The right marine heater depends less on what's available and more on how you plan to use the boat.
Four systems dominate marine heating, each with a real tradeoff profile. The wrong choice shows up as condensation, fuel anxiety, dead banks at anchor, or nuisance shutdowns mid-passage.
Wood/coal stove (Dickinson, Sardine). Cozy, off-grid, no electrical dependency. Requires a stack through the deck and someone tending the fire. Not for unattended overnight. Best for at-anchor and traditional sailboats where ambience matters.
Propane catalytic (Force 10, Olympia). Quick install, clean burn, low electrical draw. Tradeoffs: oxygen consumption in a closed cabin, condensation from combustion vapor, and ABYC-required propane locker + leak detection. Good for shoulder-season weekend use, less so for liveaboard.
Diesel forced air (Espar, Webasto). The bluewater standard. Runs off the existing tank, heats unattended overnight, dry heat. Real costs: 10-20A startup draw on the bank, dedicated combustion air intake + exhaust through-hull, annual burner servicing. Plan bank capacity around it.
Hydronic (Webasto Thermo, Hurricane, Sigmar). Diesel boiler heating coolant pumped to radiators in each cabin — and to the domestic hot water tank as a bonus. Most efficient whole-boat heat, multi-zone, quietest. Highest install cost and most plumbing complexity. Best for full-time liveaboards or expedition boats.