Water heater sizing Q&A for liveaboards.
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I’ve done exactly what you have pondered, though I never planned to use the inverter as my primary source. If I’m planning on running later in the day, or running the generator I had used the inverter to top off the water heater. Typically, in the morning my water is not completely cold, so the water heater won’t run but for about 20 minutes. I might only rack up 50-70 amp hours to do so. Often even less. Why? To avoid running the generator in a quiet anchorage, but still wanting to shower in the morning before getting going. All depends on the charge state of my bank and near term plans to recharge.
That said, my best upgrade was adding underwater exhaust to my generator. It’s almost silent now, so in all but the closest quarters, I just fire up the generator.
If I have boats rafted to me, I might use the inverter, even cook breakfast on the electric stove without firing up the generator, also about 60 amp hours for breakfast, but at the expense of what might be another hours run of generator time to put those precious amp hours back.
Having the flexibility is a good thing, but as others said if this is your primary method I think you will be disappointed. After your frig/freezer loads, even 8 golf carts start looking like a small enough bank to watch out for large loads. Plus, the biggest constraint will be the rate at which you can return the amp hours that come out so easily.
That said, my best upgrade was adding underwater exhaust to my generator. It’s almost silent now, so in all but the closest quarters, I just fire up the generator.
If I have boats rafted to me, I might use the inverter, even cook breakfast on the electric stove without firing up the generator, also about 60 amp hours for breakfast, but at the expense of what might be another hours run of generator time to put those precious amp hours back.
Having the flexibility is a good thing, but as others said if this is your primary method I think you will be disappointed. After your frig/freezer loads, even 8 golf carts start looking like a small enough bank to watch out for large loads. Plus, the biggest constraint will be the rate at which you can return the amp hours that come out so easily.
Irish Rambler
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On a previous boat I had a 30 gallon horizontal insulated domestic hot water tank with an internal coil heated via the engine and when hooked up I used domestic type 2.5 kw immersion heater.
When we refurbished our current boat I fitted a horizontal insulated 75 litre tank, heated via the engine or a 1kw electric immersion heater when on shore power.
I specified a mixer valve on the hot water tank outlet to prevent scalding (engine temp's 90') and set the mixer valve at 70', its safer for the crew and the hot water lasts much longer. I use the same type of mixer valve to set the temp on the water supply to the washing machine and dishwasher. I would highly recommend it.
I really enjoy a hot shave every morning and I can still have one on the third day.
An important point to remember is that if the head height of your hot water outlet on the cylinder is below the height of your engine header tank you'll get thermal circulation.
You won't keep your hot water for long but your nice warm engine will start first time.. But sure you knew that anyway didn't you ?
When we refurbished our current boat I fitted a horizontal insulated 75 litre tank, heated via the engine or a 1kw electric immersion heater when on shore power.
I specified a mixer valve on the hot water tank outlet to prevent scalding (engine temp's 90') and set the mixer valve at 70', its safer for the crew and the hot water lasts much longer. I use the same type of mixer valve to set the temp on the water supply to the washing machine and dishwasher. I would highly recommend it.
I really enjoy a hot shave every morning and I can still have one on the third day.
An important point to remember is that if the head height of your hot water outlet on the cylinder is below the height of your engine header tank you'll get thermal circulation.
You won't keep your hot water for long but your nice warm engine will start first time.. But sure you knew that anyway didn't you ?
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Knot Fast
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We are a couple of liveaboard cruisers. I have a 20g Seaward with heat exchanger. When heating water via engine waste heat or excess generator capacity, I view making hot water as a way to store free energy. I can store more free energy with a 20g tank than with a 10g tank.
With 20g and a water-saver shower head, we have never run out of hot water. No issues of who gets the 1st hot shower and who gets the 2nd warmish shower.
The incremental purchase cost of 20g over 6g-13g is small.
I have taken "Navy" showers when in the Navy. Get wet for 30 seconds then turn off the water, soap up, rinse off for 30 seconds. All while 20 guys waiting in line yell very loudly that you are taking a Hollywood shower and wasting all the fresh water. While that is a fond memory, I do not wish to relive it.
With 20g and a water-saver shower head, we have never run out of hot water. No issues of who gets the 1st hot shower and who gets the 2nd warmish shower.
The incremental purchase cost of 20g over 6g-13g is small.
I have taken "Navy" showers when in the Navy. Get wet for 30 seconds then turn off the water, soap up, rinse off for 30 seconds. All while 20 guys waiting in line yell very loudly that you are taking a Hollywood shower and wasting all the fresh water. While that is a fond memory, I do not wish to relive it.
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"I have taken "Navy" showers when in the Navy. Get wet for 30 seconds then turn off the water, soap up, rinse off for 30 seconds."
