There are several ways to get hot water on board, and I start with when you need hot water – while sailing, in harbor, or when the engine is not running.
230 V heating element
A standard marine water heater can have a 230 V heating element. This is convenient when on shore power. If it is to run from the battery via an inverter, the electrical power must be calculated into the battery, inverter, and cable – water heating requires a lot of energy.
Heat from the engine's cooling water
Many marine heaters have a heat exchanger coil so that the engine's hot coolant can heat the domestic water. This is attractive if the engine is running anyway, because the energy comes from heat that would otherwise need to be dissipated.
Diesel water heater / hydronic heating
A diesel-based fluid heater can heat a fluid circuit without the main engine having to run. Depending on the system, it can be used for cabin heating, a water heater, and in some solutions, engine preheating. Here, the pump, expansion tank, hoses, and controls must be planned as a complete fluid system.
How large a tank?
Look at the number of people, bathing habits, space, and how quickly the tank can be reheated. A larger tank provides more storage, but takes up more space and weighs more. Remember that water weighs approximately 1 kg per liter.
My decision-making sequence
- When does the water need to be heated?
- Which energy sources do you already have?
- How much hot water do you use?
- Where can the tank be placed and serviced?
- Should hot water be part of a larger hydronic heating system?
See water heaters · See Isotemp · See AUTOTERM fluid heaters · See 1852 diesel water heaters