal one even in warm weather.

I think Highlander is referring to the statements by some of the manufacturers that a cool flue during a burn is an indication of high efficiency - little heat is going up the chimney.

The AHS belt drive and DHW coil are valid comparison accessories to the Harman. I don't think the Harman has an ash temp capability - which is advanced and useful - but, isn't a comparable feature of the Harman.

So, figure $700 diff? That's 4.2 tons of coal at $165/ton or 420lbs/season over a 20 year life. Is the AHS that much more efficient per season? It's probably a wash.

It strikes me that that the 'value' of the various boilers for efficiency and durability is pretty accurately priced by the market.

jpen1 wrote:Coal stokers still require draft to operate even though they have a forced air draft. A coal stoker operates on positive draft and requires a drafting chimney or power vent to operate. For a chimney to draft effectively the flue gas temperature at the top of the chimney must be higher than the ambient air temperature. Yes a stoker requires less draft to operate than a hand fired appliance does but it can't operate with no draft like a pellet appliance which uses a exhaust blower which creates its own draft. that being said an external masonary chimney can be insulated as well and would be mroe effective and draft better than a metal one even in warm weather.

But the stoker with a combustion blower should not make heat when the blower is off. That's a fundamental design feature. I don't know the construction details of other brands but the AHS or A-A will only make appreciable heat when the blower is running. That's when the coal gases are really flaming above the coal bed and are being drawn into the boiler tubes, transferring the heat from the flue gas to the water. When the blower is not running the coal bed is just idling. Since it is not burning much during this time there is only a small volume of flue gas. No matter how insulated a chimney liner might be by the time any flue gas gets to the chimney thimble it will be cold. Perhaps even at the temperature where the flue gas temperature is below its dew point temperature. I have operational experience that this is true. When there is a no demand for heat for many hours, say 8-12 hours and the wind is still you get the characteristic sulfur smell. This means there are sulfur compounds being produced. Under the right still wind conditions it can be quite noticeable outside. I have to keep telling my wife, "it wasn't me dear". The reduction of heat production during the transition from the blower running to not running is not a step function. There is still some heat being produced and this is what causes temperature overshoot at the aquastat high set point. With a AHS or A-A boiler an insulated chimney would be a waste of money. What you want is resistance to sulfur compounds, i.e. a clay tile lined chimney.

I think what we are all expressing is our experience with are own stoves, boilers or furnaces. The subtle design differences and operating characteristics preclude a "one answer" fits all. What's great about this forum is we have the collective experience of many users, many brands and many appliance designs. If you understand the basic physics principles you can use this experience as it applies to your installation.

Yanche:

Where can I view a copy of the 1952 Boiler tests,I see this test referred to

many times but have not been able to find it on the internet.I would like to

see it and see how many boilers were tested at this time.


Thank You: BigBarney

Yanche you are right my experience is with boilers like the harman which combustion fan runs constantly which would require the chimney to draft at all times or you would get CO backing up into the house. The A-A and AHS are a different breed and do require less draft to operate. I definitely have to look at one of those when my central heating system needs to be replaced. I have a masonary clay lined exterior chimney it drafts very well even with temperatures in the upper 70's and for coal I wouldn't use anything but a masonary chimney.

BigBarney wrote:Yanche:
Where can I view a copy of the 1952 Boiler tests,I see this test referred to many times but have not been able to find it on the internet.I would like tosee it and see how many boilers were tested at this time.
Thank You: BigBarney

You can call Axeman Anderson and they will send you a copy, forget the Bureau of mines, they can't find it.

ph: 570-326-9114
fax: 570-326-2152
info@axeman-anderson.com

BigBarney wrote:Yanche:
Where can I view a copy of the 1952 Boiler tests,I see this test referred to many times but have not been able to find it on the internet.I would like to
see it and see how many boilers were tested at this time.
Thank You: BigBarney

The report is not on the Internet. It's 13 pages of text, one huge table of data and 23 pages of photos and plots. I'm converting it to electronic form. All of the difficult stuff is done, the table is now an Excel spreadsheet, the text was run through a optical character reader and the errors corrected. What I need to do is scan the remaining pages and then assemble it all in a single pdf file. I'm busy with many projects now, but I will get it done, surely by this fall. I believe it's a historically important document and should be more widely distributed. It's only about the A-A boiler, but much of the data applies to any residential boiler. Testing was done in 1949 and 1950 by the Bureau of Mines.

