Hot water heater through an inverter?

[LoudMusic]

Originally Posted by Sierra

When I upgraded my solar I had a timer installed that closed a contacter to heat the water when not on shore power. I set the timer to 1 hour so I did not need to remember to turn it off. As some have suggested above I wait until the batteries are close to full (gone over to absorption) then turn it on the solar starts working hard again. I have a 3000w inverter and it handles the load, about 70 amps easily.

Oh it's definitely best to use it during peak sun - this is a good point. But it's possible to run from batteries if you need a hot shower and the sun isn't shining Mine is just on a dedicated 120v circuit so it's got its own breaker switch I can turn off at any time.

[Seadevil]

Originally Posted by Sailing_Pasha

I have a 2014 Oceanis 41 and it has a (factory installed) hot water heater which gets the power from the engine at the moment.

The person who will install our new inverter says it's not a smart idea to put the hot water heater through the inverter and keep it as it is which means we'll have hot water only when we run the engine or through shore power.

What do you guys think?

I think he is correct. Most boats have the choice of shore power or the engine for hot water... Putting it through the inverter will flatten 12v batteries very quickly and then you need to use the engine to charge the batteries... Inverters are typically used for undemanding 220v appliances

[Escape Plan]

Our thought was to use this element, and have our Victron system switch the solar panel supplied energy to the water heater when the batteries go to float mode. It's 12VDC, 600 W.

https://www.amazon.com/FINE-MEN-Stai...7654835&sr=8-5

[Colin Stone]

The engine should firstly heat the water tank using engine coolant through the tank heating coil. Most engines have take offs for just that. With a reasonable sized tank, the hot water should last a couple of days.
Our engine cooling system has a heat exchanger and the entire 14 radiator system plus 2 hot water tanks can be heated by the engine in a fairly short time and tank water gets up to 85C.
Using electricity for resistive heating off a battery is always a last resort.
Otherwise, use solar PV once battery is charged. Or even a solar thermal panel which again is better than electricity. But a boat size small one might be difficult unless a DIY like the solar shower bag.

[chris mac]

Originally Posted by SaltyDogsLLC

Our thought was to use this element, and have our Victron system switch the solar panel supplied energy to the water heater when the batteries go to float mode. It's 12VDC, 600 W.

https://www.amazon.com/FINE-MEN-Stai...7654835&sr=8-5

This is what I did. Swap out the 120 volt element for a 12volt one. I went with the 300 watt, which is only a 25 amp draw. It basically runs off excess solar once the batteries hit float. 2 to 3 hours a day keeps it more than hot enough and it doesnt draw too hard on the batteries

[jackrabbit59]

I do it everyday. I have 900 Amp hours of lithium batteries, twin 3000 watt inverters to provide 240 volts, 25 amps on each 120V leg. My 11 gallon hot water heater uses 6 amps on each leg of the 240 so 12 amps at 120. I heat the water about 35 to 45 minutes and with no solar power coming in about 10 to 15 % of the batteries is used. I try to do the heating during high solar input and with 1200 watts of solar only 5% of the batteries are used up if I heat the water to maximum, about an hour. The water stays hot for at least 24 hours and warm enough to shower for 36 hours.
Also got rid of all the LP gas. I have 1000 watt microwave, 1500 watt induction cooktop and 1500 watt oven. I can run 2 of these at any time but not all 3.
Planning to add another 600 amp hours of lithium so I can run my AC overnight in the master stateroom. No having to listen to the genset.
Love the lithium but you need a big pocketbook to set it up right.

[Marathon1150]

Originally Posted by Boatwright

"What do you guys think?"

I think you should listen to your installer. Any appliance that produces heat uses lots of juice. High power electric gear for mid-size sailing yachts is practical for short use times: like an anchor winch (and there are many problems with those), for boats with a gen-set, and for those that rarely leave the dock and shore power.

For example: A 1,500 watt resistance element (the smallest size available) will draw about 140 amps @ 12v when run through your inverter @ 90% efficiency. If you don't know volts from amps, that is a large! current.

Heating water by running your engine for a short time is actually very efficient. You will have a comfortable shower in a half hour of engine run, burning a 1/2 qt. of fuel, and charging your batteries for other uses at the same time. In real world cruising, rarely a day goes by that we don't fire up the old Volvo for one thing or another.

IMO: Hook up the element in your water heater to your shore power and forget about using it when you are away from the dock.

