Your system sounds like it needs to have some time to teach you about adjusting it. Long runs for the house, however the loss should not be an issue, and an active dump zone....all good logic and piping.
Understand that your coal usage is still less than half of what oil or gas would cost- wise; so don't think a bag a day will satisfy a heat loss of 80K.....plus hot water production.
Without a heat loss, you are flying by the seat of your pants, and that may well be fine, so relax, and learn as you burn. History for next season is what you are recording right now.
I suggest you keep a log of daily usage as best you can, and/or install a run-time meter on the stoker motor.
If you are using 100 lbs a day that produced 100 times 13,000 btu's per pound/24hrs or 55,000 btu's per hour. 55K/13000=4.25 lbs/hr.
Oil would require the same btu, but run time would not be at 55k/hr so now you have 1,300,000 btu requirement and 134,000 production per hour of boiler run time...or about 10 hrs a day of run time.
Ten hours through a 1.00 gph nozzle or 10 gallon times $3.50+/- or $35.00 a day with oil. 100 lbs of coal at $7.00 a bag...or $14 a day for coal.
Simple numbers, rounded off, but coal is producing more radiant heat off the boiler, thus surrounding areas get 'conditioned' as a benefit.
Comfort level: PRICELESS!