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Old 10-15-2021, 10:08 PM   #1
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Tankless hot water heater

Has anyone ever seen or heard of an electrical one built for a boat? I have seen some that go on RV’s but they are propane based. A friend asked if I had ever seen one, so I did a little research and thought I would ask here.
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Old 10-15-2021, 11:22 PM   #2
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I haven't seen one built for a boat. I've used many in the UK. I have experience with some installed on a boat. They aren't worth the trouble. They are prone to failure. The temperature is not well controlled if controlled at all.
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Old 10-16-2021, 08:08 AM   #3
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Firs hassle with electric is a huge amount is required , many houses must be required to bring in 200A service , 60-80A at 240V is usually needed.

"The temperature is not well controlled if controlled at all.: (#2)

Same hassle as propane instant water heaters , off - on and no temperature stability.

Only cure is to hook the shower up is with a shower /tub selector valve , and send heater water back to tank for temperature stability.

There are RV propane units that will heat 6 or 10 gal of water , and can be operated on 120V power too.
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Old 10-16-2021, 08:13 AM   #4
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I've never seen or used one on a boat but they are very popular in Asia houses and hotels. You need at least 3600W to get any sort of flow and temp rise. And that's in the tropics. If you have inlet water temps below 20°C, more power or less flow will be required.
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Old 10-16-2021, 08:21 AM   #5
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I thought that might be the case. The ability to “store” hot water for a little while after heating has its benefits also.
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Old 10-16-2021, 09:16 AM   #6
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I don't like propane on boats, even though I carry it. I valve off both ends and disconnect the tank when I am done cooking. A "constant on' heater would give me nightmares. I guess I would consider a 110 volt home type model although this limits you to genny operation or plugged in.

I guess the bottom line would be..

No

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Old 10-16-2021, 09:56 AM   #7
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I don't like propane on boats, even though I carry it. I valve off both ends and disconnect the tank when I am done cooking. A "constant on' heater would give me nightmares. I guess I would consider a 110 volt home type model although this limits you to genny operation or plugged in.

I guess the bottom line would be..

No

pete
The concern with a house unit would be the possibility of tied together neutral and ground wires. I agree with you on the propane. Many folks use it successfully, though.
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Old 10-16-2021, 01:04 PM   #8
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Some fishermen use propane tankless water heaters on deck. Not inside the hull. An electric version takes more power than most boats have or is available at a marina. Even those with generators.
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Old 10-16-2021, 01:23 PM   #9
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My boat came with an electric hot water on demand faucet. It wasn’t really my thing so I removed it. It worked best on generator, you couldn’t use it on batteries. When on shore power you could use it but Then you had to balance it with other high high amp competing loads.

It really depends on how you use your boat and why you would be adverse to using a traditional hot water tank.
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Old 10-16-2021, 02:23 PM   #10
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The concern with a house unit would be the possibility of tied together neutral and ground wires. I agree with you on the propane. Many folks use it successfully, though.
If you don't like propane nor electric, the only other practical option is some form of calorifier or heat exchanger. These are available as instantaneous (very popular with the camping/4WD crowd here) or storage. You don't mention how often you motor nor how much hot water you want??
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Old 10-16-2021, 03:27 PM   #11
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We had one in a previous house that ran on natural gas and it was great. But for a boat, no way.
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Old 10-16-2021, 04:09 PM   #12
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Looked into all methods for when our 180 litre 240v electric dies.

Came to the conclusion that a $400 25 litre 240v electric will the the most viable and cost effective way to go as I can swap that out myself.
1800watt elements are about $40 extra

https://www.bunnings.com.au/dux-prof...ug-in_p5104137
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Old 10-16-2021, 04:16 PM   #13
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Originally Posted by GoneDiving View Post
If you don't like propane nor electric, the only other practical option is some form of calorifier or heat exchanger. These are available as instantaneous (very popular with the camping/4WD crowd here) or storage. You don't mention how often you motor nor how much hot water you want??
Only practical if you use the big motor every day

I thought one could run off the Genset but likely not
In the thread below a 38hp didn't work so our 21hp certainly won't
But it'll pump out plenty of juice to run an electric like I posted above
For us, solar currently gets us there most days

https://www.cruisersforum.com/forums...-152072-5.html
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Old 10-16-2021, 04:17 PM   #14
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I’ve looked at the propane units and understand the concerns. I’ve been contemplating one on the swim step as part of a transom shower but don’t think I’d want one in the hull either.
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Old 10-16-2021, 04:56 PM   #15
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Quote:
Originally Posted by Helmsman View Post
Has anyone ever seen or heard of an electrical one built for a boat? I have seen some that go on RV’s but they are propane based. A friend asked if I had ever seen one, so I did a little research and thought I would ask here.
Not built for a boat but you can always modify it. We spent a season in Brazil and these shower heads were in the majority of the houses. The water temperature to the head was probably 70 degrees which helped. It took a while to get over the idea that you are standing in water with less than code wiring. We never did got shocked though.
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Old 10-16-2021, 05:39 PM   #16
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Looked into all methods for when our 180 litre 240v electric dies.

