Your first and third statements are demonstrably false. (Your second statement is a little garbled - did you mean to say that it takes more fuel? - so I won't comment upon it.)
The combustion of human remains is without question exothermic, i.e., it yields a net plus of calories (energy).
To be sure, some initial input of energy is necessary to get the process started - and, in fact, because of the high water content of human bodies, the process may not even be self-sustaining (depending upon how well-designed the combustion chamber is; as little heat as possible should be allowed to escape through the chimney - rather, the flue should be equipped for heat recovery, this recovered heat then being returned to the combustion chamber), but it still has a net energy yield.
Consider: Carnivores eat animal cadavers, and "burn" them in their digestive tracts (in a very inefficient process that doesn't even yield ash as a final product, but rather feces which themselves still have a relatively high caloric content) - yet still don't starve, which they would if it were an endothermic ("energy-consuming") reaction.
Regards,
Good points.
100 pound person, 60 pounds of water, 1150 btus per pound to vaporize the water = 69,000 btus.
40 pounds of dry matter left. Let us assume, possibly inaccurately but no doubt conservatively, that one pound of dry human matter produces as much heat as dry wood when burned, about 8600 btus. Therefore, the 40 pounds of dry matter should produce about 344,000 btus, leaving about 275,000 after vaporization of the water to contribute to the heating of the building, assuming all heat is captured, which of course it isn’t.
So I appear to have been in error. Human bodies can be used as a source of fuel. I think I jumped to this conclusion because of the very large amounts of fuel used in cremation. But of course the purpose of cremation is not to provide energy, it’s to reduce the body to as small an amount of ash as possible, so they pour on the fuel well beyond what is needed just to burn the body.
Mea culpa for jumping to conclusions. In my partial defense, I think it is logical to expect that the actual contribution of baby corpses to heating of the facility is minimal.