LsFarm wrote:I'd be currious how a number could be arrived at.. If the stove is just idling,, and the stove pipe is only warm to the touch,, then most of the heat from the burning coal is being absorbed by the stove body, and radiated into the room.. [ High efficiency]
But if you have the fire really 'cranking' then a much larger percentage of the heat from the coal would be going up the chimney... [poor efficiency]
So I'm not sure how you would rate a hand fired stove..
I know with the the 'Bureau of Mines Report' on the Axeman Anderson boiler,, they weighed the coal coming in, the ashes going out, the amount of water being heated, and how hot and how often,, and the heat going up the chimney.. pretty sophisticated,, especially for the date it was done [~1950].
Remember you have two efficiencies, the combustion efficiency and the operating efficiency. The first measures how well you are burning the fuel (coal) by measuring the combustion gases for proper CO and O2. The second measures production of Btu's, a measure of heat exchanger performance. The Bureau of Mines Report did both. 84-86% operating efficiency. Boilers have be tested in this way since the late 1800's, only the instrumentation changes, much easier to do today. And more accurate.
Measuring the Btu's of a stove or furnace is much more difficult, but it's the same idea, measure the heat produced for a given fuel input.