Tankless hot water heater

[Helmsman]

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.

 

[Portage_Bay]

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.

 

[FF]

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.

 

[GoneDiving]

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.

 

[Helmsman]

I thought that might be the case. The ability to “store” hot water for a little while after heating has its benefits also.

 

[PM]

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

 

[Helmsman]

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.

 

[Lepke]

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.

 

[tiltrider1]

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.

 

[GoneDiving]

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??

 

[Comodave]

We had one in a previous house that ran on natural gas and it was great. But for a boat, no way.

 

[Simi 60]

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-proflo-25l-2-4kw-electric-storage-water-heater-plug-in_p5104137

 

[Simi 60]

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/f115/shower-hot-water-options-152072-5.html

 

[socalrider]

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.

 

[Larry M]

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.

 

[Mako]

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.

 

[socalrider]

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.

 

[Simi 60]

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

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.

 

[GoneDiving]

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.

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/f115/shower-hot-water-options-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.

 

[Simi 60]

.

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.

 

[O C Diver]

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/f115/shower-hot-water-options-152072-5.html

It depends on the plumbing of your engine. My JD 4045 is generating between 24 and 40 HP (6-7 knots) at cruise. In about 30 minutes, it has the 20 gallon water heater back up to 175 degrees. I could likely get the same effect out of my 8 KW Onan generator that's burning 1 GPH generating 20 HP at full load. Unfortunately it doesn't have a coolant output fitting on the head like the John Deere does.

Ted

 

[GoneDiving]

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....

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.

Obviously two days usage will take twice as long to reheat as one. However, I'd be interested to see if x litres taken from a big tank reheats more or less efficiently than x litres from a small tank and if there is a big difference.

As I said before, for our situation, the benefits of having considerable hot water on hand would be worth a minor efficiency loss. I take your point though that it's not worth a 100% loading for, if that's what it turns out to be.

I'll have the luxury of a big bank and panels but I have toyed with the idea of having the HWS on a relay that only opens when by batteries are full. Again something, I would only consider if I had a few days volume available.

Cheers

 

[Mako]

@Simi, regarding your statement about elements in a HWH, in America pretty much any heater of 39 gallons or more is dual element. Usually dual 4500 watts.

 

[Greg S]

… 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.

You should look into the propane units. In experience with mine, I think you have got some poor advice on them so far. Paloma is one brand, there must be others. I have a small unit for use in the barn and washing horses. It is very adjustable for temperature and tends to keep a steady temperature. There isn’t mixing with cold water down stream from the heater. The finished temperature is the output from the heater. You adjust the temperature on a dial and it regulates the output flow, if I want really hot water, output flow is reduced. I am aware of this knowing full well that it is a small unit. Of course my output is from a garden hose, not a bathroom shower head. Output is continuous, not dependent on a stored volume. Mine is not marine rated and I don’t know if any are.

 

[Jeff F]

Paloma propane water heaters were common on Canadian cruising sailboats in the early 1980s. But there were several deaths attributed to CO poisoning from this type of heater, and they disappeared from marine use after that.

 

[FF]

The hassle with most HW heaters is short service life, 10-12 years and you get to replace it.

Rheem makes a "Marathon" brand that uses a very well insulated tank that is plastic inside and outside.No rust , no rot.

Its guaranteed "forever" for house use. Many are used on farms and commercial places where high temperature water is required.

With great insulation they are larger than metal heaters , and start at 30gal, so not for every boat.

The alt. energy folks have heat exchangers that mount to the usual high temp pressure fitting , so heat from an engine or noisemaker coolant is easy.

An anti scald valve would be required to be safe.

The 50gal unit is claimed to loose only 3-5 deg in 24 hours!

 

[Helmsman]

Thanks for the all of the comments. As mentioned in the original post, a friend, fairly new to boating, asked me about whether there were tankless water heaters on boats. I thought I would ask here with all of the experience available. I have no intention of installing a tankless water heater on my boat, but thought I would check here and let my buddy know some of the thoughts the question would generate. After looking the comments over, he isn’t interested in one either.

As always, Appreciate the input!

 

[stevemitchell]

I installed a Hurricane Chinook hydronic heating system in January 2021. Part of its features includes what they call an on-demand domestic hot water system which I've used extensively this last year.

It's not 100% like an on-demand hot water system in that it has a reservoir which has about a 7 gallon capacity which when it is on is always hot. However, I've run that out (I like long showers) and the system can produce 1.5GPM of hot water continuously while heating. I've seen it do that many times and it's pretty impressive.

Again, I know it's not an instant or on-demand water system from the very beginning, but you can turn it on, and within 3-4 minutes have 1.5GPM of hot water pretty much until you run out of water.....

 

[PPandE]

I’m a little late to the thread but I had a tankless water heater on a previous boat that worked very well for us. I installed a small point if use unit to supply the entire boat. The heating capacity wasn’t very great but I found that by reducing the flow the temperature could be increased to greater than what was required for showers or dish washing. The power consumption wasn’t a burden on my 12kw generator.

 

[Simi 60]

@Simi, regarding your statement about elements in a HWH, in America pretty much any heater of 39 gallons or more is dual element. Usually dual 4500 watts.

Oh, ok, not aware of such a think here