this is an old thread, but worth reviving.
I have a good deal of experience with the Harman I and Iron House Newcastle coal stoves.
you don't need a manual of baro flue pipe damper with a Harman I coal stove, it's internally baffled and will control the fire right down to a simmer at 3/8 turn open on the draft control. If you look inside the stove, in the top inside, there is only a 2" opening across the front of the upper roof, for exhaust smoke to exit. It's like having a manual flue pipe damper closed partially at all times. The smoke goes up, across the top, then DOWN, then out the back horizontally, then up the chimney. Very similar to an old baseheater, etc. system, that's why Harmans cost more and are so efficient. The draft air control on a Harman I is the most precise I've ever seen. It reminds me of the idle mixture screw on a carburetor. The sweet spot for a Harman I is 3/8 open for minimum low heat, and 3/4 turn open for maximum heat. This is assuming you have at least an 20' chimney or higher. You'll never use all the draft opening available on the knob. It turns open 6.5 turns but in the past 10 years, I've never had mine open more than 3/4 turn on the COLDEST days, when it was 30 below zero outside. At 3/4 turn it is really cranking. If you are burning it in the 1 turn open, perhaps you are burning it too hot. A good setting for average NEPA winter days is 1/2 turn open and just leave it there, it won't go out if fed coal.
1 bucket of coal a day, is not a lot, that's only 40 lbs. per day, or $4/day at current NEPA prices of $200/ton. That's only $120 a month and saving a ton of money compared to oil, gas, propane, heat pump. The nice thing about the coal stove is, it's cheaper and real heat. Electric, gas and propane heat are heat in name only, the floors in the house will still be cold.
On the subject of draft and dampers, I took the time to actually measure the draft opening on my Harman I where it spends most of its time at 1/2 turn open. The opening is .025" measured with a feeler gauge, all around the knob. The knob is about 3.75" wide. Doing some math, the circumference of the draft knob is 11.775" x the opening of .025" yields .3" square inches of draft opening, or 3/10 of a square inch- less draft intake area than the size of a POSTAGE STAMP when burning and heating my entire house. That's why the Harman I gets such great coal mileage, and many using that stove can heat all winter with only 2 tons. I've already managed to heat my home with only 1 ton during a mild winter in NEPA. The new airtight stoves don't use a lot of draft air. You don't need a flue pipe dampener, because there's not a lot of draft to dampen to begin with, when the stove is set up properly.
There is a tendency for newbies to over-draft and over-fire a coal stove, trying to get a blast of heat from it like a wood stove. Resist the temptation to fire it like a wood stove. Changes in coal stove draft must be done in increments - then wait until the stove gets up to that higher burning rate- and evaluate if that's hot enough. A newbie will tend to slam the draft wide open, it then over-fires, then slam the draft closed a half hour later, then it goes out because it used up all the coal inside.
Make small changes in draft and see how it burns. With any single knob-type draft, start at 1/2 turn open, from the complete closed position. Go from there.
You will be hard pressed to find a better free standing stove than a modern Harman. The door handles, hinges, latches, stove wall, legs, fan, etc. are all high quality and a lot better than most competing designs. To be quite honest I have never seen a better stove and have owned and fired many. I have many vintage stoves and the Harman I is built better, and operates better.
IMHO the new Harmans are better than the best tall standing vintage stoves such as the baseheaters. The downside of any stove with a huge firepot is, they eat a lot of coal. People that say they can put 4 bags of coal in their stove, 40 lbs. each, are spending more on coal heat than it would cost to heat with gas baseboard. The whole idea should be, use as little coal as possible, to get maximum heat, and burn the longest time.
When in doubt, buy a smaller stove, because small stoves burn less coal by design, and are inherently more efficient. The Harman I is a perfect place to start, and most likely will be the only stove you'll ever need. Ignore the claims of "bad service" with Harman, that is laughable, because with a Harman, you won't ever need any service. Mine hasn't needed so much as a nut or bolt in 12 years. All I've ever done was feed it coal, rake it down, and take out the ashes. Once a year I clean the pipe in the back, before starting it. I burn junk mail and old bills, bank statements, etc. in it throughout the year, so paper ashes builds up there. (a coal stove is a good paper shredder)
There's a tendency for neophytes and newbies who live outside the NEPA coal region, to complicate and mystify the idea of burning coal for heat. There's nothing mysterious about it, it's not rocket science. Just use trial/error and common sense, you'll be ok. If you have trouble controlling a stove such as over-firing, usually its leaking air from somewhere, and getting excess draft.
You mentioned a Newcastle stove, they are also a good stove, but not as well built as a Harman I. The Harman has bigger, stronger hinges, latches, stove panels, a stronger fan, better draft control, and a vastly better internal baffling system. Harman has auxiliary air inlets around the glass on the door, Newcastle does not. The baffle in a Newcastle is a simple piece of sheet metal set on 2 pins, and as designed is a bit too short to effectively slow down gas flow to the top flue pipe outlet. To get one to be more efficient, it needs a taller baffle installed, i.e. Newcastles need some tweaking to get them burning right, and a relative's Newcastle stove burns 2x what my Harman I burns in coal. Newcastles have a less precise slider draft control, and tend to leak draft air around the shaker control rod in the side of the stove, I had to make a special gasket to block air leaks there on a Newcastle. The Harman also has much better shaker grates. The round grates of the Newcastle tend to create clinkers, and the ash door must be opened to rake the Newcastle in both directions. The Harman I has a much beefier raking handle, and can be raked with the ash door closed.
Having said that, the Newcastle is a decent stove, just built simpler, and less expensive. A new Harman I today is $1850 plus tax/delivery. The used Newcastle we got for a relative, was only $250. We then had to buy stovepipe, front door seals, etc. but were still all in at about $350. So the Newcastle is a good low cost used alternative. Newcastles are no longer made new, they do rebuild them, Iron House of Cape Cod made Newcastle stoves, it was their own design, they now sell mostly wood stoves, but still make/sell parts for their old Newcastle line as well. If I found a decent Newcastle for $100 I'd buy it, but much over that I'd probably pass, because replacing the firebrick, seals, etc. in one is expensive.