The one I now have on my Morgan 33 OI is freshwater cooled, and the heat exchanger routes through my hotwater tank, which is about 15 gallons, and very well insulated. I only use about two gallons for a shower, and less for washing and rinsing the dishes. This engine is a reubuild from Moyer and installed in 2001. It runs like a Swiss watch, but has some blowby that I have to take care of this winter. I think the crankcase vent is plugged. Not a big deal to fix.
All the best,