I also had an instantaneous propane heater on a boat in the past. [Wallas- made for boats/cabins] It worked great, was mounted piggy-back on the back of the gimbaled propane stove/oven, and was next to the companionway hatch
and an opening port light. It had no flue through the deck
, so I only operated it when the companionway hatch
and port lights were wide open. Despite that, it would set off the CO alarm
clear across the cabin
. That was the end of that for me...
Fast forward to the present boat and our decision to go with the IsoTemp SPA model. We love it. The heat exchanger
is very efficient, and it holds heat quite a while too [48 hours after engine shut down and we still have to mix some cold for showers... I quantified heat retention and provided many other details in the blog post I linked in my first reply in this thread...]
Regarding your question of running the electric
element it off an inverter... I have- accidentally.... [900 AH 12VDC house bank; 2800 watt 120VAC Magnum sine wave inverter] Even though I ordered the unit with the lower wattage heating element [700 vs. 1400 watts 120 VAC] It still 'pegged' the meter for amps drawn from the house bank...
It does work great on the generator
and shore power
, however. [We have a 10kw built-in. I haven't tried it with the 2000 watt portable gen but I suspect that would power it no problem as 700 watts is way under the generator
capacity, and only a resistive load...]
[Note that you can order 220VAC elements too...]
I hope this helps.