Ahh I missed the nut coal comment before, what's why the stuff you found in the cellar was smaller. I only burned pea and anyone I knew did also-- the stove shop I bought mine from reccomended pea.
you seem to be getting good hot burns, but a LOT is going up the chimney. Maybe that's why you have to load so often?
You don't have much differential between griddle and stack temps tho. only ~ 100*? When my griddle is 400* my stack is 200@ 10" above the stove top, and about 150 at the chimney above the barometric. Al low sedttings, griddle is 190-200*, stack is about 150 and at the chimney it's not much warmer than body temp. I haven't run it hotter than 400 yet, not cold enough outside.
You prob could use a baro.
I the old days (ya I'm old!!) I had one stove on a centeral chiminey that had the boiler vented into it in the cellar--- boiler had a baro on it so it relieved the hi draft somewhat upstairs at the VIgilant. the other stove is where you see in the picture. A single flue for the stove only (no baro at that time), I had to crack the clean out door some to reduce the draft.
After my 22 yr coal vacation, I set them up with baro's at each stove, no dual use flues. They burn much better with the draft control from what I remember from way back then. both stoves are way cooler at the chiminey entrance, bigger stack/griddle differential. I can stick my hand in thru the baro with a 350* griddle temp, and the exaust gasses are just warm, not hot.
Hope all this rambling helps!
My kid brother has the Vigilant in a 24X36 cape house, he took a 22 year coal vacation too. He fired his up last Jan,Feb and march, burning the coal left in the barn from 22 yrs ago (not a drop of oil during that time!) . after seeing that I I decided to fire mine up this year. My house is older, not at tight and L shaped, so I needed the 2 stoves. So we are comparing notes this year getting the routine worked out after such a long time away from coal.
Well I'll shut up now, Been too long winded I'm afraid----------------