I am in the process of building a stainless steel heat exchanger which will allow me to extract the heat from the exhaust gases when the generator is running to use for heating water with. I have two different approches to the heat exchanger issue. One would use a 1/4" thick pipe, the exhaust gases would pass through and it would be placed inside a 1/4" steel box tank, filled with Tin Lead (Solder) as the phase storage material. A 3/4" stainless steel tubing coil would also be placed inside the solder box. The generator exhaust gases (800 to 1200 degress F) would heat the solder which would store the heat for an extended period of time after the generator is turned off. Hydrualic fluid (Exxon NUTO 32) or (???) would be pumped through the 3/4" tubing, and to another coil that is wrapped around a stainless steel water heater tank in the house. Over temp valves would be used to control water temp from getting to hot (appox. 115degrees). The second approach would be to use an 8" diameter, .125" thick wall stainless steel pipe with baffles welded inside. The generator exhaust would pass through the pipe and the baffles would cause the gases to make contact with as much pipe surface as possible allowing the pipe to collect the heat energy. A 3/4" stainless steel tubing would be wrapped around the 8" pipe on the outside with the hydrualic oil running through it. There would be no Solder used with this exchanger unit. I feel the second choice may have problems with the oil getting to hot. Any advise on types of pumps, valves, or other ideas would be welcome. arcandspark

This seems like a *lot* of effort (and cost) for the heat gained.

I'm taking the "superheater" concept out of the coal boiler world and using the exhaust to add that little extra oomph to the hot water generated by the engine. Since you get better effeciency flowing hot to cold across a larger delta Tee, this would seem to be a better (cheaper, simpler, more effecient) path forward.

YMMV

d