With any type of tank water heater, the Navy shower may not be as much relaxation as the constant water pouring shower , but it works.
What is difficult to plumb and use is the instant on style of usually propane water heaters.These shut OFF when the water flow is reduced , so a batch of cold is part of the showering experience , unless you have Lots of water on board.
There are workarounds tho.
With any type of tank water heater, the Navy shower may not be as much relaxation as the constant water pouring shower , but it works.
What is difficult to plumb and use is the instant on style of usually propane water heaters.These shut OFF when the water flow is reduced , so a batch of cold is part of the showering experience , unless you have Lots of water on board.
There are workarounds tho.
AusCan
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Ahhh - good point; I didn't consider that. Thanks for the tip.
I have a bypass manifold on my hot water loop, so I'll isolate the tank while at anchor for longer lasting hot water.
Andiamo2018
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Our water heater is on the small side but I set it to its highest setting. Hotter water means you need less per shower. We do have to warn guests to be careful washing their hands etc. And we try to remember to turn it off when we leave the boat.
FF
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"I want to use those pull handle shower heads where you have to pull the handle to get water. Let go and it shuts off."
UGH!
Usually when the water is flowing 2 hands get rid of soap quicker than one.
You could make the pull chain long enough to step on or ,
Shower with a Friend?
UGH!
Usually when the water is flowing 2 hands get rid of soap quicker than one.
You could make the pull chain long enough to step on or ,
Shower with a Friend?
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ksceviour
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You won't keep an electric water tank running on batteries even with those panels (if you can even find a place to put six). In direct sunlight and perfect efficiency you'll get less than 10 amps per panel. Inverter draw for the heater will far surpass the total array. Running your engine for 20 minutes will heat an 8 gallon tank hot enough for showers. Our 11 gal tank stays hot for quite a while and is still warm the next morning.
FF
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Folks that run a noisemaker can use its cooling system to heat a water heating coil.
Might be a faster recovery than electric?
Might be a faster recovery than electric?
Lepke
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I have a 50 gallon electric water heater. It sits on 2" styrofoam and is surrounded by 2" foam, including the top. Also the water lines, including the cold and pressure relief are insulated so they don't radiate the heat. I easily go 2 or more days, depending on how many people are aboard. And my diesel stove, if running, has a coil that heats the tank.
My FW system is 3 lines. hot, cold and return hot. Both hot lines are insulated. Each water use area has a button that turns on a circulation pump, drawing hot and returning what's in the line to the tank. The pump runs about 2 minutes. This way I don't dump fw down the drain to get hot water and the water returned has more warmth than using cold. It also saves watermaker running time.
My FW system is 3 lines. hot, cold and return hot. Both hot lines are insulated. Each water use area has a button that turns on a circulation pump, drawing hot and returning what's in the line to the tank. The pump runs about 2 minutes. This way I don't dump fw down the drain to get hot water and the water returned has more warmth than using cold. It also saves watermaker running time.
OP
OP
ben2go
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So far I'm considering a 12 gallon home unit heated by 120VAC from the genny or when on shore power and diesel stove in the winter.
This is the model I like I'll have to re-evaluate it later due to the top in/out for water. Parts are available all over the US for these for not much money.
https://www.amazon.com/American-Sta...9c75222b0c730fde8742a8054e1258&language=en_US
This is the model I like I'll have to re-evaluate it later due to the top in/out for water. Parts are available all over the US for these for not much money.
https://www.amazon.com/American-Sta...9c75222b0c730fde8742a8054e1258&language=en_US
Ben: That should work but you may want to change out the pressure relief valve. Household units are rated for anywhere from 75-150psi and usually closer to 150psi. A marine water heater, Raritan as an example, pr valves are related to 75psi.
I’m impressed that the unit you’re looking at has an anode.
I’m impressed that the unit you’re looking at has an anode.
OP
OP
ben2go
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Ben: That should work but you may want to change out the pressure relief valve. Household units are rated for anywhere from 75-150psi and usually closer to 150psi. A marine water heater, Raritan as an example, pr valves are related to 75psi.
I’m impressed that the unit you’re looking at has an anode.
Larry, I think that can be changed. My AO Smith water heater at home has a 75psi T&P valve. It has an anode as well. The anode is one of the reasons I'm looking at that model. I could also go with the 20 gallon AO Smith but that single 1500 watt element would be hurting to warm 20 gallons of water, I believe.
Hot water recirculating is a great energy conserving measure. Even our cheap, mass-produced house has it installed, although not on a timer like you mention. That's the first I've head of installing it on a boat, but it makes even more sense especially for boats which do not have water makers.
FF
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"AO Smith but that single 1500 watt element would be hurting to warm 20 gallons of water, I believe."
Most HW electric elements mostly have identical screw in mounts so a higher amperage unit should be OTS.
