What makes you think it was tosh? If you start with a closed warm room  with a stove in it and a flue plus a means to replace air that is used in the stove then law of conservation of energy applies.   Say you burn 1.25kg of wood at 20% moisture content and have to use 100% excess air to do so cleanly. If we define cleanly as no visible smoke and 30ppm CO then we can assume chemical energy losses to be around zero. Also ignoring ash content of the original mass.   Then