The last few day, i've been reading about rocket mass heaters and pocket rockets. And realised that they are somewhat close to thoses stoves we have in france. There's two brands, Deom who makes an insulated round body, with a top air inlet with a tube going down into the fire. Ok you don't shove wood in the inlet, but it's not too far. They're mainly meant to work with offcuts and shavings, chips from woodworking shops, to heat up the shop. One could easily modify such a stove with a vertical feed of chips or else and do a heat riser onto the exhaust tube.
And the france turbo is an horizontal tube with a window in front, and the same type of tube feeding air into the fire, and they have a post combustion, with a tube inside which realy looks like a heat riser tube. Stainless it is. For thoses who can read french, http://www.france-turbo.com/presentation/principe.php You might have to enlarge the pic to read.
I might give a try to modify a deom if i can find a small one cheap enough.