View Full Version : Water heater inline on demand ??

05-18-2011, 10:00 AM
Ok so I'm toying with the idea of installing an inline ondemand
Electric water heater. Just for the shower.
I believe my waterpump is rated for max 2.0 gpm
Anyone have any experience with any perticular model/make?
Hoping to find one just to make the occasional shower on shorepower
A little less freezing.

05-21-2011, 08:28 AM
Ayuh,... In my experience with 'em,...
You can't plumb enough Amps to the boat to make it work Right...

need to know
10-11-2011, 01:57 AM
with a bit of plumbing the engines colling system with a heat exchanger can be used,,,,,,little out of the box but it works reliably..

10-29-2011, 07:56 AM
I realize that this thread is not current.... but what the heck, this may be useful.

Ayuh,... In my experience with 'em,...
You can't plumb enough Amps to the boat to make it work Right... I just spoke with a man last week who owns a water heater repair/replacement business. This is residential, but the On-Demand concept is apparently the same industry wide.
He confirmed what Bill just said regarding the wattage required.
Natural Gas (or Propane for that matter) is much more efficient, but Propane On-Demand is likely not legal for Marine use, unless the unit was to be mounted externally and out in the open.
Don't know for sure.... better check on this!

FYI: My boat is equipped with a 12 gallon Electric Strip/Engine coolant Water Heater.
Both engines are equipped with closed cooling systems, Port Engine provides coolant to the WH's internal heat exchanger coil.
Engine temps are approx 160*/170*.
I can leave the dock, and in approximately 45 minutes, I will have 12 gallons of fairly hot water.
When running to a destination and staying on the hook, we will have plenty of hot water the following morning.
To heat water further, my choices are to fire up the Port Engine, or to fire up the Generator.

One nice feature w/ a conventional WH, is that throughout the day we'll have warm to hot water available, and without the need to fire up any engine!

You mentioned "a little less freezing"..... and I'm not quite sure what you meant by that!
If this were to mean that an On-Demand system may be easier to winterize, I suppose that it may be a tad bit easier.
However, I believe that either will be relatively simple to winterize once you get a system down.

My WH itself is completely drained of all potable water.
The engine coolant side requires nothing done!
The cold supply is then by-passed via a valving system (turn 3 valve handles and I'm done) and is joined with the Hot out supply creating a loop. The RV type anti-freeze can then be pumped through the entire system (both Hot/Cold plumbing) and out each Hot/Cold fixture.
(you can purchase a by-pass kit, or make up your own..... I made up my own)

It takes me about 15 minutes to winterize my O/B water system.

Just a suggestion for you! :D