In my opinion insulation
is just as important as the heater. It is no use having a heating
system without adequate insulation
to keep it in. We did over winter in the Arctic (at 72 deg) and found with our steel
mono with 1 1/2" polystyrene insulation that it was inadequate when temps dropped below -25 deg Celsius. For your information the oldest day was -56 deg without wind
chill taken into account. We had a Dickinson
(Lofoten) heater. There is no doubt that the eberspacher heaters give more and quicker heat but our decision was to go the safe and sure (dinosaur?) method as I felt that there was to much that could go wrong with the hydronic systems and the voltage requirements to intolerant.
Things to keep in mind:
1.Even keeping batteries alive in the high - temperture's takes a lot of energy.
2. The window area on a cat would be a huge heat loss and I feel you would need to look at some form of double glazing. (Cut to fit foam will help as when the sun disappears for a few months you don't need to look out. Just remember that one small gap can let out 80% of your heating)
3. For a summer cruise
you don't really need a heater at all. It will just make life a little more comfortable and a hydronic heater would be the better choice.
4. Find out the real amount of fuel
that it will take to run the system you chose, from someone that has used one, not just the selling companies figures. When it gets down to -40 for a few weeks on end you are not running your heater on low and if you are iced in for 9 months and just use your heater sparingly it will use a lot of fuel
. Which brings us back to the batteries. You need some heat to stop them from freezing so you cannot afford to shut down the system to conserve fuel.
5. If your engines are salt water
cooled they will be useless as pumps do not move ice.
Someone may chip in here and say there are now batteries that can handle extreme low temperatures. That would be a plus.
Possibilities are endless. For example you may winter next to civilization and thus be able to purchase
diesel rather than have on board when iced in a few thousand litres. You could cut a hole in the ice (first year ice can reach 2.1 meters) for water
to run and cool your engines. Your head
outlet will be frozen. No trouble if you are away from civilization but a problem if you aren't. Consider also a sealed "porch" where you can step into, shut a door behind you, then open a door in front to step outside. Otherwise a large proportion of your heat will disappear every time you enter and exit.
I am not trying to be negative but just to point some things out that you may not have considered. We wish you all the best with your plans. Winter is the best time up there.
Hope this helps from someone that has done it.