Off Grid Hot Water in the Summer

My favorite method of heating a pressurized household water system is by using a wonderful Amish made wood cook stove.  They are simply wonderful and provide a completely independent means of heating water all winter, as well as much of the spring and fall.

The problem for us has been what to do in the summer when it's too hot to run the wood cook stove.  And this question becomes a year-round dilemma for folks who don't have a wood powered means of heating water in the winter.

What options are there for a modern off grid homesteaders that don't want to take cold showers?  Thankfully, we have some solid choices.


Propane Options


Standard propane water heater

The problem with heating hot water is that many homes are utilizing a standard 220 volt electric hot water heater that consumes massive amounts of electricity.  When you live off the grid, this is a problem.  It would require a massive renewable energy system that would be cost prohibitive for most people.  And there is no reason why one would need to use such a water heater.  There are many other options.

A standard propane water heater would work just fine, as long as one has propane (obviously!).  Another popular off grid option would be a propane tankless (a.k.a. on-demand) water heater.  You have to be careful with some of the tankless propane models, though, as I understand they may use greater or lesser degrees of electricity (which would be a negative for someone looking to lessen their electricity usage).  Rheem is one brand that comes to mind that I would not want to use off the grid.  The best options available at this time are made by Bosch.  They have standing pilot models and hydrospark ignition models that are both completely non-electric.  I understand that currently there have been some issues with the hydrospark models (which also require a higher level of water pressure in order to operate properly), so it seems that the good old standing pilot option may be the way to go.  These tankless propane water heaters are touted to be more efficient than standard models, but they do cost more up-front.  So either pay now, or pay later.

While propane is convenient and could be a great option when you have it, we would like to have options that don't require having to purchase fuel.


 Solar Options

There are many options for solar water heaters that range from inexpensive home-made jobs to high-end state of the art commercial models.

The home-made options are typically not suited for use during times of the year when temperatures dip below freezing and would need to be winterized before any threat of fall or winter weather arrives.  There are probably hundreds of variations that may be found on the internet that range from coils of black plastic pipe on one's roof to coils of copper inside a box with outer glass cover (creating a greenhouse effect).  Some of these utilize a DC electric circulating pump to push the heated water into a storage tank and bring fresh cool water into the heater.  This pump may be activated by a switch that is temperature controlled or it may be directly connected to a solar panel and only runs when the sun is shining (precisely the same times that the water is being heated and needs to be circulated).


Evacuated tube solar water heater

Commercial units come in two main varieties--evacuated tube and flat panel.  Evacuated tube models are composed of numerous rows of glass tubes with another smaller tube inside each of the larger tubes.  A vacuum is pulled between each of the two tubes which greatly lessens the loss of heat to outside weather.  Water or an antifreeze solution is then circulated through the inner tubes.  The advantages of evacuated tubes lie in greater efficiency and less heat lost.  So they work quite well even during surprisingly cool temperatures.  However they are somewhat fragile and may not be as suited to areas with a great amount of snow and ice due to the potential for breakage from buildup.


Flat panel solar water heater

Flat panel models look much like solar electric panels but contain tiny water passages which enable a great amount of surface area to come in contact with the heat from the sun.  While not as efficient as evacuated tubes, flat panels still work very well and are certainly more rugged when faced with heavy snow and icy conditions.

Typically an antifreeze solution is circulated through the tubes or panels and the hot fluid is routed inside to a heat exchanger which transfers the heat of the fluid to the home's hot water.  There are some varieties of evacuated tube heaters that are called drain down systems, which do not require the use of antifreeze because the water drains away from exposed areas once the water cools off.  And just for the record, it is possible to set up a solar water heating system that doesn't require an electric circulating pump.  This would be called a thermosiphon system, operating on the principle that heat rises.

This was the type of system I was planning on installing for summertime use in our rental cabin.  The disadvantages would be the amount of work involved in installation, significant cost of commercial systems, and reliance on an electric circulating pump (unless it is set up as a thermosiphon system).  For us, being in a temporary location, I was hesitant to purchase and install the equipment and then be faced with tearing it out again in a year or two.


Another Interesting Option

That brings us to the option we chose.  Our winters are cloudy with short days and it takes a substantial solar system to make any significant impact on power usage during the months of November, December, January, and sometimes even February.  Since we have a solar system that is appropriately sized, we have plenty of excess electricity during the long, hot, sunny days of summer.  Often our batteries are fully charged each day by noon or even before and that means we were wasting tons of power for the rest of the day.  What to do with all that wasted power?  Why not use it to heat water?  So that is what we did.


