The majority of today’s homes heat water with either electricity or natural gas. When we remove these from the equation, we discover the reality of how much energy it takes to heat water.
Placing a pot of water over a fire is a good method for heating some water, and you should absolutely do so whenever possible, but there is an easier DIY alternative.
How Does This Water Heater Work?
The off-grid water heater I detail here requires a wood-burning stove, and we are going to harness the heat energy that radiates off of it to warm up the water.
All that is needed is to build a run of copper pipe along the sides of your wood stove through which cold water will enter, and hot water will exit.
Since copper is such an amazing conductor of electricity and heat, the pipe will become heated and transfer that heat to the water inside. What this creates is an ‘on-demand’ hot water system.
The Wood Stove
Building your wood stove is not difficult as long as you have access to a welding machine, angle grinder, and a supply of steel.
I made a woodstove for this project out of an empty 20-pound propane tank that I had lying around.
Related: How to Make Your Own Solar Stove
If you do not have access to a welding machine, you can purchase wood stoves online.
Building a Wood Stove From a 20 Pound Propane Tank
Turning a propane tank into a wood stove is not difficult and requires only a few easily obtained materials to build.
Unfortunately, there is no way to accomplish this build without using a welding machine, angle grinder, and an oxy/acetylene cutting torch or plasma cutter.
These tools also require some skill to use, and many safety considerations need to be taken.
1. Empty the propane cylinder and thoroughly clean it inside and out. Be sure that all the liquid propane is removed before proceeding further.
2. Remove the rings at the top and bottom and remove all the paint from the tank’s exterior.
3. Lay out and cut the opening for the door. Make the opening large enough to load wood into the stove comfortably.
4. Save the piece that you cut out to fabricate the door.
5. Secure this piece to the rest of the woodstove with a section of piano hinge. Add a handle at the same time.
6. Fabricate a base from the 1x1x1/8 angle. I chose to make it 12 inches square.
7. Cut four legs on a slight angle so that they will slope upwards to join with the cylinder.
8. Weld the base frame onto the stove body.
9. Cut a hole in the top to accommodate the four-inch stove pipe.
10. Slide the stovepipe into the hole and weld it in place.
11. Cut some expanded metal to the inside diameter of the wood stove and place it inside the stove.
How you run the pipe will depend on your woodstove’s shape, but the basic principles are the same.
What we are trying to do is snake the pipe along the side of the woodstove to get as much pipe as possible exposed to the heat. We can do this in two ways.
We can use pipe elbows to snake the pipe along the side of the stove, or we can use a coil of copper pipe and wrap it in a tight coil around the chimney of the woodstove.
The difference between these two methods is that there will be less heat from the chimney, and therefore the water will not be as hot.
However, since using the woodstove sides create hotter water, the risk of too much pressure is ever-present and needs to be accounted for.
Materials For A Side Mounted Heater
• Copper Pipe
• Copper 90-degree elbows
• NPT copper fittings
1. Measure the height of the woodstove side that you want to place the heater on while figuring out how many vertical runs of pipe you will use.
2. Measure the height of the elbows and how far the pipe will fit inside of them. The difference between these dimensions multiplied by two is the length that will be subtracted from the heater’s height to figure out the cut size.
3. Cut enough small lengths of pipe to join the 90-degree elbows together. At the same time, cut the straight sections.
4. Cut two six-inch lengths of pipe for the inlet and outlet.
5. Trial fit all the components together.
6. Solder the 90-degree elbows together to form the 180 degree turns in the pipe run.
7. Layout the heater on the stove to check the fit.
8. Solder the joints together. Don’t forget to install the fittings on the inlet and outlet so you can connect the water supply.
9. Drill holes for bolts to hang the heater on the side of the stove.
10. Install bolts that are long enough to hang the heater on.
11. Insert the bolts into the holes and secure them on the inside of the stove with a nut.
12. If needed, use a piece of metal strapping to hold secure it only on one end so it can be easily lifted out of the way to remove or install the heater.
Using the Water Heater
There are a few options when it comes to operating this water heater.
The first is to use it as an on-demand type of system where you draw the coil’s water as needed to get hot water.
The problem is that there will be a buildup of pressure within the system, and you will need to have a pressure relief valve in the system.
My preference is to keep the coils removable so that you can quickly and simply install the heater on the stove when needed and remove it when not in use.
Harnessing the heat that a wood-burning stove emits is a great use of this radiant energy to provide us with heated water.
Being able to get hot water on demand is one of those comforts that will make a grid-down scenario a little bit more comfortable.
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