We're considering putting some frost potection heaters in a 12 metre boat, it's a pretty well insulated steel boat and a 5kW oil central heating system easily makes it uncomfortably hot without being turned up high. (not very scientific/accurate but it goves some idea).
Can anyone offer any ideas of what size electric heater(s) would be necessary to keep the interior above freezing? The engine is frost protected (anti-freeze in coolant) but there is other cold water pipework to the galley and loo which would be damaged if it froze.