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Old 27-11-2024, 20:56   #1
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Water heater change

Hello sailors
I’m fed up with 50-liter tanks that always end up leaking, scalding hot water coming out of the taps, semi-rigid pipes running all over the engine compartment, rusty water pooling in the bilge, and having to create engineering masterpieces every time I need to change a heating element.

Now that I’ve switched to four LiFePO4 batteries (12V, 200Ah each) for a 24V system, I’m wondering if I could install an electric tankless water heater.An electrician friend of mine has done it and is thrilled with the results—though, to be fair, his boat looks more like a solar farm than a sailboat!

Weare usually two on board, so it would need to handle two daily showers and washing the dishes.we are usualy sailing or on anchor, but we also don’t use a lot of water while sailing. For context, we have 4 140w solar panels a 3000W inverter.
We usualy sail the med or caribean and I do not mind putting the engine 1 or 2h a day.
Does anyone have experience or suggestions and brand recomendation for this setup?
Thanks
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Old 27-11-2024, 21:52   #2
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Re: Water heater change

Some things to consider:
1. Effective tankless requires 3000 - 3500W.
2. Your inveter is more likely 2400W continuous
3. You will not be able to run anything else when water heater is in use or it will trip the inverter or breaker
4 The AC wiring may need an upgrade to handle higher than normal amps


Propane tankless is an inexpensive alternative if CO issue can be sorted.
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Old 28-11-2024, 02:45   #3
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Re: Water heater change

Generally speaking, an electric tankless water heater is a substantial electrical load, for a brief time; and many/most boats will not have sufficient electrical service to handle this, along with the boat’s other electrical loads.
The size [in kiloWatts] of an electric tankless [instant] water heater is determined by its flow rate, which is measured in gallons per minute [GPM]; and temperature rise [the difference between the input cold water temperature, and the desired hot water output temperature].

An instant heater, capable of delivering 1.5 GPM, with a of 50°F rise would likely require a 12kW power supply [50 Amps @ 240 Volt].

Stiebel Eltron Mini 6 ➥ https://www.tanklesscanada.ca/stiebe...HorizontalTab2
Requires a 5.7 KW power supply [24 Amps @ 240 Volt] delivering 1.11 GPM @ 30°F rise.

Stiebel Eltron Mini 2 ➥ https://www.e-tankless.com/stiebel-e...HorizontalTab2
Only requires 1.8 KW [15 Amps @ 120 Volt] delivering only 0.32 GPM @ 30°F rise.
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Old 28-11-2024, 06:18   #4
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Re: Water heater change

I've had to change out a tank. Twice in a lifetime of boating. I might have changed an element once, but that could have been someone else's boat. I've never seen semi-rigid pipes for the engine jacket water loop from a water heater, but I suppose that could be describing the normal hot and cold domestic water piping, which frankly I find a lot easier to work with than back when we had to sweat copper pipes in the house.

As for scalding, I never understood that argument, either. Doesn't your faucet have two taps? If the hot is too hot, add some cold. Personally, I love the option to use scalding-hot water to quickly wash greasy dishes and such. But I did eventually cave in and add a thermostatic tempering valve. Mostly because it saves on hot water.

I'm not really sure what my point is here. I guess it's just that, of all the frustrations from maintaining a boat, the water heater has never been high on my list. Oh, and a tank of hot water can last quite a while without any solar, battery, engine or genset input. I like having hot water without any immediate power management effort.

But... it's your boat. You set it up to your specs. And let us know how it goes, maybe you'll change my mind!
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Old 28-11-2024, 12:26   #5
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Re: Water heater change

Maybe an Instant gas water heater?
when I was scouring the web for my boat i saw many with a household instant gas water heater.
Obs not marinized but seem like alot of boats in Europe have them, they are small and consume power (Gas+Electricity) only when needed - And you could easily adjust water temp
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Old 28-11-2024, 12:50   #6
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Re: Water heater change

I have a 50 gallon, house type water heater that is at least 30 years old. It doesn't leak. I did change the element, but it was much less than a typical yacht element.
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Old 28-11-2024, 13:36   #7
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Re: Water heater change

My water heater is ~30 years old, I've changed the element one time.
Found a replacement at Ace Hardware that was less than 1/2 the price of the OEM one.
15 minutes with a rat-tail file on the flange mounting holes of the new element made it fit perfectly.
Three things will add life to a water heater and its element.
1, A properly operating temp/pressure relief valve.
2, A good water filter ahead of the inlet.
3, an expansion tank on the outlet, or alternately, just get rid of the check valve on the inlet side and let your accumulator tank absorb the expansion of the hot water.
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