Originally Posted by Truffles
Is there a very specific variety of water heater that is capable of this type of heat exchange? (i.e. transfer heat From Webasto Heated Coolent, to Potable Water, to Glycol) What kind of key words should I be looking for? Is this system rarely discussed because of some other problem that I have not recognized yet?
I can't answer your specific questions, perhaps I can help with what I have and works for me. I don't have a Webasto, I have an Espar.
I would think the heater would make water somewhere around 170° or so which is lower than what your engine makes. I used a heat exchanger similar to this. NOT this one in particular I think mine is 20 plate but, don't remember for sure. Do your own math.
It goes in the water lines from the engine that would normally go to the heater, the other end goes in the loop that your heater is in. It works both ways if heater is on engine is warm, if engine is running and warm heater loop is warm. I also have a marine hot water heater, in the heater loop, that has an internal heat exchanger.
I have been using this for over 5 years with no problems although some will say that engine temp is over recommended for pex.
There are some pictures here.