DC water heating element

I purchased a DC 12 volt water heating element that can burn either 30 or 60 amps (depending on how it is wired).  There is also a 24 volt model available.  Currently I have a water coil in the wood cook stove that is plumbed into a heavy duty range boiler tank and circulates without any electric pump as a thermosiphon system (read all about it here: Hot water for free--from the wood cook stove!).  It just so happens that there is an additional threaded port in the middle of the tank.  Our DC water heating element screwed right into that port.

I then purchased an inexpensive Schneider (used to be Xantrex) C-60 charge controller.  This unit may be operated either as a conventional charge controller (disconnecting the charging source from the batteries once the battery voltage reaches a certain threshold) or as a diversion load charge controller (once the batteries reach a certain threshold, any excess power is diverted to a diversion load and "burned off").  For applications using solar panels to charge the batteries, the conventional charge controller mode would be used.  Once the batteries are full and voltage reaches the set point, the charge controller disconnects the solar panels from the batteries.  But for our application, we will use the diversion load mode.  We have excess power that we want to burn off and that is exactly what a diversion load charge controller accomplishes.  The charge controller is connected to the battery bank by wiring it into our system's DC disconnect box, which adds the safety of breakers to the system.


Wiring #2 wire to elements

I then purchased 2 strands of 2 gauge copper wire to run from the charge controller to the water heating element.  The size of wire you use will depend on the distance to be covered, whether you wire the water heating element to run only one or both elements, and whether you use the 12 volt or 24 volt model.  If you are not familiar with properly sizing wire, have the company you buy your heating element from assist you.  Here is an online calculator.

Since there are two heating elements on this unit, it may be wired to run only one or both, which will consume roughly 30 amps or 60 amps respectively.  To use both elements, effectively making them one 60 amps element, simply make sure that the connecting bar is connecting both elements together.  If just one is desired, simply remove the connecting bars and connect the electrical wires to one or the other element.  Our unit is set to run both elements for a maximum of 60 amps.


Schneider C60 charge controller

Next we need to set the charge controller.  Since I still have my main charge controllers connected and operating with the system, I need my new diversion load controller to start diverting power to the water heater BEFORE my main charge controllers reach their threshold and begin disconnecting the solar panels from the batteries.  If this step is not taken, your diversion load controller will never divert power to the heating element.  This is something you will need to play with for a while, but eventually you will find a setting that works fairly consistently.  As the solar panels begin charging the batteries in the morning, our voltage begins to rise.  As the batteries become more and more charged, we approach the absorption set point.  This is the point at which our main charge controllers begin restricting power to our batteries and make sure the voltage does not rise above this set point.  For a 12 volt system this set point is often 14.8 volts (29.6 volts with a 24 volt system).  But since our diversion load controller is set to kick in at perhaps 0.1 or 0.2 volts lower than the main controllers, we divert all that power to the water heater.  If our solar panels are producing so much electricity that they are powering the water heater and still have more left, the voltage will continue to rise until it reached the set point of the main charge controllers and then they will begin restricting the flow of power into the batteries.  When properly set, all the controllers operate together harmoniously.


Valves are on pipes #1 and #5

In practice, we have found this setup to work quite well in our climate.  There are only about 2 or 3 months during the summer when running the wood cook stove is uncomfortable.  During spring and fall, we can build a flash fire early in the morning to heat water and cook, without making the house too uncomfortable.  So our difficulty was during that 2 or 3 months of full summer weather.  In this area, that is also the time of year that is very sunny.  So we have found that by the end of the day, we have half a tank of hot water if we reserve the hot water for showers alone (i.e. little or no dish washing with the hot water).  The reason that only half the tank is heated is because of the location of the port on our range boiler tank.  It is located half way up, so everything from that point on up is heated.  I insulated around the tank to help the hot water stay warm during the night.  I must note that we do not have an abundance of hot water with this system, but it is sufficient for the two of us and is certainly better than the alternatives (taking a cold shower or heating up the house on a hot day).  I also found it useful to close both valves on the wood cook stove thermosiphon system.  This prevents a potential backwards flow of hot water, thus diluting the hot water in the top with the cool water in the bottom of the tank.  IMPORTANT - Be certain to open these valves before firing up the wood stove!!!  Failure to do this could result in the water coil exploding in side the firebox.  Another safer option could be to install a check valve in the upper line (#1) in order to prevent the backward circulation of water through the wood cook stove water coil.

NOTE:  Never forget to put a pressure relief valve on any hot water heating tank/system as the power of hot water is incredible.  You'll see the location of our pressure relief valve on the picture to the right (#2 on the top of the tank).  Thanks to Jeff for reminding me to mention this!




