After much research I finally installed a dhw coil in the Hitzer. My set-up is well water into 50 gal holding tank, thru coil, back to top of tank. The holding tank is then plumbed into a 66 gal hot water heater about 20' away.
I will say it was slow to heat but seems to be doing fine now. I guess heating cold well water takes a lot of energy… I haven't turned off the electric water heater as of yet but I doubt it's working very hard.
Sorry about the sideways pics.