David Lesher wrote:
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.



Check the marine engines.
We do this all the time to keep salt water out of the engine cooling jackets.


--

Richard Lamb
http://www.home.earthlink.net/~cavelamb/