I have a Tarm OT-50 and I'm interested in supplementing my wood with coal. I have read the manual but other than that I have no experience with coal and know nothing about it. Does anyone on here have any experience using coal in an OT-50? I have heard of doing things two different ways. I have heard of people using a little coal with a load of wood to stretch the burn time. I have also hear people talk about burning just coal. I am potentially interested in both ways. According to the manual a load of coal could last as long as 12 or 14 hours. That would make the boiler very convenient. Any pointers people could give me would be much appreciated.
Burning coal in a Tarm OT-50
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TimfromPittsburgh
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We have a Tarm 502 which I believe is the successor to the OT-50. I have successfully burned coal (mainly anthracite) in our 502 with the addition of coal baffles which sorta convert the unit from a cross-draft burner to an updraft burner. With coal baffles installed, the combustion air and hot exhaust gasses are forced up through the bed of burning coal If you can acquire or make coal baffles for your OT-50 you should be able to burn coal successfully. I tried burning coal without the coal baffles also mixing coal with wood, but neither of those methods worked very well for me, too much coal remained unburned. I quit burning coal a couple years ago because I am no longerr able to find good quality anthracite.
I have a baffle in my boiler that I can move to change how my boiler works. I can change it from a cross draft to an up draft or a combination of the two. I tried to burn coal about a week ago and I noticed several things. It definitely gives much more even heat. I also noticed that my boiler holds a lot of coal. I put in 100 lbs of coal. That much coal didn't even fill the firebox up to the bottom of the loading door. The manual recommends filling to the bottom of the loading door. I think if I wanted to I could fit about 125 lbs of coal in my boiler. With the 100lbs of coal in my boiler I was able to burn for at least 24 hours. I have not burned coal before so I really have no Idea what to expect but the manual said I could get as much as a 14 hour burn from one load of coal. It seems to me like I have done twice that. I really like the Idea of stoking the boiler once a day and than not having to worry much about it. I had one major problem. During the day I would go down every couple hours and shake the grates and a little ash would fall through and I could see a warm glow coming through the grates. After running all night I had a lot of trouble with boiler. When I went to shake the grates in the morning I had a lot of trouble getting the built up ash to come through. From looking through the cleanout door it was obvious that I had probably 4 or 5 inches of ash built up, but when I tried to shake the grates they would drop much ash. Finally I cleaned out the boiler and what coal was left and what I found was there was a lot of ash in the bottom maybe 6 or 8 inches of it, way more than I originally thought. I also noticed that my trouble with shaking the grates was because mixed in with the ash were these really hard chunks. They were not black like the coal, they were white and a reddish color. It seemed like too much of this mixed with the ash was making it so my grates wouldn't move very well. When coal burns does it burn completely? If the boiler was working as well as it should, would I still get these hard chunks or would I just have finer ash? Since I have not burned coal before I don't know weather these chunks are normal or if my burn is not good enough. There are two different positions the manual recommends I put the baffle in the top of the boiler at. I tried the first one and the coal seemed to light up and heat just fine so I stuck with it. I'm just not sure now if I did things right or not. I did get a good consistent burn, but I was considering that maybe if I moved the baffle to the other position maybe everything would burn more completely and I would be able to shake the grates easier. I just don't know because of my lack of knowledge about coal burning.
TimfromPittsburgh
Member
Your experience with burning coal sounds pretty similar to mine. After about about three days of burning anthricite, the firebox would be almost full of non-burned residue including ash, rocks, slate and clinkers (the hard reddish chunks). SO I would have to let the fire go out and shovel out the fire box. I could extend the time between cleanouts a bit by shaking the grate aggressively until red hot coals were falling into the ash pit, but that technique was pretty wasteful. Good quality coal should produce around 10% ash by weight. I was getting way more than that. Sounds like your coal might have high ash content as well. I have read that clinkers form when the coal is fired too hot. Some folks claim that mixing unburned coal with hot burning coal (as one might do when stiring the coal bed with a poker) can also cause clinkers to form. You might want to try coal from another supplier and see if you get less ash. In general the smaller sizes of coal produce less ash. Are you burning anthricite or bituminous coal?
When coal burns, pretty much all of the carbon is combusted, but coal is not all carbon. There are varying amounts of non-combustibles in the coal that become the ash. It might be worth while trying the other position for your baffle and see how that works.
