Here we go again, comparing apples and oranges.
Kcals = Kilojoules = Body Fuel.
Wax, Petrol, Diesel, = Fuel for a fire
Wax, Petrol, Diesel all burn into a flame in a different way, and give off slightly different fumes.
Same with Kcals/Body Fuel - Bottle of maple syrup will burn in a different way, than a plate of brown rice.