I'm not buying that for a minute.
Sorry but, that's not my opinion... that's physics. As you yourself observed later in your response, all of the electricity used goes into making heat.
Short of actually burning dollar bills, running electricity through a resistor to make heat is the most expensive way to make heat.
Apples and Oranges. I said electricity is more efficient, which it is. Cost comparisons are a completely different and rather complex analysis.
Electric resistance heat is the last resort. People heat their homes with gas, oil or heat pumps because they are all less costly ways of doing it.
Nobody uses an electric water heater if gas is an option.
That depends on the price of fuel available fuels and the cost of a Kilowatt; both of which have a great deal of regional variance.
Someone living in Arizona and drawing power from Hoover Dam might well come to a different conclusion than someone living in the OH/PA/WV region.
More importantly, I believe we are talking about a BOAT, not a house. I'll come back to that.
You may make the argument that 100% of the electricity used to heat water (or a building) goes into making heat...
Not MAY make. DID make. And it's not an argument, it is a simple statement of fact, no more remarkable that observing that the Earth's gravity at sea level is approximately 9.8 Meters/Second/Second.
...but how was that electricity produced? In most parts of the country it is produced by burning fuel to make heat to make steam to turn a generator to produce electricity. Then, it is delivered over hundreds of miles of wire with some loss to be converted back to heat.
As I said, we're not talking about use in a building on dry land, we're talking about use in a boat. There is therefore, no production of steam, no "Grid Production" generator to turn, and no "Hundreds of Miles" of wire loss to contend with. Nor, for that matter are there transformers, switch yards and all the other accoutrement of a land based power grid.
I was very clear that my understanding of the marine application of this technology was limited and I wished mainly to point out that regardless of whether you use combustion or electricity that it would take quite a bit of energy to heat water quickly enough to give a flow rate of several gallons per minute.
Now think of the your last sentence - You advocate burning diesel or gasoline to produce heat to rotate a generator to produce electricity to run through a resistor to produce heat to heat water. Think about that for a minute.
I did think about it. Respectfully, you should follow your own advice.
In the first place, I didn't "advocate" anything. I merely made a few simple and (I thought), non-controversial observations.
In the SECOND place, if YOU would "think about that for a minute" it might occur to you that unless you are on a sailboat without any backup motive power or electrical generation capacity at all, that you are ALREADY carrying gasoline or diesel and you ALREADY have a generator on board.
Simplest and most efficient - put the flame under the water and be done with it. Only when that cannot be done should another solution be considered.
You know, I am practically a complete land-lubber whose only boating experience has been on a lake; but it seems to me that adding an electrical tankless water heater to a boat that ALREADY has electrical generation capabilities and is ALREADY carrying liquid fuel for that purpose is a lot simpler than adding ANOTHER tank to carry a gaseous fuel to fuel a propane powered "on demand" heater.
Not to mention that a tankless water heater isn't a BBQ. It needs quite a bit more flow capacity to do it's job, which a 20lb BBQ won't provide. At a minimum you'll need a 100 pound tank, and even there... as it gets lower the pressure and flow volume drop. Which will happen faster than you think, because a hundred pound tank holds less than 20 gallons of propane.
So NOW we're talking about adding propane tanks to hold the fuel. Probably three or four 100 pound tanks on a manifold system. Which of course will need to be refueled on a regular basis.
Now as I said, MY only experience with boats in on a Lake. So I don't know... Is a propane pumping station a common thing at the marina's you frequent?
