The problem with trying to use your water heater for your heat source in a hydronic heater is that its thermostat is probably set at 120 degrees F. Your engine is probably 160 or 33% hotter. Your diesel furnace is probably even hotter. You'll not get much heat from your water heater. Having your engine, furnace, water heater, and cabin heat exchanger in a single loop sounds fairly workable, except that the engine is a huge heat sink if its not running, very wasteful to heat it. Valves to exclude it from the loop would save $s. Second thought, valves are probably not needed, just plumb the engine and furnace in parallel. Whichever pump is running will determine which circuit the water goes through.
The heating element of a 1500 w. ceramic forced air heater measures about 220 degrees by my infrared thermometer , compared to the less than 120 degrees you'd get from your water heater in a hydronic system.
I live aboard in the PNW on a 50ft sailboat. It has a 5000 BTU Webasto forced air heater that blows into the salon from under the companionway, nice and toasty when at anchor, but expensive for daily use in the marina. I added a 2nd 30 amp service to drive 2 electric heaters I keep under the salon table. One is the oil filled radiator type, the other a thermostat controlled ceramic type. I also have a 3rd small ceramic heater that I put outside my shower door before and during my showers. Its on its own ELCI breaker on the boats main AC circuit. I don't bother heating the cabins, I like it cool when I sleep. All three electric heaters are rated at 1500 Watts, but 2 draw 10 amps at 115V, the third is 13 amps. My water heater also draws 10 amps BTW but only cycles on once or twice a day and not for very long.
I turn the heaters off/down at night, and it takes them awhile to rewarm the boat in the morning. On really cold mornings I may turn on the diesel furnace to speed the heating.
The heating element of a 1500 w. ceramic forced air heater measures about 220 degrees by my infrared thermometer , compared to the less than 120 degrees you'd get from your water heater in a hydronic system.
I live aboard in the PNW on a 50ft sailboat. It has a 5000 BTU Webasto forced air heater that blows into the salon from under the companionway, nice and toasty when at anchor, but expensive for daily use in the marina. I added a 2nd 30 amp service to drive 2 electric heaters I keep under the salon table. One is the oil filled radiator type, the other a thermostat controlled ceramic type. I also have a 3rd small ceramic heater that I put outside my shower door before and during my showers. Its on its own ELCI breaker on the boats main AC circuit. I don't bother heating the cabins, I like it cool when I sleep. All three electric heaters are rated at 1500 Watts, but 2 draw 10 amps at 115V, the third is 13 amps. My water heater also draws 10 amps BTW but only cycles on once or twice a day and not for very long.
I turn the heaters off/down at night, and it takes them awhile to rewarm the boat in the morning. On really cold mornings I may turn on the diesel furnace to speed the heating.
