This is an eberspächer diesel heater - it works from diesel from the diesel tanks onboard. There are two theoretically very separate air circulations in the burner, one combustion circuit taking air from the outside of the boat and spewing exhaust out on the side of the boat, the other taking cold air from the outside of the boat and distributing hot air on the inside of the boat. It eats quite much electricity on fans and diesel pumps, and it produces quite some noise. One alternative would be a passive oven (running on diesel or wood, with a chimney going right up), but it takes more space and doesn't distribute the heat that well.

We've already spent more money than a new heater would cost on maintenance. Apparently the tubes for the combustion air got filled with water, and this has damaged the thing beyond repair. I'll try to have it replaced before the next season. It's a quite expensive thing, and installation is also quite hard, the latter can be solved by replacing it with a completely similar unit. Weirdly enough, the heater was working non-stop at full speed for about two weeks when we had a Polish visitor forgetting to turn off the heat before the yule vacation.

If I was to redo everything I would probably end up with a system where the heat is distributed through water rather than air. The current heater does not heat the hot water.

Theoretically I some five-six sources of heat on board, but only the diesel burner is good enough for keeping comfort temperature through the winter time.

The next source is the engine - the cooling liquid goes through the hot water tank and then through a heat-exchanger ("defroster") and then there is a fan and more tubes distributing hot air throughout the boat. The engine is 55 HP / 40 kW - that should theoretically be enough heat from it to keep the boat warm - but we're usually very light-handed on the throttle, besides I think the cooling liquid is first cooled down by sea water and then sent through the heating circuits, so a lot of heat is lost to the sea.

The third source is electricity. The hot water tank onboard is connected to the electricity, so to get hot water we either need to run the engine or be connected to land power. Usually the fuse at the land power trips at 2 kW or 3 kW - I could keep it reasonably warm if I could use all that for heating - but then I would have to disconnect the hot water tank. By average it doesn't eat much, but during the peaks it probably takes half of the available power from the socket. In the winter time I have quite many 200W heating elements distributed at strategical points in the boat to keep the water systems and engine defrozen while the boat is not in use.

Fourth, gas - we have a gas oven, of course mostly for making food, but I suppose if everything else fails, we could keep ourselves a bit warm by letting all the flames run on the gas oven, plus drink a lot of hot tea. Gas produces quite clean exhaust, but with quite much humidity, and humidity tends to be a problem in a boat in the winter time - while the hot air is relatively dry, there is enough humidity to create condensation on the windows and other cold surfaces, and in our sleeping cabins it tends to be much colder and very humid.

Fifth, the grill. Cannot be used indoors, but at least in theory we can produce hot food and even hot tea even if we're out of gas.

Sixth, people - every person onboard produces around 100W of heat. On the new years eve we were quite many persons onboard, in addition to some cooking and some candles it was hot enough without running the heater. People also tend to create quite a lot of humidity and CO2 though.

Not to forget the sunshine. Sailboats usually don't have a lot of windows, but our boat do have quite some, even in the winter time in Oslo we may gain some 5-10C from the sun shining through the windows.