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Old 25-04-2011, 06:22   #1
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Electric Flash Water Heater

Our water heater is all the way aft, behind the engine, runs off engine heat exchanger and AC when on shore power. The runs to the shower (aft head), galley, and forward head are long, and we waste water waiting for it to get hot. Does anyone have experience with flash electric water heaters? Ideally, we could place one or two so as to reduce the runs, save water, and take showers while charging batteries...

Thanks!
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Old 01-05-2011, 20:24   #2
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Re: Electric Flash Water Heater

Hum, I think you will find that the electric instantaneous type water heaters would draw way too much power. I've specified some for commercial buildings in the past but the electrical engineers hate them. For example a 4KW unit might give only a 30-40 degree F. water temperature rise, with 50 degree incoming water that would be about 90 degrees, or a fairly cool shower. Really would require a 6-8 KW to do quickly, what the standard heaters do in hours.

The standard 30amp shore cable is only 3.6 KW (In the US anyway).

You might be able to rig up an extra 12V water pump that would circulate the cold water in the hot side back to the water tank. There is something like this for light residential that recircs the hot water side back via the cold side, but nothing in a 12V motor.

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Old 09-05-2011, 17:27   #3
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Re: Electric Flash Water Heater

Beni,

Thanks! I have only seen one flash HW heater for marine use...with the "Navy" type showers we take, there would only be a few minutes of use a day, so I'm going to keep looking into it. If we time our showers for when we are charging batteries, this should work, i'm thinking.

John
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Old 09-05-2011, 17:34   #4
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Re: Electric Flash Water Heater

We have a ventless Bosch propane on demand heater. It's quite old and still going strong. It has an interlock pilot light that is simple to light when you need it and delivers pretty hot water as long as required. Works great at anchor too. Most of the nice home units are gas / propane. The ventless units use an ODP sensor in case the oxygen gets too low and you could pass out. Ours is inside the head and the other side of the bulkhead is the galley so the hot water does not go far. I crack open the port for a shower and the waste heat from the ventless burner tends to warm up the shower but also dries it out quicker too. If you can't go ventless then you need a small chimney so you don't die.

heating water with batteries is a chore. The engine can keep a tank showerable overnight if it really hot at the end of the day.
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Old 11-05-2011, 06:27   #5
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Re: Electric Flash Water Heater

Thanks, Paul. We have propane for the stove, and I'll take a look at the Bosch unit. did you need to talk with your insurance carrier about a ventless propane unit?

John
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