>Actually in Britain "Condensing Boilers" are very common these days.
>They cool the exhaust gas enough to condense the water vapour and extract
>the heat from it.

There used to be a way to make the chimney in a cabin go around the wall
before going up. The condensing part had a slight downward! slope ending
in a syphon to remove the water and then turn up towards the chimney. I
have never seen a plastic flue but I have seen corrugated aluminium ones
(expensive). The condensate will cause everything to rust and corrode (it
contains sulphuric acid among other things).

Peter

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.