Cruising in cold places means that you need a reliable way to heat your boat. A system that uses no, or little power is preferable. With heating in small spaces a C0 detector is essential, as is good air circulation. Always keep a hatch open.
Dispersing heat around the space is difficult on a boat, but not impossible. Caframo thermoelectric EcoFans make use of the heat generated by the stove to push air around without using electricity.
Below are the heating systems we're most familiar with, having had both aboard pino.
Diesel-fired forced hot air heating system: Forced air heaters are fitted with an electrically powered fuel pump, flame ignition device, forced draft combustion chamber and heat exchanger, fuel metering pump, and integrated control unit. Hot air is circulated through the boat via flex tubes to vents. They are compact, fuel efficient and make use of an existing fuel onboard(diesel). The downside is that they are not cheap, they use a lot of power on start-up, and they need to be run often otherwise they will clog up.
Solid fuel stove: A solid fuel stove requires space, a chimney on deck, and considerable heat shielding, but is a good option to heat a boat without electricity. A solid fuel stove also doubles as a cook stove, serving as a backup to the main stove. Solid fuel stoves on boats will likely be very small, and will have to be stoked often(esp wood stoves). Another thing to remember, is that you'll need to have space to store wood, or charcoal. Charcoal should be stored away from the stove in a metal, air-tight container. Wood should be kept dry, and cut small to fit into the small firebox. An option to keeping wood, is pressed wood logs, made entirely of wood byproducts from sawmills. They have long burn times and occupy less space. See our woodstove.