One other option that I haven’t tested because the boat ended up hauled for the winter: I recently installed a Webasto heat pump on the boat. (Possibly the most ludicrous over-kill gadget so far, but it came up on Craigslist at a price I couldn’t refuse...) This only draws five amps but there will be some lower (water) temperature limit for this system (presumably before the discharge water becomes super-cooled) and it remains untried by me. Because I’ve tee-d the discharge into the head through-hull, it might even have some minor ice-bubbler effect.
Coincidentally, I had to replace my domestic water heater a couple of months ago and the new unit has a heat pump. Seems quite efficient so far, but it does blow cold air into the laundry room. Brrr! Next summer, this ought to be a pleasant feature but for now I have to turn it off when I’m in there.
Coincidentally, I had to replace my domestic water heater a couple of months ago and the new unit has a heat pump. Seems quite efficient so far, but it does blow cold air into the laundry room. Brrr! Next summer, this ought to be a pleasant feature but for now I have to turn it off when I’m in there.