Definition
A calorifier is a marine hot-water tank heated by engine coolant through an internal coil, by an electric element, or by both, storing domestic hot water for use aboard.
A calorifier recovers heat the engine is producing anyway. Coolant is circulated through a coil inside an insulated tank, heating domestic water while the engine runs, with an electric element for use on shore power.
What it means for the engine
The calorifier is part of the closed coolant circuit, which has two consequences owners forget. It adds coolant volume, so a coolant change or a bleed after work has to account for it — trapped air in a calorifier loop is a common cause of overheating after a service. And a leaking coil contaminates one circuit with the other.
What goes wrong
Coil corrosion, a failed thermostatic mixing valve, and air locks after coolant work. A calorifier that has gone cold while the engine runs normally usually means flow, not heat.
Where you meet it
On any cruising boat with hot water, and in the bleeding procedure after coolant service.