DIY water heater?

Short_Shot

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'Everlanders' on youtube wrapped a 12v silicone pad around a 6 gallon heater under the insulation and I believe left the AC heater element in place. You could cap the element hole but I you ever have shore power or a generator it would be useful.

As long as you properly interrupted the 12v heater when on shore power it wouldn't see excess usage, but it might not matter if you have a big enough converter and thus 12v output to spare. Running both would just mean it heats up faster.
 

efficientPV

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Try it with a 300W element. 700W is far too much current for any thermostat I know. It takes less than a KW to heat 6 gallons so 3 hours.
 

JHovel

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We have just returned from a 5 months' trip around far northern Australia in our Transit campervan. It came with a Dometic 240V electric hot water service of 17 litres. The element was 1.4kW and heated from cold in 1hr.
Just before the trip, I replaced the element with a 12V 600W element as described above. The thread for the elemt was exactly the same (1"BSP). That heated the water in about 1-3/4hrs as the current is higher with the Lithium battery which always stays at 13.2V and the heater actually draws a bit over 60A.
I fitted an 80A relay to the thermostat - as it was designed for only 10A of course. So the thermostat only switches the 12V relay.
We found that all connections got too hot drawing 60A for that long. So I disconnected one of the heating U-tubes after a few days. So it now draws 30A and everything stays cool. It now takes almost 3 hours to heat. That actually doesn't make any difference to us: it's enough for two showers and doing dishes.
The other advantage is that on a bright sunny day, our PV system provides the power for free anyway. We ran out of hot water a couple of times and reheated after sunset off the battery alone without any issues at all.
 

Dzl

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I like the ideas being discussed in this thread, I've been thinking a lot about different ways to heat water recently (an area I have zero pre-existing knowledge/experience), and especially methods that tap into surplus energy sources. I think using excess solar with a DC element sounds cool, I think using engine heat for water and space heating is very smart, but I think at least one dependable/always available source (whether diesel/gas or propane or posisbly in some situations electric) would makes a lot of sense as a backup.
 

Dzl

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I have a Eberspacher/Espar D5 Hydronic. I use an Isotemp marine water heater. The water heater has an integral coolant heating loop. If I wanted I could also install an air heating radiator on this coolant loop.

For a couple reasons my D5 and isotemp has its own loop which is isolated through a plate heat exchanger from the engine. But this isn't required.

For on demand heating with a hydronic unit, you don't need a water tank. Instead a plate heat exchanger and a tempering valve can provide on demand water heating.
@Luthj I like the sound of your system, it sounds similar to what I would eventually like.

Am I correctly understanding that with your setup, you have 3 available methods of heating water (1) engine heat via a heat exchanger/isolated loops (2) electric via the built in heating element in the tank (3) diesel hydronic heater. And that the diesel hydronic heater is also used for living space heating and optionally pre-heating the engine? Do you use engine heat for living space heating as well?

This seems like a very efficient and smart setup.
 

Luthj

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And that the diesel hydronic heater is also used for living space heating and optionally pre-heating the engine? Do you use engine heat for living space heating as well?

I don't currently use the hydronic loop for heating my smaller van, I have a D2 air heater for that. It uses less electrical power, and its quieter. For a larger area with more rooms, separate radiators on the hydronic loop makes sense.

Engine heat for the living space is often used though. My van has a feature called "rest". When I hit a button on the dash with the engine off, a coolant pump pushes coolant through the cab/dash heater, and the fan turns on. I can get full heat for about 20 minutes, and partial heat for another 20 after a drive.

Am I correctly understanding that with your setup, you have 3 available methods of heating water

Yes. I also have the hydronic loop plumbed into an antifreeze loop for my underbody plumbing and tanks. With a separate smaller pump, I can keep all the stuff liquid even at -10F. The ~700W element in the water heater is plenty for this purpose, so I can just plug the van in when I am parked up someplace cold, and don't want to burn diesel.

Some of the details are in my build thread over on the sprinter forum.

 
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Dzl

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One thing I'm trying to understand, is if you keep the engine heating loop and the other loop (water heating, etc) separate connected only through a heat exchanger (which seems advantage in terms of minimal modifications/complexity/points of failure to the engine cooling system) how will this system actually work in practice.

When preheating the engine for instance, you would switch on the diesel heater, but what moves the coolant in the engine cooling system in that situation?

Likewise, when using engine heat only to heat the water heater, what creates flow on the water heating side of the system (a water pump switched on manually?
 

Luthj

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When preheating the engine for instance, you would switch on the diesel heater, but what moves the coolant in the engine cooling system in that situation?

Likewise, when using engine heat only to heat the water heater, what creates flow on the water heating side of the system (a water pump switched on manually?

I have a custom made controller which can control the pumps in both loops. When I hit the engine preheat button, the engines electric coolant pump runs. Conversely, when the engine is running and up to temp, and the water tank isn't the heaters coolant pump runs. Of course a few cheap electronic thermostats with remote probes could do 90% of the same functionality, without any need to code something up. In my case I have some one wire temperature sensors, an arduino, and a relay board. For display is a 24x4 LCD panel, and control is via a couple of buttons. All temperatures are hard coded, which works fine for my applications.

As you mention, there needs to be coolant flow in both loops for heat to be exchanged between.
 
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