Peter, thanks a lot for your advise. I think your desing will work better
I know about the risk of using hot water, so I plan to put security valves and a water pump to be sure that the water flow moves fast enough to prevent evaporating.
Do you think that with this I can take most of the heat from the exhaust gas or there is still enough heat lost to put another copper spiral in the horizontal exhaust?
You know if anyone use this design? I think that with the mass of the standar design you can extract more heat from the gas but it's more dificult to distribute in a house of 120 square yards, it's easyer with water pipes under the floor.
Do you have another recomendation to me? is there any plane with measures to do this?
Once again thank you very much for all your time and dedication you have to help others.
Marcelo