An appliance will never deliver its Maximum Btu Output over it's stated Maximum Burn Time
The actual burn time of an appliance is based on the consumption rate of the fuel being burned. Less consumption = longer burn time.
*Essentially the overall heat output does not change per fueling. The hourly heat output changes based on the length of the burn time.
Heat output is based on the volume and Btu value of the fuel being burned - adjusted for the efficiency of the appliance.
Use the calculator below to determine the actual appliance heat output over the burn time.
Cell Color = Drop Down Cells				Cell Color = Default / User Input Cells
Select Heating Fuel To Be Used	Selected Fuels Btu per cu.ft.	Appliance Fire Box Size - cu.ft.	Appliance Total Btu Capacity	Stated Maximum Burn Time	Appliance Btu Input Per Hour	Appliance Stated Efficiency	Appliance Btu Output Capacity	Actual    Btu Output Per Hour
Anthracite High-volatile bituminous A High-volatile bituminous B High-volatile bituminous C Lignite Low-volatile bituminous Medium-volatile bituminous Semi-Anthracite Subbituminous B Subbituminous C						50% 55% 60% 61% 62% 63% 64% 65% 66% 67% 68% 69% 70% 71% 72% 73% 74% 75% 76% 77% 78% 79% 80% 81% 82% 83% 84% 85% 86% 87% 88% 89% 90% 91% 99%
Aspen Beech Birch - White Birch - Yellow Fir Maple - Red Maple - Sugar Oak - Red Oak - White Pine - Jack Pine - Ponderosa Pine - White Poplar - White Spruce Tamarack
Use the calculator below determine the adjusted heat output based on the adjusted burn time.
The Same Appliance, Capacity and Fuel - Adjusted Fuel Combustion Rate			Appliance Total Btu  Capacity	Adjusted Burn Time - Hours	Appliance Btu Input Per Hour	Appliance Stated Efficiency	Appliance Btu Output Capacity	Adjusted   Btu Output Per Hour
				1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 30 36 42 48 54 60
For coal appliances with no efficiency stated. the assumed minimum efficiency is 50 percent. The weight of coal is based on 50lbs / cu.ft.
Wood and coal burning appliances stated burn time and Btu outputs are usually based on burning high grade coal - not wood!
"Total Btu Capacity" = Fuels Btu per cu.ft. X Fire Box Capacity                               "Btu Output" = Btu Input X Appliance Efficiency
An appliance's efficiency could be the average or the highest value from anywhere in the appliances burn cycle.
*Efficiency typically changes based on combustion rate which can effect burn time and heat output.
** Calculations are incorrectly based on the assumption that you could fill the appliance firebox by volume completely. **
Calculator USES HALF as with a wood & coal burning appliance you can typically only use half of the fire box when burning coal.