I agree with all of the above and also use a solar shower in temperate locations when the sun is shining. Most batteries have a finite number of charge/discharge cycles and conserving their useful lifetime to power things that absolutely require electricity is important to me.

In equatorial waters we find that blue jerry cans strapped to the rail and exposed to warm air and sunshine heated the water to a perfect temperature for a refreshing cockpit shower using a bucket. We learned this approach living in Indonesia (bak mandi) where it is always hot and the water supply is frequently interrupted. A barrel of water, a bucket and a dipper work really well.

On a boat, the approach is not very sophisticated but preferred over using the shower in the head which drains into the bilge. The pump that I bought to move shower water from the head collection area out through a thru hull remains uninstalled.

[Mike Banks]

I used LP gas. Simple--unlimited supply as long as there is water in tank and gas in cylinder.

Unless you have about two thousand watts of solar plus wind backup for stormy days, forget about electric hot water unless you run a genset--which is better than running an engine needlessly.

But solar water heat exchanger works fine if you shower at the end of the day, but--be careful. It gets REALLY hot.

[col50]

Originally Posted by Capt. Ray

Why would people want a hot water heater? Personally I find a cold water heater more useful.

Sorry, we don't have any of those.

[goboatingnow]

Originally Posted by Mike Banks

I used LP gas. Simple--unlimited supply as long as there is water in tank and gas in cylinder.



Unless you have about two thousand watts of solar plus wind backup for stormy days, forget about electric hot water unless you run a genset--which is better than running an engine needlessly.



But solar water heat exchanger works fine if you shower at the end of the day, but--be careful. It gets REALLY hot.

Immersion elements down to 500w are widely available here including 12v versions.

[paul2884]

We do use the inverter to power the immersion heater (800w). We do this with the engine running, the 90a from the alternator covers the draw from the batteries and we get hot water much quicker than from the engine alone. Don't think running it from batteries alone would be a great idea unless you have an all full lot of batteries!

[Don C L]

Using electricity to heat water on a boat seems a bit Rube Goldberg to me.

[pnw2022]

I actually just switched over my water to heater to also be able to run off the inverter. From a practical perspective, I don't think it will be reliable (600w now and two more 150w panels soon) overall.

I am in the Pacific Northwest, and as another poster noted, only expect it to be useful on odd occasions in the summer when I am dumping excess solar mid-day and no plans to move the boat for a few more days.

For some real world data on what I noted playing with it a few hours ago.
Inverter/Charger: Magnum 200xx, which offers 2000watt constant load and up to 3100/3300 peak.
Water Heater: 11 gallon Force 10 with a 1500 watt element.
I think the heater is set to ~140F/60C and it also has a mixer valve since it gets substantially hotter when heated by the engine.
Batteries: (3) Lifeline 210AH AGM about a year old.

First test - filling the sink with a couple gallons into the sink for some overdue dish washing.

Inverter kicked on about five minutes later with a steady draw of 137 amps at 11.8 volts for about 15 minutes. Similar to the microwave and the big electric coffee pot. That matches to about 1616watts which mean about 93% efficiency with a 1500 watt water tank element.


After this summer and some experiments and fun with this I think I will move the water tank wiring back the way it was. It was originally wired to avoid the inverter and accept power only from shoreside or the generator (panel is wired for generator I do not have one).

That wiring makes everything pretty idiot proof.

The problem being that with the my overall battery capacity it is normal with the coffee pot, microwave, (anything 1200/1500) watts to pull the battery down to ~12.0 volts or lower while the load is drawing. Something silly like taking an evening shower and accidentally leaving the water tank turned on, in combination with perhaps some other unusual high power usage that day would leave the battery in less than ideal state of charge by morning?

Also issues about somebody using the microwave or coffee pot or curling iron and having the water heater 'kick on' while doing that, etc.


Oh - this is also a handy calculator about heating water.
https://bloglocation.com/art/water-h...e-energy-power

[Franziska]

When we don't use our thermosolar panel, we heat via the inverter from our 840Ah battery.

Does not need an aweful lot of power and its replenished easily by 1200w solar on the next sunny day.
So works without issue via the inverter as long as you do not forget to switch the heating element off after a while.

[newhaul]

I have a little 1.5 gallon unit just for hot water for washing and washing dishes . One 1500 watt 120vac element takes about 15 minutes to get hot . On my inverter . Also have a 300 watt 12VDC element to use as a dump load for my solar and wind gen .
Bet it's the smallest ever seen . Was salvage item for me so no ideas but likely home or custom made . No good pictures at the moment