A little heat can go a long way towards extending and enjoying boating into the shoulder seasons when the weather gets cooler and damper. A properly installed marine heater can provide that luxury, but not all heating sources are the same.
There are all electric marine heaters that operate the same as a convection baseboard and air to engine coolant heat exchangers that remove heat from the engine cooling system and use fans to transfer the heat to the cabin air. However, both of these types have limited applicability for most cruising boats. By far the most common types of marine heaters for cruising boats operate on diesel or propane fuels.
Propane heaters tend to be passive and designed to heat an area of the boat, usually the main saloon. Some have a small auxiliary fan to help move the heat around the space and there are circulation fans that can be operated in conjunction with this type of space heater.
Diesel heaters are available in two common varieties: forced air furnaces or hydronic heaters. In the case of forced air the furnaces heat air drawn into an air heat exchanger and a powerful fan forces the hot air through 3” or 4” ducting to areas of the boat. Forced air furnaces tend to be most effective if the furnace can be located so that the ducting does not have to be too long or convoluted.
Hydronic heaters have the advantage when trying to heat isolated areas, especially on larger boats with multiple cabins. They circulate coolant heated by the furnace and the heat can be extracted from the system using water to air heat exchangers at any or many points in the system.
PYS Electrical Technician