I recently attended a workshop called "pyromania" where the instructors have been exploring so many different building techniques and ways to heat and cook with wood, that they came up with this rather ingenious technique to heat your home.
Stealing ideas from mass heaters (aka "russian stove") and from rocket stoves (more of a cooking stove with its own rich history) and from building with cob (a mud made from clay, sand and straw) they came up with something that heats a home with ten times less wood.
For about $20.
While current wood stoves claim to burn something like 90% efficient - I think what they mean is that they have only 10% of the woodsmoke they would otherwise have. But I think 90% of the heat still goes out the chimney.
A mass heater fixes this by running the smoke from the chimney through a huge mass, so all of the heat stays in the house and the exit smoke is often hovering around room temp.
A rocket stove burns wood in such a way that it not only burns it rather completely, but it also burns and reburns the smoke. This makes it so that people can burn wood indoors without a chimney (another story for another day).
And let's add in one more thing: We want to push the heat down low. But heat/smoke rises (why a chimney goes up). But if you add some insulation at the right part, all of that rising heat becomes so powerful that you can then force that moving air in any direction you want - including lower than the fire.
So here is a drawing I made:
And ... while it looks crazy ... at the workshop they had about a dozen of these contraptions. Some had design flaws from ten years ago. One was built seven years ago that worked really well and we fired it up every day. In the morning, the mass was still hot. And the fires in these things were tiny. Just some sticks. No big blocks of wood or logs.