Hot water heater critique please

[NomadicFoodie]

A hot water system originaly for boats. Isotemp SPA 20L 115V Marine Water Heater w/Heat Exchanger & Mix Valve
The water is heated as you drive by having the van’s coolant lines run through a heat exchanger. If you are not driving, there is a 750 watt AC heating element that runs off an inverter or shore power. Spendy but once installed much cheaper than on demand hot water heater.
What's wrong with it other than expense?
https://mmarineonline.com/products/...8CtbHY-flln6ZWbXZkD-MYZk0SqWvlgBoCRD0QAvD_BwE

 

[highdesertranger]

they do make 110v versions of those but heating anything with electricity is very inefficient and expensive. highdesertranger

 

[B and C]

It has a european 230V plug. The cheapest US version is almost $700! Yikes!

I'll keep using my suburban hot water heater.

 

[NomadicFoodie]

The first thing I see wrong is this:
750W/230V
Are you in Europe? how will you run 230V on a 120 V inverter?

 Thanks so much for pointing out a newbie mistake, No I am now in the US and plan on staying in N America.
I need to take a class in electronics, for idiots, I simply don't understand wattage, voltage, inverters etc.
I like the idea of all electric if possible as propane makes me nervous.
Back to the drawing board, but I like the idea of heating from the engine heat.

 

[Trebor English]

You can apply 120 volts to a 230 volt water heater.  It will heat.  Since the voltage is half the current will also be half.  That makes the power 1/4.  The 750 watt heater will only take 188 watts.  The time necessary to do the heating goes up by 4 times. 

My wife's dog's groomer had such a set up in her mobile grooming van.  First thing in the morning she filled the water tank and plugged in the water heater using a regular 120 volt extension cord.  By 9 AM when she drove off to groom dogs the water in the heater was plenty warm for the dogs.  A couple of years ago I got her a propane camping tankless water heater.  It's mounted right by the gasoline powered generator for the dog hair blow dryer.  I got her a two propane tank mounting bracket so that when one propane tank ran out she could switch over without business interruption. 

In theory, the waste heat from the generator exhaust would be plenty to heat the water.  More dogs washed, more dog hair dried, more generator exhaust heat, just not so good for the first dog of the day.

 

[B and C]

You will find that trying to do anything electrical heating (or air conditioning) wise with 12V will take a LOT of battery power. The electrical grid in a S&B house has us spoiled to unlimited electricity. A generator or shore power for those types of loads.

 

[Lemonbox]

Good thing I've found this thread. I've been thinking to try to install this electric heater https://houseweather.org/best-electric-water-heater/#product3 So I guess 12kW will use my battery quite fast