Came to the conclusion that a $400 25 litre 240v electric will the the most viable and cost effective way to go as I can swap that out myself.

1800watt elements are about $40 extra]
Simi, what are you going to do with only 6 gallons of hot water??? By the time it gets mixed down with incoming cold water you're likely to obtain about 3-4 gallons of hot. 2 people living full time, showering, washing dishes, etc.

I like the idea of a huge residential heater, say 160-200 liters, with a 240V element and a 24VDC-900watt element also, so it can run off the generator, load dump from solar, and have enough heavily insulated capacity to last several days.
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Old 10-16-2021, 05:48 PM   #17
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Simi, what are you going to do with only 6 gallons of hot water??? By the time it gets mixed down with incoming cold water you're likely to obtain about 3-4 gallons of hot. 2 people living full time, showering, washing dishes, etc.

I like the idea of a huge residential heater, say 160-200 liters, with a 240V element and a 24VDC-900watt element also, so it can run off the generator, load dump from solar, and have enough heavily insulated capacity to last several days.
Yeah your HW tank is just another form of energy storage - and a lot cheaper than batteries! Tankless really doesn’t make much sense if you’re using electric.
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Old 10-16-2021, 06:29 PM   #18
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Simi, what are you going to do with only 6 gallons of hot water??? By the time it gets mixed down with incoming cold water you're likely to obtain about 3-4 gallons of hot. 2 people living full time, showering, washing dishes, etc.
.

Maybe the 50 litre one
But we sure as hell don't need 180 litres
Washing up once a day uses probably 5 litres
A shower every second day uses a few more in winter
In summer we dont need hot water for showers at all

Quote:
I like the idea of a huge residential heater, say 160-200 liters, with a 240V element and a 24VDC-900watt element also, so it can run off the generator, load dump from solar, and have enough heavily insulated capacity to last several days
Reality is with a normal Resi system if you miss a day of charging it up it takes twice as long the next day.
By day 3 it's pretty much cold, so better off with a smaller system with shorter charge times done daily imho

Not sure how you'd get dual elements in an off the shelf HWS.
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Old 10-16-2021, 07:05 PM   #19
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Only practical if you use the big motor every day

There, sort of. 😁. Or the OP could install sufficient storage. Or have light usage to not run out. That's why I asked his usage and cruising requirements.

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I thought one could run off the Genset but likely not
In the thread below a 38hp didn't work so our 21hp certainly won't

https://www.cruisersforum.com/forums...-152072-5.html
Why didn't this work? I would have thought a smaller engine is likely to run hotter and be able to do the job. Sure longer run times may be needed but it's hard to see it not working at all on any engine with coolant at ~80°C.

25l may work for you but on vessels our size (I don't know the OP's) I'd side with the bigger, the better mentality: solar banking; extra storage for SNAFUs or greedy guests and minimal marginal costs. Given the OP's dislike of propane and electric I'd want as much buffer as possible.
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Old 10-16-2021, 07:30 PM   #20
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.

25l may work for you but on vessels our size (I don't know the OP's) I'd side with the bigger, the better mentality: solar banking; extra storage for SNAFUs or greedy guests and minimal marginal costs. Given the OP's dislike of propane and electric I'd want as much buffer as possible.
Greedy guests are never onboard our vessels

And as I said, a big HWS takes a long time to charge and is brutal on the amps or seems that way to me.

If keeping on top of ours, doing it daily from around 10am it takes 1.5 hours + or - pulling 80 amps @ 24v and that's with us not using much hot water, if we did it would surely take a lot longer.
Ok on a sunny day as we cover that and the rest of the boat running most of the time
But when a cloud goes overhead I freak out a bit seeing the spike

I would like to think a new 50 litre unit would take a lot less time to charge up.
More time for smashing amps into the LFP bank.

BUT.......as we don't have the LFP yet my views might well change when we've had in in for a month or three to access.
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