"David Lesher" wrote in message
...


The VW ones were air to air; the inner exhaust pipe was cast iron,
like a manifold. The outer part was sheet metal and soon leaked, but
that was not a hazard...it just reduced the output.

I'm hoping to heat water with the exhaust. I saw one once; I assume it
had a tubing coil wrapped around the pipe, but just got a glance at
it years back.


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There are industrial ones that are pricey like these:
http://polarpowerinc.com/products/he..._exchanger.htm
http://www.ejbowman.co.uk/products/E...Exchangers.htm

I suppose you could also adapt a standard household gas fired water
heater. One of the ones with the helical gas coil inside would probably
be more efficient than the straight tube up the center type
Art.