BTW: coal ash makes great anti-skid material. I saved all my coal ash to spread on our hilly lane when it became icy.
When coal burns, pretty much all of the carbon is combusted, but coal is not all carbon. There are varying amounts of non-combustibles in the coal that become the ash. It might be worth while trying the other position for your baffle and see how that works.
BTW: coal ash makes great anti-skid material. I saved all my coal ash to spread on our hilly lane when it became icy.
Chris Hoskin
TarmSalesGuy
We have coal grates available, but they won't be much good to you if you don't have the grate rocker mechanism. Coal has to have lots of air coming in from under the ember bed and a movable grate allows you to break up and remove the coal ash and clinkers. Without the shaker grates the ash builds up and smothers the fire. We do not have the shaker grate mechanism available.
I currently have the shaker grates. I didn't realize there was a shaker mechanism that went with them. My grates are all connected by a piece of flat iron with holes in it. One end of it has an extra hole and that goes closest to the door. I figured you just stuck the poker in the hole and shook it.
I am burning anthracite as that is what the manual recommended. It said that the bituminous coal contained more sulfur and could be dangerous if the gasses were to mix with moisture because it would form sulfuric acid and eat the metal of the boiler. After taking another look at my manual I discovered something that I missed the first time. When I open the bottom door where you would clean out the ashes there is a grate to keep the wood coals or the coal you are burning from falling out when you open the door. This grate has slots in it. Apparently they designed it with slots for a purpose. The manual says that if shaking the grates doesn't work very well to try to break up the unburned material by pushing a poker through the slots in the grate. My poker is too large to fit in those slots so I bought a piece of steel rod that was about 4 feet long and bent one end of it to form a handle. The second time I tried to burn coal I had much better results. I burned for about 7 days without much problem. I moved the baffle in the top of the fire box so it was at 45 degrees so I was getting more up draft. I found that every 3 or 4 hours when I went down to shake the grates a little I got much better results if I took the poker I made and pushed it through each of the slots all the way to the back of the firebox. Then I would shake the grates. The ash would fall through quite nicely and after only a few shakes I could see a nice glow coming from the grates all over the firebox. I burned 10 50lb bags of coal in 5 1/2 days. The only time I had trouble with ash buildup was when I got to the end of the coal and couldn't add anymore. Because of the amount of snow here I let the ash cool in the bucket for a day or so and then put it back in the coal bags. From 10 bags of coal I got about 2 bags of ash. I did notice something odd that I have not experienced before. The coal produces nice blue flame across the entire bed. After shaking the grates it appears like it would release a large amount of gasses because the blue flames would fill the firebox and start to snake up the stovepipe. Once about 5 minutes after shaking the grates I heard a bang that actually shook the house a little. I went downstairs and found the clean out door at the base of my chimney was wide open. I guessed that gasses from the coal were going up the chimney unburned and then when the flames snaked up the stovepipe it ignited everything and that is what blew open the clean out door and made the noise. Just to be sure I closed the clean out door and and leaned a stick of wood against it to make sure it couldn't just pop open on its own. Sometime the next day after shaking the grates I heard that noise again and went down to check and sure enough the clean out door was open and the piece of wood had fallen over. I'm not sure what to do about this. It does worry me a little because I don't want to blow my chimney apart. It also bothers me because if its combustible gas it could be a hazard if it were to leak into the house. And, if it is combustible then it means that I am losing efficiency because unburned gasses are going up the chimney and not creating heat.
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TimfromPittsburgh
Member
My Tarm 502, like your OT-50, has a vertical grate inside the cleanout door. Although my manual doesn't mention using the poker through the slots in this grate to break up the coal ash, that makes a lot of sense. The Tarm 502 manual also says not to burn bituminous coal but doesn't give a reason. Actually, bituminous coal with as low or lower sulphur content than anthracite is available. I did observe the blue flame you describe, although it rose only acouple of inches above the top of the coal. It was most prevalent after adding a charge of coal on top of the hot bead of coals. I have not noticed a large flareup of blue flame after shaking the grate nor have I experienced the "explosion" in the chimney that you described. I'm wondering if the coal you are using has a lot more volatiles that what I was burning. There's a really excellent forum on coal burning that I used to follow. I don't remember the forum name now, but I'll look it up and post a link.
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