Technical Question on the Harmon MK III

technical question on the Harmon MK III

PostBy: chet On: Sat Sep 01, 2007 12:05 pm

I have had my Harman MK III for 10 yrs or so, I was at a fair the other day and there were some stoves on display, I told the owner of the display who sells alot of brands that I was looking for another stove for my main level and that I burn a Harman MK III in the basement, I ask what he thought of the MK III his comments were it is a great stove with a minor issue and that the draft control in the center of the bottom door does not allow a complete burn around the edges of the fire, he did say a solution would be is to have to draft controls off to left and right of the original draft control so the air can get the sides better and get a better burn on the edges of the firebox. has anyone ever done this!


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PostBy: LsFarm On: Sat Sep 01, 2007 3:39 pm

From the posts on the forum, it appears that the cause of the incomplete burn is ash around the edges of the firebox that don't shake down as well as the ash in the middle of the grates.

In the center of the grates, the adjacent grates move in different directions, so it takes only half the movement compared to an end grate, to open up a gap for the ash to fall through to the ash pan. On the front and back and along the edges, the ash accumulates and eventually blocks the combustion air to the coal just above the ash.

Using a stiff wire, or small poker, stir the ash at the front, sides and back, and get it down to the grate where it can fall through. Once the ash is gone the coal will burn evenly all the way across the firebox.

I saw this 'problem' in GregWhite's SF150 last season. We made a small poker with a piece of 1/4" round steel rod. This worked really fast to open up the ash-clogged openings in the front grate and down the sides of his firebox. We used the small poker both from below the grate up through the coal bed as well as from the top down through the ash to the grate. Once an opening in the grate was cleared, lots of fine white ash sifted down into the pan.

Greg L
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

PostBy: Cap On: Fri Sep 07, 2007 8:41 am


I met the same guy a few years ago at the fair. West End, Right?

I used a Mark III for A few years and this may or may not be true, I don't remember.

I drilled two .5" holes in the ash door left & right of the damper control about 1/2". It worked great with this minor mod. I originally drilled 3/8" holes but they seemed too small.

You can always plug up the holes with a carbon steel bolt and nut if it allows too much draft. Give it a try.

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See small holes drilled. One has a bolt in it.
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

PostBy: dutch On: Fri Sep 14, 2007 3:37 pm

I've found with my Mark III that when I replaced the
window glass, I put gasket material around the whole
glass, instead of just the sides like Harman recommends.
This helped draw more draft up thru the coal, instead
of allowing air in around the glass, reducing draft.
I can't say as I've had a problem like you state,
but I'm still new at this, going into my 3rd season.
Hot Air Coal Stoker Furnace: Alaska Channing III

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