Faster has it right! The heater in the loop will slow down how quickly you reach operating temperature but as long as your cooling system temperature thermostat is working there will be no problem. Hot water heaters using shore power usually heat the water to 120-140 degrees wheareas most diesels run at around 160-180 degress so the engine will be the "driving" factor. If you want hot water...go right ahead and buy a new heater and don't worry about your engine temps.
Oh..and a suggestion for the install. You will be running coolant lines to and back from your engine to the heater. Put in turn off valves at the engine side so in case of a leak in the lines, you can refill coolant and still run the engine with the heater out of the loop.
Last edited by camaraderie; 10-16-2006 at 10:50 AM.