Being familiar with the Bosch on-demand hot water heaters for residential use, I’ve kept an eye similar units for boats. However, they are typically propane-fired, and propane can be a rather limited resource on-board, best saved for cooking. There are also the diesel-fired hydronic heating systems from Webasto and Espar, and you can plumb them into a hot water tank heat exchanger, but that seems a bit complex to me. The first product I’ve seen that promises to be an on-demand diesel hot water heater is the WaterHeater from ITR (International Thermal Research). It’s kind of a hybrid actually, with a five gallon holding tank, and the ability to deliver a constant rise of 52 degrees at 1.5 gallons per minute. 316 stainless construction bodes well for it’s marine-grade intentions. A heating element can be added to the system for cabin-heat of 14,000 btu/hour, but with a draw of 5.6 amps, your battery bank might have to be pretty hefty to get you through a New England winter night.
Link: www.itrheat.com
