[TheForge] Heat extracting chimney

[Dragons Watch Forge]

While living in northern Calif the house we lived in had a roof mounted 
furnace / air conditioner.  The furnace had such an efficient heat 
exchanger that it required an exhaust fan for the burner side of the 
unit.  The fan was plastic.

    I wish to build a fire place and chimney that has a heat exchanger 
in it that is this efficient.  Any one out there done this?  Any sources 
of reference materials or plans that are available?

Thanks!

Larry