Steve Lusardi wrote:

If you use a
fresh water exchanger and your hot water tank is up to temp and you continue
to run the engine, the exchanger overheats. So you need auxillary cooling,
when your heat demand is low. I guess there is no free lunch.

??? Are you suggesting there are systems out there that use
the domestic hot water system as a heat sink for the engine
cooling requirements? Or that someone would install a heat
exchanger that is rated at a lower temperature than the
operating temperature of the engine cooling circuit?

Something is missing here.

Rick