Heat = energy, so problem being once you run up above 80% efficiency they say, draft becomes an issue. On older stoves, more waste heat can be recovered in some situations. Hence, I'm learning, pellet stoves are so dependent on fans. Plenty of ways to capture heat and the more you get into wood heating the more you learn about masonry stoves (russian, finnish, ect fireplaces), soapstone stoves versus metal, wood boilers, ect. Then of course different woods have different densities dry, mass being the largest factor of Btu output in combustion.
So draft tends to be the limiting factor on efficiency, you need to waste some heat, even masonry heaters will have exiting flue temps of a few hundred degrees.
Even having bought wood this year, still cheaper than pellets, which is cheaper than electric or propane. Only thing that comes close in Btu/$ is natural gas.
Rocket stoves are cool, masonry heaters kinda take that concept on high combustion temps for their efficiency, they just load it into a large thermal mass.
In the end, we all get heat off combustion, unless you got nuc electric or solar electric, so being trees are so plentiful in this state...
