I suppose these propane hot water heaters are
doing your potable needs and your radiant heating too
they are hooked up in series and its always the way I hook up
two heaters together......
usually setting the first one on low and the second one on med to high
seems to work the best and you have better flow rate through
both of them than tieing them in parrell...
this is something you might have to turn up higher during the winter months
but it is the best way to do it...
I wonder how economical propane radiant heating with
those heaters will be??