I did some research on the primary author, J.F.Barkley. He was born in 1888, a registered civil engineer, and Chief of the Bureau of Mines, equipment utilization division. In 1948 he received a prestigious award by the ASME. He's an example of a good engineer; he directed a well designed boiler evaluation and published the extensive data in a well written report. It's timeless.

I don't know how large a file the report will be. When I just scanned it as a simple image file it was huge, over 10 MBytes. That's why I'm taken the time to convert it to a spreadsheet and text. If it can't be hosted on this web site I'll host it on one of my own web sites.

I would like to have a copy of that!

BK

Hello MXer, if I were in your shoes I would want to go with a natural draft chimney. I would only consider a power vent for propane or natural gas. If I could afford to do it I would put up a clay lined brick chimney. They hold up better than the cement block and look much better in my opinion. My second choice would be a clay lined cement block chimney if looks were less important and cost was a big factor. Either one should give at least 40 years without any repair needed.

Because it looks like cost is a big factor in what you are doing maybe you want to put up a metal chimney first and then go with a masonry chimney 10 or 15 years down the road and save money to do it until then. In your situation I think you will have a lot of cost involved with a masonry chimney. You need a footer for the chimney, the siding needs to be modified and the roof cut out where you come up through the eaves not to mention your local mafia may want you to pay for a permit to do it. These are just a few things to consider.

All boilers mentioned here have stood the test of time, Harmon being the last one to come along but you don’t hear any complaints about them. All of these boilers are made in the USA and all of them here in Pennsylvania so you can’t beat that. If you leave your boiler run year round I would guestimate 6 to 10 ton of coal used per year. I base this on people I know and myself with coal heat and hot water. Big old farm houses can use up to 12 tons a year or a bit more and newer constructed and well insulated houses use about 6 tons for the year.

Good luck with your quest for cheap heat.

Berlin wrote:yup and if you get it the 316ti is the best, however i would still reccomend strongly against stainless if you can do masonry.

Hi Berlin , I have to agree with you on the masonary chimney for coal. I have the stainless metal chimney. From the top of the chimney , down about 12 inches , I had corrosion on the surface. I cleaned it up , and sprayed with high temp aluminum paint. The chimney cap had corroded apart , and also alowed rain water to activate the acid. I now have 36 inch diameter copper cap , which keeps the rain out. You can bet I'll be keeping an eye on it. Never had that problem with masonary chimney.

Oliver, how old is that SS pipe and was it 316?


(The local oliver dealer was a friend of my dad's in town and, very young, I remember gawking at them while they talked. One of those very pleasant bit memories. We were always 'oliver people'. There were lots of Oliver and F-A and only some green around here, then.)

I made a trip to AHS this Saturday and Jeff was kind enough to give me a personal tour of the facility and how the boiler is constructed. Needless to say, I left very impressed with the design and construction.... and the proud owner of a S130 system. Jeff and I spoke pretty much all morning on details of the boiler and how the design is based on an A-A boiler with a couple improvements. (Feed tube and how the Ash is sliced off the very bottom) The Water Jacket has a slight modification to help reduce the temperatures seen at the combustion fan. I can see why the belt driven fan is optional - direct mounting the combustion fan is less costly from a construction standpoint - no pulley's, belt's and associated mounting brackets and hardware required, plus the combustion fan itself is half the size. The direct drive spins at twice the speed and see's heat off the flue gasses which leads to the failure of the high temperature bearing over time. AHS replaces the standard bearing on the mounted side of the electric motor with a high tempature bearing. I elected to go with the direct drive because the bearing is less than $20 and should last 3 - 5 years. I did elect to go with the thermal ash option even though similar performance can be had with the standard timer based unit if you constantly tweak it based on how hard the boiler is operating. The thermal ash options make it more "hands off", extends the burn season and slightly improves efficiency. I believe the Harmon VF3000 to be a well built unit as well, but with the $1000 AHS discount that ends April 30th and including the Thermal ash option - a difference of $464.06 for 35,000 more BTU's seemed worthwhile. AHS also matched the trade in option that Harmon was giving me for my Magnum Stoker. Thanks for everybody's advice and I hope sharing my experience in picking a boiler helps someone else with their decision. Now onto the Chimney - should I continue that in this discussion here or make a new thread in the Chimney section? I'll keep it here since some discussion has already happened here.