Homestead Hot Water – A Thermosiphon Loop

In my previous post on homestead hot water, homestead-hot-water-part-1/ I discussed the hot water set up we had at the Maine homestead, the most basic system possible. For 20 years, we lugged buckets of water in by hand from a hand pump outside, poured the water into pots, set the pots on one of our wood stoves to heat and then we carried the hot water to the tub, sink or washer. This was great for building muscle and character. But yikes, there had to be a better way! And there is. A thermosiphon loop!

Our Canadian homestead has a piston pump and draws from a hand dug well. You can read about it here. homestead water supply That pump/pressure tank combination supplies pressurized water to the house. A wood cook stove in the kitchen set up with a thermosiphon loop and a storage tank provide our off-grid homestead’s hot water.

A Thermosiphon Loop

Don’t let the fancy term “thermosiphon loop” intimidate you. It’s a simple concept. Just as hot air rises, hot water does as well. A couple of paragraphs from my book “Off-Grid and Free- My Path to the Wilderness” explain the concept pretty well.

“We have a standard home water heater set up next to our stove. It’s roughly a 50-gallon tank. And that’s all it’s being used for, purely a storage tank. No electricity goes to this heater. We set up plumbing from the tank to the stove’s water jacket to take advantage of the flow of heated water. Just as hot air rises, the same principal applies to hot water. As water is heated in the jacket, it starts to flow upward and into the top of the water tank and is then replaced by colder water coming out of the bottom of the tank.”

“This is a simple and efficient method of taking some of the heat from the wood stove and using it to raise the temperature of water for household use. It works great, and it’s free. There is no need for any in-line pump since the water circulates on its own. The size of the tank is balanced with the size of the stove so we don’t end up with a tank of boiling water, which would happen if we had a much smaller tank. But the water does get hot. Since this is a standard insulated water tank, the water stays hot for days even if we have no fire in the stove. A pressure relief valve, standard in all homes, is a must for our system as well.”

There are many ways to plumb thermosiphon loop systems using copper tubing in fireboxes, around chimney pipes or on the exterior of a wood stove. If you understand the basic concepts, you should be able to utilize a wood stove to either fully heat or pre-heat water for your homestead.

We purchased a modern wood cook stove complete with a stove “jacket” which is simply a small tank that fits in the firebox. The jacket comes with two threaded ports to which piping can be run.

Hot Water Tank or Range Boiler

Although we chose a standard hot water heater as our storage tank, there are tanks made just for this purpose. Here is an example.

Because both our water tank and stove jacket have ¾ “ pipe threads, I chose to use ¾ “ galvanized pipe for all of my connections. That would be the minimum pipe diameter I would ever use in a system. The range boiler as shown has 1” pipe hookups which is even better. The bigger the pipe, the less restriction which allows for easier water flow through the system. Very important since a thermosiphon loop relies solely on temperature to create and maintain water movement.

As I mentioned above, I used galvanized pipe the first time I plumbed our system. However, it had a tendency to clog up with a brownish goo. Our water in the house is filtered so I’m not sure how this goo was created but nonetheless, it was a problem. Every year or so I needed to clean out the system.. Eventually, I converted over to copper pipe and it has been trouble free ever since. Copper seems to be the best choice to plumb our system. I have 2 couplers in my copper plumbing so that if I need to remove the water tank, it is an easy job of disconnecting the couplers and the tank is free.

Let’s take a look at our thermosiphon set up. You will note a number of things in the picture. The cold water inlet to the tank and the hot water outlet each have a shut off valve. That way, I can shut the hot water off in the house if need be or prevent cold water from going into the tank.

Hot water Tank Plumbed to Wood Stove

Hot water Tank Plumbed to Wood Cook Stove

I also have a valve on the tank outlet going to the stove’s water jacket. There are a number of very important points I’ll make. As with any hot water or potential steam arrangement, safety is paramount. It is critical that this valve remain fully open under normal circumstances. Tag it, tape it open or put a small wire tie on it so that it can’t be inadvertently shut off. But, I want that valve there so that if my stove jacket or plumbing happens to spring a leak, I have a way to shut down the tank outlet and prevent the tank’s contents from draining on to the floor. We did have a situation where the water jacket developed a leak and that valve came in handy.

Here’s what happened. We found out the hard way that it is very important to have water in the system before making a fire in the cook stove. One winter, we had returned home from a vacation and I didn’t have a chance to get the water up and running before Johanna started a fire in the wood cook stove. Because of that, our water jacket cracked. When I did fill the tank with water, it was obvious something was amiss when water started coming out of the stove onto the floor.

Another critical component of the system is a minimum of one pressure relief valve. Two is better. If for some reason the water gets too hot, it has a place to vent and release some of that built up energy. We have a relief valve with a tube going to a bucket set underneath to catch any released hot water. To install a pressure relief valve, locate the port going directly into the tank’s side and put the pressure relief valve there.

Hot Water Tank Plumbing

Hot Water Tank Plumbing

Unless Johanna is canning the entire day in summer or cooking the Thanksgiving turkey, rarely do we ever get water hot enough to open that pressure relief valve. We have enough experience to know when the system is building too much hot water and we just open a tap and let hot water run down the drain. It’s a balance between the tank capacity, the amount of hot water taken out of the system on a daily basis and the duration and intensity of the wood fire. Only experience over time will tell you whether you need to modify your tank size.

3 Final Points

The last 3 points I’d like to make are:

Make sure the water tank/boiler is higher than the bottom port of your stove’s water jacket. The idea is that you want the cold water in the tank to fall out of the bottom pipe and into the water jacket. If for example, you had the tank lower than the water jacket, you would be asking the water to flow uphill into the water jacket. Our tank’s bottom port is 16 inches above the bottom port of the water jacket and it works just fine.

The next point is you’ll notice I have a pressure gauge on the top of the tank on the cold water inlet. Although I have a pressure gauge downstairs in the root cellar near the water pump, this is a more convenient way for me to monitor with a quick glance, the status of our water system and pressure.

And finally, take note of the drain valve and nearby fire hose. The drain valve is handy for draining the tank for cleaning or if we go away for an extended period. The fire hose serves two purposes. I can run the hose outdoors to facilitate easier tank draining. And if the unthinkable were to happen, and the house catches fire, if we act fast, it might be possible to save the place by spraying the contents of the tank on the fire with the fire hose. No fire department will be coming to our aid so it is our responsibility to think ahead and give ourselves a chance. Please consider placing a fire extinguisher handy to your wood stoves too.

Until next time, keep the dream alive! We wish you a great day!
Ron and Johanna

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