12v water heating setup

[JimMann]

Hi guys,



I’ve just bought this stainless 30L water heater, it has a 12v 600w/300w element and fully insulated but I have no experience with a set up like this so I was wondering if anyone can give me some tips on how to set it up safely and how to install a thermostat as I’m assuming it doesn’t have one from what I can see. Also is it possible to get a automatic pressure pump for hot water and a set up like this.

Thanks 🙏

[a64pilot]

It’s not as simple as you May think. You first need a T&P valve to keep it from becoming a bomb. It functions as a relief valve if temps or pressure go too high. Water heaters have exploded with enormous force.
Thermostat is an off the shelf item, issue may be getting one to handle the amperage, 600W at 12V is of course 50 amps, and that’s continuous for probably two hours until the water is really hot.
You will need really large, massive cabling as the voltage is so low.

Your current pressurized water system provides the water pressure, just tap into it, if you don’t have pressurized water, add it, it’s the simplest way, and gives you the most for what you pay for.

Why 12V? I can’t think of a good reason to heat water with 12V.

[JimMann]

Hi,

I planned on running that pressure relief pipe on top straight out the boat as I dont want any pressure building up at all.

I went with a 12v system because I have sufficient batteries and solar as I don’t want gas on my boat.

I’ve seen a 150w element heat 30L in about 2 hours in an open plastic tub, I only plan on using 300w. But even if I have to run it for 1.5hrs a day, it’s nothing really

Just makes sense as i can create more power than I need and it also financial sense

Thanks

[kenbo]

Originally Posted by JimMann

Hi,

I planned on running that pressure relief pipe on top straight out the boat as I dont want any pressure building up at all.

I went with a 12v system because I have sufficient batteries and solar as I don’t want gas on my boat.

I’ve seen a 150w element heat 30L in about 2 hours in an open plastic tub, I only plan on using 300w. But even if I have to run it for 1.5hrs a day, it’s nothing really

Just makes sense as i can create more power than I need and it also financial sense

Thanks

For the thermostat you'll need a 12v model. Missouri Wind and Solar sell them in the US but I'd would imagine they can be had most anywhere. To add a thermostat and T&P relief valve it looks like you'll have to install a manifold on the top outlet. Any standard marine automatic 12v water pump will work fine.
https://mwands.com/shop/product/wate...t?category=303

[kenbo]

From the looks of that t'stat you'll most likely need to use metal pipe like brass and flatten it a bit to get full contact and hold it in place with a hoseclamp. Klugey but should work well.

[JimMann]

Also. I’m currently putting in a new water system, I have everything to do it including the auto pressure pump but it’s doesn’t seem to be for hot water, I assumed I would need separate pumps

[JimMann]

Hi there,

My thought process was not to have it pressurised at all and run that pressure relief pipe out of the boat. I want the boat to be safe as possible, replacing gas with a bomb seems counter productive

Thanks

[kenbo]

Not at all, as long as the feed water for the hot water heater is part of your pressurized cold water.

[kenbo]

Also, I don't believe that you need to pipe the T&P outlet outside the boat. I've always run the discharge line into the bilge. No harm in taking it outside the hull as long as you already have the through hull but why put another hole in the hull if you don't have to.

[kenbo]

Maybe I'm comfortable with T&P relief valves but if you purchase a quality valve and replace it periodically it periodically I don't see a hot water heater like you're installing as a bomb. Do you plan on piping your boat with schedule 80 pipe or some kind of flexible tubing?

[JimMann]

Good point, I did consider running it into the bilge but I remembered there was 2 expansion copper pipes coming out of my old 2 water tanks (plastic 240L barrels) I haven’t investigated yet but they seemEd to be heading out up toward the the pilothouse. I’ll have a look this weekend but I’m sure there’s a hole one each side of the pilothouse

Thanks

[JimMann]

I’ve bought 15mm flexy stuff and all the fittings, it’s the main named brand (speed fit or summit like that) I’ve posted this question around a bit and everyone seem to be sending me the myth buster video of exploding water heaters.. or telling me 12v heating a silly idea, makes perfect sense to me as I’m planning on going cruising for a few years and free hot water sounds like sustainability

[kenbo]

Mike,

Just install the T&P valve first at the top of the tank. My only concern from what you stated as your plan is using the 300W element rather than the 600W combined. I haven't done the BTU calculations but your recovery time (° rise from incoming water temp) will be fairly low.

Have you considered installing a switch, Off/300W/600W, to give you an option?

I just did a quick calculation, it will take 35 watt-hrs to raise your 30 liter tank 1°C. Or said differently, 300W will raise 30 l of water about 8.6° C in one hour assuming 100% efficiency. You'll have to decide if that's OK.

[GILow]

Wow, you must have a lot of solar. I’ve got 760 watts and I can’t make the maths work to heat water from the batteries on my boat.

Whatever you do with this setup, I suggest you leave provision for a heat exchanger just in case you want to boost it later with something like a diesel heater or perhaps engine heating.

Incidentally, how thick is the insulation on that tank?

[belizesailor]

Originally Posted by a64pilot

It’s not as simple as you May think. You first need a T&P valve to keep it from becoming a bomb. It functions as a relief valve if temps or pressure go too high. Water heaters have exploded with enormous force.
Thermostat is an off the shelf item, issue may be getting one to handle the amperage, 600W at 12V is of course 50 amps, and that’s continuous for probably two hours until the water is really hot.
You will need really large, massive cabling as the voltage is so low.

Your current pressurized water system provides the water pressure, just tap into it, if you don’t have pressurized water, add it, it’s the simplest way, and gives you the most for what you pay for.

Why 12V? I can’t think of a good reason to heat water with 12V.

Solar dump load.

This is a project on my list too. Aux Out from my solar controller is 20A max which I think will drive a 220V element just not very hot...no problem, only need to take the chill off here in the tropics. I think my existing t-stat will handle it too, but need to research/test that. Tank already has over pressure protection.