Another "Start Here"

basic concepts and designs for "rocket" combustion units can be found courtesy of Approvecho, here:

http://www.aprovecho.org/lab/pubs/arcpubs

remember to insulate the combustion areas
beware of dangerously high temperatures
use appropriate materials
refractory materials can be insulative, or not

Andor

p.s. as a last thought, I'd recommend everyone build a "tin can rocket stove" for cooking on before attempting anything more substantial,
here's a link to a page that will assist you in building one, with all the appropriate reinforcement of basic concepts
http://solarcooking.wikia.com/wiki/Rocket_Stove

Here's a publications page from a major heating vendor that contains a LOT of information about hydronic heating systems. No. 10 on the list (displayed latest first) specifically targets wood heating. They sell "modern" technology but the principals they discuss apply across the board.

http://www.caleffi.us/caleffi/en_US/Site/Technical_library/Idraulica_magazine/index.sdo

Rufus