Threaded port half way up range boiler tank

One improvement that could help this system to operate significantly better would be to custom order a range boiler with an extra port near the bottom.  This would enable the heating element to heat the entire tank rather than only the top half.  And the reason I say an extra port, is that you could still have to option of installing a second heating element in the location mine is currently installed.  If you have a significant solar system (at least 2,000 watts), it is certainly possible to power two elements with surplus power on a sunny day.  Customization of the range boiler tank is available when ordered from Stove & More, where I purchased mine.  My tank came with the standard configuration since I didn't know I needed a custom setup at the time nor did I realize it was possible to do so.

Installing good insulation on the range boiler tank would also help significantly.  I added some makeshift insulation for a while and this definitely helped, but permanent heat resistant insulation would be much better.

Both of these improvements could go a long ways toward providing more hot water for a larger family or one that uses more hot water than we do.  And while this system probably does not produce as much hot water as a good solar hot water system, it works and was a much easier installation.  It cost far less than a solar hot water setup as well, since we already had the range boiler tank and it was already plumbed in.  So if you find yourself thinking of ways to use your extra power and need some hot water, give this a try!


b2ap3_thumbnail_question1-trans_20120704-012540_1.png How do you heat your water off the grid?


  • John leach

    July 17, 2015

    Thanks for the information about the hot water options looking now for a suitable property to set up off grid possibilities . Are you still offering me off the grid boot camp program in the future?

  • Michael

    May 22, 2017

    Nick, there are now solar panels that heat water and also harvest electricity. They are all the rage. I sometimes wonder if they are a jack of all trades and master of none sort of deal.

  • Darrell

    May 23, 2017

    I really enjoy all mail sent from you about living off grid I am inspired by all THANKS AGAIN Darrell

  • Jeff

    May 23, 2017

    Great idea! I didn't know you could get a 12 VDC heating element that big. I used to do a lot of traveling and had a 12 coffee pot that I used to joke would make a 20 oz mug of coffee in 30 miles at 70 MPH. It was only 200 watts and took forever. Knowing 240 VAC electric hot water tanks as I do, (your system is a basic analog), your system is fairly safe because you can only heat the upper half of the tank and have the lower half to absorb some of the excess heat on a daily basis. You suggested to your readers that they could order a custom made tank with the heater port at the bottom. This is all well and good but if someone direct wires one or two units in a smaller size custom tank without high temperature electrical cutoff thermostats or an over pressure safety release valve, in a high sunshine state like Florida, Hawaii or most anywhere in the south, there is the possibility of explosion, death if standing next to the tank when it blows, injury or property damage. The program, Mythbusters, had a segment on this same subject. They went to the Alameda air strip where they have room to do dangerous stunts. They took a 30 gallon, 240 VAC tank, removed the thermostats and over pressure safety release valve, filled it with water and sealed it up. They installed it in a miniature "house" built to code standards. They connected it to a 240 VAC generator and waited. They did this in response to a "myth" that one had it's safety systems fail and go through the roof of a house. After about an hour, that is just what happened to theirs. It went up through the roof and up over 100 feet. I know that hot water tanks aren't "sealed" usually but they also has the news story accompanying the "myth". Those safety systems are there for a reason and shouldn't be ignored. I think you are doing a tremendous service to the off grid community. Keep up the good work but I would hate to see you or yours or anyone else get hurt over what I believe to be an accidental oversight let alone the liability exposure you may face in some states. Thanks again for the updates. Jeff M.

    • Nick Meissner

      May 24, 2017

      Hi Jeff, Thanks for your note. Very true about the power of hot water. I would never suggest removing the pressure relief valve on any hot water system. Indeed, in our system mentioned in the article, there is a pressure relief valve on the top of the tank (where the temperature is the highest). The extra heater port I mentioned was not one that replaces a pressure relief valve, but rather is an extra port. As you mentioned, these DC heating elements put out significantly less heat than a traditional 240 volt element. If you had two of them in the tank I suppose it might be possible on a long sunny day with no water usage to build up enough pressure to set off the pressure relief valve, but I never had that happen with our system. If you did find that you had enough heating elements and your solar array was so large enough to power them for enough hours to set off the pressure relief valve more than once in a while, then it probably would be a good idea to remove or turn off one of the elements. Unfortunately, with our setup I never got close to having that problem :-).

      Thanks again for the word of caution in case someone ever has the temptation to remove their pressure relief valve for some reason!

  • Kalon

    May 24, 2017

    Thanks again for another informative and helpful article. I had never heard of this heating element idea. God bless.

  • steve

    May 30, 2017

    What about a batch heater. I knew a guy in Flagstaff, AZ (@ 7,000' elevation) that used one for over 20 years until he moved with no problems. Just uses your existing water pressure from the well.

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