Wood Stove to Heat Water in Tiny House

Hi, I am building a tiny house and I am aiming to incorporate a hot water system that relies on solar and wood fired heating to heat the water. This works by convection. The cold water supplies a hot water tank positioned above the wood stove. The cold water will cycle into the wood stove where it will be heated. The water then rises back into the top of the storage tank and will continue this cycle to create free hot water. This process is called thermosiphoning. I have drew some preliminary sketches and was curious if anyone had any suggestions, tips, advice, or see any flaws with this set-up. A couple questions I have are:

Will I need a pump to relay the hot water through the plumbing to the fixtures? I imagine that heat will produce enough pressure to push the water through the lines..is this true?

Will the hot water lines feeding to the fixtures need to re-enter the system? In my drawing it just ends at the kitchen sink..will I need to plumb this back in to the thermosiphon loop? Or will it be safe the way that it is.

Notes on the drawing: This is an overhead view of how the system will run through the tiny house. The top of the drawing runs along the right side of the house with most of the lines running through the cabinetry. It will then run along the front of the house (still in cabinetry) before entering the shower room (at the left of the house)where I was hoping the lines would rise up to the ceiling while running through the room and exit through the wall. It would then enter the storage tank located in a closet near the woodstove. The storage tank will be about 4 feet off the floor and the woodstove will be about 18 inches above the floor. I hope this helps. I would love to hear your thoughts! If you have any questions please let me know! Thank you all for your time .

If you would like to learn more about this system please see a previous forum on the matter found here:
https://permies.com/t/47521/wood-burning-stoves/Wood-fired-passive-gravity-fed#379982

Westin Tromberg : Solid fuel boilers are difficult to run safely, at the point that you have a wet back system tied to your wood stove you must have some circulation

through that system irregardless of the 'Need' for more hot water.

Even though your tiny house will be easy to heat, your designed ability to have a House that is Mobil increases the outside square foot age by your floors Sq.ft. ,

and this is the coldest Sq. Ft of your structure !

at the point that you are moving your vehicle during cold weather, when you stop you are going to want a fire -but 1st you will have to fill your plumbing system,

and make sure the system is bled ! Failure to bled the system, can case direct over heating damage to your wet back system, or possibly allow trapped water to

''flash to steam''.

Add to that the potential to lose your pump ether due to mechanical or electrical problems and you can enter into personal body harm for you and yours !

With a Fossil fuel fired boiler a simple switch can quickly shut off the fuel flow, with a solid fuel system you are left with attempting the fish burning wood out of

your wood stove, Both difficult and dangerous, or drowning your fire with water- I personally would not recommend that one ether !

So - The general recommendation would be to have an unpressurized system, and minimize shut-offs, Shutoffs always seem to get closed somehow at the wrong

time !



For theGood of the Crafts ! Big AL

Hi Allen, thanks for sharing your thoughts with me on this set up! Though the house is on wheels I don't intend on moving it more than a couple of times. It will usually be stationary. The floor is pretty well insulated and I intend to skirt the house with straw to help prevent drafts from sucking the heat away. I intend to have an unpressurized system where in the event it might overheat the pressure release valve would open and release the very hot water under the trailer safely. The stove I am using is called "The Hobbit" by Salamander Stoves and measures 18"x12"x11" and with the back boiler installed (to heat the water) the longest length of wood I can put in is 7" ! So I am a little concerned it may not have enough heat output to do the job effectively. You do bring up a good point about the pump failing. This certainly could be an issue. I am hoping though that a 30 gallon tank will be sufficient enough to keep the system supplied with water so it won't run dry I also intend on having a good size fresh water tank to keep the system topped off.

I don't think there is any reasonable way to make your system function as shown without being pressurized, which does raise the steam explosion issue seriously. If you must proceed this way, I would at least put the pressure relief valve directly next to the wetback instead of on the tank (or in addition to that). The wetback is the place where steam will happen if it happens, and you need to release it immediately, not after traveling through a bunch of piping. A safer approach might be to use a temperature and pressure relief valve (more of a commercial item) which can open if the temperature of the outlet gets near boiling - that way you have less chance of actually letting the water boil (prevention being better than cure).


An alternative would be to let the wetback water be static and open to atmosphere (with a makeup float valve to replenish it if it gets low), and run a copper coil through the wetback water. Pressurized water has a slightly higher boiling point than atmospheric water, so even if the wetback boiled the water in the coil would not flash to steam.

Hi Glenn, I appreciate the feedback. You bring up some good points about the pressure within the system. I do want to have it non-pressurized but that does bring up the issue about how the pump will run. I imagine the pump will need pressure to shut off and since this system is open I could see this being a problem. I was hoping once the tank was full this would provide the pressure needed for the pump to shut off. I had another idea (that I didn't include in the drawing) where the hot water supply line would relay through the house providing hot water to the fixtures and make a long loop back into the system. I was thinking this could provide the water an opportunity to cool some before reentering the tank.. kind of like a radiator. I am unsure how effective this would be plus I don't know how well this tiny wood stove will heat the water. Here is a picture of the lil' guy .

Hello
I found this informative thread in a search.  I am looking to heat water from my wood stove also.  Did you ever resolve this issue ? I’d love an update! I have just finished the exterior of my tiny house and want to design the inside to include off grid hot water.  Thanks in advance for any words of wisdom.

I know how to do it now but I ended up opting out due to the bulkiness of having a 30 gallon storage tank in my tiny house. I can try to answer any questions you may have !

Im currently playing with the idea of heating my water with my wood stove. My problem is I dont have endless supply of water. I rely on rain collection tanks and I gather water from a nearby stream for my fresh water supply, which is only a 50 gallon barrel. I recently came upon an old 180 gallon electric water heater I can use as a Hot Water storage tank. My rain collection tanks are capable of gravity feeding the Hot water tank located on the next floor directly above my wood stove. The collection water will go into the Hot Water tank and will then in turn gravity from the lowest drain to the lowest end of a copper coil wrapped around my flu. The water should heat up in the copper coil and thermosiphon back up to the tank. I would have to put a PT relief valve near the hot end of my copper coil along with a pressure gauge to monitor current pressures. I think I should put a back flow prevention valve or check  valve on the cold water supply line between the tank and the coil. also I will require another PT relief valve at the highest point of the hot water supply line. It seems that would work fine until I run out of cold water to the supply the system with. At that point the water remaining in the system is going to continuously get hotter and hotter and gain more and more pressure til Hopefully the PT relief valves do their job then the relief valve will pop draining the remaining water out of my tank and leaving me and my wet system high and dry and in the danger zone. The only solution I can think of is to leave the tank unpressurized and use a small pump to transfer the water thru the lines. That destroys my goal to achieve free hot water production and my electrical capabilities are scarce due to my extremely rural location. Any Ideas on how I can maintain energy free transfer without blowing myself up in the process would be extremely appreciated. Thanks. JORD