On Mon, 03 Jun 2013 15:44:01 +0000, dparent55
wrote:

I live in Maine. My heating and hot water system is a bit unorthodox.
The system is designed around an 80000BTU/h hot water heater that is used
for both potable and hot water.


I am told that the system is not to code due to the mixing of potable and
HW. Can I install a heat exchanger between the two circuits? One plumber
says that code requires the use of a hot water boiler. Another plumber
says no. Multiple pro's seem to disagree.


Not seeing your system, it is impossible to say. It is possible and
done frequently, to add a heat exchange on a regular boiler to make
potable hot water separate from the heating system.

This is one of many systems that work with a regular heating boiler. I
don't know if it can be adapted to your setup or not.
http://www.amtrol.com/boilermate.html

Efficient boilers and heat exchangers here too.
www.energykinetics.com

Since you are still alive, I guess your system works, but no way would
I buy your house like that.