the logwood boiler by marathon heater company

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New Member
Nov 4, 2007
Blairsville PA
I have a logwood boiler from marathon heater company. I am having difficulty getting used to the natural draft control (ammark control). I have not found the "sweet spot" yet . It seems that I have the fire roaring or it tapers down (not smoldering). I am currently burning seasoned wood (cherry/oak) but I may switch to coal. ($38 a ton in PA). The unit I have is the large on that can burn 36" logs by 10" diam.
Overall I am happy with my purchase it burns long and hard. But I need to get this setup fine tuned.
I had one of those (the smaller one) for about 9 years and the Ammark draft control was one of the things I really liked about it. I liked the idea that as the boiler got hotter, the air supply became correspondingly getting smaller.

However, I did notice that when the boiler was cool (like in the morning) the draft door would be wide open and you'd get a roaring fire that would shake the house and I was afraid I'd overheat the chimney.

So I installed a conventional damper in the stovepipe connecting the boiler to the chimney. You can play around with the damper until you get the right draft for conditions. Cost you about $8 and 15 minutes of your time to try it. It's really nice on really cold nights because you can throttle the boiler back and get a longer burn without sacrificing draft.

I don't know enough about coal to know whether a damper would be safe when burning it, however. You might want to check that out; CO is nothing to fool around with.

If you have a problem with the boiler puffing smoke when the draft door is completely closed, I've got a solution for that, too. It was a problem on mine because I had the oil gun option.
My solution was to take the oil gun out and plug the tube with a 4" pipe plug. There's not much point in leaving the oil nozzle in there anyway because it fouls up pretty quick if you do. Plus, the gun I had (a Beckett) allowed air into the firebox at all times. It had to. When the draft door shuts, volatile gasses are produced in the firebox and when they come in contact with oxygen, they explode, making a series of little smoke puffs down through the grates and out the draft door and into your house. On a small scale it's no big deal, and that's usually the case. However, you can wake up or come home and find your basement full of smoke.

OT, I thought the grate design on the Marathons was a really innovative idea. It's just cast iron pipes cut to length. If you ever need to replace the grates (doubtful), any place that sells cast iron pipe can give you what you need for cheap.
I can only get my boiler in the 180-190 degree range. marathon recommends the 200-212 range for secondary combustion. can you help me get the temp. up. I am burning seasoned cherry and oak.
That's true, that's what they recommend. I ran mine at those temps, or tried to whenever possible.

I'm not sure I understand the problem. If you set the Ammark to that it doesn't close until the boiler hits 212, then it should get to that temp before closing, especially if you have dry wood. Are you saying that you don't know how to adjust the draft control, or that the boiler never gets hot enough to close the door?

If it's a question of adjusting the Ammark, have you tried shortening the chain a few links? That would be obvious if you installed the boiler yourself, but maybe not if somebody else did it for you.
Shorten the chain by a couple of links is all you have to do. Just re-attach it at a higher point so that the draft door stays open longer.
No, the chain attached to the rod coming out of the controller unit on top and attached to the draft door down below. the weight of the door gave it the little tension it needed.
Eric, that is how mine is now! thank you for the insight. can you help me I need your recommendation on an aquastat for my boiler marathon recommends a honeywell L4006B or L6006A set a 205 degree (min) with a 5 degree differental. What aquastat is the better one. What are the pros and cons of each.
What are you trying to do with the aquastat?
I am running my wood coal boiler (logwood) in parallel with my burnham oil boiler. I want to controll my circ. pumps (taco) manufacture recommend min 205 degree with a 5 degree diffrential. I am in the process of running in floor pex tubing with my baseboard hot water heat. I am zoning out my house, basement, and I want to run an insulated pipe to my garage radiators and convectors. I am also thinking of getting a coil for my logwood boiler to heat my hotwater tank. I have zone valves, tempering valves, etc. I just wanted to know what the difference there was with the aquastat's
I would go with the 6006A because it is switched SPDT, which means that it works either way--it can either make or break the connection on temp rise. The 4006B, on the other hand, only makes the connection on rise. So if you're going to spend the money, might as well get a stat that can do two things, instead of just one.

The differential on both aquastats is adjustable. 5 degrees is the minimun setting. I think they go all the way up to 35 degrees on the differential.

Compare for yourself at the Honeywell website:;={2EB2F178-20ED-44E0-97FB-CCFB4218DD64}

I'd shop around on Ebay before shelling out more than $60 at a heating supply house. You can probably score either stat on Ebay (new) if you're patient, for less than $20. Other than the switching differences, they're essentially the same part.
thank you. Any recommendations on chimneys. I am building a double chimney. I am going to run a rigid stainless steel pipe insulated with thera mix.
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