You might have to install a 240v thermostat to handle the voltage/amperage.Still OTS
Here in FL with poor water, titanium elements cost a bit more but last far longer.
Most HW electric elements mostly have identical screw in mounts so a higher amperage unit should be OTS.
You might have to install a 240v thermostat to handle the voltage/amperage.Still OTS
Here in FL with poor water, titanium elements cost a bit more but last far longer.
Diesel powered tankless water heater seems to be the ultimate. I've never owned one, used one, seen one, or even talked to someone who has. But it looks good on paper or the net. I'll take a closer look sometime. It's hiding with the unicorns for now.
https://www.butlertechnik.com/marin...5wsc-water-heater-diesel-12v-252219050000-p23
After hiking and pouring cold mountain spring water over my head to bath, a bilge pump over the side while standing on the back deck would be luxury.
https://www.butlertechnik.com/marin...5wsc-water-heater-diesel-12v-252219050000-p23
After hiking and pouring cold mountain spring water over my head to bath, a bilge pump over the side while standing on the back deck would be luxury.
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OP
OP
ben2go
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Eberspacher turned one of their forced air heaters into a water heater and jacked the price up. I bet knock offs can be found for 1/10th the price and just as good of quality. I know the knock-off heaters are getting rave reviews lately.
Ever bathed in "pure glacier water" like in the advertisements? I did when backpacking through Alaska years ago. Well this here gringo showed up ready to enjoy a heavenly wash and was surprised to see that glacial runoff is horribly muddy, sandy, nasty and cold! Thank god I brought my little hand pump purifier. Yep we were a bunch of dumb 22 year old kids
I think we could start a new thread on this....
keb
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Ever bathed in "pure glacier water" like in the advertisements? I did when backpacking through Alaska years ago. Well this here gringo showed up ready to enjoy a heavenly wash and was surprised to see that glacial runoff is horribly muddy, sandy, nasty and cold! Thank god I brought my little hand pump purifier. Yep we were a bunch of dumb 22 year old kids
I think we could start a new thread on this....
I too bathed in glacier runoff in the Wrangell St. Elias National Park when I couldn’t stand the smell of myself after 13 days rafting the the Copper River and its tribs. My brother and I were visited by a bear while standing au natural in a small ICE cold runoff stream. It would have probably been a viral video if it was recorded and youtube existed. Looking back it was comical getting the he!! Out of there in a very big hurry. Great memories on that trip, but I am not a Polar Bear enthusiast by any means. You can only take so much of yourself.
Sorry OP for the drift.
Nopistn
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I easily fit a 19gallon 120v household heater. Works awesome.
FF
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In our FL house we have a Rheem 50G Marathon.
It is super insulated and has a plastic , not metal liner.
It can be used industrially , so 190F water is just fine.
The Rheem lit claims 5deg F heat loss in 24 hours.
Big to get down a hatch , but the alt energy folks have kits to use the safety valve to install a heat exchanger , so engine coolant could also power the unit.
Lifetime guarantee.
Rheem's Marathon Water Heater is the Most Durable Water Heater ...
https://www.rheem.com/innovations/innovation_residential/marathon/
Its award-winning construction makes the Rheem® Marathon® water heater the most durable electric water heater ever made. And its industry-best warranty ...
************
The downside to "instant on" HW heaters is there must be a flow thru the unit for it to operate.
On coach builds we installed a common plumbing tub or shower valve , si the water could be left on and heating , but what was not desired could be plumbed back to the FW tank.
These were propane units as no campground and few installed RV noisemakers could make the electric required.
One brand now claims their unit will stay heating water at 1/4 GMP , might work.
https://www.truma.com/us/en/products/truma-water-systems/truma-aqua-go-water-heater.html
It is super insulated and has a plastic , not metal liner.
It can be used industrially , so 190F water is just fine.
The Rheem lit claims 5deg F heat loss in 24 hours.
Big to get down a hatch , but the alt energy folks have kits to use the safety valve to install a heat exchanger , so engine coolant could also power the unit.
Lifetime guarantee.
Rheem's Marathon Water Heater is the Most Durable Water Heater ...
https://www.rheem.com/innovations/innovation_residential/marathon/
Its award-winning construction makes the Rheem® Marathon® water heater the most durable electric water heater ever made. And its industry-best warranty ...
************
The downside to "instant on" HW heaters is there must be a flow thru the unit for it to operate.
On coach builds we installed a common plumbing tub or shower valve , si the water could be left on and heating , but what was not desired could be plumbed back to the FW tank.
These were propane units as no campground and few installed RV noisemakers could make the electric required.
One brand now claims their unit will stay heating water at 1/4 GMP , might work.
https://www.truma.com/us/en/products/truma-water-systems/truma-aqua-go-water-heater.html
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