What Is a Marine Water Heater?
The boat’s hot water tank - a unit that runs on both 220V immersion heat and the engine’s waste heat, delivering a ‘free shower’ on passage days.
A marine water heater is a pressurised hot-water tank in the freshwater system, and it typically has two heat sources. The calorifier coil is one of the neatest forms of energy recovery on board: an hour’s run is enough to have the evening showers ready.
The table below sets out the two heat sources.
Two heat sources
Source | When it works |
|---|---|
220V immersion element | On shore power or with the generator running |
Engine coil | When the engine is running under way, for free |
Immersion element failure is a classic: if it is switched on with no water in the tank, it can burn out within minutes. The rule is simple: never switch it on unless the tank is full. A slight drip from the pressure relief valve may be normal as the heated water expands; a constant flow points to a faulty valve or excess pressure.
For winter lay-up, the heater must be drained completely (freezing can crack the casing), and the immersion switch should be checked twice to make sure it is off. In season, the routine is straightforward: immersion heater when alongside in the marina, engine heat when under way; there is no need for both at once.