You said coal has a btu of 14000 per pound of coal well when i do the math on my harman stoker it doesn't work it according to what harman states. Harman states this unit has a 100 pound coal capacity and can provide 85K btu's for 17 hours or stretch out over 100 hours when less heat is required. harman also states that this stoker has a max burn rate of 8.75lbs per hour. lets look at the first stated fact from harman 100/17=5.88lbs per hour 5.88*14000=82320 btu but u figure around 70% effeintcy so that = 58800 btu far from the rated 85K btu output using there stated fact. onto the second fact they claim 8.75lbs per hour is the max feed rate of this stove which would produce 122500 btu input with an output of around 87500 btu. so if i use the second figures to actual produce that much heat per hour 100 lbs of coal will last 11.43 hours. So i'm i missing something or is harman misleading the public?